Effects on heat tolerance of physical training in water and on land

Abstract

A 4-wk training program was undertaken by 15 untrained non-heat-acclimated males who were divided into three groups matched on maximal aerobic capacity (VO2max) and trained either in water or on land to determine how physical training (PT) in these different media affects heat tolerance. Subjects trained on a cycle ergometer for 1 h/day, 5 days/wk at 75% VO2max, with the exercise intensity progressively increased to maintain a constant training stimulus. Group I exercised on land, whereas groups II and III exercised while immersed to the neck in water of either 32 degrees C (II) or 20 degrees C (III). Daily exercise increased core temperature (Tc) in groups I and II but not in group III. Training elicited similar increases (approximately 15%) in VO2max in the three groups. Before and after PT, all subjects exercised at approximately 30% VO2max for 3 h at 49 degrees C, 20% rh. Compared with before training, groups I and II showed a decrease in final Tc and heart rate (HR) in the posttraining heat exposure. Sweat rate increased 25% in group II but remained the same in group I. Group III demonstrated a decrease in final HR, but final Tc was higher than before training. Sweat rate did not increase in group III and was lower than the other groups. It was concluded that PT can improve the cardiovascular response to dry heat without affecting thermoregulatory capacity. PT appears to enhance heat tolerance only if Tc is permitted to rise during exercise, thus stimulating the temperature-regulating center for heat dissipation.

Thermoregulatory Adaptations following Sprint Interval Training

“…Therefore, it was uncertain if SIT performed in the heat would provide a sufficient stimulus to promote heat acclimation. The increases we observed were lower than those (,1˚C) of other studies that have shown heat acclimation adaptations associated with elevated core body temperatures (Avellini et al, 1982;Regan et al, 1996). Our participants not only experienced smaller increases in core temperature than those in the cited studies, they also were exposed to these elevated core temperatures for less time; SIT sessions lasted ,30-40 min (total time including warm-up, etc.…”

“…The mechanism for heat acclimation adaptations has historically been attributed to chronic exposure to elevated core body temperature (Avellini et al, 1982;Piwonka, Robinson, Gay, & Manalis, 1965) and, to a lesser extent, skin temperature (Regan et al, 1996). During the SIT sessions, our participants experienced increases in T re of 0.5 ¡ 0.2˚C (0.6 ¡ 0.2˚C for hot group and 0.4 ¡ 0.1˚C for temperate group) from baseline to the end of the last WAnT on the first day of SIT and 0.8 ¡ 0.2˚C (0.9 ¡ 0.1˚C for hot group and 0.7 ¡ 0.3˚C for temperate group) from baseline to the end of the last WAnT on the final day of SIT.…”

“…Improved heat tolerance from endurance training is mediated by increased plasma volume and stroke volume and thereby improved cardiovascular stability during exercise in the heat (Avellini, Shapiro, Fortney, Wenger, & Pandolf, 1982;Senay & Kok 1977) as well as increased sweat rate (Gisolfi & Robinson, 1969;Henane, Flandrois, & Charbonnier, 1977), although this is not a consistent finding (Shvartz, Saar, Meyerstein, & Benor, 1973;Shvartz et al, 1977). Greater effects are observed if the training is performed in a hot environment (Roberts, Wenger, Stolwijk, & Nadel, 1977).…”

Influence of short-term aerobic training and hydration status on tolerance during uncompensable heat stress

“…Long-term ®tness has also been associated with an increased tolerance to exercise in the heat in both longitudinal training (Avellini et al 1982;Gisol® and Robinson 1969) and cross-sectional (Piwonka and Robinson 1967) studies. For these reasons, improvements in aerobic ®tness have been associated with a reduction in physiological strain and increased performance time during exercise in the heat, and physical training programs have been used as a method of heat acclimation (Armstrong and Pandolf 1988).…”

“…Henane et al (1977) suggest that training must increase O 2 max by approximately 15% to induce a level of physiological strain that would result in signi®cant adaptations to heat. The degree of adaptation to heat stress may also depend on both the magnitude and the duration of hyperthermia in the body (Avellini et al 1982;Fox et al 1963). Subjects in the present study did increase their T re approximately 1.2°C over the hour of exercise, though with a relatively short time at a maintained state of hyperthermia.…”