Influence Of Core Temperature On Psychomotor Performance During Cold Stress

Cold stress severity is routinely described in terms of core temperature (Tc) and heat loss, both of which are dependent upon vascular response, subcutaneous fat, body surface area, muscular composition, and metabolic rate. When exposed to cold stress, variations in each of these can contribute to large differences in heat loss among individuals, wherein some are able to preserve Tc while others are not. The impact of such Tc variations on psychomotor performance is poorly understood. Identifying underlying mechanisms that contribute to impaired performance is important so that strategies can be developed to counteract psychomotor impairments caused by cold stress. PURPOSE: Determine the influence of Tc on psychomotor performance during cold water immersion. METHODS: Thirty-six military personnel (mean ± SD; age: 26 ± 4 yr, ht: 175 ± 8 cm, wt: 79.1 ± 11.1 kg) completed a 10-min whole-body cold water immersion (1 °C). Participants’ simple reaction time (SRT) was evaluated using a psychomotor vigilance task administered prior to, during, and immediately after immersion, and at three time points (0, 15, 60 min) during a 60-min rewarming activity (entering sleeping bags with dry clothing). For analysis, participants were divided into groups based on their lowest recorded Tc (which occurred immediately after immersion or early in rewarming). Groups were classified as <35 °C (n = 7), between 35-36 °C (n = 12), and > 36 °C (n = 17). SRT, as well as mean skin temperature (Tsk), hand temperature (Thand), thermal sensation (TS), and shivering sensation (SS), were then compared between groups. Significance was set at p < 0.05. RESULTS: Cold water immersion increased response times for SRT (mean ± SE; pre: 235 ± 12, immersion: 315 ± 14, post: 366 ± 30 ms; p < 0.001). However, no differences were observed between Tc groups for SRT (mean ± SE; < 35 °C: 298 ± 31, 35-36 °C: 313 ± 18, > 36 °C: 326 ± 15 ms; p = 0.677). Additionally, no differences were observed between groups for Tsk (p = 0.409), Thand (p = 0.843), or SS (p = 0.663). CONCLUSIONS: Current findings suggest that psychomotor performance is not greatly influenced by Tc, even in the presence of mild hypothermia. Future work should evaluate other possible contributing physiological factors that impact performance, which will improve understanding of psychomotor performance during cold stress.