Local sweating on the forehead, but not forearm, is influenced by aerobic fitness independently of heat balance requirements during exercise

Abstract

The present study investigated the influence of maximal oxygen uptake (V O 2 max ) on local steadystate sudomotor responses to exercise, independently of evaporative requirements for heat balance (E req ). Eleven fit (F;V O 2 max 61.9 ± 6.0 ml kg −1 min −1 ) and 10 unfit men (UF;V O 2 max 40.4 ± 3.8 ml kg −1 min −1 ) cycled for 60 min at an air temperature of 24.5 ± 0.8 • C and ambient humidity of 0.9 ± 0.3 kPa at a set metabolic heat production per unit surface area, producing the same E req in all participants (BAL trial) and, in a second trial, at 60% ofV O 2 max . During the BAL trial, absolute power (F 107 ± 2 and UF 102 ± 2 W; P = 0.126), E req (F 175 ± 5 and UF 176 ± 9 W m −2 ; P = 0.855), steady-state whole-body sweat rate (F 0.44 ± 0.02 and UF 0.47 ± 0.02 mg cm −2 min −1 ; P = 0.385) and local sweat rate on the arm (F 0.29 ± 0.03 and UF 0.35 ± 0.03 mg cm −2 min −1 ; P = 0.129) were not different between groups; however, local sweat rate on the forehead in UF (1.67 ± 0.20 mg cm −2 min −1 ) was almost double (P = 0.002) that of F (0.87 ± 0.11 mg cm −2 min −1 ). Heart rate, ratings of perceived exertion and relative exercise intensity were also significantly greater in UF (P < 0.05). There was a trend towards an elevated minute ventilation in UF (P = 0.052), while end-tidal P CO 2 was significantly lower in UF (P = 0.028). At 60%V O 2 max , absolute power (F 174 ± 6 and UF 110 ± 5 W; P < 0.001), E req (F 291 ± 14 and UF 190 ± 17 W m −2 ; P < 0.001), steady-state whole-body sweat rate (F 0.84 ± 0.05 and UF 0.53 ± 0.03 mg cm −2 min −1 ; P < 0.001) and local sweat rate on the arm (F 0.75 ± 0.04 and UF 0.35 ± 0.03 mg cm −2 min −1 ; P < 0.001) and on the forehead (F 2.92 ± 0.42 and UF 1.68 ± 0.23 mg cm −2 min −1 ; P = 0.022) were all significantly greater in F compared with UF. Heart rate and ratings of perceived exertion were similar at all time points (P > 0.05). Significantly greater minute ventilation (P < 0.001) and end-tidal P CO 2 responses (P = 0.017) were found in F. In conclusion, aerobic fitness alters local sweating on the forehead, but not the forearm, independently of evaporative requirements for heat balance, and may be the result of differential control of sweating in these skin areas associated with the relative intensity of exercise.

Isothermic and fixed intensity heat acclimation methods induce similar heat adaptation following short and long-term timescales

“…It also remains uncertain whether isothermic heat acclimation is a more efficient method than fixed intensity heat acclimation for preparing highly trained individuals for exercise heat stress (Garrett et al, 2012). Highly trained individuals are likely to be able to sustain the greater absolute workloads required of the isothermic methods, with higher metabolic heat production elevating the rate of core temperature more rapidly (Cramer et al, 2012;Garrett et al, 2012Garrett et al, , 2011 and thus, giving greater competition specificity to their acclimation, further enhancing the efficacy of isothermic methods for this population.…”

Neither Short-term Sprint nor Endurance Training Enhances Thermal Response to Exercise in a Hot Environment

“…(14)(15)(16)(17)(18) A caveat, however, is that these studies typically employed a similar relative exercise intensity pre-and post-training, such that the absolute exercise and thus metabolic heat production and thermal stress were higher post-training. Recent studies demonstrated no difference in core temperature rise before sweating onset, nor sweating thermosensitivity, when absolute exercise intensity, and hence metabolic heat production, was controlled (19,20) . Nevertheless, the potential for physical training to complement or partially supplant traditional heat acclimatization can be particularly attractive for workers tasked with performing in hot environments who, because of other job requirements, lack of heat acclimation facilities, or rapid field deployment, may not be able to devote the necessary time for longer duration heat adaptation protocols.…”

Wheel running improves REM sleep and attenuates stress-induced flattening of diurnal rhythms in F344 rats

“…For example, increasing body temperature alone can alleviate symptoms of depression in depressed patients (Hanusch et al 2013; Koltyn et al 1992) and depressed individuals have deficits in thermoregulatory cooling (Ward et al 1986). Additionally, individuals who are exercise trained activate thermoregulatory cooling mechanisms more efficiently than untrained controls (Cramer et al 2012; Ichinose-Kuwahara et al 2010). Thus it seems plausible that the antidepressant-like effects of exercise may depend, in part, on alterations in thermoregulation; however the potential mechanisms remain poorly understood.…”