A comparison of different heat maintenance methods implemented during a simulated half-time period in professional Rugby Union players

Objectives: In thermoneutral conditions, half-time is associated with reductions in body temperature that acutely impair performance. This laboratory-based study compared active, passive, and combined methods of half-time heat maintenance. Design: Randomised, counterbalanced, cross-over. Methods: After a standardised warm-up (WU) and 15min of rest, professional Rugby Union players (n = 20) completed a repeated sprint test (RSSA1). Throughout a simulated half-time (temperature: 20.5±0.3°C; humidity: 53±5%), players then rested (Control) or wore a survival jacket (Passive) for 15min, or performed a 7min rewarm-up after either 8min of rest (Active), or 8min of wearing a survival jacket (Combined). A second RSSA (RSSA2) followed. Core temperature (T_core) and peak power output (PPO; during countermovement jumps; CMJ) were measured at baseline, post-RSSA1, pre-RSSA2. Results: All half-time interventions attenuated reductions in T_core (0.62±0.28°C) observed in Control (Passive: -0.23±0.09°C; Active: -0.17±0.09°C; Combined: -0.03±0.10°C, all p<0.001) but Combined preserved T_core the most (p<0.001). All half-time interventions attenuated the 385±137W reduction in Control PPO (Passive: -213±79W; Active: -83±72W; Combined: +10±52W; all p<0.001); with best PPO maintenance in Combined (p≤0.001). The fastest sprints occurred in RSSA2 in Combined (6.74±0.21s; p<0.001) but Passive (6.82±0.04s) and Active (6.80±0.05s) sprints were 0.4% (p=0.011) and 0.8% (p=0.002) quicker than Control (6.85±0.04s), respectively. Conclusions: While the efficacy of passive and active heat maintenance methods was supported throughout a simulated half-time, a combined approach to attenuating heat losses appeared the most beneficial for T_core and subsequent PPO and sprint performance in professional Rugby Union players.