Macro- and microcirculatory factors affecting foot temperature change during walking

Change in skin temperature is a complex process affected by several factors. During walking, increased microcirculatory activity, such as muscle metabolism, could increase foot temperature. The ensuing macrocirculatory responses, such as increased leg blood flow (LBF), might also increase foot temperature. However, it is unclear whether there is a relationship between these physiological measures and foot temperature during walking. Here, we examined the relationships among macrocicrulation (e.g., LBF), microcirculation [e.g., tissue saturation index (TSI)] and the change in foot temperature during walking on different slopes. Healthy young adults (n = 21) walked on a 0°, +5° and -5° slope in random order for 10 min at 1.2 m/s. Before and after each walking bout, LBF, TSI and foot temperature were measured on the dominant leg of the participant. TSI was measured at the vastus lateralis (VL), medial gastrocnemius (MG) and dorsal foot. Uphill walking caused a greater increase in LBF (P < 0.001) and greater reductions in TSI for VL (P < 0.001) and MG (P < 0.027) in comparison to level or downhill walking, probably reflecting the increased muscle oxygen demand. Only changes in dorsal foot TSI were positively associated with foot temperature change (β = 0.064, P = 0.026), whereas LBF and TSI for VL and MG showed no significant associations (P > 0.192). These results suggest that the macrocirculation increases to accommodate the metabolic demands of leg muscles, without affecting foot skin temperature change. We speculate that foot temperature change might be affected largely by mechanisms not tested in our study, such as cutaneous blood flow, sweating and convective heat loss, which should be investigated in the future.