Performance and pacing during cycle exercise in hyperthermic and hypoxic conditions

Introduction This study examined the influence of alterations in maximal oxygen uptake (VO 2max) in mediating performance and pacing during prolonged self-paced exercise. Methods Twelve well-trained cyclists completed a 750-kJ time trial in temperate (COOL, 18°C), hot (HOT, 35°C), and hypoxic (HYP, 18°C; FiO 2, 0.145) conditions, creating models with a stable, progressively decreasing, and acutely decreased VO 2max, respectively. Results Trial completion was faster in COOL (48.2 ± 5.7 min) compared with HOT (55.4 ± 5.0 min) and HYP (60.1 ± 6.5 min) (P < 0.001), with HOT being faster than HYP (P = 0.028). Core temperature reached 39.0°C ± 0.6°C (COOL), 39.8°C ± 0.5°C (HOT), and 38.5°C ± 0.4°C (HYP; P < 0.01). Power output during COOL was higher than HOT from 40% of work completed onward (P < 0.05) and for the entirety of HYP (P < 0.001), in which it was lower than HOT at 20%-30% (P < 0.05). Normalized power output during COOL and HYP varied by ∼13% and ∼16%, respectively, whereas a ∼27% variation occurred in HOT. VO 2 in COOL was higher than HOT from 70% onward (P < 0.01) and higher than HYP throughout exercise (P < 0.001). Relative to baseline VO 2max (%VO 2max) in normoxia (COOL and HOT) and hypoxia (HYP), %VO 2max during HOT (78% ± 8%) was lower than COOL (84% ± 7%; P = 0.005) and HYP (87% ± 5%; P = 0.003). Conclusions Despite an acutely reduced VO 2max and power output in HYP, pacing and %VO 2max were similar to COOL. In contrast, the progressive decrease in VO 2max and power output in HOT resulted in a more variable pacing pattern with %VO 2max decreasing throughout exercise. These data support the premise that pacing is associated with maintaining an optimal performance intensity, in conjunction with acute and progressive alterations in VO 2max.