The influence of acute and 23 days of intermittent hypoxic exposures on the exercise-induced forehead sweating response

Abstract

The effect of acute and 23 days of intermittent exposures to normobaric hypoxia on the forehead sweating response during steady-state exercise was investigated. Eight endurance athletes slept in a normobaric hypoxic room for a minimum of 8 h per day at a simulated altitude equivalent to 2,700 m for 23 days (sleep high-train low regimen). Peak oxygen uptake (VO2(peak)) and peak work rate (WR(peak)) were determined under normoxic (20.9%O(2)) and hypoxic (13.5%O(2)) conditions prior to (pre-IHE), and immediately after (post-IHE) the intermittent hypoxic exposures (IHE). Also, each subject performed three 30-min cycle-ergometry bouts: (1) normoxic exercise at 50% WR(peak) attained in normoxia (control trial; CT); (2) hypoxic exercise at 50% WR(peak) attained in hypoxia (hypoxic relative trial; HRT) and (3) hypoxic exercise at the same absolute work rate as in CT (hypoxic absolute trial; HAT). Exposure to hypoxia induced a 33 and 37% decrease (P < 0.001) in (VO2(peak)) pre-IHE and post-IHE, respectively. Despite similar relative oxygen uptake during HAT pre-IHE and post-IHE, the ratings of perceived whole-body exertion decreased substantially (P < 0.05) post-IHE. Pre-IHE the sweat secretion on the forehead (m(sw)f) was greater (P < 0.01) in the HAT (2.60 (0.80) mg cm(-2) min(-1)) compared to the other two trials (CT = 1.87 (1.09) mg cm(-2) min(-1); HRT = 1.57 (0.82) mg cm(-2) min(-1)) despite a similar exercise-induced elevation in body temperatures, resulting in an augmented (P < 0.01) gain of the sweating response (m(sw)f/Delta T(re)). The augmented (m(sw)f) and m(sw)f/Delta T(re) during the HAT were no longer evident post-IHE. Thus, it appears that exercise sweating on the forehead is potentiated by acute exposure to hypoxia, an effect which can be abolished by 23 days of intermittent hypoxic exposures.

The influence of fatigue-induced increase in relative work rate on temperature regulation during exercise

“…By contrast, the present fatigue-induced increase in relative work rate during prolonged exercise was not accompanied by such changes in the regulation of heat-loss responses, suggesting that acute changes of the relationship between relative and absolute work rate are not as a rule accompanied by modulations of sweating and cutaneous vasomotor tone. That ischaemia and hypoxaemia, but not fatigue, alter the regulation of heat loss during exercise supports the notion that such alterations may be triggered by stimulation of muscle metaboreceptors, as a result of reduced oxygen delivery to the working muscle (Kondo et al 1999;Eiken and Mekjavic 2004;Kacin et al 2005Kacin et al , 2007.…”

“…In previous studies we have observed that increasing relative work rate during steady-load exercise, either by experimentally restricting blood flow to the contracting muscles (Eiken and Mekjavic 2004;Kacin et al 2005) or by introducing a hypoxic breathing gas (Kacin et al 2007), substantially potentiates the rate of sweating and attenuates skin blood flow. By contrast, the present fatigue-induced increase in relative work rate during prolonged exercise was not accompanied by such changes in the regulation of heat-loss responses, suggesting that acute changes of the relationship between relative and absolute work rate are not as a rule accompanied by modulations of sweating and cutaneous vasomotor tone.…”

“…Findings from our previous studies on graded ischaemia in the working muscles (Eiken and Mekjavic 2004;Kacin et al 2005) and on exposure to hypoxaemia (Kacin et al 2007) suggest that the increase in relative work rate ð% _ VO 2peak Þ and perception of whole-body exertion is associated with an augmented sweating response and attenuated skin blood flow during dynamic exercise. The mechanisms underlying these alterations in exercise heat-loss responses are not known.…”

“…The mechanisms underlying these alterations in exercise heat-loss responses are not known. It has been postulated that, during exercise, sweating is stimulated not only by input from thermal receptors, but also by a centrogenic drive (''central command'') (Shibasaki et al 2003;Carter et al 2002;Wilson et al 2004) and/or by stimulation of metaboreceptors in the working muscles (Kondo et al 1999;Eiken and Mekjavic 2004;Kacin et al 2005Kacin et al , 2007. Based on the results of the aforementioned studies utilising ischaemia and hypoxaemia, as interventions to modulate relative work rate during constant-load exercise, it appears that the muscle metaboreflex might be a key non-thermal factor affecting the regulation of heat loss during exercise.…”

Effects of hypoxic training on physiological exercise intensity and recognition of exercise intensity in young men

“…Imakawa [14] and Kacin et al, [15] reported that if people performed endurance training at high attitude with the same intensity as that at sea level, the hypoxic stimulation to tissues at high altitude may be increased because of the relative exercise intensity being increased compared with that at sea level. In our study, the participants felt comfortable running at pace in normoxic conditions because of the effect of hypoxic training, which may have influenced the physiological exercise intensity of "fairly light" intensity.…”