Precooling and warm-up effects on time trial cycling performance during heat stress

The aim of this study was to investigate the separate and combined effects of precooling and warm-up on a subsequent cycling time trial in a hot environment. METHODS: Nine healthy men (mean±SD age=24±5 years; body mass=74.7±4.5 kg; height=171.4±7.7 cm; body fat=12.9±5.2%) completed 3 simulated 16.1-km time trials on a cycle ergometer in a hot environment (~33 °C, 45% relative humidity) after: 1) 20 min of fluid ingestion (10 °C ) followed by 30 min of ice-slurry ingestion (-1 °C ) coupled with ice-vest (PREC), 2) 30 min of ice-slurry ingestion coupled with ice-vest followed by 20 min of warm-up including ice-slurry and ice-vest (COMBO), 3) 30 min of fluid ingestion (10 °C) followed by 20 min of warm-up (WU). RESULTS: At baseline, rectal temperature (T_re ), mean skin temperature ( ₸_sk ), and mean body temperature (₸_b ) were similar among treatments (all P>0.05). After treatment administration and before the start of the time trial, T_re was lower in PREC (36.1±0.3) and COMBO (36.9±0.4) compared to WU (37.6±0.2) (all P<0.05). ₸_sk and ₸_b were all lower in PREC than COMBO and WU, and were lower in COMBO than WU (all P<0.05). Tre remained lower in PREC than WU throughout exercise and was lower in PREC than COMBO for the first 12 km (all P<0.01), while T_re in COMBO remained lower than WU for the first 4 km. ₸_sk during PREC was lower than COMBO at 4 and 8 km and lower than WU at 0 and 4 km, while during COMBO it was lower than WU at 0 and 4 km (all P<0.05). Heart rate (HR) at baseline was lower in PREC than COMBO and WU (68±10, 106±12, 101±13 beats/min, respectively; P<0.001). During exercise, HR increased similarly among all treatments throughout exercise (all P>0.05). Local sweat rate (SR) was lower in PREC than COMBO and WU for the first 4 km (P < 0.05), but whole-body SR was not different among treatments (all P>0.05). Performance times were not different among treatments (PREC: 31.96±2.05 min; COMBO: 32.64±2.90 min; WU: 33.09±3.09 min; P>0.05). CONCLUSION: Despite mitigating thermal strain during exercise, precooling alone, or combined with warm-up, did not result in improved performance of a 16.1-km simulated cycling time trial.