Precooling Can Prevent the Reduction of Self-Paced Exercise Intensity in the Heat

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Abstract
This study investigated the effects of precooling on performance and pacing during self-paced endurance cycling in the heat and, further, the effects of cooling on contractile function as a mechanism for performance changes. After familiarization, eight male cyclists performed two randomized 40-min time trials on a cycle ergometer in 33 degrees C. Before the time trials, participants underwent either a 20-min lower-body cold-water immersion procedure or no cooling intervention. Before and after the intervention and the time trial, voluntary force (maximal voluntary contraction (MVC)), superimposed force (SIF), evoked twitch force (peak twitch force (Pf)), muscle temperature, and blood metabolites were measured. Further, measures of core and skin temperature and HR were recorded before, during, and after cooling and time trial. Results indicated that cycling performance was improved with precooling (198 +/- 25 vs 178 +/- 26 W for precooling and control, respectively; P = 0.05). Although core, muscle, skin, and mean body temperatures were lower in the cooling condition until the 20th minute (P < 0.05), performance did not differ until the last 10 min of the time trial, by which time no differences in physiological measures were present. Further, while MVC and SIF were reduced postexercise in both conditions, MVC, SIF, and Pf were not different between conditions preexercise or postexercise. In conclusion, a precooling intervention improved self-paced endurance exercise; however, the improvement in performance became evident after measured physiological differences induced by precooling had dissipated. Further, the lack of difference between conditions in MVC, SIF, or Pf indicates that improvements in performance did not result from an improvement in contractile function, suggesting that improvements may result from other mechanisms such as muscle recruitment.
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