Effects of electrical cutaneous stimulation of the foot sole on voluntary plantarflexion rate of torque development after fatigue in males.

PURPOSE: Fast rate of torque development (RTD) is crucial for all movements, from balance to athletics. Aging and fatigue decrease RTD, increasing fall and injury risk. Thus, finding accessible methods to increase RTD is necessary. Given the neuromechanical coupling that exists between foot-sole skin and lower-limb motor neurons, cutaneous stimulation may impact RTD. This work investigated whether foot-sole cutaneous stimulation could mitigate the fatigue-induced declines in plantarflexion RTD.

METHODS

Adult males (n = 11, age = 28(7)) participated in three data collection sessions. Voluntary isometric plantarflexion RTD was measured during explosive plantarflexion contractions in a dynamometer. RTD was assessed at rest and post-fatigue, under three conditions: cutaneous electrical stimulation at the heel, metatarsal, or no stimulation. Fatigue was induced with a sustained maximal plantarflexion until torque dropped below 30% of maximum voluntary torque. RTD was calculated in cumulative 25ms epochs from contraction onset to 100ms. Post-fatigue, percent of rested RTD was compared between conditions.

RESULTS

Post-fatigue RTD decreased across all conditions (p < 0.001) (mean = 31(12%)). No effect of stimulation was found for the change in RTD post-fatigue. (p = 0.174). However, when removing polarity of response by comparing absolute changes in RTD post-fatigue, a main effect of stimulation was found (p = 0.002) (mean difference from control: 14.6% with heel stimulation, and 17.5% with metatarsal stimulation).

CONCLUSIONS

Although no clear location-dependent increase or decrease emerged, cutaneous stimulation did change fatigued RTD compared to control. Future work should focus on understanding the directional variability of responses across participants to isolate improved RTD as a mechanism to enhance performance and restore mobility.