Heating the skin on the foot sole enhances cutaneous reflexes in the lower limb

Cutaneous input is important in postural control and balance. Aging and diabetes impair skin sensitivity and motor control. Heat application can improve skin sensation, but its influence on motor control remains unknown. This study investigated the effects of heating the skin of the foot sole on lower limb cutaneous reflexes. Reflexes were evoked in the tibialis anterior muscle of 20 young, healthy adults before and after heating the foot sole to a maximum of 42°C. While holding a 15% maximum root mean square EMG generated during maximum isometric dorsiflexion, a filtered white noise (0-50 Hz) vibration at 10 times the perceptual threshold was applied to the heel to stimulate cutaneous mechanoreceptors. Reflexes were analyzed in both the time (cumulant density) and frequency (coherence, gain) domains. Heat increased foot skin temperature ∼15.4°C (P < 0.001). Cumulant density peak to peak amplitude significantly increased by 44% after heating (P = 0.01) while latencies did not vary (P = 0.46). Coherence and gain were significantly greater in the 30- to 40-Hz range following heating (P = 0.048; P = 0.02). Heating significantly enhances lower limb cutaneous reflexes. This may be due to the increased ability of cutaneous mechanoreceptors to encode in the 30- to 40-Hz range.NEW & NOTEWORTHY Cutaneous input is a known modulator of muscle activity. Targeting skin to intentionally enhance motor output has received little attention. We explored local skin heating to enhance skin sensitivity and found a significant increase in the amplitude, coherence, and gain of cutaneous reflexes in the tibialis anterior. Our current findings provide the first support for the use of heat as a viable and easily integrated modality in rehabilitation technology to improve balance and postural control.