Inter limb interactions and constraints in the expression of maximum force Review, implications and underlying mechanisms

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Maximal voluntary isometric elbow flexion force during unilateral versus bilateral contractions in individuals with chronic stroke

The purpose of this study was to determine whether the phenomenon of bilateral deficit in muscular force production observed in healthy subjects and mildly impaired stroke patients also exists in patients with more chronic and greater levels of stroke impairment. Ten patients with chronic hemiparesis resulting from stroke performed unilateral and bilateral maximal voluntary isometric contractions of the elbow flexors. When the total force produced by both arms was compared, 12% less force was produced in the bilateral compared with unilateral condition (p=0.01). However, studying the effect of task conditions on each arm separately revealed a significant decline in nonparetic (p=0.01) but not paretic elbow flexor force in the bilateral compared with unilateral condition. Results suggest that a significant bilateral force deficit exists in the nonparetic but not the paretic arm in individuals with chronic stroke. Bilateral task conditions do not seem to benefit or impair paretic arm maximal isometric force production in individuals with moderate-severity chronic strok

A 35-day bed rest does not alter the bilateral deficit of the lower limbs during explosive efforts

Purpose: Bilateral deficit (BLD) occurs when the force (or power) generated by both limbs together is smaller than the sum of the forces (or powers) developed separately by the two limbs. The amount of BLD can be altered by neural adaptations brought about by the repetitive execution of specific motor tasks (training). Prolonged disuse also leads to relevant neural adaptations; however, its effects on BLD are still unknown. Thus, the aim of this study was to investigate the effects of a 35-day bed rest on the BLD of the lower limbs. Methods: Ten young healthy volunteers performed maximal explosive efforts on a sledge ergometer with both lower limbs or with the right and the left limb separately. Electromyography (EMG) of vastus lateralis, rectus femoris, biceps femoris and gastrocnemius medialis was also measured. Results: Before bed rest, maximal explosive power and peak force were significantly higher in monolateral than bilateral efforts (+18.7 and +31.0 %, respectively). Conversely, peak velocity was 11.9 % greater in bilateral than monolateral efforts. BLD attained a value of 18.1 % and was accompanied by lower EMG amplitude of knee extensors ( 1217.0 %) and gastrocnemius medialis ( 1211.7 %) during bilateral efforts. Bed rest led to a ~28.0 % loss in both bilateral and monolateral maximal explosive power. Neither BLD magnitude nor the difference in EMG amplitudes as well as in peak force and velocity between bilateral and monolateral efforts were affected by bed rest. Conclusions: These results suggest that the neuromuscular factors underlying BLD are unaltered after prolonged disuse. \ua9 2015, Springer-Verlag Berlin Heidelberg