PERCEPTUAL COLD INDEX VS. PHYSIOLOGICAL COLD STRAIN INDEX DURING EXERCISE-COLD STRESS

Abstract

Recent studies have proposed the use of a perceptual index using thermal sensation (TS) and rating of perceived exertion (RPE) as an analog to the physiological strain index during exercise-heat stress (Tikuisis et al. MSSE 34:1454–1461, 2002). Whether a similar perceptual construct, analogous to the cold strain index (CSI), directly relates to physiological strain during exercise-cold stress is unknown. PURPOSE Develop a new Perceptual Cold Index (PCI) and determine: 1) the relationship of PCI to CSI and 2) whether PCI discriminates physiological strain during exercise-cold stress. METHODS Ten men exercised in cold-wet conditions (CW) for 6-h before (D0) and after 3 days of exhaustive exercise (D3). Each hour of CW consisted of 10-min standing in rain (5.4 cm·hr−1, 5°C air) followed by 45-min walking (1.34m·s−1, 5.4 m·s−1 wind, 5°C air). Exhaustive exercise consisted of 4-h/day of aerobic, anaerobic, and resistive exercise. PCI was defined as: PCI = 6.67*((TS-4.0)/-4.0)+3.33*(RPE/20) and directly analogous to CSI, defined as: CSI = 6.67*((Tcore – initial Tcore)/(35 – initial Tcore))+3.33*((Tsk – initial Tsk)/(20 – initial Tsk)). PCI used a modified Gagge TS scale (0–8) and the Borg RPE scale (6–20). TS and RPE were measured at the end of each 45-min walking period. RESULTS Rectal temperature was 0.3°C lower and skin temperature 1.3°C higher on D3 vs. D0 (P < 0.05), with no differences between trials for heart rate and ventilation. CSI increased during CW but was similar between D3 (4.6 ± 0.6) and D0 (4.2 ± 0.8) at the end of CW. PCI also increased over time during CW but values were the same (P = 0.09) between D3 (7.4 ± 0.5) and D0 (6.8 ± 0.4) with PCI values significantly higher than CSI on both D3 and D0. CONCLUSION People subjectively perceive higher strain over time during prolonged exercise-cold stress, but 1.7 times higher than indicated by the physiological index. PCI also did not discriminate between the higher heat loss and greater decline in rectal temperature during CW that occurred after 3 days of exhaustive exercise.