Effects of heat acclimation on endurance capacity and prolactin response to exercise in the heat

Abstract

We examined the effect of heat acclimation (HA) on endurance capacity and blood prolactin (PRL) response to moderate intensity exercise in the heat in young male subjects (n = 21). Three exercise tests (ET) were completed on a treadmill: H1 (walk at 60% VO(2)peak until exhaustion at 42°C), N (walk at 22°C; duration equal to H1) and H2 (walk until exhaustion at 42°C after a 10-day HA program). Heart rate (HR), skin (T (sk)) and core (T (c)) temperatures and body heat storage (HS) were measured. Blood samples were taken immediately before, during and immediately after each ET. HA resulted in lower HR, T (sk), T (c) and HS rate (P < 0.05) during ET, whereas endurance capacity increased from 88.6 ± 27.5 min in H1 to 162.0 ± 47.8 min in H2 (P < 0.001). Blood PRL concentration was lower (P < 0.05) during exercise in H2 compared to H1 but the peak PRL level observed at the time of exhaustion did not differ in the two trials. Blood PRL concentration at 60 min of exercise in H1 correlated with time to exhaustion in H1 (r = -0.497, P = 0.020) and H2 (r = -0.528, P = 0.014). In conclusion, HA slows down the increase in blood PRL concentration but does not reduce the peak PRL level occurring at the end of exhausting endurance exercise in the heat. Blood PRL response to exercise in the heat in non-heat-acclimated subjects is associated with their endurance capacity in the heat in a heat-acclimated state.

Effects of Heat Acclimation on Changes in Oxidative Stress and Inflammation Caused by Endurance Capacity Test in the Heat

“…These results are in agreement with our previous findings [20] that our subjects were acclimated through a 10-day exhaustive exercise program in the heat. As discussed earlier [20, 23] and in agreement with the findings of several studies [27, 43, 44], after the HA program, all our subjects showed improvement in EC, where the subjects' mean EC increased 86%.…”

“…The current investigation was a constituent part of a complex HA study [20, 23, 24]. To avoid natural HA, the study was conducted during the winter-spring period in Estonia.…”

“…To establish the workload for the protocol of the EC test and HA program, each subject was initially tested for peak oxygen uptake ( V O 2 peak) as described by Burk et al [23]. The test was conducted in thermoneutral conditions (20–22°C) on a motorized treadmill (Viasys/Jaeger LE300 C, Viasys Healthcare GmbH, Hoechberg, Germany) using an online breath-by-breath metabolic system (MasterScreen CPX, Viasys Healthcare GmbH, Hoechberg, Germany).…”

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

“…Isothermic heat acclimation, where endogenous thermal stimulus is consistently targeted throughout, may positively sustain the rate of adaptation, or advance adaptation should a progressive increase in core temperature be implemented (Taylor and Cotter, 2006;Taylor, 2014). Progressive isothermic methods have only previously been implemented using models where the environmental conditions or workload for acclimation are increased (Burk et al, 2012;Chen et al, 2013;Daanen et al, 2011), this presumably to offset the aforementioned ongoing adaptation. These progressive methods are not certain to increase core temperature in the manner that a progressive increase in the isothermic target temperature would.…”

Influence of Chronic Heat Acclimatization on Occupational Thermal Strain in Tropical Field Conditions

“…Physiological adaptations include lower resting core temperature, 4 lower core temperature and heart rate for a given exercise intensity, 5 and an earlier onset of sweating. 6 Collectively, such adaptations augment thermal tolerance of hot conditions to increase physical performance 7,8 and reduce the incidence of heat related illness.…”