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ABSTRACT: We utilized functional magnetic resonance imaging to investigate the brain regions activated during motor imagery of an action with an object both with and without passively holding the object. Participants performed the following tasks: (1) 'Imagery with Ball' condition: subjects imagined squeezing a foam ball (7cm diameter) while holding the ball, (2) 'Imagery' condition: subjects imagined squeezing a ball without holding the ball, and (3) 'Ball' condition: subjects held the ball without motor imagery. Regions activated by the 'Imagery with Ball' condition were located in the left dorsolateral prefrontal cortex (DLPFC), supplemental motor areas (SMA), inferior parietal lobule (IPL), superior parietal lobule (SPL), insula, cerebellum and basal ganglia. A direct comparison revealed that the right DLPFC and the right IPL showed a higher level of activation during the 'Imagery with Ball' than during the 'Imagery'+'Ball' conditions. Our studies suggested that the right front-parietal networks were involved in the motor imagery of an action with an object.
Neuroscience Research 04/2013; · 2.25 Impact Factor
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ABSTRACT: When performing oscillatory movements of two joints in the sagittal plane, there is a directional constraint for performing such movements. Previous studies could not distinguish whether the directional constraint reflected movement direction encoded in the extrinsic (outside the body) reference frame or in the intrinsic (the participants' torso/head) reference frame since participants performed coordinated movements in a sitting position where the torso/head was stationary relative to the external world. In order to discern the reference frame in the present study, participants performed paced oscillatory movements of the ipsilateral wrist and ankle in the sagittal plane in a standing position so that the torso/head moved relative to the external world. The coordinated movements were performed in one of two modes of coordination, moving the hand upward concomitant with either ankle plantarflexion or ankle dorsiflexion. The same directional mode relative to extrinsic space was more stable and accurate as compared with the opposite directional mode. When forearm position was changed from the pronated position to the supinated position, similar results were obtained, indicating that the results were independent of a particular coupling of muscles. These findings suggest that the directional constraint on ipsilateral joints movements in the sagittal plane reflects movement direction encoded in the extrinsic reference frame.
Neuroscience Research 03/2013; · 2.25 Impact Factor
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ABSTRACT: Our previous studies showed that corticospinal excitability during imagery of squeezing a foam ball was enhanced by somatosensory input generated by passively holding the ball. In the present study, using the same experimental model, we investigated whether corticospinal excitability was influenced by holding the object with the hand opposite to the imagined hand. Corticospinal excitability was assessed by monitoring motor evoked potentials (MEPs) in the first dorsal interosseous muscle following transcranial magnetic stimulation over the motor cortex during motor imagery. Subjects were asked to imagine squeezing a foam ball with the right hand (experiment 1) or the left hand (experiment 2), while either holding nothing (Null condition), a ball in the right hand (Right condition) or a ball in the left hand (Left condition). The MEPs amplitude during motor imagery was increased, only when the holding hand and the imagined hand were on the same side. These results suggest that performance improvement and rehabilitation exercises will be more effective when somatosensory stimulation and motor imagery are done on the same side.
Neuroscience Letters 03/2012; 514(1):127-30. · 2.11 Impact Factor
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ABSTRACT: Excitability of the corticospinal pathway increases during observation of an action. However, how corticospinal excitability changes during observation of sequential actions in the course of acquiring novel skills (observational learning) remains unexplored. To investigate this, we used a previously unpracticed sequence of ten hand postures. Participants were asked to repeat observation and replication of the sequence. This block of observation and replication was repeated 5 times. During observation of a given hand posture (OK sign), motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation were recorded from hand muscles. In experiment 1, the OK sign appeared in the 9th position of the sequence. Almost all participants could replicate the OK sign only at the 5th block of the experiment. MEP amplitude was greater than that in the control, and decreased with the stages. This suggested that during observational learning of sequential hand postures MEP changed with the progress of the learning. To evaluate this idea, we performed two additional experiments. In experiment 2, the OK sign appeared in the 2nd position. Almost all participants replicated the OK sign even in the 1st block. The MEP amplitude did not change across stages. In experiment 3, the OK sign appeared in the 9th position, but the order of other signs was randomized in every stage. Many participants were not able to replicate the OK sign even during the 5th block of the experiment. The MEP amplitude did not change across stages. These results suggest that: (1) During observational learning modulation of corticospinal excitability is associated with the learning process. (2) Corticospinal excitability decreases as learning progresses.
PLoS ONE 01/2012; 7(5):e37061. · 4.09 Impact Factor
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ABSTRACT: Identifying the major determinant of leg stiffness during hopping would be helpful in the development of more effective training methods. Despite the fact that overall leg stiffness depends on a combination of the joint stiffness, it is unclear how the major determinants of leg stiffness are influenced by hopping frequency. The purpose of this study was to identify the major determinant of leg stiffness over a wide range of hopping frequencies. Fourteen well-trained male athletes performed in a place hopping on two legs, at three frequencies (1.5, 2.2 and 3.0 Hz). We determined leg and joint stiffness of the hip, knee and ankle from kinetic and kinematic data. Multiple linear regression analysis revealed that knee stiffness could explain more of the variance of leg stiffness than could ankle or hip stiffness at 1.5 Hz hopping. Further, only ankle stiffness was significantly correlated with leg stiffness at both 2.2 and 3.0 Hz, and the standardized regression coefficient of ankle stiffness was higher than that of knee and hip stiffness. The results of the present study suggest that the major determinant of leg stiffness during hopping switches from knee stiffness to ankle stiffness when the hopping frequency is increased.
Arbeitsphysiologie 02/2011; 111(9):2195-201. · 2.15 Impact Factor
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ABSTRACT: We investigated whether corticospinal excitability during motor imagery of actions (the power or the pincer grip) with objects was influenced by actually touching objects (tactile input) and by the congruency of posture with the imagined action (proprioceptive input). Corticospinal excitability was assessed by monitoring motor evoked potentials (MEPs) in the first dorsal interosseous following transcranial magnetic stimulation over the motor cortex. MEPs were recorded during imagery of the power grip of a larger-sized ball (7 cm) or the pincer grip of a smaller-sized ball (3 cm)--with or without passively holding the larger-sized ball with the holding posture or the smaller-sized ball with the pinching posture. During imagery of the power grip, MEPs amplitude was increased only while the actual posture was the same as the imagined action (the holding posture). On the other hand, during imagery of the pincer grip while touching the ball, MEPs amplitude was enhanced in both postures. To examine the pure effect of touching (tactile input), we recorded MEPs during imagery of the power and pincer grip while touching various areas of an open palm with a flat foam pad. The MEPs amplitude was not affected by the palmer touching. These findings suggest that corticospinal excitability during imagery with an object is modulated by actually touching an object through the combination of tactile and proprioceptive inputs.
PLoS ONE 01/2011; 6(10):e26006. · 4.09 Impact Factor
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ABSTRACT: In humans, an inhibitory via Ia afferent pathway from the medial gastrocnemius (MG) to the soleus (SOL) motoneuron pool has been suggested. Herein, we examined the relation between MG fascicle length changes and the SOL H-reflex modulation during passive knee movement. Twelve subjects performed static and passive (5 degrees s(-1)) knee movement tasks with the ankle immobilized using an isokinetic dynamometer in sitting posture. The maximal H- and M-waves were measured at four target angles (20 degrees, 40 degrees, 60 degrees, and 80 degrees flexion from full knee extension). The MG fascicles length and velocity were measured using a B-mode ultrasonic apparatus. Results demonstrated that the SOL Hmax/Mmax; i.e., ratio of the maximal H- to M-waves, was attenuated with increasing MG fascicle length in static tasks. The SOL Hmax/Mmax at 20 degrees was significantly attenuated compared with 60 degrees and 80 degrees with increasing MG fascicle length and lengthening velocity in passive knee extension. However, no significant differences in the SOL Hmax/Mmax were found across the target angles in the passive knee flexion task. In conclusion, as muscle spindles increase their discharge with lengthening fascicle velocity, but keep silent when fascicles shorten, our data suggest that lengthening the MG facilitates an inhibitory Ia pathway from MG to SOL, and modulates SOL motoneuron activity during movements.
Journal of electromyography and kinesiology: official journal of the International Society of Electrophysiological Kinesiology 10/2009; 20(3):513-22. · 2.00 Impact Factor
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ABSTRACT: The purpose of the present study was to determine how humans adjust leg stiffness over a range of hopping frequencies. Ten male subjects performed in place hopping on two legs, at three frequencies (1.5, 2.2, and 3.0Hz). Leg stiffness, joint stiffness and touchdown joint angles were calculated from kinetic and/or kinematics data. Electromyographic activity (EMG) was recorded from six leg muscles. Leg stiffness increased with an increase in hopping frequency. Hip and knee stiffnesses were significantly greater at 3.0Hz than at 1.5Hz. There was no significant difference in ankle stiffness among the three hopping frequencies. Although there were significant differences in EMG activity among the three hopping frequencies, the largest was the 1.5Hz, followed by the 2.2Hz and then 3.0Hz. The subjects landed with a straighter leg (both hip and knee were extended more) with increased hopping frequency. These results suggest that over the range of hopping frequencies we evaluated, humans adjust leg stiffness by altering hip and knee stiffness. This is accomplished by extending the touchdown joint angles rather than by altering neural activity.
Journal of biomechanics 10/2009; 43(3):506-11. · 2.66 Impact Factor
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ABSTRACT: Excitability of the corticospinal pathway increased during observation of an action. The present study investigated whether corticospinal excitability during an action observation is modulated by physical movement executed by the observers themselves. Participants alternately repeated the observation of a pinching action with the thumb and index finger and execution (30 times) of the same action. Motor-evoked potentials (MEPs) induced by transcranial magnetic stimulation were recorded from the first dorsal interosseous muscle during observation of the action. MEP amplitude gradually increased with the number of executions of the same action. However, MEP amplitude did not change when the participants only repeated observation of the pinching action or when the participants alternately repeated observation of the pinching action and execution of the isometric abduction of the index finger. These findings suggest that enhancement of cotricospinal excitability is dependent on the execution of a particular action that is very similar to the observed action.
Experimental Brain Research 09/2009; 199(1):17-25. · 2.39 Impact Factor
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ABSTRACT: We investigated whether corticospinal excitability during the imagery of an action involving an external object was influenced by actually touching the object. Corticospinal excitability was assessed by monitoring motor evoked potentials (MEPs) in the first dorsal interosseous muscle following transcranial magnetic stimulation over the motor cortex during imagery of squeezing a ball-with or without passively holding the ball. The MEPs amplitude during imagery when the ball was held was larger than that when the ball was not held. The MEPs amplitude was not modulated just by holding the ball. In the same experimental condition, the somatosensory evoked potentials (SEPs) in response to the stimulation of median nerve were not modulated by motor imagery or by holding the ball. These results suggest that the corticospinal excitability during imagery of squeezing a ball is enhanced with the real touch of the ball, and the enhancement would be caused by some changes along the corticospinal pathway itself and not by the change in responsiveness along the afferent pathway to the primary somatosensory cortex.
Experimental Brain Research 07/2009; 196(4):529-35. · 2.39 Impact Factor
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ABSTRACT: The present study investigated whether combining observation and imagery of an action increased corticospinal excitability over the effects of either manipulation performed alone. Corticospinal excitability was assessed by motor-evoked potentials in the biceps brachii muscle following transcranial magnetic stimulation over the motor cortex during observation, imagery or both. The action utilized was repetitive elbow flexion/extension. Simultaneous observation and imagery of the elbow action facilitated corticospinal excitability as compared to that recorded during observation or imagery alone. However, facilitation due to the combination of observation and imagery was not obtained when the participants imagined the action pattern while they observed the same action presented out of phase. These findings suggest that a combination of observation and imagery can enhance corticospinal excitability. This enhancement depends on phase consistency between the observed and imagined actions.
Neuroscience Research 06/2009; 65(1):23-7. · 2.25 Impact Factor
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ABSTRACT: Understanding stiffness of the lower extremities during human movement may provide important information for developing more effective training methods during sports activities. It has been reported that leg stiffness during submaximal hopping depends primarily on ankle stiffness, but the way stiffness is regulated in maximal hopping is unknown. The goal of this study was to examine the hypothesis that knee stiffness is a major determinant of leg stiffness during the maximal hopping. Ten well-trained male athletes performed two-legged hopping in place with a maximal effort. We determined leg and joint stiffness of the hip, knee, and ankle from kinetic and kinematic data. Knee stiffness was significantly higher than ankle and hip stiffness. Further, the regression model revealed that only knee stiffness was significantly correlated with leg stiffness. The results of the present study suggest that the knee stiffness, rather than those of the ankle or hip, is the major determinant of leg stiffness during maximal hopping.
Journal of biomechanics 06/2009; 42(11):1768-71. · 2.66 Impact Factor
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ABSTRACT: The purpose of the present study was to utilise a spring-mass model to (1) continuously measure vertical stiffness (K(vert)) and leg stiffness (K(leg)) over an entire 400 m sprint, and (2) investigate the relationship between leg spring stiffness (K(vert) and K(vert)) and the performance characteristics of mean forward running velocity (V(forwad)), mean stride frequency (f(stride)), and mean stride length (L(stride)). Eight well-trained male athletes performed a 400 m sprint with maximal effort on an outdoor field track. K(vert) was calculated from the subjects' body mass, ground contact time and flight time at each step. V(forwad), f(stride) and L(stride) were determined from video images. K(vert) and V(forwad) peaked at the 50-100 m interval, and consistently decreased from the middle to the later part of the sprint. K(leg) peaked at first 50 m interval, and remained constant from next 50 m interval to finish. As compared with peak values, K(vert) and V(forward) in the last 50 m decreased by about 40% and 25%, respectively. A significant positive linear relationship existed between the K(vert) and V(forward). While K(vert) was significantly correlated with f(stride), it had no correlation with L(stride). Further, no significant positive linear relationship was found between K(leg) and V(forward), f(stride), or L(stride). This result indicates that in order to keep V(forward) at later stage of a 400 m sprint, maintaining the higher f(stride) through retaining a higher K(vert) would be necessary.
Journal of science and medicine in sport / Sports Medicine Australia. 04/2009; 13(2):256-61.
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ABSTRACT: An understanding of lower extremity stiffness is important for evaluation of sports performance and injury prevention. The aim of this study was to investigate whether stiffness regulation during hopping differed between endurance-trained athletes and untrained subjects. Eight endurance-trained athletes and eight untrained subjects performed two-legged hopping at 2.2 Hz. We determined leg and joint stiffness of hip, knee and ankle from kinetic and kinematics data. The endurance-trained athletes demonstrated significantly higher leg stiffness than untrained subjects. Further, the differences in leg stiffness were attributable to differences in ankle and knee joint stiffness. This study demonstrates a possibility that endurance training, like power training, increases leg and joint stiffness.
Journal of science and medicine in sport / Sports Medicine Australia. 11/2008; 13(1):106-11.
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ABSTRACT: Understanding the leg and joint stiffness during human movement would provide important information that could be utilized for evaluating sports performance and for injury prevention. In the present study, we examined the determinants of the difference in the leg stiffness between the endurance-trained and power-trained athletes. Seven distance runners and seven power-trained athletes performed in-place hopping, matching metronome beats at 3.0 and 1.5Hz. Leg and joint stiffness were calculated from kinetic and kinematics data. Electromyographic activity (EMG) was recorded from six leg muscles. At both hopping frequencies, the power-trained athletes demonstrated significantly higher leg stiffness than the distance runners. Hip, knee, and ankle joints were analyzed for stiffness and touchdown angles. Ankle stiffness was significantly greater in the power-trained athletes than the distance runners at 3.0Hz as was knee stiffness at 1.5Hz. There was no significant difference in touchdown angle between the DR and PT groups at either hopping frequencies. When significant difference in EMG activity existed between two groups, it was always greater in the distance runners than the power-trained athletes. These results suggest that (1) the difference in leg stiffness between endurance-trained and power-trained athletes is best attributed to increased joint stiffness, and (2) the difference in joint stiffness between the two groups may be attributed to a lack of similarity in the intrinsic stiffness of the muscle-tendon complex rather than in altered neural activity.
Journal of Biomechanics 02/2008; 41(3):506-14. · 2.43 Impact Factor
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ABSTRACT: The effects of muscle cooling on the stiffness of the human gastrocnemius muscle (GAS) were examined in vivo.
The knee joint was passively extended from 90 to 0 degrees (0 degrees = full knee extended position) with a constant ankle angle of 10 degrees dorsiflexed position (0 degrees = the sole of the foot is approximately perpendicular to the anterior margin of the shaft of the tibia) in a control condition (room temperature of 18-23 degrees C) and a cooling condition (muscle temperature decreased by 5.8 +/- 1.7 degrees C after cooling using a cold water bath at a temperature of 5-8 degrees C for 60 min). The change in passive Achilles tendon force, muscle fascicle length of GAS and muscle temperature were measured (n = 6) during the motion.
GAS stiffness was significantly greater in the cooling condition (20 +/- 8 N/mm) than the control condition (18 +/- 8 N/mm). There was no cooling effect on the muscle slack length, beyond which passive muscle force arises. The maximum passive Achilles tendon force significantly increased by 19 +/- 20% after cooling. These results suggested that cooling increased the passive muscle force due to the increase in the muscle stiffness rather than the shift of the muscle slack length.
Cells Tissues Organs 02/2008; 187(2):152-60. · 2.20 Impact Factor
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ABSTRACT: We investigated the behavior of the muscle tendon unit (MTU) of the medial gastrocnemius muscle during cyclic ankle bending exercise at eight different frequencies (ranging from 1.33 to 3.67 Hz). The changes in the length of fascicle in the muscle during the exercises were determined by real-time ultrasound imaging. The coordinates of anatomical references and the ground reaction force were determined from video recording and a force plate, respectively. The length change of the MTU (the distance from the origin to insertion of the muscle) was calculated from changes in the knee and ankle joint angles. It was found that the amplitude ratio and phase difference between the fascicle and MTU lengths were both dependent on the movement frequency. At lower frequencies, the fascicle lengths varied almost in phase with the MTU length, whereas they varied out of phase at the higher frequencies. At intermediate frequency, the amplitude of the fascicle became very small compared with that of the MTU, which is considered resonance. We constructed a mechanical model of the MTU based on a notion of forced oscillation in a mass-spring system. The obtained data were well explained by the model. It was concluded that the behavior of the MTU highly depends on the movement frequency due to the viscoelasticity of the MTU.
Journal of Applied Physiology 08/2006; 101(1):111-8. · 3.75 Impact Factor
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ABSTRACT: The purpose of this study was to investigate whether the mechanical properties of the Achilles tendon were correlated to muscle strength in the triceps surae in humans. Twenty-four men and twelve women exerted maximal voluntary isometric plantar flexion (MVIP) torque. The elongation (DeltaX) and strain of the Achilles tendon (epsilon), the proximal part of which is the composite of the gastrocnemius tendon and the soleus aponeurosis, at MVIP were determined from the displacement of the distal myotendinous junction of the medial gastrocnemius using ultrasonography. The Achilles tendon force at MVIP (F) was calculated from the MVIP torque and the Achilles tendon moment arm. There were no significant differences in either the F-DeltaX or F-epsilon relationships between men and women. DeltaX and epsilon were 9.8 +/- 2.6 mm and 5.3 +/- 1.6%, respectively, and were positively correlated to F (r = 0.39, P < 0.05; r = 0.39, P < 0.05), which meant that subjects with greater muscle strength could store more elastic energy in the tendon. The regression y-intercepts for the F-DeltaX (P < 0.01) and F-epsilon (P < 0.05) relationship were significantly positive. These results might indicate that the Achilles tendon was stiffer in subjects with greater muscle strength, which may play a role in reducing the probability of tendon strain injuries. It was suggested that the Achilles tendon of subjects with greater muscle strength did not impair the potential for storing elastic energy in tendons and may be able to deliver the greater force supplied from a stronger muscle more efficiently. Furthermore, the difference in the Achilles tendon mechanical properties between men and women seemed to be correlated to the difference in muscle strength rather than gender.
Journal of Applied Physiology 08/2005; 99(2):665-9. · 3.75 Impact Factor
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ABSTRACT: The purpose of the present study was to determine the in vivo passive mechanical properties, including the length below the slack length, of the gastrocnemius muscle (GAS) belly in humans. Transverse ultrasound images of the medial head of the GAS were taken in 11 subjects during passive knee extension from 80 degrees to 5 degrees with a constant ankle joint angle of 10 degrees (0 degrees is the neutral ankle position: positive values for dorsiflexion). The change in passive ankle joint moment (Mp), which is produced only by the GAS length change, was also measured during passive knee extension. The onset of Mp during passive knee extension was found to be 43+/-8 degrees (mean+/-SD) when the baseline of the Mp was set at the average Mp in the range of 55-60 degrees where the Mp was almost constant (SD<0.03 Nm). At this onset, the muscle fascicle length of the GAS (Lf) was 46+/-7 mm (slack length; Lfs). Lf at 80 degrees was 6+/-4 mm (13+/-6%) less than the Lfs, and Lf at 5 degrees was 12+/-5 mm (27+/-11%) greater than the Lfs. The passive force-resisting compression of the GAS did not produce a dorsiflexion moment in the joint angle range adopted. The passive ankle joint moment increased linearly with Lf (coefficient of determination (R2)=0.85-0.96), and the slopes of the relationships between Lf and Mp, and between the relative Lf to Lfs and Mp were 0.093+/-0.038 Nm/mm and 0.043+/-0.021 Nm/%Lfs. The findings of the present study can be implemented in musculoskeletal modeling, which would provide a more accurate evaluation of the passive mechanical properties of muscle during movement.
Journal of Biomechanics 06/2005; 38(6):1213-9. · 2.43 Impact Factor
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ABSTRACT: This study estimated the passive ankle joint moment during standing and walking initiation and its contribution to total ankle joint moment during that time. The decrement of passive joint moment due to muscle fascicle shortening upon contraction was taken into account. Muscle fascicle length in the medial gastrocnemius, which was assumed to represent muscle fascicle length in plantarflexors, was measured using ultrasonography during standing, walking initiation, and cyclical slow passive ankle joint motion. Total ankle joint moment during standing and walking initiation was calculated from ground reaction forces and joint kinematics. Passive ankle joint moment during the cyclical ankle joint motion was measured via a dynamometer. Passive ankle joint moment during standing and at the time (Tp) when the MG muscle-tendon complex length was longest in the stance phase during walking initiation were 2.3 and 5.4 Nm, respectively. The muscle fascicle shortened by 2.9 mm during standing compared with the length at rest, which decreased the contribution of passive joint moment from 19.9% to 17.4%. The muscle fascicle shortened by 4.3 mm at Tp compared with the length at rest, which decreased the contribution of passive joint moment from 8.0% to 5.8%. These findings suggest that (a) passive ankle joint moment plays an important role during standing and walking initiation even in view of the decrement of passive joint moment due to muscle fascicle shortening upon muscle contraction, and (b) muscle fascicle shortening upon muscle contraction must be taken into account when estimating passive joint moment during movements.
Journal of applied biomechanics 03/2005; 21(1):72-84. · 0.76 Impact Factor
