Muscle Fascicle Behavior Research Articles

The influence of strain and activation on the locomotor function of rat ankle extensor muscles

The ankle extensor muscles of the rat have different mechanical and physiological properties, providing a means of studying how changes in locomotor demands influence muscle fascicle behaviour, force and mechanical power output in different populations of muscle fibre types. Muscle fascicle strain, strain rate and activation patterns in the soleus, plantaris and medial gastrocnemius muscles of the rat were quantified from sonomicrometric and myoelectric data, collected during treadmill locomotion under nine velocity/incline conditions. Significant differences in peak-to-peak muscle fascicle strains and strain rates were identified between the three muscles (P<0.001, all cases), with much smaller strains (<0.1) and strain rates (<0.5 s(-1)) occurring in soleus and plantaris compared with medial gastrocnemius (>0.2 and >1.0 s(-1), respectively). The proportion of stride duration that each muscle was active (duty cycle) differed between locomotor conditions as did the timing of the activation and deactivation phases. A simple Hill-based muscle model was used to determine the influence of muscle activation relative to maximum fascicle strain and duty cycle on total force production and mechanical power output, from a slow and a fast muscle fibre, simulated through two peak-to-peak strain cycles (0.1 and 0.3). The predictions of the model did not complement conclusions that may be drawn from the observation of myoelectric timing and fascicle strain trajectories in each of the muscles. The model predicted that changes in mechanical power output were more sensitive to changes in activation parameters than to changes in strain trajectories, with subtle changes in activation phase and duty cycle significantly affecting predicted mechanical power output.

Afferent Contribution to Locomotor Muscle Activity During Unconstrained Overground Human Walking: An Analysis of Triceps Surae Muscle Fascicles

Plantar flexor series elasticity can be used to dissociate muscle-fascicle and muscle-tendon behavior and thus afferent feedback during human walking. We used electromyography (EMG) and high-speed ultrasonography concomitantly to monitor muscle activity and muscle fascicle behavior in 19 healthy volunteers as they walked across a platform. On random trials, the platform was dropped (8 cm, 0.9 g acceleration) or held at a small inclination (up to +/-3 degrees in the parasagittal plane) with respect to level ground. Dropping the platform in the mid and late phases of stance produced a depression in the soleus muscle activity with an onset latency of about 50 ms. The reduction in ground reaction force also unloaded the plantar flexor muscles. The soleus muscle fascicles shortened with a minimum delay of 14 ms. Small variations in platform inclination produced significant changes in triceps surae muscle activity; EMG increased when stepping on an inclined surface and decreased when stepping on a declined surface. This sensory modulation of the locomotor output was concomitant with changes in triceps surae muscle fascicle and gastrocnemius tendon length. Assuming that afferent activity correlates to these mechanical changes, our results indicate that within-step sensory feedback from the plantar flexor muscles automatically adjusts muscle activity to compensate for small ground irregularities. The delayed onset of muscle fascicle movement after dropping the platform indicates that at least the initial part of the soleus depression is more likely mediated by a decrease in force feedback than length-sensitive feedback, indicating that force feedback contributes to the locomotor activity in human walking.

Influence of step-height and body mass on gastrocnemius muscle fascicle behavior during stair ascent

To better understand the role of the ankle plantar flexor muscles in stair negotiation, we examined the effects of manipulation of kinematic and kinetic constraints on the behavior of the gastrocnemius medialis (GM) muscle during stair ascent. Ten subjects ascended a four-step staircase at four different step-heights (changing the kinematic constraints): standard (17 cm), 50% decreased, 50% increased and 75% increased. At the standard height, subjects also ascended the stairs wearing a weighted jacket, adding 20% of their body mass (changing the kinetic constraints). During stair ascent, kinematics and kinetics of the lower legs were determined using motion capture and ground reaction force measurements. The GM muscle fascicle length was measured during the task with ultrasonography. The amount of GM muscle fascicle shortening increased with step-height, coinciding with an increase in ankle joint moment. The increase in body mass resulted in an increased ankle joint moment, but the amount of GM muscle fascicle shortening during the lift-off phase did not increase, instead, the fascicles were shorter over the whole stride cycle. Increasing demands of stair ascent, by increasing step-height or body mass, requires higher joint moments. The increased ankle joint moment with increasing demands is, at least in part, produced by the increase in GM muscle fascicle shortening.

Influence of gait velocity on gastrocnemius muscle fascicle behaviour during stair negotiation

The gastrocnemius medialis (GM) muscle plays an important role in stair negotiation. The aim of the study was to investigate the influence of cadence on GM muscle fascicle behaviour during stair ascent and descent. Ten male subjects (young adults) walked up and down a four-step staircase (with forceplates embedded in the steps) at three velocities (63, 88 and 116 steps/min). GM muscle fascicle length was measured using ultrasonography. In addition, kinematic and kinetic data of the lower legs, and GM electromyography (EMG) were measured. For both ascent and descent, the amount of fascicular shortening, shortening velocity, knee moment, ground reaction force and EMG activity increased monotonically with gait velocity. The ankle moment increased up to 88 steps/min where it reached a plateau. The lack of increase in ankle moment coinciding with further shortening of the fascicles can be explained by an increased shortening of the GM musculotendon complex (MTC), as calculated from the knee and ankle angle changes, between 88 and 116 steps/min only. For descent, the relative instant of maximum shortening, which occurred during touch down, was delayed at higher gait velocities, even to the extent that this event shifted from the double support to the single support phase.

EFFECT OF GAIT VELOCITY ON HUMAN GASTROCNEMIUS FASCICLE BEHAVIOR DURING STAIR DESCENT

present study, fascicular shortening of the GM muscle is investigated at different gait velocities. Ankle joint moment would be expected to increase with increasing gait velocity, hence it is hypothesized that GM muscle fascicles will shorten more at a higher gait velocity. METHODS Ten young adult male subjects performed stair ascent at 3 different velocities (63, 88 and 116 step/min, controlled using a metronome). Kinematics and kinetics of the lower legs were measured using a 9-camera VICON system and a 4-step staircase with embedded forceplates. Ultrasound was used to determine muscle fascicle behavior; a lineararray probe (60mm probe width) was placed at the midsagittal plane of the left GM muscle, and tightly secured with a custom build fixation device. GM muscle fascicle length and pennation angle were measured for every frame in the stride from the first to the third step. To account for inter-individual fascicle length differences, values were calculated relative to a reference length, which was measured when standing upright. Influence of velocity was investigated for the stride period in which the muscle was active (assessed from Electrical activity (EMG) measurements): during the push-off phase, from peak EMG until lift-off. General Estimated Equations (GEE) were used for statistical analysis. RESULTS AND DISCUSSION During push-off, the ankle plantar-flexed caused by GM muscle fascicle shortening. At higher velocities, GM EMG was higher and peaked relatively earlier, while lift-off was also relatively early at higher velocities. Fascicle shortening increased in magnitude (1.3, 2.3 and 4.2 cm [mean] for resp. 63, 88 and 116 st/min, p<0.05) and shortening velocity (p<0.05) with increasing gait velocity. The increased shortening at higher velocities caused a higher ankle moment (p<0.05), however, the ankle moment did not increase any further beyond 88 st/min (p=0.628). Therefore, the increase in GM muscle fascicle shortening beyond 88 st/min can be explained by the shorter MTC length at 116 compared to that at 88 st/min (p<0.05), there was no difference in MTC length between 63 and 88 st/min (p=0.241). The results of the present study indicate that increases in fasci

Gastrocnemius muscle fascicle behavior during stair negotiation in humans

The aim of the present study was to establish the behavior of human medial gastrocnemius (GM) muscle fascicles during stair negotiation. Ten healthy male subjects performed normal stair ascent and descent at their own comfortable speed on a standard-dimension four-step staircase with embedded force platforms in each step. Kinematic, kinetic, and electromyographic data of the lower limbs were collected. Real-time ultrasound scanning was used to determine GM muscle fascicle length changes. Musculotendon complex (MTC) length changes were estimated from ankle and knee joint kinematics. The GM muscle was mainly active during the push-off phase in stair ascent, and the muscle fascicles contracted nearly isometrically. The GM muscle was mainly active during the touch-down phase of stair descent where the MTC was lengthened; however, the GM muscle fascicles shortened by approximately 7 mm. These findings show that the behavior and function of GM muscle fascicles in stair negotiation is different from that expected on the basis of length changes of the MTC as derived from joint kinematics.

Human muscle fascicle behaviour during stair negotiation

Human muscle fascicle behaviour during stair negotiation