The application of heating film to hands reduces the decline in manual dexterity performance associated with cold exposure

Purpose: Exposure to cold temperatures decreases finger temperature (T_fing) and dexterity. Decreased manual function and dexterity can be serious safety risks, especially in tasks that require fine motor movements that must be performed outdoors. The aim of this study was to determine whether hand heating with a minimal power requirement (14.8 W) results in a smaller reduction in T_fing and manual dexterity performance during mild cold exposure compared to a non-heated control condition. Methods: In a randomized crossover design, twenty-two healthy participants were exposed to a moderately cold environment (5 ºC) for 90 min. One condition had no intervention (CON), while the other had the palmar and dorsal hands heated (HEAT) by using electric heating films. T_fing and cutaneous vascular conductance (CVC) were continuously monitored using laser Doppler flowmetry. Manual dexterity performance and cognitive function were assessed by the Grooved Pegboard Test (GPT) and Stroop Color-Word (SCW) test, respectively, during the baseline period and every 30 min during the cold exposure. Results: After the cold exposure, T_fing was higher in HEAT relative to CON (CON 9.8 vs. HEAT 13.7 ºC, p < 0.0001). GPT placing time, as an index of dexterity performance, was also shorter in HEAT by 14.5% (CON 69.10 ± 13.08 vs. HEAT 59.06 ± 7.99 s, p < 0.0001). There was no difference in CVC between the two conditions during the cold exposure (p > 0.05 for all). Cognitive function was similar between two conditions (p > 0.05 for all). Conclusion: The proposed hand heating method offers a practical means of heating fingers to maintain dexterity throughout prolonged cold exposure.