Do spike insoles enhance postural stability and plantar-surface cutaneous sensitivity in the elderly?

Balance problems are often related to a loss of plantar-sensitivity in elderly people. The purpose of this study was to explore the contribution of plantar cutaneous inputs induced by a spike support surface to the control of stance. Nineteen elderly (mean age 69.0 years, range 62-80) and 19 young adults (mean age 25.9 years, range 21-32) were instructed to stand (standing session) or to walk (walking session) for 5 min with sandals equipped with spike insoles (spike condition). Both sessions also involved a no spike condition in which participants stood or walked for 5 min without these insoles (no spike condition). In all conditions, postural responses were assessed during unperturbed stance and were performed (1) immediately after putting the spike or the no spike insoles, and (2) 5 min after standing or walking with them. Sway parameters, such as centre of foot pressure mean location, surface area, mean speed, root mean square and median frequency on the antero-posterior and medio-lateral axes, were calculated. As postural performances are often related to plantar-surface sensitivity, cutaneous sensitivity threshold was also evaluated with Semmes-Weinstein monofilaments. Although no immediate effect of the spike insoles was found, results indicated that standing or walking for 5 min with sandals equipped with spike insoles led to a significant improvement of quiet standing in the elderly. Balance improvement was also observed in young adults. The results provided evidence that wearing sandals with spike insoles can contribute, at least temporarily, to the improvement of unperturbed stance in elderly people with relatively intact plantar cutaneous sensation. Further research is needed to assess the effects of longer and discontinuous stimulations with spike insoles on postural control.