The influence of passive heat maintenance on lower body power output and repeated sprint performance in professional rugby league players

Objectives: The pre-competition warm-up mediates many temperature related physiological changes which generally lead to an improvement in performance. However, after ceasing exercise body temperature declines rapidly, which reduces some of the benefits of the initial warm-up. We examined the effects of a passive heat maintenance strategy on post-warm-up core temperature (T(core)) and performance in professional rugby league players. Design: Twenty professional rugby league players completed this randomised and counter-balanced study. Methods: After a standardised warm-up, players completed a countermovement jump (CMJ) before resting for 15min wearing normal training attire (control) or wearing a passive heat maintenance jacket (PHM), players then completed another CMJ and a repeated sprint protocol (RSA). T(core) was measured at baseline, post-warm-up, pre-RSA and post-RSA. CMJ were analysed for peak power output (PPO), and RSA for fastest, mean and total sprint time. Results: Post-warm-up T(core) (mean±SD; control 37.70±0.28; PHM 37.70±0.27°C; p=0.741) and PPO (control 5220±353 vs. PHM 5213±331W; p=0.686) were similar between conditions. At pre-RSA, PHM was associated with greater T(core) (control 37.14±0.31 vs. PHM 37.51±0.30°C; p