Environmental associations with heart-rate responses during field-based submaximal fitness testing in female football players: an exploratory multi-centre study.

This exploratory multi-centre study examined associations between wet-bulb temperature (WBT) and exercise heart-rate responses (HRex) obtained during routine field-based submaximal fitness testing (SMFT) in female football players. Data were collected from 84 players across three clubs competing in the Australian National Premier League, yielding 971 observations (12 ± 6 observations per player). Associations between WBT and HRex were examined using linear mixed-effects models accounting for repeated observations within players and testing sessions. A positive association was observed between WBT and HRex, with a 10 °C increase in WBT corresponding to an approximately 1.0 percentage point higher HRex (90% CIs: 0.1 to 1.9% points). This association remained relatively consistent across multiple model specifications. Allowing WBT slopes to vary between players improved model fit. Variation in individual WBT slopes (SD = 2.2% points) and residual within-athlete variability (SD = 2.0% points) exceeded the magnitude of the population-average association, although uncertainty surrounding these individual estimates was substantial. These findings should be interpreted as hypothesis-generating rather than evidence of causal relationships. Future confirmatory and experimental studies are required to determine whether higher environmental temperatures cause higher SMFT HRex regardless of changes in physiological state in female football players.