Sigurbjo ̈rn A ́ . Arngrı ́msson, Darby S. Petitt, Fabio Borrani, Kristie A. Skinner, Kirk J. Cureton
Accepted: 5 January 2004 / Published online: 19 May 2004 Springer-Verlag 2004
ABSTRACT
To compare the effect of hyperthermia on maximal oxygen uptake (VO2max) in men and women, VO2max was measured in 11 male and 11 female runners under seven conditions involving various ambient temperatures (Ta at 50% RH) and preheating designed to manipulate the esophageal (Tes) and mean skin ðTskÞ temperatures at VO2max. The conditions were: 25C, no preheating (control); 25, 35, 40, and 45C, with exercise-induced preheating by a 20-min walk at 33% of control V_ O2max; 45C, no preheating; and 45C, with passive preheating during which Tes and Tsk were increased to the same degree as at the end of the 20-min walk at 45C. Compared to V_ O2max (1/min) in the control condition (4.52±0.46 in men, 3.01±0.45 in women), VO2max in men and women was reduced with exercise-induced or passive preheating and increased Ta, 4% at 35C, 9% at 40C and 18% at 45C. Percentage reductions (7–36%) in physical performance (treadmill test time to exhaustion) were strongly related to reductions in VO2max (r=0.82–0.84). The effects of hyperthermia on VO2max and physical performance in men and women were almost identical. We conclude that men and women do not differ in their thermal responses to maximal exercise, or in the relationship of hyperthermia to reductions in VO2max and physical performance at high temperature. Data are reported as mean (SD) unless otherwise stated.
INTRODUCTION
Physical performance in prolonged strenuous exercise is reduced in the heat (Rowell et al. 1969; MacDougal et al. 1974; Sakate 1978; Nielsen et al. 1993). However, the literature is conflicting as to whether the reduction in performance is related to reduced maximal oxygen uptake (VO2max) at high temperature. Some studies suggest that high ambient temperature (Ta) reduces VO2max slightly (3–8%) (Taylor et al. 1955; Klausen et al. 1967; Rowell et al. 1969; Sakate 1978; Sawka et al. 1985), whereas other studies reported no effect (Williams et al. 1962; Rowell et al. 1965, 1966). In studies that found little or no change in VO2max, exposure to the heat was for relatively short durations, and/or rectal temperature (Tre) often was not elevated to high levels (Rowell et al. 1965). Pirnay et al. (1970) were the first to observe a marked decrease (27%) in VO2max when measured in the heat (46C). Their protocol differed from those employed in the earlier studies in that VO2max was measured following 20 min of low-intensity exercise that elevated core temperature (Tc). Only a 7% reduction was observed without preheating in another set of subjects (Pirnay et al. 1970). Nybo et al. (2001) observed a 16% decrease in VO2max following pre-heating with a water-perfused jacket and water-proof pants that elevated Tc and mean skin temperature (Tsk). However, the effect of different combinations of Tc and Tsk on VO2max has not been studied. In addition, there are no data on the effects of high Tc andTsk on VO2max in women. Whether the effect of high Tc and Tsk on VO2max and performance in women is qualitatively or quantitatively different from that in men is unknown.