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Статті в журналах з теми "Muscle mechanical power"
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Blake, Ollie M., and James M. Wakeling. "Muscle coordination limits efficiency and power output of human limb movement under a wide range of mechanical demands." Journal of Neurophysiology 114, no. 6 (December 1, 2015): 3283–95. http://dx.doi.org/10.1152/jn.00765.2015.
Повний текст джерелаАнотація:
This study investigated the influence of cycle frequency and workload on muscle coordination and the ensuing relationship with mechanical efficiency and power output of human limb movement. Eleven trained cyclists completed an array of cycle frequency (cadence)-power output conditions while excitation from 10 leg muscles and power output were recorded. Mechanical efficiency was maximized at increasing cadences for increasing power outputs and corresponded to muscle coordination and muscle fiber type recruitment that minimized both the total muscle excitation across all muscles and the ineffective pedal forces. Also, maximum efficiency was characterized by muscle coordination at the top and bottom of the pedal cycle and progressive excitation through the uniarticulate knee, hip, and ankle muscles. Inefficiencies were characterized by excessive excitation of biarticulate muscles and larger duty cycles. Power output and efficiency were limited by the duration of muscle excitation beyond a critical cadence (120–140 rpm), with larger duty cycles and disproportionate increases in muscle excitation suggesting deteriorating muscle coordination and limitations of the activation-deactivation capabilities. Most muscles displayed systematic phase shifts of the muscle excitation relative to the pedal cycle that were dependent on cadence and, to a lesser extent, power output. Phase shifts were different for each muscle, thereby altering their mechanical contribution to the pedaling action. This study shows that muscle coordination is a key determinant of mechanical efficiency and power output of limb movement across a wide range of mechanical demands and that the excitation and coordination of the muscles is limited at very high cycle frequencies.
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Roberts, Thomas J., and Jeffrey A. Scales. "Mechanical power output during running accelerations in wild turkeys." Journal of Experimental Biology 205, no. 10 (May 15, 2002): 1485–94. http://dx.doi.org/10.1242/jeb.205.10.1485.
Повний текст джерелаАнотація:
SUMMARYWe tested the hypothesis that the hindlimb muscles of wild turkeys(Meleagris gallopavo) can produce maximal power during running accelerations. The mechanical power developed during single running steps was calculated from force-plate and high-speed video measurements as turkeys accelerated over a trackway. Steady-speed running steps and accelerations were compared to determine how turkeys alter their running mechanics from a low-power to a high-power gait. During maximal accelerations, turkeys eliminated two features of running mechanics that are characteristic of steady-speed running: (i) they produced purely propulsive horizontal ground reaction forces, with no braking forces, and (ii) they produced purely positive work during stance, with no decrease in the mechanical energy of the body during the step. The braking and propulsive forces ordinarily developed during steady-speed running are important for balance because they align the ground reaction force vector with the center of mass. Increases in acceleration in turkeys correlated with decreases in the angle of limb protraction at toe-down and increases in the angle of limb retraction at toe-off. These kinematic changes allow turkeys to maintain the alignment of the center of mass and ground reaction force vector during accelerations when large propulsive forces result in a forward-directed ground reaction force. During the highest accelerations, turkeys produced exclusively positive mechanical power. The measured power output during acceleration divided by the total hindlimb muscle mass yielded estimates of peak instantaneous power output in excess of 400 W kg-1 hindlimb muscle mass. This value exceeds estimates of peak instantaneous power output of turkey muscle fibers. The mean power developed during the entire stance phase increased from approximately zero during steady-speed runs to more than 150 W kg-1muscle during the highest accelerations. The high power outputs observed during accelerations suggest that elastic energy storage and recovery may redistribute muscle power during acceleration. Elastic mechanisms may expand the functional range of muscle contractile elements in running animals by allowing muscles to vary their mechanical function from force-producing struts during steady-speed running to power-producing motors during acceleration.
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Ellington, C. P. "Power and efficiency of insect flight muscle." Journal of Experimental Biology 115, no. 1 (March 1, 1985): 293–304. http://dx.doi.org/10.1242/jeb.115.1.293.
Повний текст джерелаАнотація:
The efficiency and mechanical power output of insect flight muscle have been estimated from a study of hovering flight. The maximum power output, calculated from the muscle properties, is adequate for the aerodynamic power requirements. However, the power output is insufficient to oscillate the wing mass as well unless there is good elastic storage of the inertial energy, and this is consistent with reports of elastic components in the flight system. A comparison of the mechanical power output with the metabolic power input to the flight muscles suggests that the muscle efficiency is quite low: less than 10%.
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Josephson, Robert K., Jean G. Malamud, and Darrell R. Stokes. "The efficiency of an asynchronous flight muscle from a beetle." Journal of Experimental Biology 204, no. 23 (December 1, 2001): 4125–39. http://dx.doi.org/10.1242/jeb.204.23.4125.
Повний текст джерелаАнотація:
SUMMARYMechanical power output and metabolic power input were measured from an asynchronous flight muscle, the basalar muscle of the beetle Cotinus mutabilis. Mechanical power output was determined using the work loop technique and metabolic power input by monitoring CO2 production or both CO2 production and O2 consumption. At 35°C, and with conditions that maximized power output (60 Hz sinusoidal strain, optimal muscle length and strain amplitude, 60 Hz stimulation frequency), the peak mechanical power output during a 10 s burst was approximately 140 W kg–1, the respiratory coefficient 0.83 and the muscle efficiency 14–16 %. The stimulus intensity used was the minimal required to achieve a maximal isometric tetanus. Increasing or decreasing the stimulus intensity from this level changed mechanical power output but not efficiency, indicating that the efficiency measurements were not contaminated by excitation of muscles adjacent to that from which the mechanical recordings were made. The CO2 produced during an isometric tetanus was approximately half that during a bout of similar stimulation but with imposed sinusoidal strain and work output, suggesting that up to 50 % of the energy input may go to muscle activation costs. Reducing the stimulus frequency to 30 Hz from its usual value of 60 Hz reduced mechanical power output but had no significant effect on efficiency. Increasing the frequency of the sinusoidal strain from 60 to 90 Hz reduced power output but not CO2 consumption; hence, there was a decline in efficiency. The respiratory coefficient was the same for 10 s and 30 s bursts of activity, suggesting that there was no major change in the fuel used over this time range.The mass-specific mechanical power output and the efficiency of the beetle muscle were each 2–3 times greater than values measured in previous studies, using similar techniques, from locust flight muscles, which are synchronous muscles. These results support the hypothesis that asynchronous flight muscles have evolved in several major insect taxa because they can provide greater power output and are more efficient than are synchronous muscles for operation at the high frequencies of insect flight.
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Konow, Nicolai, Emanuel Azizi, and Thomas J. Roberts. "Muscle power attenuation by tendon during energy dissipation." Proceedings of the Royal Society B: Biological Sciences 279, no. 1731 (September 28, 2011): 1108–13. http://dx.doi.org/10.1098/rspb.2011.1435.
Повний текст джерелаАнотація:
An important function of skeletal muscle is deceleration via active muscle fascicle lengthening, which dissipates movement energy. The mechanical interplay between muscle contraction and tendon elasticity is critical when muscles produce energy. However, the role of tendon elasticity during muscular energy dissipation remains unknown. We tested the hypothesis that tendon elasticity functions as a mechanical buffer, preventing high (and probably damaging) velocities and powers during active muscle fascicle lengthening. We directly measured lateral gastrocnemius muscle force and length in wild turkeys during controlled landings requiring rapid energy dissipation. Muscle-tendon unit (MTU) strain was measured via video kinematics, independent of muscle fascicle strain (measured via sonomicrometry). We found that rapid MTU lengthening immediately following impact involved little or no muscle fascicle lengthening. Therefore, joint flexion had to be accommodated by tendon stretch. After the early contact period, muscle fascicles lengthened and absorbed energy. This late lengthening occurred after most of the joint flexion, and was thus mainly driven by tendon recoil. Temporary tendon energy storage led to a significant reduction in muscle fascicle lengthening velocity and the rate of energy absorption. We conclude that tendons function as power attenuators that probably protect muscles against damage from rapid and forceful lengthening during energy dissipation.
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Aerts, P. "Vertical jumping in Galago senegalensis: the quest for an obligate mechanical power amplifier." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 353, no. 1375 (October 29, 1998): 1607–20. http://dx.doi.org/10.1098/rstb.1998.0313.
Повний текст джерелаАнотація:
Bushbabies ( Galago senegalensis ) are renowned for their phenomenal jumping capacity. It was postulated that mechanical power amplification must be involved. Dynamic analysis of the vertical jumps performed by two bushbabies confirms the need for a power amplifier. Inverse dynamics coupled to a geometric musculo–skeletal model were used to elucidate the precise nature of the mechanism powering maximal vertical jumps. Most of the power required for jumping is delivered by the vastus muscle–tendon systems (knee extensor). Comparison with the external joint–powers revealed, however, an important power transport from this extensor (about 65%) to the ankle and the midfoot via the bi–articular calf muscles. Peak power output likely implies elastic recoil of the complex aponeurotic system of the vastus muscle. Patterns of changes in length and tension of the muscle–tendon complex during different phases of the jump were found which provide strong evidence for substantial power amplification (times 15). It is argued here that the multiple internal connective tissue sheets and attachment structures of the well–developed bundles of the vastus muscle become increasingly stretched during preparatory crouching and throughout the extension phase, except for the last 13 ms of the push–off (i.e. when power requirements peak). Then, tension in the knee extensors abruptly falls from its maximum, allowing the necessary fast recoil of the tensed tendon structures to occur.
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James, R. S., V. M. Cox, I. S. Young, J. D. Altringham, and D. F. Goldspink. "Mechanical properties of rabbit latissimus dorsi muscle after stretch and/or electrical stimulation." Journal of Applied Physiology 83, no. 2 (August 1, 1997): 398–406. http://dx.doi.org/10.1152/jappl.1997.83.2.398.
Повний текст джерелаАнотація:
James, R. S., V. M. Cox, I. S. Young, J. D. Altringham, and D. F. Goldspink Mechanical properties of rabbit latissimus dorsi muscle after stretch and/or electrical stimulation. J. Appl. Physiol. 83(2): 398–406, 1997.—The work loop technique was used to measure the mechanical performance in situ of the latissimus dorsi (LD) muscles of rabbits maintained under fentanyl anesthesia. After 3 wk of incrementally applied stretch the LD muscles were 36% heavier, but absolute power output (195 mW/muscle) was not significantly changed relative to that of external control muscle (206 mW). In contrast, continuous 10-Hz electrical stimulation reduced power output per kilogram of muscle >75% after 3 or 6 wk and muscle mass by 32% after 6 wk. When combined, stretch and 10-Hz electrical stimulation preserved or increased the mass of the treated muscles but failed to prevent an 80% loss in maximum muscle power. However, this combined treatment increased fatigue resistance to a greater degree than electrical stimulation alone. These stretched/stimulated muscles, therefore, are more suitable for cardiomyoplasty. Nonetheless, further work will be necessary to find an ideal training program for this surgical procedure.
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Syme, D. A. "The efficiency of frog ventricular muscle." Journal of Experimental Biology 197, no. 1 (December 1, 1994): 143–64. http://dx.doi.org/10.1242/jeb.197.1.143.
Повний текст джерелаАнотація:
Mechanical power and oxygen consumption (VO2) were measured simultaneously from isolated segments of trabecular muscle from the frog (Rana pipiens) ventricle. Power was measured using the work-loop technique, in which bundles of trabeculae were subjected to cyclic, sinusoidal length change and phasic stimulation. VO2 was measured using a polarographic O2 electrode. Both mechanical power and VO2 increased with increasing cycle frequency (0.4-0.9 Hz), with increasing muscle length and with increasing strain (= shortening, range 0-25% of resting length). Net efficiency, defined as the ratio of mechanical power output to the energy equivalent of the increase in VO2 above resting level, was independent of cycle frequency and increased from 8.1 to 13.0% with increasing muscle length, and from 0 to 13% with increasing strain, in the ranges examined. Delta efficiency, defined as the slope of the line relating mechanical power output to the energy equivalent of VO2, was 24-43%, similar to that reported from studies using intact hearts. The cost of increasing power output was greater if power was increased by increasing cycle frequency or muscle length than if it was increased by increasing strain. The results suggest that the observation that pressure-loading is more costly than volume-loading is inherent to these muscle fibres and that frog cardiac muscle is, if anything, less efficient than most skeletal muscles studied thus far.
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Mizisin, Andrew P., and Robert K. Josephson. "Mechanical power output of locust flight muscle." Journal of Comparative Physiology A 160, no. 3 (1987): 413–19. http://dx.doi.org/10.1007/bf00613030.
Повний текст джерела
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Askew, G. N., and D. J. Ellerby. "The mechanical power requirements of avian flight." Biology Letters 3, no. 4 (May 16, 2007): 445–48. http://dx.doi.org/10.1098/rsbl.2007.0182.
Повний текст джерелаАнотація:
A major goal of flight research has been to establish the relationship between the mechanical power requirements of flight and flight speed. This relationship is central to our understanding of the ecology and evolution of bird flight behaviour. Current approaches to determining flight power have relied on a variety of indirect measurements and led to a controversy over the shape of the power–speed relationship and a lack of quantitative agreement between the different techniques. We have used a new approach to determine flight power at a range of speeds based on the performance of the pectoralis muscles. As such, our measurements provide a unique dataset for comparison with other methods. Here we show that in budgerigars ( Melopsittacus undulatus ) and zebra finches ( Taenopygia guttata ) power is modulated with flight speed, resulting in U-shaped power–speed relationship. Our measured muscle powers agreed well with a range of powers predicted using an aerodynamic model. Assessing the accuracy of mechanical power calculated using such models is essential as they are the basis for determining flight efficiency when compared to measurements of flight metabolic rate and for predicting minimum power and maximum range speeds, key determinants of optimal flight behaviour in the field.
Дисертації з теми "Muscle mechanical power"
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Lewandowski, Beth Elaine. "An Implantable, Stimulated Muscle Powered Piezoelectric Generator." Cleveland, Ohio : Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1238702705.
Повний текст джерела
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Mendez, Villanueva Alberto. "Mechanical power output and neuromuscular activity during and following recovery from repeated-sprint exercise in man." University of Western Australia. School of Human Movement and Exercise Science, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0055.
Повний текст джерелаАнотація:
The purpose of the present study was to examine the time-course of mechanical power output and neuromuscular activity during fatiguing repeated-sprint exercise and recovery in man. Prior to the main study, we also investigated the reproducibility of power output during a single 6-s cycling sprint. For this study, eleven healthy moderately trained males performed a 6-s standing sprint on the front-access cycle ergometer on four separate occasions. The results of the study showed that reliable power outputs can be obtained after one familiarization session in subjects unfamiliar with maximal cycling sprint exercise. However, the inclusion of an extra familiarization session ensured more stable power outputs. Therefore, two trials should allow adequate familiarization with the maximal 6-s cycling test. For the main study, eight young moderately trained adult men performed an exercise protocol that consisted of ten, 6-s sprints on a wind-braked cycle ergometer interspersed with 30 s of recovery. After 6 min of passive recovery, five, 6-s sprints were repeated, again interspersed by 30 s of recovery. Peak power output (PPO) and mean power output (MPO) were measured during each sprint and EMG data (i.e., RMS) from the vastus lateralis muscle were also recorded. A one-way ANOVA with repeated measures (i.e., sprint number) was used to allocate the significant differences in each dependent variable over time. Analysis revealed a decline in power output during the fatiguing exercise that was accompanied by a decrease in EMG amplitude of the vastus lateralis muscle. Six minutes after the fatiguing exercise, power output during sprint 11 significantly recovered with respect to values recorded in sprint 10, but remained significantly lower than that recorded in the initial sprint. Thus, 6 min was insufficient to fully recover from the fatiguing repeated sprint protocol utilised in this study. The main findings in the present study were that: 1) the partial recovery of power output in sprint 11 was not accompanied by the recovery V of EMG amplitude; 2) similar mean power outputs were recorded during sprint 4 and 11 despite a significantly lower EMG activity recorded during the latter sprint; and 3) despite comparable mean power outputs during sprint 4 and 11, the decrease in power output over the next five sprints was greater for sprints 11 to 15 than for sprints 4 to 8.
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Telli, R. "RECUMBENT VS UPRIGHT BICYCLES: OPERATIVE RANGE OF PROPULSIVE MUSCLES, 3D TRAJECTORY OF BODY CENTRE OF MASS AND LIMB MECHANICAL WORK." Doctoral thesis, Università degli Studi di Milano, 2014. http://hdl.handle.net/2434/243748.
Повний текст джерелаАнотація:
Introduction. Humans have always tried to move safely and faster in a variety of environment, even through the aid of passive tools that help to improve the limits imposed by the body characteristics. These means of locomotion, without supplying additional mechanical energy, are able to greatly improve the performance exploiting the use of muscular force alone. Bicycles are probably the passive tool most known and used in the world. The origin of this thesis comes from the interest to increase the knowledge about the features of a particular kind of bike: the Recumbent bicycle (RB). It is a high performance human powered vehicle where the cyclist is in a reclined position, with the back against a backrest. The peculiarity of the RB is that it allows to reach higher speeds than Normal/upright bicycles (NB), at the same metabolic power, principally due to aerodynamic advantages. Indeed, with the use of particular fairings that improve aerodynamics, these vehicles allow to exceed 130 km/h only with muscles power. The change in posture of the rider, consequent to the different characteristics and design of the bicycles, alters kinematics and energetics of cycling and could also affects muscle-tendon lengths and the operating range of the muscles length-tension curves. Despite the interest of the scientific community on the topic of cycling, some aspects still need to be investigated, especially with respect to the differences between traditional and recumbent bikes, which represent the most advanced evolution of that tool.
Aim. The aim of this work is to analyze and compare the pedalling cycle on both bicycles from a biomechanical point of view. Indeed, with a comprehensive description of mechanical and metabolic consequences during cycling in both configuration, new vehicles could be designed with those technological changes that could increase the performance. Particular focus has been posed on the effect of the different position while riding the two bicycles:
- on the muscle-tendon length of different muscle-tendon unit involved in cycling;
- on the 3D displacement of the Body Centre of Mass (BCoM);
- on the mechanical work (in particular the internal and the "additional" external mechanical work).
Methods. The issues have been investigated both experimentally and trough simulations. By using 3D kinematic data and a physical simulation program we measured muscles-tendon length, 3D Body Centre of Mass (BCoM) trajectory and its symmetries and the components of the total mechanical work necessary to sustain cycling during stationary cycling, at different pedalling cadences (50, 70, 90 and 110 rpm). This approach allows to investigate the biomechanics of riding the two bicycles both through direct measurements of mechanical work and indirect estimation performed with simulation models.
Results and Discussion. Joint kinematics and muscle-tendon length were analyzed with the musculoskeletal modelling software Opensim®. This analysis showed that, differently from cadence, the two bicycles caused changes in joint angles and, consequently, in muscle-tendon length. As a results in RB, when compared to NB, some muscles are slightly stretched while other are shortened, making the propulsive effectiveness impossible to be assessed. This work confirms experimentally, for the first time, that the BCoM in cycling moves along all three spatial axes, while before this study an elliptical movement in the sagittal plane was appreciated only with a 2D simulation. BCoM trajectory, confined in a 15 mm side cube, changed its orientation maintaining a similar pattern in both configurations, with advantages for RB: a smaller additional mechanical external power (on average 16.1 ± 9.7 W on RB versus 20.3 ± 8.8 W on NB), a greater Symmetry Index on progression axis and no differences in the internal mechanical power (ranged from 7.90 W to 65.15 W in NB and from 7.25 W to 62.16 W in RB, increasing as function of the rpm).
Conclusion. Despite the human physiological characteristics have remained almost unchanged over the last millennia, performance on bicycles has increased significantly. This has been possible thanks to the work of mechanical engineers, exercise physiologists and biomechanists. In this thesis the body centre of mass trajectory and the associated additional external mechanical work while pedalling on recumbent bicycle has been studied experimentally for the first time. It is thought that the development of mechanisms reducing additional external power through a further containment of BCoM trajectory, together with additional studies on the effectiveness of propulsive muscles could be necessary to further refine design and improve performance of RB.
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LOPES, STORNIOLO JUNIOR JORGE LUIZ. "CURRENT TOPICS IN LOCOMOTION PHYSIOLOGY: A) MUSCLE EFFICIENCY IN HEAVILY LOADED GRADIENT WALKING AND B) HEART RATE OFF-KINETICS AS A PREDICTOR OF VO2MAX." Doctoral thesis, Università degli Studi di Milano, 2018. http://hdl.handle.net/2434/528064.
Повний текст джерелаАнотація:
The human locomotion has been constantly analysed from both bioenergetics and biomechanical point of views (Saibene & Minetti, 2003; Cavagna, 2010). Since earliest times, hunting for food and escaping from predators already has proven how important is to comprehend this complex engineering that is our locomotor machine.
Gradient locomotion has been investigated in the past, and the concept of the optimum gradient for walking, running and mountain paths are well known in the literature. The existence of an optimum gradient is based on the different partitioning between positive and negative mechanical work (that mirrors concentric and eccentric muscular activity) and the related metabolic demand. In the literature, the ratio between negative and positive work efficiency during unloaded locomotion was found to be 5/1. The purpose of this new study is to analyse the mechanical, metabolic and electromyography parameters during gradient loaded walking in order to understand how an extra-load can affect locomotion and especially the efficiency of positive and negative work.
Still, another important topic referred to the human locomotion physiology is about the cardiovascular system. Related to this, oxygen uptake (V'O2) refers to the product of cardiac output and the volume of oxygen extracted from the blood, and its maximal value (V'O2peak) strengthen the maximal capacity of the cardiovascular system to provide O2 to muscle cells during continued exercise, being the most widely used measure of physical fitness (Plasqui & Westerterp, 2005; Koeneman et al., 2011). Although there is a large genetic component, it is mainly determined by a person’s activity level, and inversely related to several health outcomes such as cardiovascular disease (Daanen et al., 2012).
Besides of heart rate (HR) control and its relationship with V'O2, the HR recovery (off transient, after exercise) has received more attention by current researchers (Myers et al., 2007; Dupuy et al., 2012; Haddad et al., 2012). The rate of decline in HR following termination of exercise, which is regulated by the autonomic nervous system and thereby, provides information concerning sympathetic and parasympathetic activity (Daanen et al., 2012). In general, the more rapid the HR recovery, the better the fitness (Daanen et al., 2012; Buchheit, 2014).
While exercise-training studies usually report HR values at a given time during the recovery period (Daanen et al., 2012), in most clinical studies, HR recovery is defined as the difference between HR at the end of exercise and HR at a given time during the recovery period (Otsuki et al., 2007; Dupuy et al., 2012). Moreover, in some studies a mono-exponential model fit the HR off-kinetics to derive global parameters of HR recovery kinetics such as the time constant or the asymptotic value (Stanley et al., 2013; Peinado et al., 2014).
Based on these results and the growing interest in new smart devices for health monitoring, here we aimed to estimate V'O2peak from a short test (60 m) with variables that can be detected by the smart sensors. We ask to 25 healthy subjects to perform a maximal sprint over 60-m. Beat-by-beat HR was recorded by a chest belt during the whole test including resting period before and recovery post sprint. (n = 25). HR off kinetics was fitted by a mono-exponential function and tau value was calculated in order to obtain a velocity of HR decrement post exercise. V'O2peak was then estimate with a multiple regression analysis: V'O2peak = 7.46∙vtest + 261.4∙voff - 0.19∙∆HR (R2= 0.65, p<0.001). Where vtest represents the velocity performed during the 60-m test, voff corresponds to the velocity of HR decreasing during off-transient (recovery phase), and "∆HR" is the difference of HR during on-transient of exercise and it is the difference between maximum and the resting value.
This new equation does not aim to replace the laboratory-standard protocols for V'O2peak determination, but it can give an insight about fitness level to laymen that use smart devices for monitoring their physical activity. Whenever these new models (smart watches) would perform a beat-by-beat analysis this equation could be introduced to the software and give a first general estimate of the user's fitness level.
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Caruel, Matthieu. "Mechanics of Fast Force Recovery in striated muscles." Phd thesis, Ecole Polytechnique X, 2011. http://pastel.archives-ouvertes.fr/pastel-00668301.
Повний текст джерелаАнотація:
Cette thèse est consacrée à la modélisation de la réponse transitoire d'une fibre musculaire squelettique soumise à des sollicitations mécaniques rapides. A l'échelle du nanomètre, la fibre musculaire contient des filaments d'actine et de myosine regroupés en unités contractiles appelées "sarcomères". Le filament de myosine est un assemblage de moteurs mol ́eculaires qui, en présence d'ATP, s'attachent et se d ́etachent p ́eriodiquement au filament d'actine. Au cours de ce processus d'attachement-détachement, la myosine génère une force lors d'un changement de conformation appelé "power-stroke". Ses caractéristiques peuvent être étudiées lors de la réponse transitoire de la fibre soumise à des sollicitations mécaniques rapides. Nous proposons un modèle mécanique innovant du demi-sarcomere permettant de relier les caractéristiques de la myosine à la réponse de la fibre complète. A la différence des modèles existants, privilégiant une approche discrète, ce modèle s'appuie sur la définition d'un potentiel d'énergie continu qui prend en compte une interaction de champ moyen entre les moteurs moléculaires. Ce système présente des réponses radicallement différentes à longueur imposée et à force imposée. Nous proposons en particulier une explication à la différence de cinétique observée expérimentalement. Nous montrons également que le demi-sarcomere est m ́ecaniquement instable ce qui explique les inhomogénéités de longueurs observées dans une myofibrille.
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Rice, Paige Elizabeth. "Determining muscle-tendon characteristics and function of stretch-shortening cycle performance in dancers." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2021. https://ro.ecu.edu.au/theses/2481.
Повний текст джерелаАнотація:
Dancers are aesthetic athletes with extraordinary skillsets defined by muscle-tendon unit (MTU) properties and stretch-shortening cycle (SSC) proficiency. Early on in athletic development, dancers are instructed to maintain aesthetic posture, wherein the hips are directly beneath the shoulders, during most jumps and leaps. Different from a countermovement jump, leaps such as the saut de chat (split leap) have been shown to cause distal shifts in torque from the hips to the ankle, likely due to postural maintenance. Thus, the role of the ankle in dance is potentially twofold as the primary joint: to both generate torque during dance-specific SSC’s and to achieve stylistic “pointing” of the toes – hyper-plantarflexion. Little research has delineated the MTU properties surrounding the ankle-joint of dancers and how they might influence dance-specific SSC performance, like saut de chat leaping. Furthermore, ankle-specific strength and conditioning tactics to simultaneously improve maximal strength capacity, MTU properties, and saut de chat leaping performance have yet to be investigated in dancers. Therefore, this thesis was founded in the following purposes: 1) to elucidate whether isolated ankle-joint SSC performance, maximal isometric and isokinetic plantarflexion strength, and maximal Achilles tendon force and elongation differ between dancers, endurance runners, and untrained controls; 2) to determine the relationship between saut de chat weighted parameter rankings, leap height, maximal voluntary isometric plantarflexion strength, medial gastrocnemius stiffness, Achilles tendon stiffness, and leaping peak power; 3) to investigate the effect of an ankle-focused block progression training program (24 sessions) on saut de chat leaping performance, maximal plantarflexion strength, and Achilles tendon stiffness. and 4) to successfully perform single fibre and fibre bundle mechanics on micro-biopsy samples from medial gastrocnemii of dancers.
Study one demonstrated that dance is likely a stimulus for enhanced ankle-joint SSC function, plantarflexion isometric and isokinetic strength, and Achilles tendon elongation. Endurance running also appeared to be a possible stimulus for increased muscular strength. Study two revealed that relative peak power during leaping, maximal voluntary isometric plantarflexion strength, and medial gastrocnemius stiffness strongly and moderately predicted saut de chat performance as defined by a novel weighted parameter ranking tool. Study three showed that twelve weeks of ankle-specific block progression training appears to benefit saut de chat leaping performance, peak power output, ankle-joint kinetics, maximal strength, and Achilles tendon stiffness, while not affecting kinematic aesthetic measures. We found that by employing additional training that targets ankle-specific stretch-shortening cycle, neuromechanical, and muscle-tendon unit development, dancers are capable of improving already well-engrained movement execution strategies. Study four discovered that muscle fibre mechanics can be performed on micro-biopsy samples from medial gastrocnemius muscle, which will allow for future research on dancers’ basic muscle force-length and force-velocity properties to be more feasibly investigated.
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CONTE, Davide. "Muscle mechanical work in walker-assisted locomotion: Instrumentationand modelling for an integrated gait analysis in cerebral palsy." Doctoral thesis, 2012. http://hdl.handle.net/11562/417939.
Повний текст джерелаАнотація:
La stima del lavoro meccanico muscolare è un utile strumento per valutare l'efficienza di un movimento, ma il processo di calcolo presenta ancora molte criticità dal punto di vista biomeccanico.
Diversi metodi per stimare il lavoro meccanico muscolare durante il cammino sono stati presentati in letteratura, ma nonostante i tentativi fatti per confrontarli, tutti i metodi sono tuttora utilizzati in ambito di ricerca e in ambito clinico. Una più profonda comprensione delle differenze, sia dal punto di vista teorico, che pratico, potrebbe permettere di capire cosa venga effettivamente calcolato da ciascun metodo ed aiutare a fare un uso più appropriato di questa informazione. A questo scopo è stato validato un modello tridimensionale a corpo completo, consistente in 16 segmenti, utilizzato per raccogliere informazioni cinematiche e dinamiche durante il cammino in ragazzi e bambini sani e in ragazzi e bambini affetti da paralisi cerebrale infantile (CP), camminati a velocità spontanea.
Lo sviluppo di due maniglie strumentate fissabili sulla struttura di deambulatori pediatrici posteriori ha permesso di misurare cinematica e dinamica dell'arto superiore anche in soggetti con maggiori difficoltà di deambulazione. Curve di potenza e valori di lavoro meccanico muscolare totale, positivo, negativo o netto, durante cammino normale e durante cammino con deambulatore, sono stati stimati dimostrando che tutti i metodi sono equivalenti quando vengono permessi trasferimenti di energia tra segmenti. Senza possibilità di trasferimento di energia, i metodi differiscono tra loro, con differenze dipendenti dal metodo utilizzato e dal movimento studiato. Eccetto alcune criticità evidenziate e discusse, l'analisi delle curve di potenza muscolare e dei valori di lavoro meccanico muscolare stimati può fornire utili informazioni sulla funzione locomotoria nel suo complesso, mettendo in luce deficit di propulsione, asimmetrie del cammino, inefficienze di movimento associate ad una ridotta capacità di recupero di energia.The estimation of muscle mechanical work can be useful to assess movement efficiency, but it is still a challenging task in biomechanics. Different methods to estimate muscle work during walking have been presented in the literature and, although attempts have been made to investigate differences among them, all methods are still used in research and clinical applications. A deeper understanding of theoretical differences and analogies would allow to know what is exactly computed by each method and help to make a more appropriate use of this information. To this purpose, a 16 segments full-body 3D model was validated and used to collect kinematic and kinetic data from healthy children and cerebral palsy (CP) children walking at self-selected speed. Two instrumented handles fixable on the frame of posterior paediatric walkers were also developed, to measure upper limb kinetics in subjects with more severe walking impairements. Whole-body muscle mechanical power curves and work values, either positive, negative or net, during normal gait and during walker locomotion were obtained, demonstrating that all methods are equivalent when energy transfers between segments are allowed. With no transfers allowed, methods differ among each other, with differences depending on the movements and the methods considered. Apart from some critical issues evidenced and discussed, the analysis of whole-body muscle mechanical power curves and work estimates can provide valuable information on the overall locomotion function, highlighting propulsive deficits, gait asymmetries, movement inefficiencies associated to reduced energy recuperation.
Книги з теми "Muscle mechanical power"
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A biomechanical comparison of the vertical jump and Margaria power tests. 1988.
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A biomechanical comparison of the vertical jump and Margaria power tests. 1990.
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Nava, Stefano, and Luca Fasano. Ventilator Liberation Strategies. Oxford University Press, 2014. http://dx.doi.org/10.1093/med/9780199653461.003.0039.
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The weaning process should ideally begin as soon as the patient is intubated and continue through the treatment of the cause inducing acute respiratory failure. Weaning includes the assessment of readiness to extubate, extubation, and post-extubation monitoring; it also includes consideration of non-invasive ventilation which has been shown to reduce the duration of invasive mechanical ventilation in selected patients. Weaning accounts for approximately 40% of the total time spent on mechanical ventilation and should be achieved rapidly, since prolonged mechanical ventilation is associated with increased risk of complications and mortality and with increased costs. During mechanical ventilation, medical management should seek to correct the imbalance between respiratory load and ventilatory capacity (reducing the respiratory and cardiac workload, improving gas exchange and the ventilatory pump power). Ventilator settings delivering partial ventilatory pump support may help prevent ventilator-induced respiratory muscles dysfunction. Daily interruption of sedation has been associated with earlier extubation. Critically ill patients should be repeatedly and carefully screened for readiness to wean and readiness to extubate, and objective screening variables should be fully integrated in clinical decision making.
Частини книг з теми "Muscle mechanical power"
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Borelli, Giovanni Alfonso. "Mechanical lemmas useful to explain the power or the moment of the muscles." In On the Movement of Animals, 20–23. Berlin, Heidelberg: Springer Berlin Heidelberg, 1989. http://dx.doi.org/10.1007/978-3-642-73812-8_9.
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Fehring, Thomas H., and Terry S. Reynolds. "Energy Production and Conversion." In Chronicles of Mechanical Engineering in the United States, 201–50. ASME, 2021. http://dx.doi.org/10.1115/1.356056_ch6.
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In many ways, energy production and its conversion from one form to another is the heart of mechanical engineering. The history of energy is vast, beginning with efforts to make the energy produced by human muscle more effective through the use of lubricants or the application of the so-called six simple machines in pre-history. By the end of Classical antiquity, inventors and engineers had harnessed the power of wind to move ships and water to grind flour. In the eighteenth century the first practical heat engines opened the era of fossil fuels, utilizing the expansive power of steam to convert thermal energy to mechanical energy.
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Ino, Shuichi, and Mitsuru Sato. "Human-Centered Metal Hydride Actuator Systems for Rehabilitation and Assistive Technology." In Handbook of Research on Personal Autonomy Technologies and Disability Informatics, 154–70. IGI Global, 2011. http://dx.doi.org/10.4018/978-1-60566-206-0.ch010.
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Metal hydride materials can store a huge amount of hydrogen and can convert energy due to enthalpy change through a hydride reaction. Artificial actuation systems that employ this special physicochemical property are named metal hydride actuators. The actuators utilize the mechanical energy formed from hydrogen equilibrium pressure through thermal energy given to the metal hydride alloys as output. Metal hydride actuators have a simple structure and a number of features that make them attractive for use in rehabilitation engineering and assistive technology. They provide a high power-to-weight ratio, high strain actuation, human-compatible softness and noiselessness, and they are environmentally benign. The behavior of metal hydride actuators is also useful for overall human-machine interface applications. This article reviews the motivation for the development of some of the leading artificial muscle-like actuators, outlines the metal hydride actuators and describes its applications in quality-of-life technology.
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"Chapter 1 Introduction, Anatomy and Physiology of Striated Skeletal Muscle ... The Source of Human Power." In Mechanics of Muscle, 1–50. New York University Press, 2021. http://dx.doi.org/10.18574/nyu/9780814788776.003.0008.
Повний текст джерелаТези доповідей конференцій з теми "Muscle mechanical power"
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Slightam, Jonathon E., and Mark L. Nagurka. "Theoretical Modeling, Analysis, and Experimental Results of a Hydraulic Artificial Muscle Prototype." In ASME/BATH 2019 Symposium on Fluid Power and Motion Control. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/fpmc2019-1654.
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Abstract Fluidic braided artificial muscles have been studied for close to seventy years. Their high power-to-weight ratio and force-to-weight ratio make them a desirable actuation technology for compact and lightweight mobile manipulation. Use of hydraulics with fluidic artificial muscles has helped realize high actuation forces with new potential applications. To achieve large actuation forces produced from high internal pressure, artificial muscles operate near the limitations of their mechanical strength. Design improvements and future applications in mechanical systems will benefit from detailed theoretical analysis of the fluidic artificial muscle mechanics. This paper presents the theoretical modeling of a hydraulic artificial muscle, analysis of its mechanics, and experimental results that validate the model. A prototype is analyzed that operates at 14 MPa and can generate up to 6.3 kN of force and a displacement of 21.5 mm. This model promises to be useful for mechanical system design and model-based control.
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Hakansson, Nils A., and Maury L. Hull. "Influence of Pedaling Rate on Muscle Mechanical Energy in Low Power Recumbent Pedaling Using Forward Dynamic Simulations." In ASME 2007 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/detc2007-35108.
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An understanding of the muscle power contributions to the crank and limb segments in recumbent pedaling would be useful in the development of rehabilitative pedaling exercises. The objectives of this work were to (i) develop a forward dynamic model to simulate low-power pedaling in the recumbent position, (ii) use the model to quantify the power contributions of the muscles to driving the crank and limb segments, and (iii) determine whether there were differences in the muscle power contributions required to simulate recumbent pedaling at three different pedaling rates. A forward dynamic model was used to determine the individual muscle excitation amplitude and timing to drive simulations that best replicated experimental kinematics and kinetics of recumbent pedaling. The segment kinematics, pedal reaction forces, and electromyograms (EMG) of 10 muscles of the right leg were recorded from 16 subjects as they pedaled a recumbent ergometer at 40, 50, and 60 rpm and a constant 50 W workrate. Intersegmental joint moments were computed using inverse dynamics and the muscle excitation onset and offset timing were determined from the EMG data. All quantities were averaged across ten cycles for each subject and averaged across subjects. The model-generated kinematic and kinetic quantities tracked almost always within 1 SD of the experimental data for all three pedaling rates. The uniarticular hip and knee extensors generated 65 percent of the total mechanical work in recumbent pedaling. The triceps surae muscles transferred power from the limb segments to the crank and the bi-articular muscles that crossed the hip and knee delivered power to the crank during the leg transitions between flexion and extension. The functions of the individual muscles did not change with pedaling rate, but the mechanical energy generated by the knee extensors and hip flexors decreased as pedaling rate increased. By varying the pedaling rate, it is possible to manipulate the individual muscle power contributions to the crank and limb segments in recumbent pedaling and thereby design rehabilitative pedaling exercises to meet specific objectives.
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Jafarzadeh, Mohsen, Lianjun Wu, and Yonas Tadesse. "System Identification of Force of a Silver Coated Twisted and Coiled Polymer Muscle." In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-71985.
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The demand of using artificial muscle similar to the human muscle is significantly increased during past decades. Recently, silver-plated Twisted and Coiled Polymer (TCP) muscle was employed in many research projects. A first order differential equations (1st ODE) was used to predict the force of this muscle, assuming that the TCP muscle acts similar to a mechanical spring that has variable stiffness depending on the electrical power supplied. Thus, extensive study should be performed on different types of TCP muscles to reach a conclusion. In this paper, a black box system identification method is used to examine the behavior of TCP muscles under different input conditions. Different order differential equations are compared with experimental results. Prediction error method (PEM) is used for estimation of the force of silver-plated TCP muscle with several linear time invariant (LTI) discrete time state space system. In addition, we suggest a fast method (rule of thumb) to model a TCP muscle. Moreover, two key parameters have been introduced to compare the quality of the TCP muscle from force perspective.
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Chen, Siqing, and He Xu. "Modeling, Analysis, and Function Extension of the McKibben Hydraulic Artificial Muscles." In BATH/ASME 2020 Symposium on Fluid Power and Motion Control. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/fpmc2020-2741.
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Abstract Compared with rigid robots, flexible robots have soft and extensible bodies enforcing their abilities to absorb shock and vibration, hence reducing the impact of probable collisions. Due to their high adaptability and minimally invasive features, soft robots are used in various fields. The McKibben hydraulic artificial muscles are the most popular soft actuator because of the controllability of hydraulic actuator and high force to weight ratio. When its deformation reaches a certain level, the actuators can be stopped automatically without any other braking mechanism. The research of McKibben hydraulic artificial muscles is beneficial to the theoretical analysis of soft actuators in the mechanical system. The design of soft actuators with different deformations promotes the development of soft robots. In this paper, a static modeling of the McKibben hydraulic artificial muscles is established, and its correctness is verified by theoretical analysis and experiment. In this model, the deformation mechanism of the artificial muscle and the law of output force is put forward. The relationship between muscle pressure, load, deformation, and muscle design parameters is presented through the mechanical analysis of the braid, elastic tube, and sealed-end. The law of the muscle deformation with high pressure is predicted. The reason for the muscle’s tiny elongation with extremely high pressure is found through the analysis of the relationship between the angle of the braid, the length of single braided thread, and the pressure. With the increase of pressure, the angle of the braid tends to a fixed value. As the stress of braided thread increases, so does its length. The length changes obviously when the stress is extremely enormous. The angle of the braid and the length of the braided thread control the deformation of artificial muscles, resulting in a slight lengthening with extreme high pressure. Under normal pressure, the length of the braided wire is negligible, so that the entire muscle becomes shorter. According to the modeling and theoretical analysis, a new McKibben hydraulic artificial muscle that can elongate under normal rising pressure is designed. This artificial muscle can grow longer with pressure increases, eventually reaching its maximum length. During this time, its diameter barely changes. Its access pressure is higher than that of conventional elongated artificial muscles. Through experiments, the relationship between the muscle deformation, pressure, and load still conform to this theoretical model. This model can be used for the control of soft actuators and the design of new soft robots. This extensional McKibben hydraulic artificial muscles and the conventional McKibben hydraulic artificial muscles can be used in the bilateral control of soft robots.
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Lee, Hyunglae, and Neville Hogan. "Modeling Dynamic Ankle Mechanical Impedance in Relaxed Muscle." In ASME 2011 Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power and Motion Control. ASMEDC, 2011. http://dx.doi.org/10.1115/dscc2011-5976.
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This paper presents identification and modeling of dynamic ankle mechanical impedance in relaxed muscles. A multi-variable estimation method using a wearable therapeutic robot enabled clear interpretation of dynamic ankle impedance both in the sagittal and frontal planes. Estimation results showed that dynamic ankle behavior apparently cannot be reconciled with a simple 2nd order model. Measurements in a seated and standing position verified that ankle impedance changes substantially depending on lower-limb posture. Identification results were fitted with a modified Hill model with a mass between the muscle and tendon elements. When coupled with foot inertia, either singly or antagonistically, this model successfully captured the dynamic behavior of the ankle impedance both in the seated and standing positions up to 20 Hz. At least a 4th order model having 2 complex zero and 1 complex pole pairs was required to describe relaxed ankle impedance either in the sagittal or frontal plane up to 20Hz. In the seated position, a 6th order model was slightly better than the 4th order model but with the expense of complexity, and a 8th order model might be used to describe dynamic ankle behavior up to 30∼40Hz.
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Dorn, Tim W., Yi-Chung Lin, Anthony G. Schache, and Marcus G. Pandy. "Which Muscles Power the Human Running Stride?" In ASME 2012 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/sbc2012-80065.
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Running is a physically demanding activity that requires explosive delivery of muscle power to the ground during stance, and precise, yet rapid limb coordination during swing. In particular, as running speed increases, greater metabolic energy in the form of muscle mechanical work is required to power the motion of: i) the center-of-mass (i.e., external power); and ii) the individual limb segments (i.e., internal power) [1,2]. The purpose of this study was to quantify the contributions that individual muscles make to the external and internal power of the body across a range of running speeds so as to identify the key muscle groups in coordinating a full running stride.
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Jouppila, V., and A. Ellman. "Multiplexed Force Control of Pneumatic Muscles." In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-13645.
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Pneumatic actuators are often used in applications that require high power-to-weight ratio, combined with low price and clean and fast operation. However, due to the compressibility of air and highly nonlinear behavior of seal friction, the position and force control of these actuators is difficult to manage. As a result, pneumatic cylinders have been used for many years solely in simple repetitive tasks requiring only a very limited amount of system control. Nonetheless, the pneumatic actuators have properties such as compactness, high power-to-weight ratio, and simplicity that are desirable features in advanced robotics. To overcome the shortcomings, a number of advanced pneumatic components have been developed, of which the most promising is the pneumatic muscle. Compared to a cylinder, a pneumatic muscle not only has a higher power-to-weight and power-to-volume ratio but it is also almost frictionless and has zero leakage. In spite of the muscle actuator's nonlinear force-to-contraction characteristics, many motion and force control methods have been successfully applied to it. The characteristics of the actuator enable it to be used in simple positioning systems and as a variable gas spring. The actuator's almost linear pressure-to-force ratio is extremely well-suited to a variety of gripping and pressing applications. Due to the muscle actuator's characteristics and recent developments in pneumatic valve technology, there is an opportunity to share a single pressure control servo valve among multiple muscle actuators. The multiplexed control of the actuators with only one servo valve reduces the system costs significantly. In this paper we investigate the feasibility of employing multiplexed force control of four pneumatic muscle actuators. In the system, pressure is controlled by a single proportional pressure valve. High-speed switching valves are used for activating the pressure control for each muscle actuator in the desired manner. Pneumatic cylinders are attached to the other ends of the muscles in order to cause controllable position disturbances. The displacement, force and pressure of each muscle are measured with appropriate sensors. The system behavior is investigated under position disturbances.
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Gustafson, Kenneth J., and Steven H. Reichenbach. "In Situ Thermal Measurements for Estimaton of Relative Metabolic Utilization in Skeletal Muscle." In ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-0181.
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Abstract A variety of systems to drive cardiac assist devices with power from skeletal muscle have been proposed and are under development. The power available from a fixed mass of muscle is metabolically limited and maximizing sustained power is required for the successful application of such devices. The purpose of this study is to develop an approach that can yield relative metabolic utilization measures from single contractions of whole muscle used for cardiac assistance. Similar to classical muscle energetic studies, myothermic methods were employed in which muscle temperature was measured with a fast responding thermister and an infrared radiation thremopile transducer. In a series of tests on rabbit soleus muscle, the relative temperature increases during contractions were recorded. Relative muscle temperature increase was linearly related to the contraction duration. This relationship was incorporated into an existing muscle model to predict the optimum parameters for sustained skeletal muscle power generation.
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Saharan, Lokesh, and Yonas Tadesse. "A Novel Design of Thermostat Based on Fishing Line Muscles." In ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-67298.
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Recently reported fishing line muscles are soft actuators which can be fabricated by twist insertion in commercially available Nylon 6 monofilament fibers under certain amount of tension. Annealing and Training are needed to retain the twist inserted to complete the fabrication process. These actuators are soft polymeric materials with high stresses, large strain, relatively high power to weight ratio when compared to conventional actuators apart from being cost effective. Though the performance of the muscles is largely dependent on parameters of fabrication, these actuators deform linearly in response to thermal gradient. Actuation can be triggered by varying temperature by any means such as blowing hot fluid or resistive (Joule) heating. The response of the muscles depends on the rate of change of temperature, magnitude of temperature, and applied load. We recognized the potential application of the muscle as a mechanical thermostat as a new design or for use in opening and closing a control valves. Mostly the working range for this muscle is 50–150°C, which is the working range of a wide variety of devices and instruments. This study presents a novel design, fabrication, working principle and preliminary experiments of the thermostat device that is light in weight, simple to manufacture and cost effective.
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Segala, David B., David Chelidze, Jeffrey M. Schiffman, Deanna Gates, and Jonathan Dingwell. "Tracking Muscle Fatigue Markers Through Nonlinear and Multivariate Analysis of Motion Kinematics." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11569.
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Both athletes and soldiers subject their body to extensive prolonged movements at the price of completing their tasks. The purpose of his study is to show that phase space warping (PSW) concept and smooth orthogonal decomposition (SOD) can be used to extract muscle fatigue related information from easily obtainable and noninvasive movement kinematics data. Two experimental setups are considered: load carrying soldiers walking on a treadmill and subjects performing a sawing motion. PSW and SOD based fatigue related trends are compared against local muscle fatigue markers obtained from surface electromyography (sEMG) measurements. In particular, a decrease in the mean power frequencies (MNF) or median power frequencies (MDF) of the sEMGs are used to indicate the onset of muscle fatigue, since a muscle fatigue causes a shift in the power spectrum of sEMG to lower frequencies.