We investigated performance, energy metabolism, acid–base balance, and endocrine responses to repeated‐sprint exercise in hot and/or hypoxic environment. In a single‐blind, cross‐over study, 10 male highly trained athletes completed a repeated cycle sprint exercise (3 sets of 3?×?10‐s maximal sprints with 40‐s passive recovery) under four conditions (control [CON; 20°C, 50% rH, FiO2: 20.9%; sea level], hypoxia [HYP; 20°C, 50% rH, FiO2: 14.5%; a simulated altitude of 3,000?m], hot [HOT; 35°C, 50% rH, FiO2: 20.9%; sea level], and hot?+?hypoxia [HH; 35°C, 50% rH, FiO2: 14.5%; a simulated altitude of 3,000?m]). Changes in power output, muscle and skin temperatures, and respiratory oxygen uptake were measured. Peak (CON: 912?±?26?W, 95% confidence interval [CI]: 862–962?W, HYP: 915?±?28?W [CI: 860–970?W], HOT: 937?±?26?W [CI: 887–987?W], HH: 937?±?26?W [CI: 886–987?W]) and mean (CON: 808?±?22?W [CI: 765–851?W], HYP: 810?±?23?W [CI: 765–855?W], HOT: 825?±?22?W [CI: 781–868?W], HH: 824?±?25?W [CI: 776–873?W]) power outputs were significantly greater when exercising in heat conditions (HOT and HH) during the first sprint (p??.05). Heat exposure (HOT and HH) elevated muscle and skin temperatures compared to other conditions (p??.05). Oxygen uptake and arterial oxygen saturation were significantly lower in hypoxic conditions (HYP and HH) versus the other conditions (p??.05). In summary, additional heat stress when sprinting repeatedly in hypoxia improved performance (early during exercise), while maintaining low arterial oxygen saturation.
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