Proprioceptive control of posture: a review of new concepts

The assumption that proprioceptive inputs from the lower legs are used to trigger balance and gait movements is questioned in this review (an outgrowth of discussions initiated during the Neural Control of Movement Satellite meeting held in Cozumel, Mexico, April 1997). Recent findings presented here suggest that trunk or hip inputs may be more important in triggering human balance corrections and that proprioceptive input from the lower legs mainly helps with the final shaping and intermuscular coordination of postural and gait movements. Three major questions were considered. First, what role, if any, do lower-leg proprioceptive inputs play in the triggering of normal balance corrections? If this role is negligible, which alternative proprioceptive inputs then trigger balance corrections? Second, what is the effect of proprioceptive loss on the triggering of postural and gait movements? Third, how does proprioceptive loss affect the output of central pattern generators in providing the final shaping of postural movements? The authors conclude that postural and gait movements are centrally organized at two levels. The first level involves the generation of the basic directionally-specific response pattern based primarily on hip or trunk proprioceptive input and secondarily on vestibular inputs. This pattern specifies the spatial characteristics of muscle activation, that is which muscles are primarily activated, as well as intermuscular timing, or the sequence in which muscles are activated. The second level is involved in the shaping of centrally set activation patterns on the basis of multi-sensorial afferent input (including proprioceptive input from all body segments and vestibular sensors) in order that movements can adapt to different task conditions.