Repeated-sprint training in heat and hypoxia: Acute responses to manipulating exercise-to-rest ratio

The aim of this study was to investigate acute performance and physiological responses to the manipulation of exercise-to-rest ratio (E:R) during repeated-sprint hypoxic training (RSH) in hot conditions. Twelve male team-sport players completed two experimental sessions at a simulated altitude of similar to 3000 m (FIO2 0.144), air temperature of 40 degrees C and relative humidity of 50%. Exercise involved either 3 x 5 x 10-s (E:R-1:2) or 3 x 10 x 5-s (E:R-1:4) maximal cycling sprints interspersed with active recoveries at 120W (20-s between sprints, 2.5 and 5-min between sets for E:R-1:2 and E:R-1:4 respectively). Sessions were matched for overall sprint and total session duration (47.5-min). Peak and mean power output, and total work were greater in E:R-1:4 than E:R-1:2 (p < 0.05). Peak core temperature was significantly higher in E:R-1:4 than E:R-1:2 (38.44 +/- 0.33 vs. 38.20 +/- 0.35 degrees C, p = 0.028). Muscle deoxygenation magnitude during sprints was greater in E:R-1:2 (28.2 +/- 1.6 vs. 22.4 +/- 4.6%, p < 0.001), while muscle reoxygenation did not differ between conditions (p > 0.05). These results indicate E:R-1:4 increased mechanical power output and core temperature compared to E:R-1:2. Both protocols had different effects on measures of muscle oxygenation, with E:R-1:2 generating greater muscle oxygen extraction and E:R-1:4 producing more muscle oxygenation flux, which are both important signals for peripheral adaptation. We conclude that the E:R manipulation during RSH in the heat might be used to target different physiological and performance outcomes, with these findings forming a strong base for future mechanistic investigation.