Journal articles on the topic 'Length Contraction'
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1
Mehta, D., M. F. Wu, and 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, no. 1 (January 1, 1996): C243—C252. http://dx.doi.org/10.1152/ajpcell.1996.270.1.c243.
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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.
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Conley, Kevin E., and Stan L. Lindstedt. "Energy-saving mechanisms in muscle: the minimization strategy." Journal of Experimental Biology 205, no. 15 (August 1, 2002): 2175–81. http://dx.doi.org/10.1242/jeb.205.15.2175.
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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.
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Varian, Kenneth D., Ying Xu, Carlos A. A. Torres, Michelle M. Monasky, and Paul M. L. Janssen. "A random cycle length approach for assessment of myocardial contraction in isolated rabbit myocardium." American Journal of Physiology-Heart and Circulatory Physiology 297, no. 5 (November 2009): H1940—H1948. http://dx.doi.org/10.1152/ajpheart.01289.2008.
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It is well known that the strength of cardiac contraction is dependent on the cycle length, evidenced by the force-frequency relationship (FFR) and the existence of postrest potentiation (PRP). Because the contractile strength of the steady-state FFR and force-interval relationship involve instant intrinsic responses to cycle length as well as slower acting components such as posttranslational modification-based mechanisms, it remains unclear how cycle length intrinsically affects cardiac contraction and relaxation. To dissect the impact of cycle length changes from slower acting signaling components associated with persisting changes in cycle length, we developed a novel technique/protocol to study cycle length-dependent effects on cardiac function; twitch contractions of right ventricular rabbit trabeculae at different cycle lengths were randomized around a steady-state frequency. Patterns of cycle lengths that resulted in changes in force and/or relaxation times can now be identified and analyzed. Using this novel protocol, taking under 10 min to complete, we found that the duration of the cycle length before a twitch contraction (“primary” cycle length) positively correlated with force. In sharp contrast, the cycle length one (“secondary”) or two (“tertiary”) beats before the analyzed twitch correlated negatively with force. Using this protocol, we can quantify the intrinsic effect of cycle length on contractile strength while avoiding rundown and lengthiness that are often complications of FFR and PRP assessments. The data show that the history of up to three cycle lengths before a contraction influences myocardial contractility and that primary cycle length affects cardiac twitch dynamics in the opposite direction from secondary/tertiary cycle lengths.
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Joumaa, Venus, Ian C. Smith, Atsuki Fukutani, Timothy R. Leonard, Weikang Ma, Srboljub M. Mijailovich, Thomas C. Irving, and Walter Herzog. "Effect of Active Lengthening and Shortening on Small-Angle X-ray Reflections in Skinned Skeletal Muscle Fibres." International Journal of Molecular Sciences 22, no. 16 (August 8, 2021): 8526. http://dx.doi.org/10.3390/ijms22168526.
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Our purpose was to use small-angle X-ray diffraction to investigate the structural changes within sarcomeres at steady-state isometric contraction following active lengthening and shortening, compared to purely isometric contractions performed at the same final lengths. We examined force, stiffness, and the 1,0 and 1,1 equatorial and M3 and M6 meridional reflections in skinned rabbit psoas bundles, at steady-state isometric contraction following active lengthening to a sarcomere length of 3.0 µm (15.4% initial bundle length at 7.7% bundle length/s), and active shortening to a sarcomere length of 2.6 µm (15.4% bundle length at 7.7% bundle length/s), and during purely isometric reference contractions at the corresponding sarcomere lengths. Compared to the reference contraction, the isometric contraction after active lengthening was associated with an increase in force (i.e., residual force enhancement) and M3 spacing, no change in stiffness and the intensity ratio I1,1/I1,0, and decreased lattice spacing and M3 intensity. Compared to the reference contraction, the isometric contraction after active shortening resulted in decreased force, stiffness, I1,1/I1,0, M3 and M6 spacings, and M3 intensity. This suggests that residual force enhancement is achieved without an increase in the proportion of attached cross-bridges, and that force depression is accompanied by a decrease in the proportion of attached cross-bridges. Furthermore, the steady-state isometric contraction following active lengthening and shortening is accompanied by an increase in cross-bridge dispersion and/or a change in the cross-bridge conformation compared to the reference contractions.
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Del Valle, Alejandro, and Christine K. Thomas. "Motor unit firing rates during isometric voluntary contractions performed at different muscle lengths." Canadian Journal of Physiology and Pharmacology 82, no. 8-9 (July 1, 2004): 769–76. http://dx.doi.org/10.1139/y04-084.
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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.
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Rode, Christian, Tobias Siebert, Andre Tomalka, and Reinhard Blickhan. "Myosin filament sliding through the Z-disc relates striated muscle fibre structure to function." Proceedings of the Royal Society B: Biological Sciences 283, no. 1826 (March 16, 2016): 20153030. http://dx.doi.org/10.1098/rspb.2015.3030.
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Striated muscle contraction requires intricate interactions of microstructures. The classic textbook assumption that myosin filaments are compressed at the meshed Z-disc during striated muscle fibre contraction conflicts with experimental evidence. For example, myosin filaments are too stiff to be compressed sufficiently by the muscular force, and, unlike compressed springs, the muscle fibres do not restore their resting length after contractions to short lengths. Further, the dependence of a fibre's maximum contraction velocity on sarcomere length is unexplained to date. In this paper, we present a structurally consistent model of sarcomere contraction that reconciles these findings with the well-accepted sliding filament and crossbridge theories. The few required model parameters are taken from the literature or obtained from reasoning based on structural arguments. In our model, the transition from hexagonal to tetragonal actin filament arrangement near the Z-disc together with a thoughtful titin arrangement enables myosin filament sliding through the Z-disc. This sliding leads to swivelled crossbridges in the adjacent half-sarcomere that dampen contraction. With no fitting of parameters required, the model predicts straightforwardly the fibre's entire force–length behaviour and the dependence of the maximum contraction velocity on sarcomere length. Our model enables a structurally and functionally consistent view of the contractile machinery of the striated fibre with possible implications for muscle diseases and evolution.
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Lou, F., N. A. Curtin, and R. C. Woledge. "Elastic energy storage and release in white muscle from dogfish scyliorhinus canicula." Journal of Experimental Biology 202, no. 2 (January 15, 1999): 135–42. http://dx.doi.org/10.1242/jeb.202.2.135.
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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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Héroux, Martin Eric, Ida Anderman, Sofia Nykvist Vouis, Joanna Diong, Peter William Stubbs, and Robert D. Herbert. "History-dependence of muscle slack length in humans: effects of contraction intensity, stretch amplitude, and time." Journal of Applied Physiology 129, no. 4 (October 1, 2020): 957–66. http://dx.doi.org/10.1152/japplphysiol.00106.2020.
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The slack length of a relaxed human skeletal muscle is not fixed; it can be modified by contraction and stretch. Contraction of the human vastus lateralis muscle at short lengths reduces the muscle’s slack length. Even very weak contractions are sufficient to induce this effect. The effect persists for at least 5 min but can be reduced or abolished with a large-amplitude passive stretch.
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Siegle, M. L., and H. J. Ehrlein. "Effects of various agents on ileal postprandial motor patterns and transit of chyme in dogs." American Journal of Physiology-Gastrointestinal and Liver Physiology 257, no. 5 (November 1, 1989): G698—G703. http://dx.doi.org/10.1152/ajpgi.1989.257.5.g698.
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Effects of intravenous infusions of somatostatin, methionine-enkephalin, and 5-hydroxytryptophan on canine ileal motor patterns and transit of chyme were investigated postprandially. Motility was recorded by multiple closely spaced extraluminal strain gauges. By a computerized method, the length of contraction spread and other motility parameters were evaluated. Transit rates were measured fluoroscopically. Somatostatin and methionine-enkephalin initiated a mixing activity by reducing the incidence and the length of spread of contraction waves induced by a noncaloric meal. Methionine-enkephalin, but not somatostatin, decreased both the number of contractions per minute and the motility index. 5-Hydroxytryptophan converted the mixing activity induced by a nutrient meal into a propulsive pattern. The incidence and the length of spread of contraction waves as well as the number of contractions per minute, the contraction force, and the motility index were enhanced. Results suggest that somatostatin, methionine-enkephalin, and 5-hydroxytryptophan are effective modulators of ileal propulsive activity. Effects are largely similar to those observed in the proximal jejunum, although the lengths of contraction spread and the transit rates were generally less in the ileum.
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Raiteri, Brent J., Andrew G. Cresswell, and 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 (July 28, 2016): e2260. http://dx.doi.org/10.7717/peerj.2260.
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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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Skurvydas, Albertas, Nerijus Masiulis, Danguolė Satkunskienė, Aleksas Stanislovaitis, Gedminas Mamkus, Sigitas Kamandulis, and Vilma Dudonienė. "Bimodal recovery of quadriceps muscle force within 24 hours after sprint cycling for 30 seconds." Medicina 43, no. 3 (February 17, 2007): 226. http://dx.doi.org/10.3390/medicina43030028.
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The aim of the study was to investigate the manifestation of potentiation and fatigue as well as the coexistence of these phenomena at different muscle lengths during a 24-hour period after a sprint cycling for 30 s. Material and methods. Twelve healthy untrained men (mean age 23.6±1.7 years) took part in the experiment. The contractility of quadriceps muscle was studied before (Initial) and 2, 5, 30, 60 min and 24 h after exercise via the electrically evoked contractions at 1, 15, 50 Hz and maximal voluntary contractions at short and long muscle length. Results. 1) In early, fast-recovery phase (within the first 5 min), muscle force evoked by electrical stimulation of 1, 15, 50 Hz was restored at short muscle length, conversely at long length (Initial vs. 5 min: 15 Hz and 50 Hz, both P<0.05), whereas maximal voluntary contraction force was still suppressed at both muscle lengths; 2) in the second phase (from 5 min to 30–60 min), muscle force decreased at low- and high-frequency stimulations and was more expressed at low-frequency stimulation and at short muscle length than that at long length, but the maximum voluntary contraction force recovered to initial; 3) in long-lasting phase (within 24 hours), 15 Hz force was still suppressed at both muscle lengths. Conclusion. A bimodal recovery of contractility of the quadriceps following sprint cycling for 30 s is determined by the concomitant complex interaction of mechanisms enhancing (potentiation) and suppressing (fatigue) contractile potential of the muscle.
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Boels, P. J., V. A. Claes, and D. L. Brutsaert. "Mechanics of K(+)-induced isotonic and isometric contractions in isolated canine coronary microarteries." American Journal of Physiology-Cell Physiology 258, no. 3 (March 1, 1990): C512—C523. http://dx.doi.org/10.1152/ajpcell.1990.258.3.c512.
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The effects of shortening in isotonic contractions on the mechanics of microvascular smooth muscle were investigated. Intramyocardial canine coronary microarteries (in situ diameter 60 +/- 3 microns) were mounted as rings, connected to a newly developed photoelectromagnetic force-length transducer, and activated with 125 mM K+. Shortening during isotonic contractions depressed the length-force relation (shortening deactivation) compared with the length-force relation obtained from isometric contractions; the effect was present at the earliest moments after activation, suggesting that a fundamental mechanism associated with the actual sliding of contractile filaments delayed onset of contractile activity in isotonic contractions compared with isometric contractions. Force-velocity relations were obtained by isotonic quick releases from isotonic and isometric contractions at various times. Isotonic shortening before the quick releases reduced the constants of the apparent hyperbolic force-velocity relations and maximal velocity of shortening (Vmax) compared with isometric contractions released at the same time. Increasing contraction duration reduced Vmax but more so in isotonic than in isometric contractions. Vmax also decreased with decreasing instantaneous length. A possible effect of force development on Vmax before the isotonic quick release was also described. Quick increments of load during isotonic contractions were sustained during active shortening in the phasic part, but during the tonic part loading resulted in a pronounced transient relaxation. Thus, in microvascular preparations, active isotonic shortening altered the length-force, force-velocity, and velocity-time relations and uncovered a time-dependent sensitivity to loading conditions. These experiments suggested that the mechanics of smooth muscle contraction may contribute significantly to the mechanisms of the physiological control of coronary microvascular diameter.
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Pandolfino, John E., Zhiyue Lin, Sabine Roman, and Peter J. Kahrilas. "The time course and persistence of “concurrent contraction” during normal peristalsis." American Journal of Physiology-Gastrointestinal and Liver Physiology 301, no. 4 (October 2011): G679—G683. http://dx.doi.org/10.1152/ajpgi.00214.2011.
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Whereas conventional manometry depicts peristalsis as pressure variation over time, high-resolution manometry makes it equally feasible to depict pressure variation along the lumen (spatial pressure variation plots). This study analyzed the characteristics of spatial pressure variation plots during normal peristalsis. High-resolution manometry studies of 72 normal subjects were analyzed with custom MATLAB programs. A coordinate-based strategy was used to normalize both timing of peristalsis and esophageal length. A spatial pressure variation function was devised to localize the proximal (P) and the distal troughs (D) on each subject's composite pressure topography and track the length within the P-D segment contracting concurrently in the course of peristalsis. The timing at which this function peaked was compared with that of the contractile deceleration point (CDP). The length of concurrent contraction during normal peristalsis had an average span of 9.3 cm, encompassing 61% of the distal P-D length of the esophagus. The timing of the CDP position closely matched that of maximal length within the P-D segment contracting concurrently ( r = 0.90, P < 0.001). The pressure morphology of the maximal concurrent contraction was that of a smooth curve, and it was extremely rare to see multiple peaks along the vertical axis (seen in 4 of 72 subjects). Concurrent contraction involving ∼60% of the P-D span occurred with normal peristalsis. The segment of concurrent contraction progressively increased as peristalsis progressed, peaked at the CDP, and then progressively decreased. How abnormalities of the extent or timing of concurrent contraction relate to clinical syndromes requires further investigation.
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Ettema, G. J., P. A. Huijing, and A. de Haan. "The potentiating effect of prestretch on the contractile performance of rat gastrocnemius medialis muscle during subsequent shortening and isometric contractions." Journal of Experimental Biology 165, no. 1 (April 1, 1992): 121–36. http://dx.doi.org/10.1242/jeb.165.1.121.
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The aim of the present study was to investigate the effect of an active stretch during the onset of a muscle contraction on subsequent active behaviour of the contractile machinery within an intact mammalian muscle-tendon complex. Muscle length and shortening velocity were studied because they may be important variables affecting this so-called prestretch effect. Seven gastrocnemius medialis (GM) muscles of the rat were examined. Tetanic, isovelocity shortening contractions from 3 mm above muscle optimum length (l0) to l0 - 2 mm, at velocities of 10–50 mm s-1 (dynamic experiments), were preceded by either an isometric contraction (PI) or an active stretch (PS). By imposing quick length decreases between the prephase and the concentric phase, all excess force generated in the prephase was instantaneously eliminated. This procedure only allowed small force changes during subsequent shortening (caused by the intrinsic properties of the contractile machinery). In this way, the influence of series elastic structures on subsequent muscle performance was minimized. Experiments were also performed at lengths ranging from l0 + 2.5 mm to l0 - 1.5 mm, keeping the length constant after the initial quick length changes (isometric experiments). For the dynamic experiments, enhancement of the performance of the contractile machinery (potentiation) was calculated as the ratio of the average force level over each millimetre of shortening during PS to that during PI conditions (PS/PI). For the isometric experiments, the PS/PI force ratio after 300 ms of stimulation was used. The main result of the present study confirmed results reported in the literature and experiments on isolated muscle fibres. For all conditions, a potentiation effect was found, ranging from about 2 to 16%. Muscle length appeared to have a large positive effect on the degree of potentiation. At the greatest lengths potentiation was largest, but at lengths below optimum a small effect was also found. A negative influence of shortening velocity was mainly present at increased muscle lengths (l0 + 2.5 mm and l0 + 1.5 mm). For the dynamic experiments, no interaction was found between the effects of muscle length and shortening velocity on potentiation. However, there was a clear difference between the isometric and dynamic responses: the dependence of potentiation on muscle length was significantly greater for the isometric contractions than for the dynamic ones. These isometric-dynamic differences indicate that the processes underlying prestretch effects operate differently under isometric and dynamic conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
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Southern, Jordan B., Jasmine R. Frazier, Amy S. Miner, John E. Speich, Adam P. Klausner, and Paul H. Ratz. "Elevated steady-state bladder preload activates myosin phosphorylation: detrusor smooth muscle is a preload tension sensor." American Journal of Physiology-Renal Physiology 303, no. 11 (December 1, 2012): F1517—F1526. http://dx.doi.org/10.1152/ajprenal.00278.2012.
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In rabbit bladder wall (detrusor) muscle, the degree of tone induced during physiological filling (filling tone) is the sum of adjustable preload tension and autonomous contractile tension. The present study was designed to determine whether the level of filling tone is dependent on detrusor muscle length. Maximum active tension induced by KCl was parabolic in relation to length [tension increased from 70% to 100% of a reference length ( Lref) and decreased at longer muscle lengths]. Filling tone, however, increased in a linear fashion from 70% to 120% Lref. In the presence of ibuprofen to abolish autonomous contraction and retain adjustable preload tension, tension was reduced in strength but remained linearly dependent on length from 70% to 120% Lref. In the absence of autonomous contraction, stretching detrusor muscle from 80% to 120% Lref still caused an increase in tone during PGE2-induced rhythmic contraction, suggesting that muscle stretch caused increases in detrusor muscle contractile sensitivity rather than in prostaglandin release. In the absence of autonomous contraction, the degree of adjustable preload tension and myosin phosphorylation increased when detrusor was stretched from 80% to 120% Lref, but also displayed length-hysteresis, indicating that detrusor muscle senses preload rather than muscle length. Together, these data support the hypothesis that detrusor muscle acts as a preload tension sensor. Because detrusor muscle is in-series with neuronal mechanosensors responsible for urinary urgency, a more thorough understanding of detrusor muscle filling tone may reveal unique targets for therapeutic intervention of contractile disorders such as overactive bladder.
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Siegle, M. L., and H. J. Ehrlein. "Digestive motor patterns and transit of luminal contents in canine ileum." American Journal of Physiology-Gastrointestinal and Liver Physiology 254, no. 4 (April 1, 1988): G552—G559. http://dx.doi.org/10.1152/ajpgi.1988.254.4.g552.
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In the present study ileal motor patterns caused by orally administered noncaloric and nutrient meals were investigated. Effects of nutrients were additionally elucidated by an ileal infusion of nutrients. Conscious dogs equipped with closely spaced extraluminal transducers were used. Motor patterns were quantified by a computerized method. Transit rates were measured fluoroscopically. Compared with the motor pattern caused by the noncaloric meal, the nutrient meal diminished the number of contractions from 11.7 to 5.9/min, reduced the incidence of contraction waves from 70.8 to 39.4%, shortened the length of contraction spread from 4.0 to 1.4 cm, and slowed the transit rate from 18.4 to 3.2 cm/min. Ileal infusion of nutrients induced a motor pattern similar to that of the nutrient meal. The transit rate correlated with the length of contraction spread (r = 0.75), the ratio between contraction waves and stationary contractions (r = 0.77), and the number of contractions (r = 0.69). The length of contraction spread was the most characteristic feature of motor patterns and the most important factor influencing transit.
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MacIntosh, Brian R., and Meredith B. MacNaughton. "The length dependence of muscle active force: considerations for parallel elastic properties." Journal of Applied Physiology 98, no. 5 (May 2005): 1666–73. http://dx.doi.org/10.1152/japplphysiol.01045.2004.
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The purpose of this study was to choose between two popular models of skeletal muscle: one with the parallel elastic component in parallel with both the contractile element and the series elastic component ( model A), and the other in which it is in parallel with only the contractile element ( model B). Passive and total forces were obtained at a variety of muscle lengths for the medial gastrocnemius muscle in anesthetized rats. Passive force was measured before the contraction ( passive A) or was estimated for the fascicle length at which peak total force occurred ( passive B). Fascicle length was measured with sonomicrometry. Active force was calculated by subtracting passive ( A or B) force from peak total force at each fascicle or muscle length. Optimal length, that fascicle length at which active force is maximized, was 13.1 ± 1.2 mm when passive A was subtracted and 14.0 ± 1.1 mm with passive B ( P < 0.01). Furthermore, the relationship between double-pulse contraction force and length was broader when calculated with passive B than with passive A. When the muscle was held at a long length, passive force decreased due to stress relaxation. This was accompanied by no change in fascicle length at the peak of the contraction and only a small corresponding decrease in peak total force. There is no explanation for the apparent increase in active force that would be obtained when subtracting passive A from the peak total force. Therefore, to calculate active force, it is appropriate to subtract passive force measured at the fascicle length corresponding to the length at which peak total force occurs, rather than passive force measured at the length at which the contraction begins.
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Han, June-Chiew, Toan Pham, Andrew J. Taberner, Denis S. Loiselle, and Kenneth Tran. "Solving a century-old conundrum underlying cardiac force-length relations." American Journal of Physiology-Heart and Circulatory Physiology 316, no. 4 (April 1, 2019): H781—H793. http://dx.doi.org/10.1152/ajpheart.00763.2018.
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In the late 19th century, Otto Frank presented a diagram (Frank O. Z Biol 37: 483–526, 1899) showing that cardiac end-systolic pressure-volume relations are dependent on the mode of contraction: one for isovolumic contractions that locate above that for afterloaded ejecting contractions. Conflicting results to Frank’s have been subsequently demonstrated in various species, both within and among preparations, ranging from the whole hearts to single myocytes, showing a single pressure-volume or force-length relation that is independent of the mode of contraction. Numerous explanations for these conflicting results have been proposed but are mutually contradictory and hence unsatisfying. The present study aimed to explore how these conflicting findings can be reconciled. We thus explored the cardiac force-length relation across a wide spectrum of both preloads and afterloads, encompassing the physiological working range. Experiments were performed using isolated ventricular trabeculae at physiological temperature and stimulus frequency. The force-length relation obtained from isometric contractions was indeed located above a family of those obtained from shortening contractions. Low preload conditions rendered the relation contraction mode independent. High afterload conditions also showed a comparable effect. Our exploration allowed us to reveal the loading conditions that can explain the apparent single, contraction mode-independent, force-length relation that is in contrast with that presented by Frank. Resolving this century-old cardiac conundrum highlights the caution that must be taken when using the end-systolic force-length relation to illustrate as well as to understand the concepts of the Frank-Starling law of the heart, “potential energy,” and cardiac contractility. NEW & NOTEWORTHY Our exploration of the cardiac force-length relation under wide ranges of preload and afterload has allowed us to reconcile conflicting results in the literature regarding its length dependency. We show that the relation is dependent on the mode of contraction but can appear to be otherwise under certain conditions. This finding highlights the need for caution when using the force-length relation to understand key concepts in cardiac physiology.
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Babault, Nicolas, Michel Pousson, Anne Michaut, and Jacques Van Hoecke. "Effect of quadriceps femoris muscle length on neural activation during isometric and concentric contractions." Journal of Applied Physiology 94, no. 3 (March 1, 2003): 983–90. http://dx.doi.org/10.1152/japplphysiol.00717.2002.
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The effect of muscle length on neural drive (here termed “neural activation”) was investigated from electromyographic activities and activation levels (twitch interpolation). The neural activation was measured in nine men during isometric and concentric (30 and 120°/s) knee extensions for three muscle lengths (35, 55, and 75° knee flexion, i.e., shortened, intermediate, and lengthened muscles, respectively). Long (76°), medium (56°), and short (36°) ranges of motion were used to investigate the effect of the duration of concentric contraction. Neural activation was found to depend on muscle length. Reducing the duration of contraction had no effect. Neural activation was higher with short muscle length during isometric contractions and was weaker for shortened than for intermediate and lengthened muscles performing 120°/s concentric contractions. Muscle length had no effect on 30°/s concentric neural activation. Peripheral mechanisms and discharge properties of the motoneurons could partly explain the observed differences in the muscle length effect. We thus conclude that muscle length has a predominant effect on neural activation that would modulate the angular velocity dependency.
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Maganaris, Constantinos N., Vasilios Baltzopoulos, and Anthony J. Sargeant. "Repeated contractions alter the geometry of human skeletal muscle." Journal of Applied Physiology 93, no. 6 (December 1, 2002): 2089–94. http://dx.doi.org/10.1152/japplphysiol.00604.2002.
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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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Rassier, Dilson E., and Brian R. MacIntosh. "Length-dependent twitch contractile characteristics of skeletal muscle." Canadian Journal of Physiology and Pharmacology 80, no. 10 (October 1, 2002): 993–1000. http://dx.doi.org/10.1139/y02-127.
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The length dependence of force development of mammalian skeletal muscles was evaluated during twitch, double-pulse, and tetanic contractions, and the relation between muscle length and the time-dependent characteristics of twitch and double-pulse contractions were determined. In situ isometric contractions of the rat gastrocnemius muscle were analyzed at seven different lengths, based on a reference length at which the maximal response to double-pulse contractions occurred (Lopt-2P). Twitch and double-pulse contractions were analyzed for developed tension (DT), contraction time (tC), average rate of force development (DT·tC1), half-relaxation time (t50%R), peak rate of relaxation (DT·dtmin1), and 90%-relaxation time (t90%R). Considering the length at which maximal tetanic DT occurred to be the optimal length (Lo-TET), the peak DT for twitch contractions and double-pulse contractions was observed at Lo-TET + 0.75 mm (p < 0.05) and Lo-TET + 0.1 mm (p > 0.05), respectively. When measured at the length for which maximal twitch and double-pulse contractions were obtained, tetanic DT was 95.2 ± 3 and 99.0 ± 2% of the maximal value, respectively. These observations suggest that double-pulse contractions are more suitable for setting length for experimental studies than twitch contractions. Twitch and double-pulse contraction tC were 15.53 ± 1.14 and 25.0 ± 0.6 ms, respectively, at Lopt-2P, and increased above Lopt-2P and decreased below Lopt-2P. Twitch t50%R was 12.18 ± 0.90 ms at Lopt-2P, and increased above Lopt-2P and below Lopt-2P. Corresponding changes for double-pulse contractions were greater. Stretching the muscle leads to slower twitch contractions and double-pulse contractions, but the mechanisms of this change in time course remain unclear.Key words: muscle activation, forcelength relation, gastrocnemius muscle, Ca2+ sensitivity.
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Pitsyshyn, Bohdan, Vadym Orel, and Tetiana Konyk. "Profiling of sudden contraction of circular pipe by sharp-edged pipe insert." Problems of Water supply, Sewerage and Hydraulic, no. 36 (October 5, 2021): 48–55. http://dx.doi.org/10.32347/2524-0021.2021.36.48-55.
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Measures to reduce energy losses in pipeline transport systems must be implemented already at the design stage. In particular, this also applies to local resistances of pipelines. For symmetrical sudden pipe contraction, one of such measure is profiling using insert. The paper considers a sharp-edged pipe insert, which in comparison with others has larger areas of flow separation. The diameter of the insert was calculated as the arithmetic mean between the diameters forming the sudden pipe contraction. Using the methodology described in the literature, the contraction length ratio as the areas of influence between two symmetrical sudden contractions of a circular pipe during the flow of a single-phase turbulent flow of Newtonian fluid was investigated. The coefficient of mutual influence of these local resistances was determined by formulae for direct-flowing and non-direct-flowing locking devices, which simulated symmetrical and asymmetrical fluid flow after the constriction plane, respectively. The contraction rate from 0.064 to 0.696 inclusive are considered. According to the results of calculations, no mutual influence of two sudden contractions of circular pipe was found. This indicates the unsuitability of using formulae for locking devices in this methodology for determining the contraction length ratio. Therefore, to study this problem on the sudden pipe contraction with different contraction rates, it is proposed to conduct a physical experiment. In a mathematical experiment, you can use formulae to determine the following values: upstream recirculation length and downstream recirculation length; inlet length of cylindrical pipes with turbulized the flow devices; length of the velocity profile stabilization after local resistances.
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Almasri, Atheer M., Paul H. Ratz, Hersch Bhatia, Adam P. Klausner, and John E. Speich. "Rhythmic contraction generates adjustable passive stiffness in rabbit detrusor." Journal of Applied Physiology 108, no. 3 (March 2010): 544–53. http://dx.doi.org/10.1152/japplphysiol.01079.2009.
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The length-tension ( L-T) relationships in airway and vascular smooth muscles have been shown to adapt with length changes over time. Our prior studies have shown that the active and passive L-T relationships in rabbit detrusor smooth muscle (DSM) can adapt and that DSM exhibits adjustable passive stiffness (APS) characterized by a passive L-T curve that is a function of strain and activation history. The present study demonstrates that passive tension due to APS can represent a substantial fraction of total tension over a broad length range. Our previous studies have shown that maximal KCl-induced contractions at short muscle lengths generate APS that is revealed by increased pseudo-steady-state passive tension at longer lengths compared with previous measurements at those lengths. The objective of the present study was to determine the mechanisms involved in APS generation. Increasing the number of KCl-induced contractions or the duration of a contraction increased the amount of APS generated. Furthermore, a fraction of APS was restored in calcium-free solution and was sensitive to the general serine and threonine protein kinase inhibitor staurosporine. Most importantly, rhythmic contraction (RC) generated APS, and because RC occurs spontaneously in human bladder, a physiological role for RC was potentially identified.
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Fukunaga, Tetsuo, Yoshiho Ichinose, Masamitsu Ito, Yasuo Kawakami, and Senshi Fukashiro. "Determination of fascicle length and pennation in a contracting human muscle in vivo." Journal of Applied Physiology 82, no. 1 (January 1, 1997): 354–58. http://dx.doi.org/10.1152/jappl.1997.82.1.354.
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Fukunaga, Tetsuo, Yoshiho Ichinose, Masamitsu Ito, Yasuo Kawakami, and Senshi Fukashiro. Determination of fascicle length and pennation in a contracting human muscle in vivo. J. Appl. Physiol. 82(1): 354–358, 1997.—We have developed a technique to determine fascicle length in human vastus lateralis muscle in vivo by using ultrasonography. When the subjects had the knee fully extended passively from a position of 110° flexion (relaxed condition), the fascicle length decreased from 133 to 97 mm on average. During static contractions at 10% of maximal voluntary contraction strength (tensed condition), fascicle shortening was more pronounced (from 126 to 67 mm), especially when the knee was closer to full extension. Similarly, as the knee was extended, the angle of pennation (fascicle angle, defined as the angle between fascicles and aponeurosis) increased (relaxed, from 14 to 18°; tensed, from 14 to 21°), and a greater increase in the pennation angle was observed in the tensed than in the relaxed condition when the knee was close to extension (<40°). We conclude that there are differences in fascicle lengths and pennation angles when the muscle is in a relaxed and isometrically tensed conditions and that the differences are affected by joint angles, at least at the submaximal contraction level.
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Yamaguchi, H., M. Takaki, H. Matsubara, S. Yasuhara, and H. Suga. "Constancy and variability of contractile efficiency as a function of calcium and cross-bridge kinetics: simulation." American Journal of Physiology-Heart and Circulatory Physiology 270, no. 4 (April 1, 1996): H1501—H1508. http://dx.doi.org/10.1152/ajpheart.1996.270.4.h1501.
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We simulated myocardial Ca2+ (Ca) and cross-bridge (CB) kinetics to get insight into the experimentally observed constancy and variability of cardiac contractile efficiency in generating total mechanical energy under various inotropic and pathological conditions. The simulation consisted of a Ca transient, Ca association and dissociation rate constants of troponin C, and CB on and off rate constants. We evaluated sarcomere isometric twitch contractions at a constant muscle length. We assumed that each CB cycle hydrolyzes one ATP and that the force-length area (FLA) quantifies the total mechanical energy generated by CB cycles in a twitch contraction. FLA is a linear version of pressure-volume area, which quantifies the total mechanical energy of cardiac twitch contraction and correlates linearly with cardiac oxygen consumption (H. Suga, Physiol. Rev. 70: 247-277, 1990). The simulation shows that the contractile efficiency varies with changes in the Ca transient and Ca and CB kinetics except when they simultaneously speed up or slow down proportionally. These results point to possible mechanisms underlying the constancy and variability of cardiac contractile efficiency.
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Gunst, S. J., M. F. Wu, and D. D. Smith. "Contraction history modulates isotonic shortening velocity in smooth muscle." American Journal of Physiology-Cell Physiology 265, no. 2 (August 1, 1993): C467—C476. http://dx.doi.org/10.1152/ajpcell.1993.265.2.c467.
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The effect of contraction history on the isotonic shortening velocity of canine tracheal smooth muscle was investigated. Muscles were contracted isometrically for 20 s at initial lengths of L(o) (length of maximal active force), 85% L(o), or 70% L(o) using electrical field stimulation. Muscles were then allowed to shorten isotonically under different afterloads either with or without first being subjected to a step decrease in length to 70% L(o). Instantaneous velocities were plotted against instantaneous muscle length during isotonic shortening. Regardless of protocol, the velocity at any muscle length during shortening was lower when the muscle was initially activated at a longer length. The isotonic shortening velocity decreased progressively during shortening at a nearly linear rate with respect to instantaneous muscle length under all conditions. Results suggest that a longer muscle length at the time of activation leads to the development of higher loads on the contractile element during subsequent shortening, resulting in a slower shortening velocity. This plasticity of the force-velocity relationship may result from cytostructural reorganization of the smooth muscle cells in response to contractile activation at different muscle lengths.
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Gunst, S. J., R. A. Meiss, M. F. Wu, and M. Rowe. "Mechanisms for the mechanical plasticity of tracheal smooth muscle." American Journal of Physiology-Cell Physiology 268, no. 5 (May 1, 1995): C1267—C1276. http://dx.doi.org/10.1152/ajpcell.1995.268.5.c1267.
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In smooth muscle tissues, the relationship between muscle or cell length and active force can be modulated by altering the cell or tissue length during stimulation. Mechanisms for this mechanical plasticity were investigated by measuring muscle stiffness during isometric contractions in which contractile force was graded by changing stimulus intensity or muscle length. Stiffness was significantly higher in contracted than in resting muscles at comparable forces; however, the relationship between stiffness and force during force development was curvilinear and independent of muscle length and stimulus intensity. This suggests that muscle stiffness during force development reflects properties of cellular components other than cross bridges which contribute to the series elasticity only during activation. During the tonic phase of isometric contraction, muscle stiffness increased while force remained constant. A step decrease in the length of a contracted muscle resulted in a high level of stiffness relative to force during isometric force redevelopment following the length step. We propose that the arrangement of the cytoskeleton can adjust to changes in the conformation of resting smooth muscle cells but that the organization of the cytoskeleton becomes more fixed upon contractile activation and is modulated very slowly during a sustained contraction. This may provide a mechanism for optimizing force development to the physical conformation of the cell at the time of activation.
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Appell, David. "The invisibility of length contraction." Physics World 32, no. 8 (August 2019): 41–45. http://dx.doi.org/10.1088/2058-7058/32/8/35.
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Graham, John R. "Special relativity and length contraction." American Journal of Physics 63, no. 7 (July 1995): 637–39. http://dx.doi.org/10.1119/1.17825.
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Jin, Warren, Ronald G. Polcawich, Paul A. Morton, and John E. Bowers. "Phase tuning by length contraction." Optics Express 26, no. 3 (January 30, 2018): 3174. http://dx.doi.org/10.1364/oe.26.003174.
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Sastry, G. P. "Is length contraction really paradoxical?" American Journal of Physics 55, no. 10 (October 1987): 943–46. http://dx.doi.org/10.1119/1.14911.
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Chang, Yi-Wen, Fong-Chin Su, Hong-Wen Wu, and Kai-Nan An. "Optimum length of muscle contraction." Clinical Biomechanics 14, no. 8 (October 1999): 537–42. http://dx.doi.org/10.1016/s0268-0033(99)00014-5.
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Janson, L. W., and D. L. Taylor. "In vitro models of tail contraction and cytoplasmic streaming in amoeboid cells." Journal of Cell Biology 123, no. 2 (October 15, 1993): 345–56. http://dx.doi.org/10.1083/jcb.123.2.345.
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We have developed a reconstituted gel-sol and contractile model system that mimics the structure and dynamics found at the ectoplasm/endoplasm interface in the tails of many amoeboid cells. We tested the role of gel-sol transformations of the actin-based cytoskeleton in the regulation of contraction and in the generation of endoplasm from ectoplasm. In a model system with fully phosphorylated myosin II, we demonstrated that either decreasing the actin filament length distribution or decreasing the extent of actin filament cross-linking initiated both a weakening of the gel strength and contraction. However, streaming of the solated gel components occurred only under conditions where the length distribution of actin was decreased, causing a self-destruct process of continued solation and contraction of the gel. These results offer significant support that gel strength plays an important role in the regulation of actin/myosin II-based contractions of the tail cortex in many amoeboid cells as defined by the solation-contraction coupling hypothesis (Taylor, D. L., and M. Fechheimer. 1982. Phil. Trans. Soc. Lond. B. 299:185-197). The competing processes of solation and contraction of the gel would appear to be mutually exclusive. However, it is the temporal-spatial balance of the rate and extent of two stages of solation, coupled to contraction, that can explain the conversion of gelled ectoplasm in the tail to a solated endoplasm within the same small volume, generation of a force for the retraction of tails, maintenance of cell polarity, and creation of a positive hydrostatic pressure to push against the newly formed endoplasm. The mechanism of solation-contraction of cortical cytoplasm may be a general component of the normal movement of a variety of amoeboid cells and may also be a component of other contractile events such as cytokinesis.
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MacNaughton, M. B., and B. R. MacIntosh. "Reports of the length dependence of fatigue are greatly exaggerated." Journal of Applied Physiology 101, no. 1 (July 2006): 23–29. http://dx.doi.org/10.1152/japplphysiol.01373.2005.
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Relative force depression associated with muscle fatigue is reported to be greater when assessed at short vs. long muscle lengths. This appears to be due to a rightward shift in the force-length relationship. This rightward shift may be caused by stretch of in-series structures, making sarcomere lengths shorter at any given muscle length. Submaximal force-length relationships (twitch, double pulse, 50 Hz) were evaluated before and after repetitive contractions (50 Hz, 300 ms, 1/s) in an in situ preparation of the rat medial gastrocnemius muscle. In some experiments, fascicle lengths were measured with sonomicrometry. Before repetitive stimulation, fascicle lengths were 11.3 ± 0.8, 12.8 ± 0.9, and 14.4 ± 1.2 mm at lengths corresponding to −3.6, 0, and 3.6 mm where 0 is a reference length that corresponds with maximal active force for double-pulse stimulation. After repetitive stimulation, there was no change in fascicle lengths; these lengths were 11.4 ± 0.8, 12.6 ± 0.9, and 14.2 ± 1.2 mm. The length dependence of fatigue was, therefore, not due to a stretch of in-series structures. Interestingly, the rightward shift that was evident when active force was calculated in the traditional way (subtraction of the passive force measured before contraction) was not seen when active force was calculated by subtracting the passive force that was associated with the fascicle length reached at the peak of the contraction. This calculation is based on the assumption that passive force decreases as the fascicles shorten during a fixed-end contraction. This alternative calculation revealed similar postfatigue absolute active force depression at all lengths. In relative terms, a length dependence of fatigue was still evident, but this was greatly diminished compared with that observed when active force was calculated with the traditional method.
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Stokes, D., and R. Josephson. "CONTRACTILE PROPERTIES OF A HIGH-FREQUENCY MUSCLE FROM A CRUSTACEAN - CONTRACTION KINETICS." Journal of Experimental Biology 187, no. 1 (February 1, 1994): 275–93. http://dx.doi.org/10.1242/jeb.187.1.275.
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1. The flagella (small appendages on the maxillipeds) of the crab Carcinus maenas beat regularly when active at about 10 Hz (15 °C). The beat of a flagellum is due to contraction of a single small muscle, the flagellum abductor (FA). The optimal stimulus frequency for tetanic contraction of the FA was about 200 Hz. When the muscle was stimulated at 10 Hz with paired stimuli per cycle, the interstimulus interval that maximized peak force was 2­4 ms, which corresponded well to the interspike intervals within bursts recorded from motor axons during normal beating. 2. Contraction of the isolated FA showed pronounced neuromuscular facilitation and many stimuli were needed to activate the muscle fully. The dependence on facilitation in isolated muscles appeared to be greater than that in vivo. It is suggested that neuromodulators in the blood of the crab enhance neuromuscular transmission and reduce the dependency on facilitation in intact animals. 3. The FA had a narrow length­tension curve. Tetanic tension became vanishingly small at muscle lengths less than about 90 % of the maximum in vivo length. The maximum length change of the muscle during in vivo contraction was about 5 %. 4. The maximum isometric force of the FA was low (about 6 N cm-2) but its shortening velocity was high. Vm, the maximum shortening velocity determined from isotonic shortening, was 4.0 muscle lengths s-1; V0, the maximum shortening velocity from slack test measurements, was about 8 lengths s-1. 5. The structure and physiology of the FA are compared with those of locust flight muscle, chosen because it too is a muscle capable of long-duration, high-frequency performance.
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Vaz, João R., Tiago Neto, José Pedro Correia, Jorge Infante, and Sandro R. Freitas. "Regional Differences in Biceps Femoris Long Head Stiffness during Isometric Knee Flexion." Journal of Functional Morphology and Kinesiology 6, no. 1 (February 10, 2021): 18. http://dx.doi.org/10.3390/jfmk6010018.
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This study sought to investigate whether the stiffness of the biceps femoris long head differs between proximal and distal regions during isometric knee flexion at different contraction intensities and muscle lengths. Twelve healthy individuals performed knee flexion isometric contractions at 20% and 60% of maximum voluntary isometric contraction, with the knee flexed at 15 and 45 degrees. Muscle stiffness assessment was performed using ultrasound-based shear wave elastography. Proximal and distal regions of the biceps femoris long head were assessed. Biceps femoris long head muscle showed a greater stiffness (i) in the distal region, (ii) at higher contraction intensity, and (iii) at longer muscle length. The proximal-to-distal stiffness ratio was significantly lower than 1 (i.e., heterogenous) at lower contraction intensity regardless of the muscle length. However, this was not observed at higher contraction intensity. This study is the first to show heterogeneity in the active stiffness of the biceps femoris long head. Given the greater incidence of injury at the proximal region of biceps femoris long head, this study opens new directions for future research. Additionally, the present study results indicate that studies assessing muscle stiffness at one single muscle region should be interpreted with caution.
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Sollott, S. J., and E. G. Lakatta. "Novel method to alter length and load in isolated mammalian cardiac myocytes." American Journal of Physiology-Heart and Circulatory Physiology 267, no. 4 (October 1, 1994): H1619—H1629. http://dx.doi.org/10.1152/ajpheart.1994.267.4.h1619.
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We have devised a novel technique enabling reversible gradations in the resting and contraction length of intact mammalian ventricular myocytes of up to 15-18% over slack length. Enzymatically isolated single cells are embedded in a transparent, elastic, cross-linked fibrin matrix, contained within a narrow elastic tube. Reversible gradations in cell length are produced via fibrin matrix stretch, produced by stretching the tube. Simultaneous measurement of cell length, edge motion, and indo 1 fluorescence during auxotonic contractions permits characterization of cell contractile function. Although force cannot be directly measured, the time integral of contractile force (i.e., relative contractile impulse, a contractile index that is independent of shortening constraints) is derived combining myocyte shortening and matrix loading. Relatively small degrees of myocyte stretch produce a lightly afterloaded model dominated by variations in preload in which there is parallel augmentation of shortening and contractile impulse (force) development. At higher degrees of stretch, significant afterloading is introduced, resulting in the development of an inverse relationship between shortening and impulse (approaching isometric conditions). Length-dependent Ca2+ myofilament activation and load-dependent relaxation are readily demonstrated in intact isolated mammalian ventricular myocytes.
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Patel, Tina J., Ronnie Das, Jan Fridén, Gordon J. Lutz, and Richard L. Lieber. "Sarcomere strain and heterogeneity correlate with injury to frog skeletal muscle fiber bundles." Journal of Applied Physiology 97, no. 5 (November 2004): 1803–13. http://dx.doi.org/10.1152/japplphysiol.00505.2003.
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Sarcomere length and first-order diffraction line width were measured by laser diffraction during elongation of activated frog tibialis anterior muscle fiber bundles (i.e., eccentric contraction) at nominal fiber strains of 10, 25, or 35% ( n = 18) for 10 successive contractions. Tetanic tension, measured just before each eccentric contraction, differed significantly among strain groups and changed dramatically during the 10-contraction treatment ( P < 0.01). Average maximum tetanic tension for the three groups measured before any treatment was 203.7 ± 6.8 kN/m2, but after the 10-eccentric contraction sequence decreased to 180.3 ± 3.8, 125.1 ± 7.8, and 78.3 ± 5.1 kN/m2 for the 10, 25, and 35% strain groups, respectively ( P < 0.0001). Addition of 10 mM caffeine to the bathing medium decreased the loss of tetanic tension in the 10% strain group but had only a minimal effect on either the 25 or 35% strain groups. Diffraction pattern line width, a measure of sarcomere length heterogeneity, increased significantly with muscle activation and then continued to increase with successive stretches of the activated muscle. Line width increase after each stretch was significantly correlated with the lower yield tension of the successive contractile record. These data demonstrate a direct association and, perhaps, a causal relationship between sarcomere strain and fiber bundle injury. They also demonstrate that muscle injury is accompanied by a progressive increase in sarcomere length heterogeneity, yielding lower yield tension as injury progresses.
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Rassier, D. E., B. R. MacIntosh, and W. Herzog. "Length dependence of active force production in skeletal muscle." Journal of Applied Physiology 86, no. 5 (May 1, 1999): 1445–57. http://dx.doi.org/10.1152/jappl.1999.86.5.1445.
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The sliding filament and cross-bridge theories of muscle contraction provide discrete predictions of the tetanic force-length relationship of skeletal muscle that have been tested experimentally. The active force generated by a maximally activated single fiber (with sarcomere length control) is maximal when the filament overlap is optimized and is proportionally decreased when overlap is diminished. The force-length relationship is a static property of skeletal muscle and, therefore, it does not predict the consequences of dynamic contractions. Changes in sarcomere length during muscle contraction result in modulation of the active force that is not necessarily predicted by the cross-bridge theory. The results of in vivo studies of the force-length relationship suggest that muscles that operate on the ascending limb of the force-length relationship typically function in stretch-shortening cycle contractions, and muscles that operate on the descending limb typically function in shorten-stretch cycle contractions. The joint moments produced by a muscle depend on the moment arm and the sarcomere length of the muscle. Moment arm magnitude also affects the excursion (length change) of a muscle for a given change in joint angle, and the number of sarcomeres arranged in series within a muscle fiber determines the sarcomere length change associated with a given excursion.
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HERZOG, W., and D. E. RASSIER. "HISTORY DEPENDENCE OF SKELETAL MUSCLE FORCE PRODUCTION: A FORGOTTEN PROPERTY." Journal of Mechanics in Medicine and Biology 02, no. 03n04 (September 2002): 347–58. http://dx.doi.org/10.1142/s0219519402000447.
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Steady-state force enhancement following active muscle stretching has been observed for well over fifty years, and is a widely accepted property of skeletal muscle contraction. Force enhancement has typically been associated with instability of sarcomere length on the descending limb of the force-length relationship. Here, we demonstrate that the sarcomere length non-uniformity paradigm, based on instability, cannot explain much of the newly discovered results. We provide evidence that force enhancement can occur on the stable ascending limb of the force-length relationship, that force enhancement can exceed the isometric tetanic plateau forces, that it is associated with an increased passive force, and that it occurs for perfectly stable sarcomere lengths on the descending limb of the force-length relationship. Combining all the results, we conclude that force enhancement has at least two components, an active and a passive component, that contribute towards the total force enhancement to varying degrees, depending on the contractile history of muscle contraction.
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Janssen, P. M., and W. C. Hunter. "Force, not sarcomere length, correlates with prolongation of isosarcometric contraction." American Journal of Physiology-Heart and Circulatory Physiology 269, no. 2 (August 1, 1995): H676—H685. http://dx.doi.org/10.1152/ajpheart.1995.269.2.h676.
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Recent studies have emphasized the importance of the late systolic phase for understanding ventricular ejection. To examine the myocardial factors controlling this phase, we studied the timing of twitch contraction in nine excised rat trabeculae contracting isosarcometrically. By varying both sarcomere length (SL) and extracellular Ca2+ concentration ([Ca2+]) we determined which of these factors or the developed peak twitch force correlated better with the prolongation of contraction. We focused on the period from just before the peak of force to the time of half relaxation. SL was measured by laser diffraction and kept constant using adaptive control. Peak twitch force was the factor most tightly correlated with prolongation of contraction: as force rose from 10 to 100 mN/mm2, duration tripled from 100 to 300 ms. When the trend with force was removed, however, no separate influence of SL remained. Increase in [Ca2+]o abbreviated contraction equally at all force levels. Prolongation of late systolic contraction was also highly correlated with prolongation of the time constant for late relaxation, suggesting a common mechanism by which peak twitch force lengthens the entire subsequent time course of a twitch. We hypothesize that 1) increased force correlates with prolonged Ca2+ binding to troponin-C, and/or 2) attached cross bridges act cooperatively to oppose the inhibiting effects of tropomyosin as Ca2+ is lost from the thin filaments.(ABSTRACT TRUNCATED AT 250 WORDS)
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Mellors, L. J., C. L. Gibbs, and C. J. Barclay. "Comparison of the efficiency of rat papillary muscles during afterloaded isotonic contractions and contractions with sinusoidal length changes." Journal of Experimental Biology 204, no. 10 (May 15, 2001): 1765–74. http://dx.doi.org/10.1242/jeb.204.10.1765.
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The results of previous studies suggest that the maximum mechanical efficiency of rat papillary muscles is lower during a contraction protocol involving sinusoidal length changes than during one involving afterloaded isotonic contractions. The aim of this study was to compare directly the efficiency of isolated rat papillary muscle preparations in isotonic and sinusoidal contraction protocols. Experiments were performed in vitro (27 degrees C) using left ventricular papillary muscles from adult rats. Each preparation performed three contraction protocols: (i) low-frequency afterloaded isotonic contractions (10 twitches at 0.2 Hz), (ii) sinusoidal length change contractions with phasic stimulation (40 twitches at 2 Hz) and (iii) high-frequency afterloaded isotonic contractions (40 twitches at 2 Hz). The first two protocols resembled those used in previous studies and the third combined the characteristics of the first two. The parameters for each protocol were adjusted to those that gave maximum efficiency. For the afterloaded isotonic protocols, the afterload was set to 0.3 of the maximum developed force. The sinusoidal length change protocol incorporated a cycle amplitude of +/−5 % resting length and a stimulus phase of −10 degrees. Measurements of force output, muscle length change and muscle temperature change were used to calculate the work and heat produced during and after each protocol. Net mechanical efficiency was defined as the proportion of the energy (enthalpy) liberated by the muscle that appeared as work. The efficiency in the low-frequency, isotonic contraction protocol was 21.1+/−1.4 % (mean +/− s.e.m., N=6) and that in the sinusoidal protocol was 13.2+/−0.7 %, consistent with previous results. This difference was not due to the higher frequency or greater number of twitches because efficiency in the high-frequency, isotonic protocol was 21.5+/−1.0 %. Although these results apparently confirm that efficiency is protocol-dependent, additional experiments designed to measure work output unambiguously indicated that the method used to calculate work output in isotonic contractions overestimated actual work output. When net work output, which excludes work done by parallel elastic elements, rather than total work output was used to determine efficiency in afterloaded isotonic contractions, efficiency was similar to that for sinusoidal contractions. The maximum net mechanical efficiency of rat papillary muscles performing afterloaded isotonic or sinusoidal length change contractions was between 10 and 15 %.
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Redzic, D. V. "Relativistic length agony continued." Serbian Astronomical Journal, no. 188 (2014): 55–65. http://dx.doi.org/10.2298/saj1488055r.
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We made an attempt to remedy recent confusing treatments of some basic relativistic concepts and results. Following the argument presented in an earlier paper (Redzic 2008b), we discussed the misconceptions that are recurrent points in the literature devoted to teaching relativity such as: there is no change in the object in Special Relativity, illusory character of relativistic length contraction, stresses and strains induced by Lorentz contraction, and related issues. We gave several examples of the traps of everyday language that lurk in Special Relativity. To remove a possible conceptual and terminological muddle, we made a distinction between the relativistic length reduction and relativistic FitzGerald-Lorentz contraction, corresponding to a passive and an active aspect of length contraction, respectively; we pointed out that both aspects have fundamental dynamical contents. As an illustration of our considerations, we discussed briefly the Dewan-Beran-Bell spaceship paradox and the ?pole in a barn? paradox.
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Youn, Thomas, Son A. Kim, and Chi-Ming Hai. "Length-dependent modulation of smooth muscle activation: effects of agonist, cytochalasin, and temperature." American Journal of Physiology-Cell Physiology 274, no. 6 (June 1, 1998): C1601—C1607. http://dx.doi.org/10.1152/ajpcell.1998.274.6.c1601.
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We tested the hypothesis that mechanical strain modulates agonist sensitivity of smooth muscle by measuring myosin phosphorylation and contractile force in bovine tracheal smooth muscle activated by various concentrations of the muscarinic receptor agonist carbachol and at various muscle lengths. Increasing carbachol concentration by 10,000-fold did not restore myosin phosphorylation levels at shorter muscle lengths to the level at optimal length ( L o). Maximum levels of myosin phosphorylation induced by carbachol at 0.6, 0.8, and 1.0 L o were similar but became lower at <0.6 L o. Cytochalasin D significantly attenuated carbachol-induced contraction by 54%. In addition, cytochalasin D treatment induced a parallel downward shift in the length-myosin phosphorylation relation. Lowering temperature from 37 to 23°C did not significantly change the length dependencies of carbachol-induced active force and myosin phosphorylation. These results have led us to conclude that 1) agonist sensitivity and maximum level of activation (as measured by myosin phosphorylation) are targets of length-dependent modulation, 2) actin filaments involved in contraction and length-dependent modulation are distinct in sensitivity to cytochalasin D, and 3) length-dependent modulation is relatively temperature insensitive.
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COSTA, Tarciana Vieira, and Roberto Oliveira DANTAS. "ALTERED ESOPHAGEAL MOTILITY DURING PERCEPTION OF BOLUS TRANSIT IN HEALTHY VOLUNTEERS." Arquivos de Gastroenterologia 56, no. 4 (October 2019): 386–89. http://dx.doi.org/10.1590/s0004-2803.201900000-78.
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ABSTRACT BACKGROUND: The perception of bolus transit through the thoracic esophagus may be caused by altered esophageal anatomy and function. OBJECTIVE: To evaluate the hypothesis that, in healthy volunteers, swallows followed by perception of esophageal bolus transit are associated with changes in esophageal motility. METHODS: Simultaneous evaluation of motility and perception of esophageal bolus transit was performed in 22 healthy volunteers. Esophageal motility was evaluated by high-resolution manometry with a 32-channel solid state catheter. Each volunteer performed, in the sitting position, 10 swallows of a 5 mL bolus of saline and 10 swallows of pieces of 1 cm3 of bread, with an interval of at least 30 seconds between swallows. After each swallow the volunteers were asked about the perception of bolus transit through the esophagus. RESULTS: Perception of bolus transit occurred in 11.7% of liquid swallows and in 48.1% of solid swallows. In liquid swallows the perception was associated with higher distal contractile integral and shorter proximal contraction length. Perception of solid bolus transit was associated with a longer distal latency, longer proximal contraction length, lower proximal contractile integral and shorter proximal contraction duration. CONCLUSION: The perception of swallowed bolus transit through the esophagus in healthy individuals is more frequent with solid than liquid swallows and is associated with changes in proximal esophageal contractions.
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Horowits, R., and R. J. Podolsky. "The positional stability of thick filaments in activated skeletal muscle depends on sarcomere length: evidence for the role of titin filaments." Journal of Cell Biology 105, no. 5 (November 1, 1987): 2217–23. http://dx.doi.org/10.1083/jcb.105.5.2217.
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Electron microscopy was used to study the positional stability of thick filaments in isometrically contracting skinned rabbit psoas muscle as a function of sarcomere length at 7 degrees C. After calcium activation at a sarcomere length of 2.6 micron, where resting stiffness is low, sarcomeres become nonuniform in length. The dispersion in sarcomere length is complete by the time maximum tension is reached. A-bands generally move from their central position and continue moving toward one of the Z-discs after tension has reached a plateau at its maximum level. The lengths of the thick and thin filaments remain constant during this movement. The extent of A-band movement during contraction depends on the final length of the individual sarcomere. After prolonged activation, all sarcomeres between 1.9 and 2.5 micron long exhibit A-bands that are adjacent to a Z-disc, with no intervening I-band. Sarcomeres 2.6 or 2.7 micron long exhibit a partial movement of A-bands. At longer sarcomere lengths, where the resting stiffness exceeds the slope of the active tension-length relation, the A-bands remain perfectly centered during contraction. Sarcomere symmetry and length uniformity are restored upon relaxation. These results indicate that the central position of the thick filaments in the resting sarcomere becomes unstable upon activation. In addition, they provide evidence that the elastic titin filaments, which join thick filaments to Z-discs, produce almost all of the resting tension in skinned rabbit psoas fibers and act to resist the movement of thick filaments away from the center of the sarcomere during contraction.
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Ratz, Paul H., and John E. Speich. "Evidence that actomyosin cross bridges contribute to “passive” tension in detrusor smooth muscle." American Journal of Physiology-Renal Physiology 298, no. 6 (June 2010): F1424—F1435. http://dx.doi.org/10.1152/ajprenal.00635.2009.
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Contraction of detrusor smooth muscle (DSM) at short muscle lengths generates a stiffness component we termed adjustable passive stiffness (APS) that is retained in tissues incubated in a Ca2+-free solution, shifts the DSM length-passive tension curve up and to the left, and is softened by muscle strain and release (strain softened). In the present study, we tested the hypothesis that APS is due to slowly cycling actomyosin cross bridges. APS and active tension produced by the stimulus, KCl, displayed similar length dependencies with identical optimum length values. The myosin II inhibitor blebbistatin relaxed active tension maintained during a KCl-induced contraction and the passive tension maintained during stress-relaxation induced by muscle stretch in a Ca2+-free solution. Passive tension was attributed to tension maintaining rather than tension developing cross bridges because tension did not recover after a rapid 10% stretch and release as it did during a KCl-induced contraction. APS generated by a KCl-induced contraction in intact tissues was preserved in tissues permeabilized with Triton X-100. Blebbistatin and the actin polymerization inhibitor latrunculin-B reduced the degree of APS generated by a KCl-induced contraction. The degree of APS generated by KCl was inhibited to a greater degree than was the peak KCl-induced tension by rhoA kinase and cyclooxygenase inhibitors. These data support the hypothesis that APS is due to slowly cycling actomyosin cross bridges and suggest that cross bridges may play a novel role in DSM that uniquely serves to ensure proper contractile function over an extreme working length range.
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Willems, Mark E. T., and William T. Stauber. "Effect of Contraction History on Torque Deficits by Stretches of Active Rat Skeletal Muscles." Canadian Journal of Applied Physiology 27, no. 4 (August 1, 2002): 323–35. http://dx.doi.org/10.1139/h02-018.
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Effects of contraction history on torque deficits by stretches of active skeletal muscles were examined. After three contractions using maximal and submaximal activation (80 and 20 Hz) at an ankle position of 40° (i.e., long muscle length) and with maximal activation at 120° (i.e., short muscle length), the isometric and stretch torques (15 stretches) of rat plantar flexor muscles (bout 1) were measured. Controls were unconditioned. Stretches (i.e., ankle rotation from 90° to 40°, velocity: 50°•s−1) were imposed on maximal isometric contractions at 90° (i.e. preloaded stretches). All groups performed a second bout following 2 hours of rest after bout 1. After maximal contractions at long muscle length, preload torque at 90° and stretch torque at 40° for stretch 1 of bout 1 were 25% and 18% lower than the other groups. However, for all groups, bout 1 ended and bout 2 began and ended with similar isometric and stretch torques. Stretches early in bout 2, with preloads similar to stretches in bout 1, had greater stretch torques resulting in larger torque deficits. Torque deficits, possibly caused by damage to muscle structures and excitation-contraction uncoupling, were not prevented by a history of isometric contractions. Different contraction histories can result in similar isometric torques but different stretch torques. Key words: injury, warm-up, isometric contractions, prevention, eccentric contractions
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Butterfield, Timothy A., Timothy R. Leonard, and Walter Herzog. "Differential serial sarcomere number adaptations in knee extensor muscles of rats is contraction type dependent." Journal of Applied Physiology 99, no. 4 (October 2005): 1352–58. http://dx.doi.org/10.1152/japplphysiol.00481.2005.
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Sarcomerogenesis, or the addition of sarcomeres in series within a fiber, has a profound impact on the performance of a muscle by increasing its contractile velocity and power. Sarcomerogenesis may provide a beneficial adaptation to prevent injury when a muscle consistently works at long lengths, accounting for the repeated-bout effect. The association between eccentric exercise, sarcomerogenesis and the repeated-bout effect has been proposed to depend on damage, where regeneration allows sarcomeres to work at shorter lengths for a given muscle-tendon unit length. To gain additional insight into this phenomenon, we measured fiber dynamics directly in the vastus lateralis (VL) muscle of rats during uphill and downhill walking, and we measured serial sarcomere number in the VL and vastus intermedius (VI) after chronic training on either a decline or incline grade. We found that the knee extensor muscles of uphill walking rats undergo repeated active concentric contractions, and therefore they suffer no contraction-induced injury. Conversely, the knee extensor muscles during downhill walking undergo repeated active eccentric contractions. Serial sarcomere numbers change differently for the uphill and downhill exercise groups, and for the VL and VI muscles. Short muscle lengths for uphill concentric-biased contractions result in a loss of serial sarcomeres, and long muscle lengths for downhill eccentric-biased contractions result in a gain of serial sarcomeres.
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Andersen, Ole Emil, Ole Bækgaard Nielsen, and Kristian Overgaard. "Early effects of eccentric contractions on muscle glucose uptake." Journal of Applied Physiology 126, no. 2 (February 1, 2019): 376–85. http://dx.doi.org/10.1152/japplphysiol.00388.2018.
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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.