Limited Effects of Short-Term Heat Acclimation during a Rugby League Training Week

We investigated the effects of five consecutive days of short-term heat acclimation (STHA), with a 48-h recovery,on simulated rugby league performance, peakoxygen uptake (O2peak), physiological and perceptual responses in a temperate environment.Twelve male rugby league players took part in a matched-pairs design, cycling 60-min/day, for five days at 40% O2peak, in a control (19 ± 1C; 50 ± 3 % RH;n = 6) or STHA group (33 ± 0.5 C; 70 ± 4 % RH; n = 6). Subjects completed aO2peak test and rugby simulation, followed by a time-to-exhaustion,pre- and post-intervention, with physiological and perceptual responses measured during the interventions. Despite no effect on simulatedperformance (P> 0.05), there were increases in time-to-exhaustion among both groups (P= 0.016), without group effects (P = 0.802). The STHA group adapted across the intervention, with lower tympanic temperature, perceptual responses and heart rate over time (P< 0.05),whichwere typically higher than the control group (P< 0.05). Plasma volume did not increase over time or change between groups (P = 0.290) and O2peak reduced pre-to-post (P < 0.001).There was a relationship between body mass losses and plasma volume expansion (r = -0.79, P = 0.022). STHA improvedtolerance to the heatbut not performance in simulated matches or exhaustive tests in temperate conditions, compared to thermoneutralexercise. The limited effects of STHA might relate to the brief post-intervention recovery period or the lack of fluid ingestion control during acclimation.

Keywords: Team sports, heat, endurance performance.