Isolating the independent effect of decreasing mean skin temperature on local thermal sensitivity of human hands and feet during cold stress

Whether reductions in whole-body mean skin temperature (Tsk), with no concurrent changes in core temperature (Tc), alter local thermal sensitivity (TS) of human skin is currently unknown. On 4 separate occasions, 8 males (27±5y) underwent a 30-min whole-body cooling protocol (water-perfused suit: ~5°C), during which a quantitative thermo-sensory test, consisting of reporting (visual analogue scale) perceived magnitude of local warm (38°C) and cold (22°C) thermal stimuli (25-cm2 thermal probe) applied to hand (palm/dorsum) and foot (sole/dorsum), was performed before cooling and every 10min thereafter. The cooling protocol resulted in large progressive reductions in Tsk (10min: −3.36±0.67°C; 20min: −5.21±1.00°C; 30min: −6.32±1.14°C; p<0.001), with minimal changes in Tc (10min: −0.08±0.04°C; 20min: −0.07±0.07°C; 30min: −0.07±0.09°C; p<0.001). While no differences in TS to the local cold stimulus were observed for any skin region at any stage of the cooling protocol (ΔTS from baseline; 10min: −2.05±5.9%; 20min: −0.3±7.8%; 30min: −1.1±8.5%; p=0.790), a significant and progressive increase in warm TS occurred at each level of Tsk for all skin regions (10min: +4.9±7.5; 20 min: +6.1±4.5; 30 min: +7.9±6.1%; p=0.004). A significant association between decreasing levels of Tsk and increases in warm TS was observed (y= −1.217x+0.2139; R2=0.98; p=0.003), indicating a 1.4% increase in warm TS per 1°C drop in whole-body Tsk. Overall, the same local warm stimulus (hence same increase in skin temperature) was perceived to be warmer with progressive reductions in whole-body Tsk, indicating that, independently of Tc, decreases in whole-body Tsk significantly alter local warmth, but not cold, TS of human hands and feet.