Characterisation of elite swimmers’ core temperature responses in European swimming competition and a pilot passive-heating intervention strategy

Elite pool-based swimming (PBS) competition presents nuanced thermoregulatory challenges. Including multiple cycles of warm-up, transition phases, races and cool-downs within-day, often over consecutive days. Sprint swimmers target elevated core temperature (Tc) during warm-up and seek to maintain this through the transition phase until race-start, to optimise performance. Yet this can be challenged by real-world competition logistical/scheduling constraints, thus a heat intervention may be useful. Firstly, characterise ( n = 6) Tc responses during elite PBS competition ( CHARACTERISATION ). Secondly, a non-randomised crossover pilot study ( n = 12) investigated whether a passive heating intervention could sustain warm-up–derived Tc elevations throughout the transition phase and affect performance ( INTERVENTION ). CHARACTERISATION – Tc (ingestible telemetry) was characterised at the 2023 European U23 Championships. INTERVENTION – Tc was assessed at the 2024 Mare Nostrum Swimming Tour, with heated garments worn during the transition phase (TP; HEAT ) and regular clothing in the CONTROL condition. CHARACTERISATION – Tc increased during the warm-up (WU; P =.001) and decreased during the TP ( P =.001) with no difference between Tc at WU onset and race start ( P =.304). As there were no differences between CHARACTERISATION and INTERVENTION CONTROL Tc ( P ≥.549), data were collapsed and referred to as CONTROL COL . Tc increased during the WU in HEAT and CONTROL COL ( P =.006), decreasing during CONTROL COL TP, but not during the HEAT TP. Tc did not increase from WU to race start in either condition ( P =.152). Heated garment use ( HEAT ) improved TP Tc retention compared to CONTROL COL . The heat stimulus in HEAT was insufficient to elevate Tc beyond WU-derived increases.