Short-term exercise-heat acclimation enhances skin vasodilation but not hyperthermic hyperpnea in humans exercising in a hot environment

Abstract

We tested the hypothesis that short-term exercise-heat acclimation (EHA) attenuates hyperthermia-induced hyperventilation in humans exercising in a hot environment. Twenty-one male subjects were divided into the two groups: control (C, n = 11) and EHA (n = 10). Subjects in C performed exercise-heat tests [cycle exercise for ~75 min at 58% [Formula: see text] (37°C, 50% relative humidity)] before and after a 6-day interval with no training, while subjects in EHA performed the tests before and after exercise training in a hot environment (37°C). The training entailed four 20-min bouts of exercise at 50% [Formula: see text] separated by 10 min of rest daily for 6 days. In C, comparison of the variables recorded before and after the no-training period revealed no changes. In EHA, the training increased resting plasma volume, while it reduced esophageal temperature (T (es)), heart rate at rest and during exercise, and arterial blood pressure and oxygen uptake ([Formula: see text]) during exercise. The training lowered the T (es) threshold for increasing forearm vascular conductance (FVC), while it increased the slope relating FVC to T (es) and the peak FVC during exercise. It also lowered minute ventilation ([Formula: see text]) during exercise, but this effect disappeared after removing the influence of [Formula: see text] on [Formula: see text]. The training did not change the slope relating ventilatory variables to T (es). We conclude that short-term EHA lowers ventilation largely by reducing metabolism, but it does not affect the sensitivity of hyperthermia-induced hyperventilation during submaximal, moderate-intensity exercise in humans.

Effect of acute heat stress on adrenocorticotropic hormone, cortisol, interleukin-2, interleukin-12 and apoptosis gene expression in rats

“…The apoptotic cells activate the immune response (8) and they also start an immune tolerance (9). Of note, numerous studies have shown that strong stress is harmful to the organs, tissues, cells and immune system, but occasionally mild stress is beneficial for the body in the heat acclimatization (10)(11)(12). Therefore, the present study aimed to explore whether the heat exposure is harmful to the body by detecting the expression of apoptosis genes in order to observe whether the cells are damaged under the moderate thermal environment and to discuss the influence of heat stress on the body by evaluating the changes of neuroendocrine and immune function.…”

Kalman Filter Models for the Prediction of Individualised Thermal Work Strain

“…Future work will include testing our Kalman filter model's reliability and precision on different test occasions based on repeated measures data from the same subjects. Last, while we showed that the OKF approach can estimate Tc with less error than the EKF model, appreciable variability in the Tc still remains unexplained by HR and ST. Future work will include the evaluation of breathing rate to improve Tc estimations since hyperthermia has been shown to increase ventilation [19].…”

Short-term, low-volume training improves heat acclimatization in an operational context

“…Heat loss may be ensured through convection. Indeed, the body core temperature threshold for the onset of cutaneous vasodilation decreases during acclimation (Fujii et al, 2012;Périard et al, 2016). It is likely that blood flow was reoriented toward cutaneous tissues after 7 days of heat acclimatization, therefore promoting thermal exchange via convection.…”