Fluid balance and thermoregulatory responses of competitive triathletes.

Unlabelled: As little as 2% total body mass (BM) loss from sweat has been shown to compromise physiological functioning during prolonged exercise in the heat, subsequently compromising endurance performance.

Purpose: This observational study aims to describe the fluid balance and thermoregulatory responses of competitive triathletes racing at a major international competition in a cool environment.

Methods: Fluid balance and thermoregulatory responses was measured in six (3 male, 3 female) national-level triathletes competing at the ITU World Triathlon Grand Finale in ambient temperatures of 19-20 °C (relative humidity (RH) ~55%). Dry, nude BM was recorded before and immediately following the race. Fluid intake was monitored throughout the race. Pre-race urine samples were measured for specific gravity (USG). Each athlete ingested a core temperature (Tc) pill 5 h prior to the event and was monitored before and after the race.

Results: Three of six triathletes arrived at the race mildly dehydrated (USG 1.021,1.024,1.030). One of these athletes (1F) subsequently withdrew from the race providing no further data. Another athlete (1M) ended the race vomiting providing invalid hydration data. The four remaining competitors' sweat loss was on average 2.15 L (range: 1.65-2.80 L), while fluid intake was 0.66 L (0.50-0.85 L). A mean loss of 3.3% (2.2-4.5%) BM was recorded. Tc increased by 2.0 °C (1.1-2.9 °C) and 4/5 athletes' (2 M, 2 F) Tc exceeded 39 °C by race-end. Both female athletes self-reported feelings of heat-related exhaustion at the completion of the race.

Conclusions: Despite cool environmental conditions, elite triathletes lost ~3.3% BM, replacing only 33% of sweat losses, and achieved a Tc > 39 °C by race-end.