Article

Humans have a remarkable capacity to perform complex movements requiring agility,
timing, and strength. Disuse, aging, and disease can lead to a loss of muscle
strength, which frequently limits the performance of motor tasks. It is unknown,
however, how much weakness can be tolerated before normal daily activities become
impaired. This study examines the extent to which lower limb muscles can be
weakened before normal walking is affected. We developed muscle-driven
simulations of normal walking and then progressively weakened all major muscle
groups, one at the time and simultaneously, to evaluate how much weakness could
be tolerated before execution of normal gait became impossible. We further
examined the compensations that arose as a result of weakening muscles. Our
simulations revealed that normal walking is remarkably robust to weakness of some
muscles but sensitive to weakness of others. Gait appears most robust to weakness
of hip and knee extensors, which can tolerate weakness well and without a
substantial increase in muscle stress. In contrast, gait is most sensitive to
weakness of plantarflexors, hip abductors, and hip flexors. Weakness of
individual muscles results in increased activation of the weak muscle, and in
compensatory activation of other muscles. These compensations are generally
inefficient, and generate unbalanced joint moments that require compensatory
activation in yet other muscles. As a result, total muscle activation increases
with weakness as does the cost of walking. By clarifying which muscles are
critical to maintaining normal gait, our results provide important insights for
developing therapies to prevent or improve gait pathology.
CI - Copyright (c) 2012 Elsevier B.V. All rights reserved.

Langue : ANGLAIS