Reduced plantar sensitivity alters postural responses to lateral perturbations of balance

There is considerable evidence that lower-limb somatosensation contributes to the control of upright balance. In this study, we investigated the specific role of foot sole cutaneous afferents in the generation of balance corrections following lateral accelerations of the support surface. Participants were subjected to balance perturbations before and after targeted anesthesia of the cutaneous soles induced by intradermal injections of local anesthetic. Subject responses were quantified in terms of net joint torques at the ankles, hips and trunk. Contrary to the conclusions drawn in earlier studies, response torque impulses at the ankles and hips were clearly scaled with the perturbation impulse under both control and anesthetized conditions. Reduced plantar sensitivity produced a relative shift in compensatory torque production from the ankles and trunk to the hips. These findings demonstrate that plantar cutaneous afferents play an important role in the shaping of dynamic postural responses. Furthermore, the results suggest that loss of plantar sensation may be an important contributor to the dynamic balance deficits and increased risk of falls associated with peripheral neuropathies.