Abstract
Understanding the processing of tactile information is crucial for the development of biofeedback interventions that target cutaneous mechanoreceptors. Mechanics of the skin have been shown to influence cutaneous tactile sensitivity. It has been established that foot skin mechanics are altered due to foot posture, but whether these changes affect cutaneous sensitivity are unknown. The purpose of this study was to investigate the potential effect of posture-mediated skin deformation about the ankle joint on perceptual measures of foot skin sensitivity. Participants (N = 20) underwent perceptual skin sensitivity testing on either the foot sole (N = 10) or dorsum (N = 10) with the foot positioned in maximal dorsiflexion/toe extension, maximal plantarflexion/toe flexion, and a neutral foot posture. Perceptual tests included touch sensitivity, stretch sensitivity, and spatial acuity. Regional differences in touch sensitivity were found across the foot sole (p < 0.001) and dorsum (p < 0.001). Touch sensitivity also significantly increased in postures where the skin was compressed (p = 0.001). Regional differences in spatial acuity were found on the foot sole (p = 0.002) but not dorsum (p = 0.666). Spatial acuity was not significantly altered by posture across the foot sole and dorsum, other than an increase in sensitivity at the medial arch in the dorsiflexion posture (p = 0.006). Posture*site interactions were found for stretch sensitivity on the foot sole and dorsum in both the transverse and longitudinal directions (p < 0.005). Stretch sensitivity increased in postures where the skin was pre-stretched on both the foot sole and dorsum. Changes in sensitivity across locations and postures were believed to occur due to concurrent changes in skin mechanics, such as skin hardness and thickness, which follows our previous findings. Future cutaneous biofeedback interventions should be applied with an awareness of these changes in skin sensitivity, to maximize their effectiveness for foot sole and dorsum input.
Highlights
Therapeutic and ergogenic interventions have recently focused on the use of biofeedback to improve function and performance
In addition to corroborating previous accounts of location dependent sensitivity, we found that foot posture influences tactile perceptual sensitivity measures
Based on our current data set we conclude that tactile perceptual sensitivity on the foot differs according to ankle joint posture
Summary
Therapeutic and ergogenic interventions have recently focused on the use of biofeedback to improve function and performance. Understanding of skin function is essential for development of biofeedback interventions such as athletic taping, haptics, bracing, prosthetics, and clothing design. Receptors are classified by receptive field size, with small defined boundaries categorized as Type 1 and large undefined boundaries as Type 2. They are further classified by afferent firing, as fast adapting (FA) or slow adapting (SA) based on response to indentation. Each group of mechanoreceptors responds differently to stimuli such as vibration, stretch, stroking, and sustained indentation based on their properties, which are due to their morphology and location of the receptor endings in the skin tissue matrix (Johnson, 2001; Macefield, 2005)
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