European journal of applied physiology
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Eur. J. Appl. Physiol. · Dec 2010
Randomized Controlled TrialChanges in muscle fascicles of tibialis anterior during anisometric contractions are not associated with motor-output variability of the ankle dorsiflexors in young and old adults.
This study examined the associations between the fluctuations of foot acceleration during shortening and lengthening contractions with the electromyographic (EMG) activity of lower leg muscles and ultrasound measures of tibialis anterior fascicle length and pennation angle. Young (24.9 ± 4.17 years) and old (74.8 ± 3.31 years) adults lifted and lowered a submaximal load with the foot at different speeds (3°/s-50°/s). The standard deviation (SD) of foot acceleration normalized to the load lifted was similar for young (12.2 ± 7.22 cm s(-2)/kg) and old adults (14.3 ± 8.03 cm s(-2)/kg; P = 0.093). ⋯ The changes in fascicle length and pennation angle were not associated with the SD of foot acceleration (r(2) ≤ 0.031; P ≥ 0.092). The surface EMG of tibialis anterior was greater for the shortening contractions than for the lengthening contractions (P < 0.001), but triceps surae EMG was similar for the two types of contractions (P = 0.304). The results suggested that the influence of movement speed on variability in performance was similar for shortening and lengthening contractions with the dorsiflexor muscles; furthermore, old adults were able to match the performance of young adults.
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Eur. J. Appl. Physiol. · Dec 2010
Randomized Controlled TrialEffect of lower limb muscle fatigue on anticipatory postural adjustments associated with bilateral-forward reach in the unipedal dominant and non-dominant stance.
Voluntary arm movements are preceded by dynamical and electromyographical (EMG) phenomena in "postural segments" (i.e. body segments not directly involved in the voluntary movement) called "anticipatory postural adjustments" (APA). The present study examined how the central nervous system organizes APA under fatigued state of postural musculature elicited by series of high-level isometric contractions (HIC), i.e. corresponding to 60% of maximal voluntary contraction. Subjects (N = 14) purposely performed series of bilateral-forward reach task (BFR) under unipodal stance (dominant and non-dominant) before ("no fatigue" condition, NF) and after ("fatigue" condition, F) a procedure designed to obtain major fatigue in hamstrings. ⋯ Similar results were obtained whether dominant or non-dominant leg was considered. The changes in biomechanical APA features could not be ascribed to a different focal movement performance (maximal BFR velocity and acceleration) between F and NF. These results suggest that, when fatigue is induced by HIC, the capacity of the central nervous system to adapt APA programming to the fatigued state of the postural muscle system might be altered.