Posture dependent changes in perceptual threshold during light touch foot sole stimulation

OBJECTIVE: Light touch sensitivity of the foot sole is typically measured when individuals are seated or lying down; yet, a critical function of the foot sole is to support cutaneous feedback during standing and walking activities. The objective of this study was to evaluate how individuals perceive light touch stimulation across the foot sole while in different postures including standing. METHODS: We measured light touch perceptual threshold (LTPT) in standing, seated, and supine postures in 19 volunteers (10 females, 9 males), using Semmes-Weinstein Monofilaments. Perceptual thresholds were calculated at three foot sole locations (1st metatarsal, lateral arch, and heel) in each posture. RESULTS: Perceptual thresholds were significantly higher in the standing condition compared to the seated and supine conditions across all foot locations; perceptual thresholds were significantly higher while seated compared to supine only at the heel and not at the lateral arch or 1st metatarsal. Our results demonstrate that postural changes significantly influence sensitivity across the foot sole. CONCLUSION: Performing perceptual threshold assessments of the foot sole while standing may offer more relevant insights into the capacity of foot sole cutaneous afferents to convey light touch information in conditions where such feedback plays a vital role in maintaining balance.