The effect of a team sport-specific heat acclimation protocol on plasma volume in elite female soccer players

Objectives: The purpose of this study was to investigate the efficacy of a short-term, soccer-specific, isothermic heat acclimation (HA) protocol on plasma volume (PV) expansion in international female soccer players.Subjects: Eighteen non-HA players trained for 5 days in the heat (34.8 ± 0.2°C; 36.6%rh).Methods: Heart rate (HR), core temperature (Tc), sweat rate (SR) and perceptual ratings were recorded during all sessions, with pre- and post-HA measurements of PV and thermoneutral performance (30–15 Intermittent Fitness Test (IFT) completed at 20°C).Results: Session average time spent at target Tc (~38.5°C) was 43 ± 21min across the 5 days. Plasma volume showed a typical robust, but variable, increase (Standardized effect; SE = 0.51; 90% CL: [0.31, 0.70]) pre-to-post HA by 9.5% (CL: [5.8, 13.4]). Inferential statistics showed a 99% chance of very likely positive PV change. The regression model demonstrated that average percentage of HRmax from 20 to 90 min of the workouts as well as total 5-day heat load best predicted the change in PV (R2 = 0.45). There was a small meaningful change post-HA in the 30–15 IFT (SE = 0.50; CL: [−0.12, 1.12]).Conclusions: The implementation of a unique short-term HA circuit specific to soccer was successful at inducing heat-specific physiological adaptations and enhancing soccer-specific performance in thermoneutral conditions.