香蕉直播

Moderate ambient temperatures are known to present sufficient heat stress that result in an elevated core temperature and reduce endurance capacity. Changes in core temperature represent the rate of change in body heat storage, which in turn reflects the balance between metabolic heat production, heat absorbed from the environment and total body heat loss. Work by Nielsen in 1996 provided data to suggest an endurance athlete may experience up to a 1°C rise in core temperature every nine minutes when racing in high ambient conditions. This rate of rise in core temperature would result in a runner reaching a core temperature of 40°C within 25–30 min, with the immediate dangers of heat exhaustion.

Heat tolerance tests are currently used to evaluate military personal that have had a previous experience of exertional heat illness, to determine whether they are able to return to duty. In spite of the significant role of the Israeli Defence Force heat tolerance test to screen military personnel for heat intolerance, the application has been questioned in reference to endurance athletes due to differences in exercise intensity and duration. Endurance runners typically race for a shorter duration and at a higher exercise intensity compared with military personnel. The incidence of exertional heat illness in endurance athletes raises the importance of developing a heat tolerance screening procedure that informs medical personal about an endurance runners current heat tolerance state, and is capable of monitoring changes in heat tolerance.

Repeated heat exposure to a stressful thermal environment initiates a phenotypic adaptation known as heat acclimation, an element of which has been identified as thermotolerance. Heat acclimation improves thermal comfort, submaximal exercise performance, and increases maximal aerobic capacity in the heat. The benefits arise from enhanced sudomotor and skin blood flow responses, plasma volume expansion, cardiovascular stability and an improved fluid balance. Thermotolerance or acquired cellular thermotolerance describes the cellular adaptation accompanying systemic changes induced by successful heat acclimation. As a result, heat acclimation is the consensus recommendation strategy to attenuate the physiological strain associated with training and competing in the heat. However, heat acclimation it is not routinely adopted by endurance athletes and there is little information published on females’ responses to heat acclimation.

Sex differences in temperature regulation during exercise have been reported, irrespective of confounding differences in metabolic heat production and physical characteristics. Interestingly, these differences only become evident above a certain requirement for heat loss and are solely attributed to peripherally mediated control of the sudomotor function. Furthermore, fluctuations in hormonal concentrations associated with the menstrual cycle have a known effect on thermoregulation in females. During the luteal phase of the menstrual cycle there is an elevation in progesterone concentration which modifies central regulatory mechanisms resulting in alterations in basal core temperature, the body temperature threshold for sweating and cutaneous vasodilation. These sex differences in thermoregulatory responses to acute exercise heat stress raise the question of whether females adapt to chronic heat exposure differently to males. Thus, research investigating females’ phenotypic and cellular responses to controlled hyperthermia heat acclimation over short-term and long-term timescales is required.

Recently, novel heat acclimation strategies have been investigated in male participants. These methods involve permissive dehydration, sauna bathing, and hot water immersion. These methods aim to establish an accelerated adaptation via targeting adaptation pathways including, plasma volume expansion, increased sudomotor function, and altered cutaneous vascular function. Once the temporal patterning to controlled hyperthermia in females has been determined, further research is required to establish novel heat acclimation strategies that accelerate adaption responses in females.