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 ∼3000 m (FO 0.144), air temperature of 40°C and relative humidity of 50%. Exercise involved either 3 × 5 × 10-s (E:R) or 3 × 10 × 5-s (E:R) maximal cycling sprints interspersed with active recoveries at 120W (20-s between sprints, 2.5 and 5-min between sets for E:R and E:R 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 than E:R ( < 0.05). Peak core temperature was significantly higher in E:R than E:R (38.44 ± 0.33 vs. 38.20 ± 0.35°C,  = 0.028). Muscle deoxygenation magnitude during sprints was greater in E:R (28.2 ± 1.6 vs. 22.4 ± 4.6%,  < 0.001), while muscle reoxygenation did not differ between conditions ( > 0.05). These results indicate E:R increased mechanical power output and core temperature compared to E:R. Both protocols had different effects on measures of muscle oxygenation, with E:R generating greater muscle oxygen extraction and E:R 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. During a typical repeated-sprint training session conducted in hot and hypoxic conditions, an exercise-to-rest ratio of 1:4 during sprint efforts displayed an increased mechanical power output compared to an exercise-to-rest ratio of 1:2. This represents a potentially useful increase in training stimulus.An exercise-to-rest ratio of 1:2 generated greater muscle oxygen extraction, while an exercise-to-rest ratio of 1:4 resulted in more muscle oxygenation flux and a higher core temperature, indicating key markers of environment-related physiological strain were varied between conditions.Exercise-to-rest ratio manipulation may be used to target different physiological and performance outcomes when prescribing repeated-sprint training in hot and hypoxic conditions.