Effect of facilitation of sensation from planter foot-surface boundaries on postural stabilization in young and older adults

Background. One of the more pervasive effects of aging is loss of cutaneous sensation, which appears to correlate with impaired postural control and i ncreased risk of falling. This study examined the potential for compensatin g for the destabilizing effects of reduced cutaneous sensitivity by placing a raised edge underneath the perimeter of the plantar foot surface, so as to facilitate sensation from the stability boundaries of the base of suppor t Methods. The main experiment involved 14 healthy alder adults (aged 65-73) selected because they were known, from a previous study, to have moderate p lantar cutaneous insensitivity. We also report results of an initial experi ment involving 7 healthy young adults (aged 23-31). In both experiments, we studied effects of the plantar facilitation on control of rapid stepping r eactions evoked by unpredictable postural perturbation, applied via sudden platform movement in for-ward backward, and lateral directions. We also stu died effects on "feet-in-place" responses evoked by continuous pseudorandom platform motion in mediolateral and anteroposterior directions. Subjects w ere blindfolded in all tests. Results. Plantar facilitation reduced the incidence of "extra" limb movemen ts, beyond the initial step, during forward-step reactions in the older adu lts. There also appeared to be an improved ability to control feet-in-place reactions: young subjects were better able to recover balance without step ping when falling backward (given instructions to "try not to step"), and b oth young and older subjects reduced the extent to which the center of foot pressure approached the posterior foot boundary during continuous anteropo sterior platform motion. Conclusions. This study provides evidence that mechanical facilitation of s ensation from the boundaries of the plantar surface of the foot can improve the efficacy of certain types of stabilizing reactions evoked by unpredict able postural perturbation. The results may be directly transferable to the design of special footwear insoles to reduce instability and risk of falli ng in older adults.