The influence of whole-body vs. torso pre-cooling on physiological strain and performance of high-intensity exercise in the heat

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Abstract

Little research has been reported examining the effects of pre-cooling on high-intensity exercise performance, particularly when combined with strategies to keep the working muscle warm. This study used nine active males to determine the effects of pre-cooling the torso and thighs (LC), pre-cooling the torso (ice-vest in 3°C air) while keeping the thighs warm (LW), or no cooling (CON: 31°C air), on physiological strain and high-intensity (45-s) exercise performance (33°C, 60% rh). Furthermore, we sought to determine whether performance after pre-cooling was influenced by a short exercise warm-up. The 45-s test was performed at different (P<0.05) mean core temperature [(rectal+oesophageal)/2] [CON: 37.3±0.3 (S.D.), LW: 37.1±0.3, LC: 36.8±0.4°C] and mean skin temperature (CON: 34.6±0.6, LW: 29.0±1.0, LC: 27.2±1.2°C) between all conditions. Forearm blood flow prior to exercise was also lower in LC (3.1±2.0 ml 100 ml tissue−1 min−1) than CON (8.2±2.5, P=0.01) but not LW (4.3±2.6, P=0.46). After an exercise warm-up, muscle temperature (Tm) was not significantly different between conditions (CON: 37.3±1.5, LW: 37.3±1.2, LC: 36.6±0.7°C, P=0.16) but when warm-up was excluded, Tm was lower in LC (34.5±1.9°C, P=0.02) than in CON (37.3±1.0) and LW (37.1±0.9). Even when a warm-up was performed, torso+thigh pre-cooling decreased both peak (−3.4±3.8%, P=0.04) and mean power output (−4.1±3.8%, P=0.01) relative to the control, but this effect was markedly larger when warm-up was excluded (peak power −7.7±2.5%, P=0.01; mean power −7.6±1.2%, P=0.01). Torso-only pre-cooling did not reduce peak or mean power, either with or without warm-up. These data indicate that pre-cooling does not improve 45-s high-intensity exercise performance, and can impair performance if the working muscles are cooled. A short exercise warm-up largely removes any detrimental effects of a cold muscle on performance by increasing Tm.

Introduction

Pre-cooling before prolonged exercise in the heat has been studied extensively over the last 15 years (e.g. Schmidt and Bruck, 1981, Lee and Haymes, 1995, Booth et al., 1997), but little work has been published reporting on the effects of pre-cooling prior to high-intensity exercise in the heat. The literature indicates that pre-cooling should be detrimental to this type of performance, largely because a lower muscle temperature is generally associated with lower mechanical power output (Asmussen and Boje, 1945, Bergh and Ekblom, 1979, Crowley et al., 1991, Holewijn and Heus, 1992). It is notable however that in the study by Crowley et al. (1991), which demonstrated that pre-cooling impairs a 30-s Wingate test performance, pre-cooling was applied specifically to the legs. Given the direct relationship between muscle temperature and maximal power (Davies and Young, 1983), it is not surprising that these studies found that pre-cooling impairs high-intensity performance. A recent study that reported little effect of pre-cooling on high-intensity intermittent treadmill exercise, had also used whole-body cooling (i.e. including leg cooling; Drust et al., 2000).

Somewhat surprisingly, one study that utilised water immersion to cool the torso but not the legs reported a small enhancement of 70-s sprint cycling performance (Marsh and Sleivert, 1999). The cooling strategy in that study differed from those above in that the leg muscles probably remained relatively warm, but the mechanism for an increased power output after pre-cooling was not explained. Another recent study has demonstrated that intermittent cooling can enhance high-intensity performance (Verducci, 1999). In that study, no cooling during rest periods (control) was compared to ice-cooling the arm and shoulder for the first 3 min of an 8-min rest period, between work-bouts of 22 maximal velocity arm-pull repetitions, at 75% of a one-repetition maximum load. The work-bouts were continued until fatigue. Intermittent cooling increased total work, velocities and power production, but no mechanism was offered in explanation of these results.

Mechanisms that might enhance high-intensity performance after pre-cooling include increased blood flow to working muscle or reduced glycogenolysis. There is competition between the skin and muscles for blood flow in prolonged, relatively strenuous exertion in the heat (Bell et al., 1983, Gonzalez-Alonso et al., 1999). Therefore, it is possible that pre-cooling could increase muscle blood flow during high-intensity exercise in the heat, by decreasing cutaneous blood volume and perfusion and increasing central blood volume. This might improve oxygen delivery and metabolite removal, thereby increasing power output. If these effects occurred as a result of pre-cooling, then a performance enhancement would be most obvious when these benefits were added to the benefits of a warm working muscle. Warm muscles could be maintained either by avoiding direct cooling of the muscle during the pre-cooling manoeuvre, or through warming the muscle after pre-cooling, but little research has been reported examining pre-cooling combined with either of these two approaches. Therefore, the purpose of the present study was to determine whether pre-cooling, with and without surface pre-cooling over the working muscles, influenced high-intensity (45-s) exercise performance, and to determine whether the effects of pre-cooling were influenced by a short exercise warm-up. Specifically, three conditions were examined in a balanced, crossover fashion: (1) warm thighs, cold remainder; (2) cold thighs, cold remainder; and (3) warm thighs, warm remainder (control). It was hypothesised that pre-cooling the torso and thighs would impair high-intensity exercise performance whereas torso-only cooling would optimise performance, and that a short exercise warm-up would remove any detrimental effects of cooling the thighs.

Section snippets

Subjects

Nine healthy males [mean±S.D. age=32.4±3.6 years, body mass=80.8±9.9 kg, height=175.6±6.9 cm, surface area (AD)=1.96±0.15 m2, V̇o2peak=50.1±8.0 ml kg−1 min−1] participated in these trials after providing their informed consent. All procedures followed the ethical approval of the Australian Defence Medical Ethics Committee. The experiments were conducted in two climatically controlled laboratories during the period of February to August, 1999. Subjects’ pre-trial physical activity and hydration

Results

Relative to no pre-cooling, both peak and mean power were decreased (P<0.05) after torso+thigh cooling, but not after torso-only cooling, and this finding was more pronounced in the absence of a short warm-up (Fig. 1). The absolute power data are presented in Table 1 for the five subjects who completed all trials with and without warm-up, further indicating that cooling of the torso and thighs impaired peak and mean power while cooling of the torso did not. Additionally, a short exercise

Discussion

The most important findings of this study were that pre-cooling impaired peak and short-term (45-s) high-intensity power outputs, but only if pre-cooling incorporated thigh cooling. As might be expected, these effects were most strongly evident in the absence of an active warm-up. The finding that peak and mean power were affected equivalently suggests that the mechanism of impaired power production was probably not cardiovascular in nature. Cardiovascular factors would not be expected to

Acknowledgements

This study was partially supported by Sport Science New Zealand.

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