Acute physiological and performance responses to repeated sprints in varying degrees of hypoxia

Abstract Objectives Our aim was to determine the effects of different inspired oxygen fractions on repeated sprint performance and cardiorespiratory and neuromuscular responses, to construct a hypoxic dose response. Design Nine male well-trained multi-sport athletes completed 10 × 6 s all-out running sprints with 30 s recovery in 5 conditions with different inspired oxygen fraction (FIO 2 : 12%, 13%, 14%, 15%, 21%). Methods Peak running speed was measured in each sprint and electromyography data were recorded from m. vastus lateralis in parallel with heart rate and blood oxygen saturation. Cardiorespiratory response was assessed via breath by breath expired air analysis and muscle oxygenation status was evaluated via near infrared spectroscopy. Results In parallel with the higher heart rate, minute ventilation, blood lactate concentration, and muscle deoxygenation; lower blood oxygen saturation, pulmonary oxygen uptake and integrated EMG (all p p Conclusions Physiological responses associated with performing 10 × 6 s sprints interspersed with 30 s passive recovery was incrementally greater as FIO 2 decreased to 13%, yet fatigue development was significantly exacerbated relative to normoxia (FIO 2 : 21%) only at the 12% FIO 2 .