| Despite the vast research conducted on postural control, little is known about the influence of somatosensation on postural sway. This study determined the influence of enhanced cutaneous input from the finger and plantar foot on postural sway control. Neuromuscular vibrators applied to the Achilles tendons were used to disrupt normal posture, while various conditions of either light fingertip touch or enhanced plantar foot sensation were used to stabilize the posture. Light fingertip contact (<1N) occurred with a horizontal or vertically oriented target while the shoulder was in a flexed or abducted position. The plantar foot sensation was enhanced using differing lengths of tubing placed under the sole of the foot in various locations. A force platform was used to measure ground reaction forces to calculate center of pressure (COP) variables: peak posterior excursions (CPn), root mean square (RMSn) and velocity of COP (CPvel) in the sagittal plane, normalized to a baseline, no-vibration interval. It was found that hindfoot tubing significantly reduced RMS and CPvel during vibration, while forefoot tubing was less effective. Light fingertip touch significantly diminished the deleterious effects of vibration on CPn and CPvel. Horizontal target and flexed shoulder orientations yielded the greatest effects. CPvel was significantly reduced using a horizontal target, however shoulder orientation did not have an impact on CPvel. Cutaneous sensation enhancement does not fully mitigate the effects of vibration, but does provide valuable information for the control of vibration-perturbed posture. Perhaps the nervous system functions in a hierarchical manner, in that it weighs and utilizes the most appropriate sensory information to regulate bipedal postural control. These enhancement techniques could lead to the development of therapeutic postural compensatory mechanisms. |
