Significance of load receptor input during locomotion: a review

A basic aspect of the neuronal control of quadrupedal locomotion of cat and of bipedal stance and gait of humans concerns the antigravity function of leg extensors. in humans proprioceptive reflexes involved in the maintenanc e of body equilibrium depend on the presence of contact forces opposing gra vity. Extensor load receptors are thought to signal changes of the projecti on of body's centre of mass with respect to the feet. According to observat ions in the cat, this afferent input probably arises from Golgi tendon orga ns and represents a newly discovered function of these receptors in the reg ulation of stance and gait. From these experiments it can be concluded that during locomotion there is a closing of Ib inhibitory and an opening of Ib extensor facilitatory paths. In humans evidence for a significant contribu tion of load receptor contribution to the leg muscle activation came from i mmersion experiments. Compensatory leg muscle activation depends on the act ual body weight. Also during gait the strength of leg extensor activation d uring the stance phase is load dependent. In patients with Parkinson's dise ase there is a reduced load sensitivity and decreased leg extensor activati on, which might contribute to the movement disorder. Recent experiments in paraplegic patients show that the beneficial effects of a locomotor trainin g critically depends on the initial degree of body unloading and reloading during the course of the training period. (C) 2000 Elsevier Science B.V. Al l rights reserved.