PRE-COOLING DOES NOT AFFECT THE CONTRACTILE FUNCTION OF MUSCLES
Duffield, R., Green, R., Castle, P., & Maxwell, N. (2009). The effects of pre-cooling on performance, pacing strategy, and contractile function during endurance cycling in the heat. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.
This study investigated the effects of pre-cooling on performance and pacing during free-paced endurance cycling in the heat, and the effects of pre-cooling on contractile function as a mechanism for performance improvement. Following familiarization, male cyclists (N = 8) performed two randomized 40-minute time-trials on a cycle ergometer in 33°C. Before the time-trials, Ss underwent either a 20-minute lower-body cold-water immersion procedure (14°C) or no-cooling intervention. Prior to and following the respective interventions and time-trials, 10 x 5-second isometric voluntary force (and evoked twitch force, muscle temperature, and anaerobic blood metabolites were measured. Before, during, and following the interventions and time-trials, core (rectal) and skin temperatures and heart rate were recorded.
Performance improved with pre-cooling, with a greater distance covered and a higher mean power output maintained. While core, muscle, skin, and mean body temperatures were lower in the pre-cooling condition until the 20th minute, performance did not differ until the latter parts of the time trial (~29th minute), by which time no differences in physiological measures were present. While isometric voluntary force was reduced post-exercise in both conditions, neither isometric voluntary force nor evoked twitch force were different between conditions pre- or post-exercise.
Implication. A 20-minute lower-body pre-cooling intervention can improve free-paced endurance exercise. However, improvements in performance become evident after physiological differences induced by pre-cooling dissipate. Pre-cooling appears to prevent the reduction in self-selected exercise intensity (noted in the final 10-minutes during exercise without pre-cooling). The lack of difference between conditions in contractile functions suggests improvements in performance do not result from contractile function, but pre-cooling induced improvements result from mechanisms related to muscle recruitment and/or activation.
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