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1
Conley, Kevin E., e Stan L. Lindstedt. "Energy-saving mechanisms in muscle: the minimization strategy". Journal of Experimental Biology 205, n. 15 (1 agosto 2002): 2175–81. http://dx.doi.org/10.1242/jeb.205.15.2175.
Testo completoAbstract (sommario):
SUMMARYMany mechanisms reduce the cost of muscle activity. Here, we describe a set of specializations that reduce the cost of contraction in the high-frequency twitches that are used by a wide variety of animals for either sound production or flight. Minimizing the cost of these contractions means that cellular ATP production can meet ATP demand and sustain the high contractile rate. Two classes of specialization are found that minimize the contractile cost. The first class reduces the muscle work required per contraction. Light appendages such as rattles, insect limbs and membranous wings that require little work for movement are used in high-frequency contractions. The second set of specializations involves processes that minimize energy use. High-frequency muscles tend to have a lower cross-bridge content, fewer attached cross-bridges and shorter length changes per contraction. The result is low muscle-specific forces (stress), small length changes (strain) and rapid contraction times that suggest that these muscles push the lower limit of contractile function. The consequence of function at this lower extreme of contraction is to minimize the contractile cost of high-frequency muscles. Thus, specializations that permit rapid contractions at a low rate of ATP use per twitch are the basis of a minimization strategy for energy saving in muscles contracting at high frequency.
2
Hogan, Michael C., Erica Ingham e S. Sadi Kurdak. "Contraction duration affects metabolic energy cost and fatigue in skeletal muscle". American Journal of Physiology-Endocrinology and Metabolism 274, n. 3 (1 marzo 1998): E397—E402. http://dx.doi.org/10.1152/ajpendo.1998.274.3.e397.
Testo completoAbstract (sommario):
It has been suggested that during a skeletal muscle contraction the metabolic energy cost at the onset may be greater than the energy cost related to holding steady-state force. The purpose of the present study was to investigate the effect of contraction duration on the metabolic energy cost and fatigue process in fully perfused contracting muscle in situ. Canine gastrocnemius muscle ( n = 6) was isolated, and two contractile periods (3 min of isometric, tetanic contractions with 45-min rest between) were conducted by each muscle in a balanced order design. The two contractile periods had stimulation patterns that resulted in a 1:3 contraction-to-rest ratio, with the difference in the two contractile periods being in the duration of each contraction: short duration 0.25-s stimulation/0.75-s rest vs. long duration 1-s stimulation/3-s rest. These stimulation patterns resulted in the same total time of stimulation, number of stimulation pulses, and total time in contraction for each 3-min period. Muscle O2 uptake, the fall in developed force (fatigue), the O2 cost of developed force, and the estimated total energy cost (ATP utilization) of developed force were significantly greater ( P < 0.05) with contractions of short duration. Lactate efflux from the working muscle and muscle lactate concentration were significantly greater with contractions of short duration, such that the calculated energy derived from glycolysis was three times greater in this condition. These results demonstrate that contraction duration can significantly affect both the aerobic and anaerobic metabolic energy cost and fatigue in contracting muscle. In addition, it is likely that the greater rate of fatigue with more rapid contractions was a result of elevated glycolytic production of lactic acid.
3
Thomas, G. D., J. Hansen e R. G. Victor. "Inhibition of alpha 2-adrenergic vasoconstriction during contraction of glycolytic, not oxidative, rat hindlimb muscle". American Journal of Physiology-Heart and Circulatory Physiology 266, n. 3 (1 marzo 1994): H920—H929. http://dx.doi.org/10.1152/ajpheart.1994.266.3.h920.
Testo completoAbstract (sommario):
Previous studies have produced conflicting evidence as to whether sympathetic vasoconstriction is impaired in active skeletal muscle. Because alpha 2-, not alpha 1-, adrenergic vasoconstriction is attenuated by mild acidosis, we hypothesized that alpha 2-mediated sympathetic vasoconstriction would be attenuated in contracting glycolytic muscle, which produces more acidosis than oxidative muscle. We compared effects of lumbar sympathetic nerve stimulation and alpha-adrenergic agonists on arterial pressure, femoral blood flow, and force output during contractions of oxidative or glycolytic muscles in anesthetized rats. We found that 1) sympathetic vasoconstriction was preserved during contractions of oxidative soleus muscle and during low-intensity contractions of glycolytic gastrocnemiusplantaris muscles but was abolished during maximal contractions of these glycolytic muscles; 2) this sympatholytic effect was caused by impaired alpha 2-, not alpha 1-, vasoconstriction; and 3) the increased muscle blood flow resulting from a combination of impaired vasconstriction and increased arterial pressure was paralleled by increased force of gastrocnemius-plantaris muscle contraction. Thus contraction-induced impairment of alpha 2-vasoconstriction can augment muscle blood flow and muscle contraction, but the degree of impairment depends on fiber type and intensity of muscle contraction.
4
Todd, Gabrielle, Janet L. Taylor, Jane E. Butler, Peter G. Martin, Robert B. Gorman e Simon C. Gandevia. "Use of motor cortex stimulation to measure simultaneously the changes in dynamic muscle properties and voluntary activation in human muscles". Journal of Applied Physiology 102, n. 5 (maggio 2007): 1756–66. http://dx.doi.org/10.1152/japplphysiol.00962.2006.
Testo completoAbstract (sommario):
Force responses to transcranial magnetic stimulation of motor cortex (TMS) during exercise provide information about voluntary activation and contractile properties of the muscle. Here, TMS-generated twitches and muscle relaxation during the TMS-evoked silent period were measured in fresh, heated, and fatigued muscle. Subjects performed isometric contractions of elbow flexors in two studies. Torque and EMG were recorded from elbow flexor and extensor muscles. One study ( n = 6) measured muscle contraction times and relaxation rates during brief maximal and submaximal contractions in fresh and fatigued muscle. Another study ( n = 7) aimed to 1) assess the reproducibility of muscle contractile properties during brief voluntary contractions in fresh muscle, 2) validate the technique for contractile properties in passively heated muscle, and 3) apply the technique to study contractile properties during sustained maximal voluntary contractions. In both studies, muscle contractile properties during voluntary contractions were compared with the resting twitch evoked by motor nerve stimulation. Measurement of muscle contractile properties during voluntary contractions is reproducible in fresh muscle and reveals faster and slower muscle relaxation rates in heated and fatigued muscle, respectively. The technique is more sensitive to altered muscle state than the traditional motor nerve resting twitch. Use of TMS during sustained maximal contractions reveals slowing of muscle contraction and relaxation with different time courses and a decline in voluntary activation. Voluntary output from the motor cortex becomes insufficient to maintain complete activation of muscle, although slowing of muscle contraction and relaxation indicates that lower motor unit firing rates are required for fusion of force.
5
Günther, Michael, Oliver Röhrle, Daniel F. B. Haeufle e Syn Schmitt. "Spreading out Muscle Mass within a Hill-Type Model: A Computer Simulation Study". Computational and Mathematical Methods in Medicine 2012 (2012): 1–13. http://dx.doi.org/10.1155/2012/848630.
Testo completoAbstract (sommario):
It is state of the art that muscle contraction dynamics is adequately described by a hyperbolic relation between muscle force and contraction velocity (Hill relation), thereby neglecting muscle internal mass inertia (first-order dynamics). Accordingly, the vast majority of modelling approaches also neglect muscle internal inertia. Assuming that such first-order contraction dynamics yet interacts with muscle internal mass distribution, this study investigates two questions: (i) what is the time scale on which the muscle responds to a force step? (ii) How does this response scale with muscle design parameters? Thereto, we simulated accelerated contractions of alternating sequences of Hill-type contractile elements and point masses. We found that in a typical small muscle the force levels off after about 0.2 ms, contraction velocity after about 0.5 ms. In an upscaled version representing bigger mammals' muscles, the force levels off after about 20 ms, and the theoretically expected maximum contraction velocity is not reached. We conclude (i) that it may be indispensable to introduce second-order contributions into muscle models to understand high-frequency muscle responses, particularly in bigger muscles. Additionally, (ii) constructing more elaborate measuring devices seems to be worthwhile to distinguish viscoelastic and inertia properties in rapid contractile responses of muscles.
6
Kato, Tatsuya, Atsushi Sasaki, Hikaru Yokoyama, Matija Milosevic e Kimitaka Nakazawa. "Effects of neuromuscular electrical stimulation and voluntary commands on the spinal reflex excitability of remote limb muscles". Experimental Brain Research 237, n. 12 (10 ottobre 2019): 3195–205. http://dx.doi.org/10.1007/s00221-019-05660-6.
Testo completoAbstract (sommario):
Abstract It is well known that contracting the upper limbs can affect spinal reflexes of the lower limb muscle, via intraneuronal networks within the central nervous system. However, it remains unknown whether neuromuscular electrical stimulation (NMES), which can generate muscle contractions without central commands from the cortex, can also play a role in such inter-limb facilitation. Therefore, the objective of this study was to compare the effects of unilateral upper limb contractions using NMES and voluntary unilateral upper limb contractions on the inter-limb spinal reflex facilitation in the lower limb muscles. Spinal reflex excitability was assessed using transcutaneous spinal cord stimulation (tSCS) to elicit responses bilaterally in multiple lower limb muscles, including ankle and thigh muscles. Five interventions were applied on the right wrist flexors for 70 s: (1) sensory-level NMES; (2) motor-level NMES; (3) voluntary contraction; (4) voluntary contraction and sensory-level NMES; (5) voluntary contraction and motor-level NMES. Results showed that spinal reflex excitability of ankle muscles was facilitated bilaterally during voluntary contraction of the upper limb unilaterally and that voluntary contraction with motor-level NMES had similar effects as just contracting voluntarily. Meanwhile, motor-level NMES facilitated contralateral thigh muscles, and sensory-level NMES had no effect. Overall, our results suggest that inter-limb facilitation effect of spinal reflex excitability in lower limb muscles depends, to a larger extent, on the presence of the central commands from the cortex during voluntary contractions. However, peripheral input generated by muscle contractions using NMES might have effects on the spinal reflex excitability of inter-limb muscles via spinal intraneuronal networks.
7
Stebbins, C. L., O. A. Carretero, T. Mindroiu e J. C. Longhurst. "Bradykinin release from contracting skeletal muscle of the cat". Journal of Applied Physiology 69, n. 4 (1 ottobre 1990): 1225–30. http://dx.doi.org/10.1152/jappl.1990.69.4.1225.
Testo completoAbstract (sommario):
Results of previous studies from our laboratory suggest that bradykinin has a role in the exercise pressor reflex elicited by static muscle contraction. The purpose of this study was to quantify the release of bradykinin from contracting skeletal muscle. In 18 cats, blood samples were withdrawn directly from the venous effluent of the triceps surae muscles immediately before and after 30 s of static contraction producing peak muscle tensions of 33, 50, and 100% of maximum electrically stimulated contraction. Contractions producing muscle tensions of 50 and 100% of maximum increased muscle venous bradykinin levels by 27 +/- 9 and 19 +/- 10 pg/ml, respectively. Conversely, 33% maximum contraction did not alter muscle venous bradykinin concentrations. However, when captopril was administered to slow the degradation of bradykinin, muscle venous bradykinin increased from 68 +/- 15 pg/ml at rest to 106 +/- 18 after contractions of 33% of maximum. When muscle ischemia was induced by 2 min of arterial occlusion before and during 30 s of 33% of maximum contraction, muscle venous bradykinin increased by 15 +/- 5 pg/ml. In addition, contraction-induced changes in muscle venous pH and lactate strongly correlated with bradykinin concentrations (r = 0.80 and 0.83, respectively). These data demonstrate that static contraction of relatively high intensity evokes the release of bradykinin from skeletal muscle and that ischemia, decreased pH, and increased lactate are strongly correlated with this release.
8
Hogan, Michael C., Bruno Grassi, Michele Samaja, Creed M. Stary e L. B. Gladden. "Effect of contraction frequency on the contractile and noncontractile phases of muscle venous blood flow". Journal of Applied Physiology 95, n. 3 (settembre 2003): 1139–44. http://dx.doi.org/10.1152/japplphysiol.00226.2003.
Testo completoAbstract (sommario):
The purpose of this study was to test the hypothesis that increasing muscle contraction frequency, which alters the duty cycle and metabolic rate, would increase the contribution of the contractile phase to mean venous blood flow in isolated skeletal muscle during rhythmic contractions. Canine gastrocnemius muscle ( n = 5) was isolated, and 3-min stimulation periods of isometric, tetanic contractions were elicited sequentially at rates of 0.25, 0.33, and 0.5 contractions/s. The O2 uptake, tension-time integral, and mean venous blood flow increased significantly ( P < 0.05) with each contraction frequency. Venous blood flow during both the contractile (106 ± 6, 139 ± 8, and 145 ± 8 ml·100 g-1·min-1) and noncontractile phases (64 ± 3, 78 ± 4, and 91 ± 5 ml·100 g-1·min-1) increased with contraction frequency. Although developed force and duration of the contractile phase were never significantly different for a single contraction during the three contraction frequencies, the amount of blood expelled from the muscle during an individual contraction increased significantly with contraction frequency (0.24 ± 0.03, 0.32 ± 0.02, and 0.36 ± 0.03 ml·N-1·min-1, respectively). This increased blood expulsion per contraction, coupled with the decreased time in the noncontractile phase as contraction frequency increased, resulted in the contractile phase contribution to mean venous blood flow becoming significantly greater (21 ± 4, 30 ± 4, and 38 ± 6%) as contraction frequency increased. These results demonstrate that the percent contribution of the muscle contractile phase to mean venous blood flow becomes significantly greater as contraction frequency (and thereby duty cycle and metabolic rate) increases and that this is in part due to increased blood expulsion per contraction.
9
Hespel, P., e E. A. Richter. "Mechanism linking glycogen concentration and glycogenolytic rate in perfused contracting rat skeletal muscle". Biochemical Journal 284, n. 3 (15 giugno 1992): 777–80. http://dx.doi.org/10.1042/bj2840777.
Testo completoAbstract (sommario):
The influence of differences in glycogen concentration on glycogen breakdown and on phosphorylase activity was investigated in perfused contracting rat skeletal muscle. The rats were preconditioned by a combination of swimming exercise and diet (carbohydrate-free or carbohydrate-rich) in order to obtain four sub-groups of rats with varying resting muscle glycogen concentrations (range 10-60 mumol/g wet wt.). Pre-contraction muscle glycogen concentration was closely positively correlated with glycogen breakdown over 15 min of intermittent short tetanic contractions (r = 0.75; P less than 0.001; n = 56) at the same tension development and oxygen uptake. Additional studies in supercompensated and glycogen-depleted hindquarters during electrical stimulation for 20 s or 2 min revealed that the difference in glycogenolytic rate was found at the beginning rather than at the end of the contraction period. Phosphorylase alpha activity was approximately twice as high (P less than 0.001) in supercompensated muscles as in glycogen-depleted muscles after 20 s as well as after 2 min of contractions. It is concluded that glycogen concentration is an important determinant of phosphorylase activity in contracting skeletal muscle, and probably via this mechanism a regulator of glycogenolytic rate during muscle contraction.
10
Herdmann, J., P. Enck, P. Zacchi-Deutschbein e U. Ostermann. "Speed and pressure characteristics of external anal sphincter contractions". American Journal of Physiology-Gastrointestinal and Liver Physiology 269, n. 2 (1 agosto 1995): G225—G231. http://dx.doi.org/10.1152/ajpgi.1995.269.2.g225.
Testo completoAbstract (sommario):
The principle of isochronism reflects constant contraction time for varying strengths of muscle contraction. This principle was studied for the innervation of the pelvic floor in humans using motor-evoked potentials (MEPs) and evoked pressure curves (EPCs) from the external anal sphincter muscle (EAS). MEPs and EPCs were simultaneously recorded after transcranial magnetic stimulation of the motor cortex. Voluntary contractions were also studied. Contraction times of the EAS were significantly longer in voluntary contractions (mean, 237 ms) than in EPCs (mean, 90 ms). Depending on either mode of contraction, contraction times varied only slightly despite a wide range of contraction strengths. It is shown that the contractile behavior of the EAS is a function of slow- and fast-twitch muscle fiber distribution and that the principle of isochronism governs motor performance not only of limb muscles but also of the EAS. There exists a unique optimal working range of each muscle to meet its individual function. Disturbance of this principle results in a less efficient contraction with either inappropriate basic tone or disturbed reflex activation in the EAS. Both are possible causes of incontinence.
11
Sosnowska, Anna J., Aleksandra Vuckovic e Henrik Gollee. "Automated semi-real-time detection of muscle activity with ultrasound imaging". Medical & Biological Engineering & Computing 59, n. 9 (16 agosto 2021): 1961–71. http://dx.doi.org/10.1007/s11517-021-02407-w.
Testo completoAbstract (sommario):
AbstractUltrasound imaging (USI) biofeedback is a useful therapeutic tool; however, it relies on qualitative assessment by a trained therapist, while existing automatic analysis techniques are computationally demanding. This study aims to present a computationally inexpensive algorithm based on the difference in pixel intensity between USI frames. During an offline experiment, where data was analyzed after the study, participants performed isometric contractions of the gastrocnemius medialis (GM) muscle, as executed (30% of maximum contraction) or attempted (low force contraction up to a point when the participant is aware of exerting force or contracting the muscle) movements, while USI, EMG, and force data were recorded. The algorithm achieved 99% agreement with EMG and force measurements for executed movements and 93% for attempted movements, with USI detecting 1.9% more contractions than the other methods. In the online study, participants performed GM muscle contractions at 10% and 30% of maximum contraction, while the algorithm provided visual feedback proportional to the muscle activity (based on USI recordings during the maximum contraction) in less than 3 s following each contraction. We show that the participants reached the target consistently, learning to perform precise contractions. The algorithm is reliable and computationally very efficient, allowing real-time applications on standard computing hardware. It is a suitable method for automated detection, quantification of muscle contraction, and to provide biofeedback which can be used for training of targeted muscles, making it suitable for rehabilitation. Graphical abstract Biofeedback session based on ultrasound imaging (USI) during muscle training. Novel, computationally inexpensive algorithm based on the difference in pixel intensity between USI frames is used to process the video and provide quantitative feedback on the strength of muscle contraction.
12
Goodyear, L. J., P. A. King, M. F. Hirshman, C. M. Thompson, E. D. Horton e E. S. Horton. "Contractile activity increases plasma membrane glucose transporters in absence of insulin". American Journal of Physiology-Endocrinology and Metabolism 258, n. 4 (1 aprile 1990): E667—E672. http://dx.doi.org/10.1152/ajpendo.1990.258.4.e667.
Testo completoAbstract (sommario):
To study the interactions between insulin and contraction on the skeletal muscle glucose transport system, the hindquarters of male rats were perfused in the absence of insulin, in the presence of insulin (30 mU/ml), during contractions induced by sciatic nerve stimulation, or during contractions plus insulin. Compared with control preparations, rates of glucose uptake in the perfused hindquarter were increased by 2.5- and 2.6-fold in the insulin and insulin plus contraction groups, respectively, but not significantly increased in the contraction only preparations. After perfusion, soleus and red and white gastrocnemius muscles from the hindquarter were pooled and used for the preparation of plasma membranes. Skeletal muscle plasma membrane vesicle glucose transport rates were 2.2 +/- 0.5, 7.9 +/- 1.7, 9.0 +/- 2.2, and 10.8 +/- 2.0 nmol.mg protein-1.s-1 (40 mM glucose), and plasma membrane glucose transporter numbers were 4.7 +/- 0.5, 8.1 +/- 0.9, 9.1 +/- 1.0, and 8.6 +/- 0.6 pmol/mg protein in the control, contraction, insulin, and insulin plus contraction groups, respectively. The transport-transporter ratio, an indication of plasma membrane glucose transporter intrinsic activity, was increased by contraction, insulin, and insulin plus contraction. These results demonstrate that contractile activity in the absence of insulin increases muscle plasma membrane glucose transport by increasing transporter number and intrinsic activity. In addition, under these experimental conditions, the effects of insulin and contraction to increase muscle glucose transport are not additive.
13
Mehta, D., M. F. Wu e S. J. Gunst. "Role of contractile protein activation in the length-dependent modulation of tracheal smooth muscle force". American Journal of Physiology-Cell Physiology 270, n. 1 (1 gennaio 1996): C243—C252. http://dx.doi.org/10.1152/ajpcell.1996.270.1.c243.
Testo completoAbstract (sommario):
The active isometric force developed by a muscle decreases at muscle lengths below an optimal length (Lo). However, when the length of an actively contracting muscle is abruptly decreased, a lower level of isometric force is reached during force redevelopment than when the contraction is initiated at the shorter length. This has been attributed to a deactivation of contractile proteins caused by shortening. In this study, intracellular Ca2+ and myosin light chain (MLC) phosphorylation were measured to assess the mechanisms for the modulation of isometric force caused by changing smooth muscle length before or during isometric contraction. The decline in isometric force between Lo and 0.5Lo was associated with decreases in MLC phosphorylation and intracellular Ca2+ during contractions elicited by acetylcholine or 60 mM KCl. Quick release of the muscle during contraction depressed force redevelopment at the shorter length but not MLC phosphorylation. We conclude that decreases in Ca(2+)-calmodulin-dependent MLC phosphorylation contribute significantly to the decline in isometric force at lengths below Lo, but the depression of contractility associated with the quick release of actively contracted smooth muscle is not caused by a shortening-induced deactivation of contractile proteins.
14
Lockhart, Nicole C., e Susan V. Brooks. "Neutrophil accumulation following passive stretches contributes to adaptations that reduce contraction-induced skeletal muscle injury in mice". Journal of Applied Physiology 104, n. 4 (aprile 2008): 1109–15. http://dx.doi.org/10.1152/japplphysiol.00850.2007.
Testo completoAbstract (sommario):
Skeletal muscles can be injured by their own contractions, especially when the muscle is stretched during a lengthening contraction. Exposing a muscle to a conditioning protocol of stretches without activation (passive stretches) before lengthening contractions reduces contraction-induced injury. Although passive stretching does not damage muscle fibers, neutrophils are elevated in the muscle after passive stretches. Our purpose was to investigate the relationship between neutrophil accumulation following passive stretches and the protection from subsequent contraction-induced injury provided by the passive stretches. Our hypothesis was that passive stretch conditioning would not provide protection from subsequent lengthening contraction-induced injury under circumstances when the increase in muscle neutrophils in response to the conditioning was prevented. Extensor digitorum longus muscles of mice were conditioned with passive stretches 14 days before exposure to a protocol of damaging lengthening contractions. Mice were either untreated or treated with an antibody (RB6-8C5) that reduced the level of circulating neutrophils by over 95% before administration of passive stretches. Neutrophil levels recovered in treated mice by the time lengthening contractions were performed. Lengthening contractions were also administered to muscles with no prior exposure to passive stretches. Maximum isometric force, number of damaged fibers, and muscle neutrophil concentration were measured 3 days after lengthening contractions. Compared with nonconditioned control muscles, the severity of contraction-induced injury was not reduced by prior passive stretch conditioning when mice were treated with RB6-8C5 before conditioning. We conclude that neutrophils contribute to adaptations that protect muscles from injury.
15
Eng, Carolyn M., e Thomas J. Roberts. "Aponeurosis influences the relationship between muscle gearing and force". Journal of Applied Physiology 125, n. 2 (1 agosto 2018): 513–19. http://dx.doi.org/10.1152/japplphysiol.00151.2018.
Testo completoAbstract (sommario):
Aponeuroses are connective tissues found on the surface of pennate muscles and are in close association with muscle fascicles. In addition to transmitting muscle forces to the external tendon, aponeurosis has been hypothesized to influence the direction of muscle shape change during a contraction. Muscle shape changes affect muscle contractile force and velocity because they influence the gear ratio with which muscle fascicles transmit force and velocity to the tendon. If aponeurosis modulates muscle shape changes, altering the aponeurosis’ radial integrity with incisions should alter gearing. We tested the hypothesis that incising the aponeurosis would lead to decreased gearing across force conditions with an in situ preparation of the turkey lateral gastrocnemius muscle. We found that multiple full-length incisions in the aponeurosis altered the relationship between gearing and force relative to the intact aponeurosis condition. Specifically, after multiple aponeurosis incisions, gear ratio decreased by 19% in the high-force contractions compared with the intact condition. These results suggest that aponeuroses influence muscle shape change and can alter muscle contractile force and speed through their effect on muscle gearing. NEW & NOTEWORTHY Muscle gearing is determined by muscle shape change during a contraction and varies with the force of contraction. Variable gearing influences muscle force and speed, but how gearing is modulated is not well understood. Incising the aponeurosis before and after contractions demonstrates that aponeurosis plays a role in modulating gearing.
16
AlMohimeed, Ibrahim, e Yuu Ono. "Ultrasound Measurement of Skeletal Muscle Contractile Parameters Using Flexible and Wearable Single-Element Ultrasonic Sensor". Sensors 20, n. 13 (27 giugno 2020): 3616. http://dx.doi.org/10.3390/s20133616.
Testo completoAbstract (sommario):
Skeletal muscle is considered as a near-constant volume system, and the contractions of the muscle are related to the changes in tissue thickness. Assessment of the skeletal muscle contractile parameters such as maximum contraction thickness ( T h ), contraction time ( T c ), contraction velocity ( V c ), sustain time ( T s ), and half-relaxation ( T r ) provides valuable information for various medical applications. This paper presents a single-element wearable ultrasonic sensor (WUS) and a method to measure the skeletal muscle contractile parameters in A-mode ultrasonic data acquisition. The developed WUS was made of double-layer polyvinylidene fluoride (PVDF) piezoelectric polymer films with a simple and low-cost fabrication process. A flexible, lightweight, thin, and small size WUS would provide a secure attachment to the skin surface without affecting the muscle contraction dynamics of interest. The developed WUS was employed to monitor the contractions of gastrocnemius (GC) muscle of a human subject. The GC muscle contractions were evoked by the electrical muscle stimulation (EMS) at varying EMS frequencies from 2 Hz up to 30 Hz. The tissue thickness changes due to the muscle contractions were measured by utilizing a time-of-flight method in the ultrasonic through-transmission mode. The developed WUS demonstrated the capability to monitor the tissue thickness changes during the unfused and fused tetanic contractions. The tetanic progression level was quantitatively assessed using the parameter of the fusion index (FI) obtained. In addition, the contractile parameters ( T h , T c , V c , T s , and T r ) were successfully extracted from the measured tissue thickness changes. In addition, the unfused and fused tetanus frequencies were estimated from the obtained FI-EMS frequency curve. The WUS and ultrasonic method proposed in this study could be a valuable tool for inexpensive, non-invasive, and continuous monitoring of the skeletal muscle contractile properties.
17
Andersen, Ole Emil, Ole Bækgaard Nielsen e Kristian Overgaard. "Early effects of eccentric contractions on muscle glucose uptake". Journal of Applied Physiology 126, n. 2 (1 febbraio 2019): 376–85. http://dx.doi.org/10.1152/japplphysiol.00388.2018.
Testo completoAbstract (sommario):
Muscle-damaging eccentric exercise impairs muscle glucose uptake several hours to days after exercise. Little, however, is known about the acute effects of eccentric exercise on contraction- and insulin-induced glucose uptake. This study compares glucose uptake rates in the first hours following eccentric, concentric, and isometric contractions with and without insulin present. Isolated rat extensor digitorum longus muscles were exposed to either an eccentric, concentric, or isometric contraction protocol, and muscle contractions were induced by electric stimulation that was identical between contraction protocols. In eccentric and concentric modes, length changes of 0.6 or 1.2 mm were used during contractions. Both contraction- and insulin-induced glucose uptake were assessed immediately and 2 h after contractions. Glucose uptake increased significantly following all modes of contraction and was higher after eccentric contractions with a stretch of 1.2 mm compared with the remaining contraction groups when assessed immediately after contractions [eccentric (1.2 mm) > eccentric (0.6 mm), concentric (1.2 mm), concentric (0.6 mm), isometric > rest; P < 0.05]. After 2 h, contraction-induced glucose uptake was still higher than noncontracting levels, but with no difference between contraction modes. The presence of insulin increased glucose uptake markedly, but this response was blunted by, respectively, 39–51% and 29–36% ( P < 0.05) immediately and 2 h after eccentric contractions stretched 1.2 mm compared with concentric and isometric contractions. The contrasting early effects of eccentric contractions on contraction- and insulin-induced glucose uptake suggest that glucose uptake is impaired acutely following eccentric exercise because of reduced insulin responsiveness.NEW & NOTEWORTHY This study shows that, in isolated rat muscle, muscle-damaging eccentric contractions result in a transient increase in contraction-induced glucose uptake compared with isometric and concentric contractions induced by identical muscle activation protocols. Furthermore, our results demonstrate that, in contrast, the insulin-stimulated glucose uptake is impaired immediately following muscle-damaging eccentric contractions.
18
Zuo, Li, Leonardo Nogueira e Michael C. Hogan. "Reactive oxygen species formation during tetanic contractions in single isolated Xenopus myofibers". Journal of Applied Physiology 111, n. 3 (settembre 2011): 898–904. http://dx.doi.org/10.1152/japplphysiol.00398.2011.
Testo completoAbstract (sommario):
Contracting skeletal muscle produces reactive oxygen species (ROS) that have been shown to affect muscle function and adaptation. However, real-time measurement of ROS in contracting myofibers has proven to be difficult. We used amphibian ( Xenopus laevis) muscle to test the hypothesis that ROS are formed during contractile activity in isolated single skeletal muscle fibers and that this contraction-induced ROS formation affects fatigue development. Single myofibers were loaded with 5 μM dihydrofluorescein-DA (Hfluor-DA), a fluorescent probe that reacts with ROS and results in the formation of fluorescein (Fluor) to precisely monitor ROS generation within single myofibers in real time using confocal miscroscopy. Three identical periods of maximal tetanic contractions (1 contraction/3 s for 2 min, separated by 60 min of rest) were conducted by each myofiber ( n = 6) at 20°C. Ebselen (an antioxidant) was present in the perfusate (10 μM) during the second contractile period. Force was reduced by ∼30% during each of the three contraction periods, with no significant difference in fatigue development among the three periods. The Fluor signal, indicative of ROS generation, increased significantly above baseline in both the first (42 ± 14%) and third periods (39 ± 10%), with no significant difference in the increase in fluorescence between the first and third periods. There was no increase of Fluor in the presence of ebselen during the second contractile period. These results demonstrated that, in isolated intact Xenopus myofibers, 1) ROS can be measured in real time during tetanic contractions, 2) contractile activity induced a significant increase above resting levels of ROS production, and 3) ebselen treatment reduced ROS generation to baseline levels but had no effect on myofiber contractility and fatigue development.
19
Hamann, Jason J., Heidi A. Kluess, John B. Buckwalter e Philip S. Clifford. "Blood flow response to muscle contractions is more closely related to metabolic rate than contractile work". Journal of Applied Physiology 98, n. 6 (giugno 2005): 2096–100. http://dx.doi.org/10.1152/japplphysiol.00400.2004.
Testo completoAbstract (sommario):
The magnitude of the blood flow response to exercise has been linked to both the contractile work performed and the metabolic cost of the activity. Under certain conditions, contractile work and metabolic cost may be dissociated. This study examined the blood flow response to trains of contractions when contraction duration was manipulated under conditions of similar tension-time indexes (isometric analog of work). Previous investigations have shown that trains of short-duration contractions have a greater ATP utilization, which may result from an augmented ion transport required for muscle activation and relaxation. On the basis of these findings, we hypothesized that the blood flow response would be greater to a train of short-duration contractions than a train of long-duration contractions. Canine gastrocnemius-plantaris muscle ( n = 8) was isolated, and blood flow assessed with an ultrasound flow probe placed around the popliteal artery. The sciatic nerve was stimulated to produce two contraction protocols that resulted in similar contraction-to-rest ratios: short duration: 0.25 s/0.75 s vs. long duration: 1 s /3 s. In accord with the design of the experiment, the tension-time indexes were identical for the two contraction protocols (short: 18.6 ± 1.0 vs. long: 18.6 ± 1.0 kN·s). Steady-state oxygen consumption was greater in the short-duration contractions (17.2 ± 0.9 ml·100 g−1·min−1) than in the long-duration contractions (11.7 ± 0.7 ml·100 g−1·min−1). Similarly, the steady-state blood flow was greater in contractions of short duration (125 ± 7 ml/min) compared with long-duration contractions (92 ± 7 ml/min). Contractions of short duration resulted in significantly higher oxygen consumptions and blood flows compared with contractions of long duration despite the same total contractile work. The blood flow response to muscle contraction appears to be more closely associated with muscle metabolism than contractile work performed.
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Nedachi, Taku, Hideaki Fujita e Makoto Kanzaki. "Contractile C2C12 myotube model for studying exercise-inducible responses in skeletal muscle". American Journal of Physiology-Endocrinology and Metabolism 295, n. 5 (novembre 2008): E1191—E1204. http://dx.doi.org/10.1152/ajpendo.90280.2008.
Testo completoAbstract (sommario):
Adequate exercise leads to a vast variety of physiological changes in skeletal muscle as well as other tissues/organs and is also responsible for maintaining healthy muscle displaying enhanced insulin-responsive glucose uptake via GLUT4 translocation. We generated highly developed contractile C2C12 myotubes by manipulating intracellular Ca2+ transients with electric pulse stimulation (EPS) that is endowed with properties similar to those of in vivo skeletal muscle in terms of 1) excitation-induced contractile activity as a result of de novo sarcomere formation, 2) activation of both the AMP kinase and stress-activated MAP kinase cascades, and 3) improved insulin responsiveness as assessed by GLUT4 recycling. Tbc1d1, a Rab-GAP implicated in exercise-induced GLUT4 translocation in skeletal muscle, also appeared to be phosphorylated on Ser231 after EPS-induced contraction. In addition, a switch in myosin heavy-chain (MHC) expression from “fast type” to “slow type” was observed in the C2C12 myotubes endowed with EPS-induced repetitive contractility. Taking advantage of these highly developed contractile C2C12 myotubes, we identified myotube-derived factors responsive to EPS-evoked contraction, including the CXC chemokines CXCL1/KC and CXCL5/LIX, as well as IL-6, previously reported to be upregulated in contracting muscles in vivo. Importantly, animal treadmill experiments revealed that exercise significantly increased systemic levels of CXCL1/KC, perhaps derived from contracting muscle. Taken together, these results confirm that we have established a specialized muscle cell culture model allowing contraction-inducible cellular responses to be explored. Utilizing this model, we identified contraction-inducible myokines potentially linked to the metabolic alterations, immune responses, and angiogenesis induced by exercise.
21
Lai, Adrian K. M., Andrew A. Biewener e James M. Wakeling. "Metabolic cost underlies task-dependent variations in motor unit recruitment". Journal of The Royal Society Interface 15, n. 148 (novembre 2018): 20180541. http://dx.doi.org/10.1098/rsif.2018.0541.
Testo completoAbstract (sommario):
Mammalian skeletal muscles are comprised of many motor units, each containing a group of muscle fibres that have common contractile properties: these can be broadly categorized as slow and fast twitch muscle fibres. Motor units are typically recruited in an orderly fashion following the ‘size principle’, in which slower motor units would be recruited for low intensity contraction; a metabolically cheap and fatigue-resistant strategy. However, this recruitment strategy poses a mechanical paradox for fast, low intensity contractions, in which the recruitment of slower fibres, as predicted by the size principle, would be metabolically more costly than the recruitment of faster fibres that are more efficient at higher contraction speeds. Hence, it would be mechanically and metabolically more effective for recruitment strategies to vary in response to contraction speed so that the intrinsic efficiencies and contraction speeds of the recruited muscle fibres are matched to the mechanical demands of the task. In this study, we evaluated the effectiveness of a novel, mixed cost function within a musculoskeletal simulation, which includes the metabolic cost of contraction, to predict the recruitment of different muscle fibre types across a range of loads and speeds. Our results show that a metabolically informed cost function predicts favoured recruitment of slower muscle fibres for slower and isometric tasks versus recruitment that favours faster muscles fibres for higher velocity contractions. This cost function predicts a change in recruitment patterns consistent with experimental observations, and also predicts a less expensive metabolic cost for these muscle contractions regardless of speed of the movement. Hence, our findings support the premise that varying motor recruitment strategies to match the mechanical demands of a movement task results in a mechanically and metabolically sensible way to deploy the different types of motor unit.
22
Lowe, D. A., G. L. Warren, D. A. Hayes, M. A. Farmer e R. B. Armstrong. "Eccentric contraction-induced injury of mouse soleus muscle: effect of varying [Ca2+]o". Journal of Applied Physiology 76, n. 4 (1 aprile 1994): 1445–53. http://dx.doi.org/10.1152/jappl.1994.76.4.1445.
Testo completoAbstract (sommario):
The objective of this study was to determine the effect of varying extracellular Ca2+ concentration ([Ca2+]o) on eccentric contraction-induced muscle injury. Isolated mouse soleus muscles (n = 64) performed either 20 eccentric or 20 isometric contractions over a 40-min period in a Krebs buffer containing 0.5, 1.25, or 5.0 mM Ca2+. Measurements of contractile function and lactate dehydrogenase accumulation in the buffer were then made every 15 min for 2 h. Prostaglandin E2, leukotriene B4, and tyrosine accumulation in the incubation medium and total muscle [Ca2+] were measured at the end of the experiment. Reductions in maximal isometric tetanic force for muscles immediately after performance of 20 eccentric and 20 isometric contractions were 21.1 +/- 1.4 and 1.2 +/- 0.7%, respectively. Total muscle [Ca2+] was 28–37% higher in muscles that performed eccentric contractions than in those that performed isometric contractions. However, estimates made with a confocal laser scanning microscope and fluo 3 do not indicate that there was a difference in free cytosolic [Ca2+] between fibers from injured and control muscles. Also, leukotriene B4, prostaglandin E2, and tyrosine accumulation in the buffer from muscles that performed eccentric contractions was not elevated over that from muscles that performed isometric contractions. Furthermore, lactate dehydrogenase accumulation and reductions of contractile function over the 2-h incubation period were not enhanced by higher [Ca2+]o or influenced by the type of contraction. These findings suggest that muscles that were injured by eccentric contractions were able to buffer the increased influx of extracellular Ca2+, maintain a normal free cytosolic [Ca2+], and avoid activation of Ca(2+)-sensitive degradative pathways.
23
Wang, Huiping, Yuxi Guo, Wenjing Yan, Liqi Cao, Xiaozhuo Bai, Jing Zhao, Kai Dang e Yunfang Gao. "Weakened Contractile Performance and Mitochondrial Respiratory Complex Activity in Skeletal Muscle Improve during Interbout Arousal in Hibernating Daurian Ground Squirrel, Spermophilus dauricus". International Journal of Molecular Sciences 24, n. 21 (30 ottobre 2023): 15785. http://dx.doi.org/10.3390/ijms242115785.
Testo completoAbstract (sommario):
Mammalian hibernation is composed of multiple episodes of torpor bout, separated by phases of interbout arousal. During torpor, the skeletal muscles of mammals are undoubtedly inactive, but it has been proven to mitigate disuse atrophy. While interbout arousal has been implicated in the prevention of muscle atrophy, the underlying mechanisms sustaining muscle contraction remain to be explored. In the present study, Daurian ground squirrels (Spermophilus dauricus) were divided into four groups: pre-hibernation (PRE), torpor (TOR), interbout arousal (IBA), and post-hibernation (POST). The contractile performance of slow-twitch soleus muscle (SOL) and fast-twitch extensor digitorum longus muscle (EDL) was detected both in situ and in vitro. Concurrently, mitochondrial respiratory chain complex activity in these muscles was quantified. Our findings revealed that in situ contractile properties of both muscles, including force, power output, time duration, and force development/relaxation rates of twitch contraction, and force and power output of tetanic contraction declined in the TOR group compared to the PRE group, but improved in the IBA and POST groups. Fatigue resistance of muscles, determined by the power output of repetitive tetanic contractions in situ, decreased in the TOR group but recovered in the IBA and POST groups. In vitro studies demonstrated that tetanic contraction power output in isolated muscles increased with muscle temperature in both TOR and IBA groups. However, at the same temperature, power output was consistently lower in the TOR group compared to the IBA group. Moreover, the activity of the mitochondrial respiratory chain complex, especially Complexes I and II, decreased in the TOR group but showed recovery in the IBA and POST groups. These findings suggest that both the contractile performance and fatigue resistance of mammalian skeletal muscle are compromised during torpor but can be improved during interbout arousal and post-hibernation. The rebound in body temperature and rise in mitochondrial respiratory chain complex activity in skeletal muscle are involved in enhancing contractile performance and fatigue resistance. This study suggests that interbout arousal functions as a vital temporal interval during which skeletal muscles can transition from the inactivity induced by torpor to a state of restored contractile functionality. Thus, interbout arousal serves as a behavioral safeguard against disuse-induced damage to skeletal muscles during hibernation.
24
Spriet, L. L., K. Soderlund, M. Bergstrom e E. Hultman. "Anaerobic energy release in skeletal muscle during electrical stimulation in men". Journal of Applied Physiology 62, n. 2 (1 febbraio 1987): 611–15. http://dx.doi.org/10.1152/jappl.1987.62.2.611.
Testo completoAbstract (sommario):
The quadriceps femoris muscles of seven men were electrically stimulated under extended anaerobic conditions to quantitate anaerobic energy release and the contribution of the glycolytic system to total ATP production. Muscles were intermittently stimulated 64 times at 20 Hz while leg blood flow was occluded. Each contraction lasted 1.6 s and was followed by 1.6 s of rest. The total contraction time was 102.4 s. Muscle biopsies were taken at rest and following 16, 32, 48, and 64 contractions. The ATP turnover rates during the four 16-contraction periods were 6.12, 2.56, 2.17, and 0.64 mmol X kg dry muscle-1 X s-1 contraction time. Glycolysis provided 58%, phosphocreatine 40% and a decreased ATP store 2% of the consumed energy during the initial 16 contractions. Glycolysis was responsible for 90% of the total ATP production beyond contraction 16. Absolute glycolytic ATP production decreased to 60, 55, and 17% of the amount in the initial 16 contractions during the final three periods, respectively. In conclusion glycolysis produced approximately 195 mmol ATP/kg dry muscle during the initial 48 contractions (76.8 s) and only approximately 15 mmol ATP/kg dry muscle during the final 16 contractions. Equivalent values for total ATP turnover were 278 and 16.5 mmol/kg dry muscle.
25
Ushiyama, Junichi, Yoshihisa Masakado, Toshiyuki Fujiwara, Tetsuya Tsuji, Kimitaka Hase, Akio Kimura, Meigen Liu e Junichi Ushiba. "Contraction level-related modulation of corticomuscular coherence differs between the tibialis anterior and soleus muscles in humans". Journal of Applied Physiology 112, n. 8 (15 aprile 2012): 1258–67. http://dx.doi.org/10.1152/japplphysiol.01291.2011.
Testo completoAbstract (sommario):
The sensorimotor cortex activity measured by scalp EEG shows coherence with electromyogram (EMG) activity within the 15- to 35-Hz frequency band (β-band) during weak to moderate intensity of isometric voluntary contraction. This coupling is known to change its frequency band to the 35- to 60-Hz band (γ-band) during strong contraction. This study aimed to examine whether such contraction level-related modulation of corticomuscular coupling differs between muscles with different muscle compositions and functions. In 11 healthy young adults, we quantified the coherence between EEG over the sensorimotor cortex and rectified EMG during tonic isometric voluntary contraction at 10–70% of maximal voluntary contraction of the tibialis anterior (TA) and soleus (SOL) muscles, respectively. In the TA, the EEG-EMG coherence shifted from the β-band to the γ-band with increasing contraction level. Indeed, the magnitude of β-band EEG-EMG coherence was significantly decreased, whereas that of γ-band coherence was significantly increased, when the contraction level was above 60% of maximal voluntary contraction. In contrast to the TA, the SOL showed no such frequency changes of EEG-EMG coherence with alterations in the contraction levels. In other words, the maximal peak of EEG-EMG coherence in the SOL existed within the β-band, irrespective of the contraction levels. These findings suggest that the central nervous system regulates the frequency of corticomuscular coupling to exert the desired levels of muscle force and, notably, that the applicable rhythmicity of the coupling for performing strong contractions differs between muscles, depending on the physiological muscle compositions and functions of the contracting muscle.
26
Dalton, Brian H., Brad Harwood, Andrew W. Davidson e Charles L. Rice. "Triceps surae contractile properties and firing rates in the soleus of young and old men". Journal of Applied Physiology 107, n. 6 (dicembre 2009): 1781–88. http://dx.doi.org/10.1152/japplphysiol.00464.2009.
Testo completoAbstract (sommario):
Mean maximal motor unit firing rates (MUFRs) of the human soleus are lower (5–20 Hz) than other limb muscles (20–50 Hz) during brief sustained contractions. With healthy adult aging, maximal MUFRs are 20–40% lower and twitch contractile speed of lower limb muscles are 10–40% slower compared with young adults. However, it is unknown whether the inherently low maximal MUFRs for the soleus are further reduced with aging in association with age-related slowing in contractile properties. The purpose of the present study was to compare the changes in triceps surae contractile properties and MUFRs of the soleus throughout a variety of contraction intensities in six old (∼75 yr old) and six young (∼24 yr old) men. Neuromuscular measures were collected from the soleus and triceps surae during repeated sessions (2–6 sessions). Populations of single MUFR trains were recorded from the soleus with tungsten microelectrodes during separate sustained 6- to 10-s isometric contractions of varying intensities [25%, 50%, 75%, and 100% maximal voluntary isometric contraction (MVC)]. The old men had weaker triceps surae strength (MVC; 35% lower) and slower contractile properties (contraction duration; 20% longer) than the young men. However, there was no difference in average MUFRs of the soleus at 75% and 100% MVC (∼14.5 Hz and ∼16.5 Hz, respectively). At 25% and 50% MVC, average rates were 10% and 20% lower in the old men compared with young, respectively. Despite a significant slowing in triceps surae contraction duration, there was no age-related change in MUFRs recorded at high contractile intensities in the soleus. Thus the relationship between the whole muscle contractile properties and MUFRs found in other muscle groups may not exist between the triceps surae and soleus and may be muscle dependent.
27
Pal, Anupam, e James G. Brasseur. "The Mechanical Advantage of Local Longitudinal Shortening on Peristaltic Transport". Journal of Biomechanical Engineering 124, n. 1 (24 settembre 2001): 94–100. http://dx.doi.org/10.1115/1.1427700.
Testo completoAbstract (sommario):
Whereas bolus transport along the esophagus results from peristaltic contractions of the circular muscle layer, it has been suggested that local shortening of the longitudinal muscle layer concentrates circular muscle fibers in the region where the highest contractile pressures are required. Here we analyze the mechanical consequences of local longitudinal shortening (LLS) through a mathematical model based on lubrication theory. We find that local pressure and shear stress in the contraction zone are greatly reduced by the existence of LLS. In consequence, peak contractile pressure is reduced by nearly 2/3 at physiological LLS, and this reduction is greatest when peak in LLS is well aligned with peak contractile pressure. We conclude that a peristaltic wave of local longitudinal muscle contraction coordinated with the circular muscle contraction wave has both a great physiological advantage (concentrating circular muscle fibers), and a great mechanical advantage (reducing the level of contractile force required to transport the bolus), which combine to greatly reduce circular muscle tone during esophageal peristalsis.
28
Chen, Ting, Timothy M. Moore, Mark T. W. Ebbert, Natalie L. McVey, Steven R. Madsen, David M. Hallowell, Alexander M. Harris et al. "Liver kinase B1 inhibits the expression of inflammation-related genes postcontraction in skeletal muscle". Journal of Applied Physiology 120, n. 8 (15 aprile 2016): 876–88. http://dx.doi.org/10.1152/japplphysiol.00727.2015.
Testo completoAbstract (sommario):
Skeletal muscle-specific liver kinase B1 (LKB1) knockout mice (skmLKB1-KO) exhibit elevated mitogen-activated protein kinase (MAPK) signaling after treadmill running. MAPK activation is also associated with inflammation-related signaling in skeletal muscle. Since exercise can induce muscle damage, and inflammation is a response triggered by damaged tissue, we therefore hypothesized that LKB1 plays an important role in dampening the inflammatory response to muscle contraction, and that this may be due in part to increased susceptibility to muscle damage with contractions in LKB1-deficient muscle. Here we studied the inflammatory response and muscle damage with in situ muscle contraction or downhill running. After in situ muscle contractions, the phosphorylation of both NF-κB and STAT3 was increased more in skmLKB1-KO vs. wild-type (WT) muscles. Analysis of gene expression via microarray and RT-PCR shows that expression of many inflammation-related genes increased after contraction only in skmLKB1-KO muscles. This was associated with mild skeletal muscle fiber membrane damage in skmLKB1-KO muscles. Gene markers of oxidative stress were also elevated in skmLKB1-KO muscles after contraction. Using the downhill running model, we observed significantly more muscle damage after running in skmLKB1-KO mice, and this was associated with greater phosphorylation of both Jnk and STAT3 and increased expression of SOCS3 and Fos. In conclusion, we have shown that the lack of LKB1 in skeletal muscle leads to an increased inflammatory state in skeletal muscle that is exacerbated by muscle contraction. Increased susceptibility of the muscle to damage may underlie part of this response.
29
Bark, H., G. S. Supinski, J. C. Lamanna e S. G. Kelsen. "Relationship of changes in diaphragmatic muscle blood flow to muscle contractile activity". Journal of Applied Physiology 62, n. 1 (1 gennaio 1987): 291–99. http://dx.doi.org/10.1152/jappl.1987.62.1.291.
Testo completoAbstract (sommario):
The effect of increases in diaphragmatic muscle contractile activity on diaphragm blood flow remains unclear. The present study examined the effect of electrically induced isometric diaphragmatic muscle contractions on diaphragmatic blood flow. Studies were performed on diaphragmatic muscle strips prepared in anesthetized mechanically ventilated dogs. Diaphragmatic contractile activity was quantitated as the tension-time index (TTI) (i.e., the product of tension magnitude and duration). Blood flow to the strip (Qdi) was measured from the volume of the phrenic venous effluent using a drop counter. The separate effects on Qdi of 30-s periods of continuous and rhythmic contractions were examined. Qdi increased with increases in TTI and peaked at a TTI of 20–30% of maximum after which Qdi fell progressively with further increases in TTI. At levels of TTI greater than 30%, the pattern of muscle contraction significantly affected blood flow. Qdi was significantly lower during activity and the postcontraction hyperemia significantly greater at a given TTI when contractions were continuous than when contractions were intermittent. Above a TTI of 30%, Qdi during contraction decreased linearly with increases in duty cycle and curvilinearly with increases in tension. We conclude that during isometric diaphragmatic contractions, diaphragmatic blood flow may become mechanically impeded, and the magnitude of the impediment in blood flow depends on the pattern of diaphragmatic contractions. With increases in contractile activity above a critical level, changes in duty cycle exert progressively greater effects on diaphragmatic blood flow than changes in muscle tension.
30
Giuriato, Gaia, Stephen J. Ives, Cantor Tarperi, Lorenzo Bortolan, Federico Ruzzante, Anna Pedrinolla, Camilla Martignon et al. "Timed synchronization of muscle contraction to heartbeat enhances muscle hyperemia". Journal of Applied Physiology 128, n. 4 (1 aprile 2020): 805–12. http://dx.doi.org/10.1152/japplphysiol.00898.2019.
Testo completoAbstract (sommario):
Blood flow (BF) to exercising muscles is susceptible to variations of intensity, and duration of skeletal muscle contractions, cardiac cycle, blood velocity, and vessel dilation. During cyclic muscle activity, these elements may change proportionally with or without direct optimal temporal alignment, likely influencing BF to active muscle. Ideally, the pulsed delivery of blood to active muscle timed with the inactive phase of muscle duty-cycle would enhance the peak and average BF. To investigate the phenomenon of muscle contraction and pulse synchronicity, electrically evoked muscle contractions (trains of 20 Hz, 200-ms duration) were synchronized with each systolic phase of the anterograde blood velocity spectrum (aBVS). Specifically, unilateral quadriceps contractions matched in-phase (IP) with the aBVS were compared with contractions matched out-of-phase (OP) with the aBVS in 10 healthy participants (26 ± 3 yr). During each trial, femoral BF of the contracting limb and central hemodynamics were recorded for 5 min with an ultrasound Doppler, a plethysmograph, and a cardioimpedance device. At steady state (5th min) IP BF (454 ± 30 mL/min) and vascular conductance (4.3 ± 0.2 mL·min−1·mmHg−1), and OP MAP (108 ± 2 mmHg) were significantly lower ( P < 0.001) in comparison to OP BF (784 ± 25 mL/min) and vascular conductance (6.7 ± 0.2 mL·min−1·mmHg−1), and IP MAP (113 ± 3 mmHg). On the contrary, no significant difference (all, P > 0.05) was observed between IP and OP central hemodynamics (HR: 79 ± 10 vs. 76 ± 11 bpm, CO: 8.0 ± 1.6 vs. 7.3 ± 1.6 L/min), and ventilatory patterns (V̇e:14 ± 2 vs. 14 ± 1 L/min, V̇o2:421 ± 70 vs. 397 ± 34 mL/min). The results suggest that muscle contractions occurring during OP that do not interfere with aBVS elicit a maximization of muscle functional hyperemia. NEW & NOTEWORTHY When muscle contraction is synchronized with the pulsed delivery of blood flow to active muscle, muscle functional hyperemia can be either maximized or minimized. This suggests a possibility to couple different strategies to enhance the acute and chronic effects of exercise on the cardiovascular system.
31
Del Valle, Alejandro, e Christine K. Thomas. "Motor unit firing rates during isometric voluntary contractions performed at different muscle lengths". Canadian Journal of Physiology and Pharmacology 82, n. 8-9 (1 luglio 2004): 769–76. http://dx.doi.org/10.1139/y04-084.
Testo completoAbstract (sommario):
Firing rates of motor units and surface EMG were measured from the triceps brachii muscles of able-bodied subjects during brief submaximal and maximal isometric voluntary contractions made at 5 elbow joint angles that covered the entire physiological range of muscle lengths. Muscle activation at the longest, midlength, and shortest muscle lengths, measured by twitch occlusion, averaged 98%, 97%, and 93% respectively, with each subject able to achieve complete activation during some contractions. As expected, the strongest contractions were recorded at 90° of elbow flexion. Mean motor unit firing rates and surface EMG increased with contraction intensity at each muscle length. For any given absolute contraction intensity, motor unit firing rates varied when muscle length was changed. However, mean motor unit firing rates were independent of muscle length when contractions were compared with the intensity of the maximal voluntary contraction (MVC) achieved at each joint angle.Key words: muscle activation, length–tension relationships, force–frequency relationships.
32
Yu, Ming-Fu, Isabelle Gorenne, Xiaoling Su, Robert S. Moreland e Michael I. Kotlikoff. "Sodium hydrosulfite contractions of smooth muscle are calcium and myosin phosphorylation independent". American Journal of Physiology-Lung Cellular and Molecular Physiology 275, n. 5 (1 novembre 1998): L976—L982. http://dx.doi.org/10.1152/ajplung.1998.275.5.l976.
Testo completoAbstract (sommario):
In an effort to further understand the processes underlying hypoxic pulmonary vasoconstriction, we examined the mechanism by which sodium hydrosulfite (Na2S2O4), a potent reducing agent and oxygen scavenger, induces smooth muscle contraction. In rat pulmonary arterial strips, sodium hydrosulfite (10 mM) induced contractions that were 65.9 ± 12.8% of the response to 60 mM KCl ( n = 9 segments). Contractions were not inhibited by nisoldipine (5 μM) or by repeated stimulation with caffeine (10 mM), carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (10 μM), or cyclopiazonic acid (10 μM), all of which eliminated responses to contractile agonists. Maximum force generation after exposure to sodium hydrosulfite was 0.123 ± 0.013 mN in the presence of 1.8 mM calcium and 0.127 ± 0.015 mN in the absence of calcium. Sodium hydrosulfite contractions in pulmonary arterial segments were not due to the generation of H2O2and occurred in the presence of chelerythrine (10 μM), which blocked phorbol ester contractions, and solution hyperoxygenation. Similar contractile responses were obtained in rat aortic and tracheal smooth muscles. Finally, contractions occurred in the complete absence of an increase in myosin light chain phosphorylation. Therefore sodium hydrosulfite-induced smooth muscle contraction is not specific to pulmonary arterial smooth muscle, is independent of calcium and myosin light chain phosphorylation, and is not mediated by either hypoxia or protein kinase C.
33
Lafleur, J., D. Zytnicki, G. Horcholle-Bossavit e L. Jami. "Declining inhibition in ipsi- and contralateral lumbar motoneurons during contractions of an ankle extensor muscle in the cat". Journal of Neurophysiology 70, n. 5 (1 novembre 1993): 1797–804. http://dx.doi.org/10.1152/jn.1993.70.5.1797.
Testo completoAbstract (sommario):
1. Motoneurons of pretibial ankle flexor and knee flexor and extensor muscles were recorded intracellularly in chloralose- or pentobarbitone-anesthetized cats during sustained submaximal contractions of either ipsi- or contralateral gastrocnemius medialis muscle (GM). 2. In a majority of ipsilateral motoneurons, a sustained GM contraction elicited inhibitory potentials that quickly subsided before the end of the contraction. An abrupt increase in contractile force could elicit a new series of inhibitory potentials, which declined again in spite of a maintained force level. 3. Contraction-induced effects were only exceptionally detected in contralateral triceps surae and plantaris motoneurons. In a small number of pretibial flexor and knee flexor and extensor motoneurons, declining inhibitions were observed during sustained contractions of the contralateral GM muscle. 4. At the onset of GM contractions, a variety of motoneurons uniformly receive inhibitory inputs that are quickly filtered out. Although the functional significance of this widespread initial inhibition remains to be elucidated, its rapid decline seems useful to allow subsequent recruitment of motor units as may be required for coordination of posture and movement. 5. Tendon organs are activated during muscle contraction, but it is not certain whether Ib inputs from GM can account for all the effects observed. Contribution of other afferents was considered and tested using a different experimental approach. The companion paper reports observations suggesting that effects elicited by group II afferents may cooperate in the contraction-induced inhibition of motoneurons.
34
Komalavilas, Padmini, Shyamal Mehta, Christopher J. Wingard, Daniel T. Dransfield, Jyoti Bhalla, Julie E. Woodrum, Jason R. Molinaro e Colleen M. Brophy. "PI3-kinase/Akt modulates vascular smooth muscle tone via cAMP signaling pathways". Journal of Applied Physiology 91, n. 4 (1 ottobre 2001): 1819–27. http://dx.doi.org/10.1152/jappl.2001.91.4.1819.
Testo completoAbstract (sommario):
Phosphatidylinositol 3-kinase (PI3-kinase) activates protein kinase B (also known as Akt), which phosphorylates and activates a cyclic nucleotide phosphodiesterase 3B. Increases in cyclic nucleotide concentrations inhibit agonist-induced contraction of vascular smooth muscle. Thus we hypothesized that the PI3-kinase/Akt pathway may regulate vascular smooth muscle tone. In unstimulated, intact bovine carotid artery smooth muscle, the basal phosphorylation of Akt was higher than that in cultured smooth muscle cells. The phosphorylation of Akt decreases in a time-dependent manner when incubated with the PI3-kinase inhibitor, LY-294002. Agonist (serotonin)-, phorbol ester (phorbol 12,13-dibutyrate; PDBu)-, and depolarization (KCl)-induced contractions of vascular smooth muscles were all inhibited in a dose-dependent fashion by LY-294002. However, LY-294002 did not inhibit serotonin- or PDBu-induced increases in myosin light chain phosphorylation or total O2 consumption, suggesting that inhibition of contraction was not mediated by reversal or inhibition of the pathways that lead to smooth muscle activation and contraction. Treatment of vascular smooth muscle with LY-294002 increased the activity of cAMP-dependent protein kinase and increased the phosphorylation of the cAMP-dependent protein kinase substrate heat shock protein 20 (HSP20). These data suggest that activation of the PI3-kinase/Akt pathway in unstimulated smooth muscle may modulate vascular smooth muscle tone (allow agonist-induced contraction) through inhibition of the cyclic nucleotide/HSP20 pathway and suggest that cyclic nucleotide-dependent inhibition of contraction is dissociated from the myosin light chain contractile regulatory pathways.
35
Locke, Marius, e Stephanie A. Salerno. "Ovariectomy alters lengthening contraction induced heat shock protein expression". Applied Physiology, Nutrition, and Metabolism 45, n. 5 (maggio 2020): 530–38. http://dx.doi.org/10.1139/apnm-2019-0212.
Testo completoAbstract (sommario):
Estrogen appears to play a role in minimizing skeletal muscle damage as well as regulating the expression of the protective heat shock proteins (HSPs). To clarify the relationship between estrogen, muscle HSP content, and muscle damage, tibialis anterior (TA) muscles from ovary-intact (OVI; n = 12) and ovariectomized (OVX; 3 weeks, n = 12) female Sprague–Dawley rats were subjected to either 20 or 40 lengthening contractions (LCs). Twenty-four hours after stimulation, TA muscles were removed, processed, and assessed for HSP25 and HSP72 content as well as muscle (damage) morphology. No differences in muscle contractile properties were observed in TA muscles between OVI and OVX animals for peak torque during the LCs. In unstressed TA muscles, the basal expression of HSP72 expression was decreased in OVX animals (P < 0.05) while HSP25 content remained unchanged. Following 20 LCs, HSP25 content was elevated (P < 0.05) in TA muscles from OVX animals but unchanged in muscles from OVI animals. Following 40 LCs, HSP25 content was elevated (P < 0.01) in TA muscles from both OVI and OVX animals while HSP72 content was elevated only in TA muscles from OVI animals (P < 0.05). Taken together, these data suggest the loss of ovarian hormones, such as estrogen, may impair the skeletal muscle cellular stress response thereby rendering muscles more susceptible to certain types of contraction induced damage. Novelty Ovariectomy alters muscle HSP72 content. Muscle contractile measures are maintained following ovariectomy.
36
Brozinick, J. T., G. J. Etgen, B. B. Yaspelkis e J. L. Ivy. "The effects of muscle contraction and insulin on glucose-transporter translocation in rat skeletal muscle". Biochemical Journal 297, n. 3 (1 febbraio 1994): 539–45. http://dx.doi.org/10.1042/bj2970539.
Testo completoAbstract (sommario):
The effect of electrically induced muscle contraction, insulin (10 m-units/ml) and electrically-induced muscle contraction in the presence of insulin on insulin-regulatable glucose-transporter (GLUT-4) protein distribution was studied in female Sprague-Dawley rats during hindlimb perfusion. Plasma-membrane cytochalasin B binding increased approximately 2-fold, whereas GLUT-4 protein concentration increased approximately 1.5-fold above control with contractions, insulin, or insulin + contraction. Microsomal-membrane cytochalasin B binding and GLUT-4 protein concentration decreased by approx. 30% with insulin or insulin + contraction, but did not significantly decrease with contraction alone. The rate of muscle glucose uptake was assessed by determining the rate of 2-deoxy[3H]glucose accumulation in the soleus, plantaris, and red and white portions of the gastrocnemius. Both contraction and insulin increased glucose uptake significantly and to the same degree in the muscles examined. Insulin + contraction increased glucose uptake above that of insulin or contraction alone, but this effect was only statistically significant in the soleus, plantaris and white gastrocnemius. The combined effects of insulin + contraction of glucose uptake were not fully additive in any of the muscles investigated. These results suggest that (1) insulin and muscle contraction are mobilizing two separate pools of GLUT-4 protein, and (2) the increase in skeletal-muscle glucose uptake due to insulin + contraction is not due to an increase in plasma-membrane GLUT-4 protein concentration above that observed for insulin or contraction alone.
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Teplov, A. Yu, A. M. Farkhutdinov, S. N. Grishin, M. M. Minnebaev e V. I. Torshin. "Possible involvement of adenosine triphosphate in the mechanisms of protein sensibilization effect on the functional properties of the diaphragm and skeletal muscles". Kazan medical journal 93, n. 1 (15 febbraio 2012): 113–16. http://dx.doi.org/10.17816/kmj2159.
Testo completoAbstract (sommario):
Aim. To study the effect of adenosine triphosphate on the contractile function and non-quantum secretion of acetylcholine at the endplate zone (H-effect) of isolated mouse muscles on the background of protein sensibilization. Methods. The experiments were performed on white mice. Sensibilization was carried out by ovalbumin with an aluminum hydroxide gel. Mechanomyography studies were performed on isolated preparations of the diaphragm and of two leg muscles in isometric conditions. The contractions were recorded by a photoelectric converter. In order to study the condition of the postsynaptic membrane of the muscle fibers measured was the non-quantum secretion of acetylcholine. Compared were the parameters of muscle contraction before and after 5 min of perfusion with a solution of adenosine triphosphate. Results. In the diaphragm and in the soleus muscle the dynamics of the force vector of the muscular contraction correlated with the changes in the H-effect in all the studied experimental models. However, the extent of these changes in the sensibilized animals is less pronounced. Conclusion. It is possible that adenosine triphosphate affects the functional properties of both muscle during protein sensibilization; the change in the contraction force of the long extensor digitorum muscle during sensibilization is not related to the mechanisms of muscle excitation, mediated by adenosine triphosphate.
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Lou, F., N. A. Curtin e R. C. Woledge. "Elastic energy storage and release in white muscle from dogfish scyliorhinus canicula". Journal of Experimental Biology 202, n. 2 (15 gennaio 1999): 135–42. http://dx.doi.org/10.1242/jeb.202.2.135.
Testo completoAbstract (sommario):
The production of work by the contractile component (CC) and the storage and release of work in the elastic structures that act in series (the series elastic component, SEC) with the contractile component were measured using white muscle fibres from the dogfish Scyliorhinus canicula. Heat production was also measured because the sum of work and heat is equivalent to the energy cost of the contraction (ATP used). These energy fluxes were evaluated in contractions with constant-velocity shortening either during stimulation or during relaxation. The muscle preparation was tetanized for 0.6 s and shortened by 1 mm (approximately 15 % of L0) at 3.5 or 7.0 mm s-1 (approximately 15 or 30 % of V0), where L0 is the muscle length at which isometric force is greatest and V0 is the maximum velocity of shortening. In separate experiments, the stiffness of the SEC was characterized from measurements of force responses to step changes in the length of contracting muscle. Using the values of SEC stiffness, we evaluated separately the work and heat associated with the CC and with the SEC. The major findings were (1) that work stored in the SEC could be completely recovered as external work when shortening occurred during relaxation (none of the stored work being degraded into heat) and (2) that, when shortening occurred progressively later during the contraction, the total energy cost of the contraction declined towards that of an isometric contraction.
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Beaty, O. "Arterial blood pressure control during hindlimb and forelimb contraction in the dog". American Journal of Physiology-Heart and Circulatory Physiology 248, n. 5 (1 maggio 1985): H678—H687. http://dx.doi.org/10.1152/ajpheart.1985.248.5.h678.
Testo completoAbstract (sommario):
This study examined the differential reflex cardiovascular responses evoked by separate contractions of the right hindlimb and forelimb and established the mechanism of a regional reflex vasodilation associated with hindlimb skeletal muscle contraction. The two groups of skeletal muscle were contracted separately by electrical stimulation (2-48 Hz) of the peripheral motor nerves. The left nonexercising hindlimb was perfused at constant flow. All blood pressure-regulating mechanisms were intact. Arterial blood pressure (ABP), left nonexercising hindlimb perfusion pressure (HLPP), and heart rate (HR) were recorded. HR was increased by skeletal muscle contraction. This response was independent of muscle group and contraction frequency. Increases in both ABP and HLPP were produced by high-frequency contractions (greater than 16 Hz) of either the hindlimb or forelimb. Decreases were evoked only by hindlimb contractions (greater than 8 Hz). The nonexercising skeletal muscle vascular bed contributed to this systemic depressor response by vasodilating. The mechanism involved a contraction-induced withdrawal of sympathetic nerve activity to that vascular bed. Concomitant with this response was an increase in heart rate that was blocked with propranolol. Similar heart rate changes evoked by forelimb contractions also were blocked with propranolol. These data indicate that sympathetic outflow to resting skeletal muscle depends on the origin and magnitude of the afferent signal from the contracting skeletal muscle.
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Sarna, S. K. "Gastrointestinal longitudinal muscle contractions". American Journal of Physiology-Gastrointestinal and Liver Physiology 265, n. 1 (1 luglio 1993): G156—G164. http://dx.doi.org/10.1152/ajpgi.1993.265.1.g156.
Testo completoAbstract (sommario):
The patterns of longitudinal muscle contractions of the stomach and the small intestine and their relationship with circular muscle contractions during the fasting and the fed state were investigated in conscious dogs. In the stomach, the longitudinal muscle contracted in a 1:1 relationship with the circular muscle contractions. There was no significant difference between the frequency, duration, and time of onset of gastric longitudinal and circular muscle contractions, and their amplitudes were significantly correlated with each other. In the small intestine when the circular muscle contracted, the longitudinal muscle exhibited passive elongation during the fasting and the fed state. There was no significant difference between the onset, duration, and frequency of small intestinal circular muscle contractions and the passive longitudinal muscle elongations; their amplitudes were strongly correlated with each other. During a circular muscle giant migrating contraction, the longitudinal muscle exhibited a monophasic contraction, initially a contraction followed by passive elongation or a pure passive elongation. During a retrograde giant contraction, the longitudinal muscle exhibited only a pure monophasic contraction or a contraction-elongation complex. These data suggest that the enteric nerves in the small intestine innervate the two muscle layers in a reciprocal fashion and those in the stomach in a complementary fashion.
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Yoshinaga, M., Y. Chijiiwa, T. Misawa, N. Harada e H. Nawata. "EndothelinB receptor on guinea pig small intestinal smooth muscle cells". American Journal of Physiology-Gastrointestinal and Liver Physiology 262, n. 2 (1 febbraio 1992): G308—G311. http://dx.doi.org/10.1152/ajpgi.1992.262.2.g308.
Testo completoAbstract (sommario):
We investigated the binding characteristics of the endothelin (ET) receptor and the mechanism by which ET induces contraction of longitudinal smooth muscle cells of the guinea pig small intestine by using vasoactive intestinal contractor (VIC), a mouse variant of ET-2. A functional receptor for VIC was found to exist on longitudinal smooth muscle cells. These cells showed a similar binding of and contractile response to ET-1, ET-2, and ET-3. Inhibitors of both intracellular and extracellular Ca2+ movement attenuated the VIC-induced contraction of longitudinal smooth muscle cells. These results suggest that smooth muscle cells of the guinea pig small intestine express the ETB receptor that primarily mediates the contractile effect on smooth muscle cells. In addition, ET-induced contraction depends on intracellular as well as extracellular Ca2+.
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Wigmore, D. M., B. M. Damon, D. M. Pober e J. A. Kent-Braun. "MRI measures of perfusion-related changes in human skeletal muscle during progressive contractions". Journal of Applied Physiology 97, n. 6 (dicembre 2004): 2385–94. http://dx.doi.org/10.1152/japplphysiol.01390.2003.
Testo completoAbstract (sommario):
Although skeletal muscle perfusion is fundamental to proper muscle function, in vivo measurements are typically limited to those of limb or arterial blood flow, rather than flow within the muscle bed itself. We present a noninvasive functional MRI (fMRI) technique for measuring perfusion-related signal intensity (SI) changes in human skeletal muscle during and after contractions and demonstrate its application to the question of occlusion during a range of contraction intensities. Eight healthy men (aged 20–31 yr) performed a series of isometric ankle dorsiflexor contractions from 10 to 100% maximal voluntary contraction. Axial gradient-echo echo-planar images (repetition time = 500 ms, echo time = 18.6 ms) were acquired continuously before, during, and following each 10-s contraction, with 4.5-min rest between contractions. Average SI in the dorsiflexor muscles was calculated for all 240 images in each contraction series. Postcontraction hyperemia for each force level was determined as peak change in SI after contraction, which was then scaled to that obtained following a 5-min cuff occlusion of the thigh (i.e., maximal hyperemia). A subset of subjects ( n = 4) performed parallel studies using venous occlusion plethysmography to measure limb blood flow. Hyperemia measured by fMRI and plethysmography demonstrated good agreement. Postcontraction hyperemia measured by fMRI scaled with contraction intensity up to ∼60% maximal voluntary contraction. fMRI provides a noninvasive means of quantifying perfusion-related changes during and following skeletal muscle contractions in humans. Temporal changes in perfusion can be observed, as can the heterogeneity of perfusion across the muscle bed.
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Maganaris, Constantinos N., Vasilios Baltzopoulos e Anthony J. Sargeant. "Repeated contractions alter the geometry of human skeletal muscle". Journal of Applied Physiology 93, n. 6 (1 dicembre 2002): 2089–94. http://dx.doi.org/10.1152/japplphysiol.00604.2002.
Testo completoAbstract (sommario):
The aim of this study was to investigate the effect of repeated contractions on the geometry of human skeletal muscle. Six men performed two sets ( sets Aand B) of 10 repeated isometric plantarflexion contractions at 80% of the moment generated during plantarflexion maximal voluntary contraction (MVC), with a rest interval of 15 min between sets. By use of ultrasound, the geometry of the medial gastrocnemius (MG) muscle was measured in the contractions of set A and the displacement of the MG tendon origin in the myotendinous junction was measured in the contractions of set B. In the transition from the 1st to the 10th contractions, the fascicular length at 80% of MVC decreased from 34 ± 4 (means ± SD) to 30 ± 3 mm ( P < 0.001), the pennation angle increased from 35 ± 3 to 42 ± 3° ( P < 0.001), the myotendinous junction displacement increased from 5 ± 3 to 10 ± 3 mm ( P < 0.001), and the average fascicular curvature remained constant ( P > 0.05) at ∼4.3 m−1. No changes ( P > 0.05) were found in fascicular length, pennation angle, and myotendinous junction displacement after the fifth contraction. Electrogoniometry showed that the ankle rotated by ∼6.5° during contraction, but no differences ( P > 0.05) were obtained between contractions. The present results show that repeated contractions induce tendon creep, which substantially affects the geometry of the in-series contracting muscles, thus altering their potential for force and joint moment generation.
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James, Arlene N., James P. Ryan e Henry P. Parkman. "Inhibitory effects of botulinum toxin on pyloric and antral smooth muscle". American Journal of Physiology-Gastrointestinal and Liver Physiology 285, n. 2 (agosto 2003): G291—G297. http://dx.doi.org/10.1152/ajpgi.00296.2002.
Testo completoAbstract (sommario):
Botulinum toxin injection into the pylorus is reported to improve gastric emptying in gastroparesis. Classically, botulinum toxin inhibits ACh release from cholinergic nerves in skeletal muscle. The aim of this study was to determine the effects of botulinum toxin on pyloric smooth muscle. Guinea pig pyloric muscle strips were studied in vitro. Botulinum toxin type A was added; electric field stimulation (EFS) was performed every 30 min for 6 h. ACh (100 μM)-induced contractile responses were determined before and after 6 h. Botulinum toxin caused a concentration-dependent decrease of pyloric contractions to EFS. At a low concentration (2 U/ml), botulinum toxin decreased pyloric contractions to EFS by 43 ± 9% without affecting ACh-induced contractions. At higher concentrations (10 U/ml), botulinum toxin decreased pyloric contraction to EFS by 75 ± 7% and decreased ACh-induced contraction by 79 ± 9%. In conclusion, botulinum toxin inhibits pyloric smooth muscle contractility. At a low concentration, botulinum toxin decreases EFS-induced contractile responses without affecting ACh-induced contractions suggesting inhibition of ACh release from cholinergic nerves. At higher concentrations, botulinum toxin directly inhibits smooth muscle contractility as evidenced by the decreased contractile response to ACh.
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Raiteri, Brent J., Andrew G. Cresswell e Glen A. Lichtwark. "Three-dimensional geometrical changes of the human tibialis anterior muscle and its central aponeurosis measured with three-dimensional ultrasound during isometric contractions". PeerJ 4 (28 luglio 2016): e2260. http://dx.doi.org/10.7717/peerj.2260.
Testo completoAbstract (sommario):
Background.Muscles not only shorten during contraction to perform mechanical work, but they also bulge radially because of the isovolumetric constraint on muscle fibres. Muscle bulging may have important implications for muscle performance, however quantifying three-dimensional (3D) muscle shape changes in human muscle is problematic because of difficulties with sustaining contractions for the duration of anin vivoscan. Although two-dimensional ultrasound imaging is useful for measuring local muscle deformations, assumptions must be made about global muscle shape changes, which could lead to errors in fully understanding the mechanical behaviour of muscle and its surrounding connective tissues, such as aponeurosis. Therefore, the aims of this investigation were (a) to determine the intra-session reliability of a novel 3D ultrasound (3DUS) imaging method for measuringin vivohuman muscle and aponeurosis deformations and (b) to examine how contraction intensity influencesin vivohuman muscle and aponeurosis strains during isometric contractions.Methods.Participants (n= 12) were seated in a reclined position with their left knee extended and ankle at 90° and performed isometric dorsiflexion contractions up to 50% of maximal voluntary contraction. 3DUS scans of the tibialis anterior (TA) muscle belly were performed during the contractions and at rest to assess muscle volume, muscle length, muscle cross-sectional area, muscle thickness and width, fascicle length and pennation angle, and central aponeurosis width and length. The 3DUS scan involved synchronous B-mode ultrasound imaging and 3D motion capture of the position and orientation of the ultrasound transducer, while successive cross-sectional slices were captured by sweeping the transducer along the muscle.Results.3DUS was shown to be highly reliable across measures of muscle volume, muscle length, fascicle length and central aponeurosis length (ICC ≥ 0.98, CV < 1%). The TA remained isovolumetric across contraction conditions and progressively shortened along its line of action as contraction intensity increased. This caused the muscle to bulge centrally, predominantly in thickness, while muscle fascicles shortened and pennation angle increased as a function of contraction intensity. This resulted in central aponeurosis strains in both the transverse and longitudinal directions increasing with contraction intensity.Discussion.3DUS is a reliable and viable method for quantifying multidirectional muscle and aponeurosis strains during isometric contractions within the same session. Contracting muscle fibres do work in directions along and orthogonal to the muscle’s line of action and central aponeurosis length and width appear to be a function of muscle fascicle shortening and transverse expansion of the muscle fibres, which is dependent on contraction intensity. How factors other than muscle force change the elastic mechanical behaviour of the aponeurosis requires further investigation.
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Gunst, S. J., e J. M. Pisoni. "Effects of extracellular calcium on canine tracheal smooth muscle". Journal of Applied Physiology 61, n. 2 (1 agosto 1986): 706–11. http://dx.doi.org/10.1152/jappl.1986.61.2.706.
Testo completoAbstract (sommario):
Strips of canine tracheal smooth muscle were studied in vitro to determine the effects of changes in the extracellular calcium (Cao) concentration on tonic contractions induced by acetylcholine and 5-hydroxytryptamine. Strips were contracted with graded concentrations of the above agents in 2.4 mM Ca, after which CaCl2 was administered to achieve final concentrations of 5.0, 10.0, and 20.0 mM. Increases in Cao to 5 mM or above caused significant relaxation of muscles contracted with 5-hydroxytryptamine but did not significantly relax muscles contracted with acetylcholine. Increases in Cao also caused significant relaxation of muscles contracted with low concentrations of K+ (20 or 30 mM). However, in 60 or 120 mM K+, increases in Cao resulted predominantly in muscle contraction. Inhibition of the Na+-K+-ATPase by ouabain (10(-5) M) or K+ depletion reversed the effects of Cao from relaxation to contraction in tissues contracted with 5-hydroxytryptamine. Increases in Cao also caused contraction rather than relaxation in the presence of verapamil (10(-6) M). We conclude that calcium has both excitatory and inhibitory effects on the contractile responses of canine tracheal smooth muscle. The inhibitory effects of Ca2+ appear to be linked to the activity of the membrane Na+-K+-ATPase.
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Selseth, Angie, Marilyn Dayton, Mitchell L. Cordova, Christopher D. Ingersoll e Mark A. Merrick. "Quadriceps Concentric EMG Activity Is Greater than Eccentric EMG Activity during the Lateral Step-Up Exercise". Journal of Sport Rehabilitation 9, n. 2 (maggio 2000): 124–34. http://dx.doi.org/10.1123/jsr.9.2.124.
Testo completoAbstract (sommario):
Purpose:To analyze vastus medialis obliquus (VMO) and vastus lateralis (VL) muscle activity during the concentric and eccentric phases of a lateral step-up exercise.Design:Repeated-measures. Dependent variable: the integrated electromyogram measured as a percentage of the maximal voluntary isometric contraction of the VMO and VL muscles. Independent variable: muscle contraction with 2 levels (concentric and eccentric).Subjects:Twenty-three volunteers with no previous history of knee surgery or anterior knee pain.Methods:Surface electrodes were positioned over the VMO and VL, and electromyographic data were collected during the exercise.Results:The 2 muscle phases of contraction were different when both dependent variables were considered simultaneously (F2,7= 33.2,P< .001). Concentric contractions produced greater muscle activity for VL (P< .05) and VMO (P< .05).Conclusions:Because concentric contractions produce greater activity than eccentric contractions do during the lateral step-up exercise, they provide a stronger stimulus for muscle activation, which might result in greater muscle strength gains.
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Kristiansen, S., S. Asp e E. A. Richter. "Decreased muscle GLUT-4 and contraction-induced glucose transport after eccentric contractions". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 271, n. 2 (1 agosto 1996): R477—R482. http://dx.doi.org/10.1152/ajpregu.1996.271.2.r477.
Testo completoAbstract (sommario):
Eccentric exercise causes muscle damage and decreased muscle glycogen and glucose transporter isoform (GLUT-4) protein content. We investigated whether the contraction-induced increase in skeletal muscle glucose transport and muscle performance is affected by prior eccentric contractions. The calf muscles from rats were stimulated for eccentric (EC) or concentric (CC) contractions or were passively stretched (ST). Muscles from unstimulated control (CT) rats were also studied. Two days later, all rats had their isolated hindlimbs perfused either at rest or during 15 min of isometric muscle contractions. EC rats had a significantly lower total GLUT-4 protein content in the white gastrocnemius (GW) muscle (55%) and red gastrocnemius (GR) muscle (34%) compared with muscle from the CT, ST, and CC rats. In contrast, GLUT-1 protein content was approximately twofold higher in the GW muscle in EC rats than in CT rats. In the GW and GR muscle, prior eccentric exercise decreased contraction-induced stimulation of glucose transport compared with CT, ST, and CC rats despite no difference in tension development and oxygen uptake among the groups. There was no change in total GLUT-4 content and glucose transport in the soleus (S) muscle among the four group. It is concluded that the GLUT-4 and GLUT-1 protein contents in fast-twitch muscle are decreased and increased, respectively, 2 days after eccentric contractions. The functional consequence of these changes appears to be decreased contraction-induced increase in skeletal muscle glucose transport.
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Young, J. C., T. G. Kurowski, A. M. Maurice, R. Nesher e N. B. Ruderman. "Polymyxin B inhibits contraction-stimulated glucose uptake in rat skeletal muscle". Journal of Applied Physiology 70, n. 4 (1 aprile 1991): 1650–54. http://dx.doi.org/10.1152/jappl.1991.70.4.1650.
Testo completoAbstract (sommario):
Glucose transport in muscle is activated by contractile activity, an effect that persists in the postexercise state. Polymyxin B, a cyclic decapeptide antibiotic, inhibits the stimulation of glucose uptake in isolated muscle by contractile activity but also decreases tension development in electrically stimulated muscle. The purpose of this study was to determine whether polymyxin B also inhibits contraction-stimulated glucose uptake after in vivo administration of the drug and to examine the relationship between the effects of polymyxin B on tension development and its effects on contraction-stimulated glucose uptake. When polymyxin B was administered to rats in vivo, glucose uptake in muscle after electrical stimulation was decreased, despite the same amount of tension developed as in control rats, indicating an effect of polymyxin B on glucose transport independent of tension development. Our results also indicate that the postexercise increase in glucose uptake is a function of the tension developed by prior contractions. When muscles were perfused with medium containing polymyxin B, this relationship was disrupted. These results provide evidence that polymyxin B causes a decrease in muscle glucose uptake independent of its effects on tension development. The extent to which its effects on glucose uptake are also the result of a diminution in contractile force is uncertain.
50
Beaty, O. "Carotid sinus and blood pressure control during hindlimb and forelimb contractions". American Journal of Physiology-Heart and Circulatory Physiology 248, n. 5 (1 maggio 1985): H688—H694. http://dx.doi.org/10.1152/ajpheart.1985.248.5.h688.
Testo completoAbstract (sommario):
Arterial blood pressure (ABP) regulation during exercise involves in part medullary interaction of afferent information from contracting skeletal muscles and the major baroreceptors. This study examined in chloralose-anesthetized dogs the role of the carotid sinus baroreceptors in modulating reflex changes in ABP, nonexercising hindlimb skeletal muscle vascular resistance, and heart rate (HR) evoked by two separately contracting (4, 16, and 48 Hz) groups of skeletal muscle, the right hindlimb and forelimb. When arterial and cardiopulmonary baroreceptor afferent information was interrupted, hindlimb contractions evoked a greater augmentation of ABP (16 and 48 Hz) and no further increase in nonexercising hindlimb perfusion pressure (HLPP). Forelimb contractions, which in the presence of baroreceptors had not affected ABP (4 and 16 Hz), now reduced it profoundly. Nonexercising HLPP, which increased independently of contraction frequency, now was decreased by 4 Hz, not affected by 16 Hz, and increased by 48 Hz. The increase in HR was abolished. Increasing carotid sinus pressure to 220 mmHg in vagotomized dogs abolished the reflex changes evoked by hindlimb skeletal muscle contractions. However, forelimb contractions continued to decrease ABP. Nonexercising HLPP and HR did not change from the precontraction values. These data indicate that the carotid sinus baroreceptor could buffer completely those changes in the selected cardiovascular variables evoked by hindlimb but not forelimb skeletal muscle contractions. Thus the role of the carotid sinus baroreceptors in controlling ABP during exercise depends on the group of skeletal muscle initiating the somatic afferent signal and its influence on the contraction-induced distribution of the efferent signals.