Heat acclimation improves intermittent sprinting in the heat but additional pre-cooling offers no further ergogenic effect

Abstract

The aim of this study was to determine the effect of 10 days of heat acclimation with and without pre-cooling on intermittent sprint exercise performance in the heat. Eight males completed three intermittent cycling sprint protocols before and after 10 days of heat acclimation. Before acclimation, one sprint protocol was conducted in control conditions (21.8 ± 2.2°C, 42.8 ± 6.7% relative humidity) and two sprint protocols in hot, humid conditions (33.3 ± 0.6°C, 52.2 ± 6.8% relative humidity) in a randomized order. One hot, humid condition was preceded by 20 min of thigh pre-cooling with ice packs (-16.2 ± 4.5°C). After heat acclimation, the two hot, humid sprint protocols were repeated. Before heat acclimation, peak power output declined in the heat (P < 0.05) but pre-cooling prevented this. Ten days of heat acclimation reduced resting rectal temperature from 37.8 ± 0.3°C to 37.4 ± 0.3°C (P < 0.01). When acclimated, peak power output increased by ∼2% (P < 0.05, main effect) and no reductions in individual sprint peak power output were observed. Additional pre-cooling offered no further ergogenic effect. Unacclimated athletes competing in the heat should pre-cool to prevent reductions in peak power output, but heat acclimate for an increased peak power output.

The effect of cooling prior to and during exercise on exercise performance and capacity in the heat: a meta-analysis

“…Unlike isolated sprint performance the data show that precooling offers a small beneficial effect (d=0.44) to intermittent sprint performance12 17 20 21 27 – 30 and it is likely that this difference is due to differences in the demands of the protocols. The intermittent protocols were longer in duration than the acute sprint test (32–80 min vs 45–70 s) and involved a greater total volume of work being undertaken.…”

“…The weighted-mean estimate of the effect size for the effect of precooling on subsequent sprint exercise performance calculated was d=−0.26, and the unweighted-mean effect size was d=−0.32 (95% CI −0.18 to −0.45; figure 2). The overall weighted-mean estimate of the effect size for the effect of precooling on subsequent intermittent sprint exercise performance calculated from the eight investigations,12 17 20 21 27 – 30 involving a total of 26 cooling interventions/performance measure combinations, was d=0.47. The unweighted-mean effect size was d=0.47 (95% CI 0.40 to 0.53; figure 2).…”

“…Various methods of precooling have been investigated prior to exercise in a hot environment and these include water-immersion7 11 – 16; the application of ice packs onto the skin12 17; the wearing of ice-cooling garments12 18 – 24; cold air exposure25 and a combination of these approaches 21 23 26 – 31. It has been postulated that precooling may benefit subsequent exercise performance or capacity in hot environments, both directly and indirectly.…”

Isothermic and fixed intensity heat acclimation methods induce similar heat adaptation following short and long-term timescales

“…Primary adaptations induced by heat acclimation include decreased core temperature (Armstrong and Maresh, 1991;Buono et al, 1998;Garrett et al, 2011) and reduced heat storage (Aoyagi et al, 1997) facilitated by increased sudomotor function (Chinevere et al, 2008;Machado-Moreira et al, given workload (Frank et al, 2001). These adaptations contribute to a decreased thermal and perceptual strain (Castle et al, 2011), ultimately facilitating increased exercise performance in hot and cool environments . Heat acclimation is often categorised into short term (STHA) and long term (LTHA) induction periods.…”

“…The balance between work and rest to target and maintain specific core temperatures ensures a consistency, or a progression of endogenous heat strain to induce adaptation, albeit requiring alterations in administration throughout each session. Implementation of fixed intensity heat acclimation methods is in comparison relatively simple, with participants maintaining a fixed workload throughout each active acclimation session (Amorim et al, 2011;Castle et al, 2011;Cheung and McLellan, 1998;Houmard et al, 1990;Kresfelder et al, 2006;Marshall et al, 2007;Nielsen et al, 1997Nielsen et al, , 1993Sandström et al, 2008;Watkins et al, 2008;Yamada et al, 2007). Fixed methods derive exercise workloads from a pre acclimation baseline, and the exogenous (external) environment are consistent day-on-day.…”