Are diurnal changes in foot sole sensation dependent on gait activity?

The foot sole is loaded during stance and gait and plantar cutaneous mechanoreceptors sense the local stress distribution. It is not clear whether the perception thresholds of these mechanoreceptors change during the day and how they respond to walking activities. The primary aim of the present study was to investigate diurnal changes of plantar sensitivity. Furthermore, the aim was to find out whether daily changes depend on the individual level of step activity. Twenty-six healthy subjects, 17 women and 9 men, aged 28.6±6.7 years participated in the study. Detection thresholds to light touch were measured in six plantar regions with Semmes-Weinstein monofilaments in the morning, noon and afternoon. Step activity was recorded with a StepWatch™ Activity Monitor and analyzed for three periods (8 a.m.-4 p.m., 8 a.m.-12 p.m., 12 p.m.-4 p.m.). The hallux, the 3rd metatarsal head and the heel showed significantly decreased detection thresholds from 8 a.m. to 4 p.m. (p≤0.05). A fair correlation between the decrease of detection threshold and the total number of steps was found for the 3rd metatarsal head and the heel (p≤0.05). Foot sole sensation appears to improve during the day and seems to be associated with the step activity. This may reflect an improving transfer of afferent information to the central nervous system during the day as well as an adaptation of receptors to gait activity.