The influence of maximal sprint exercise in moderate hypoxia on muscle oxygenation and systemic metabolic responses has not been fully elucidated. PURPOSE: The purpose of the present study was to determine the effects of maximal sprint exercise in moderate hypoxia on muscle oxygenation, systemic oxygen uptake and power output among competitive athletes. METHODS: Seven sprinters (height; 176.1 ± 2.2 cm, body weight; 67.8 ± 3.4 kg, BMI; 22.6 ± 0.7 kg/m2) participated. They performed two trials under either hypoxic (HYP, FiO2: 14.5%, a simulated altitude of 3000m) or normoxic (NOR, FiO2: 20.9%) conditions in a randomized, with a single-blind and crossover design. The exercise in each trial consisted of three consecutive sets of 20-s maximal sprints with a 5 min rest period between sets. Time-course changes in percutaneous oxygen saturation (SpO2), power output during exercise, blood lactate, glucose concentrations, and muscle oxygenation [oxy-hemoglobin (Hb), deoxy-Hb, total-Hb], and respiratory variables were evaluated. RESULTS: A significant main effect of number of set was observed for mean power output during exercise (P<0.01). However, no significant interaction (trial × number of set, P=0.76) or main effect of trial (P=0.66) for mean power output was observed. There were significant main effects of trial (P<0.01) and time (P<0.01) for blood lactate concentration, and post-exercise blood lactate concentrations were significantly higher in the HYP (22.8 ± 0.6 mmol/L) than in the NOR (20.0 ± 0.7 mmol/L, P<0.05). Both trials showed significant increases in deoxy-Hb and total-Hb during the exercise (main effect of time, P<0.01). However, deoxy-Hb and total-Hb tended to be higher in the HYP during the latter sets of sprint. Accumulated VO2 during exercise was significantly lower in the HYP (1419 ± 76 ml) than in the NOR (1973 ± 120 ml, P<0.01), whereas accumulated VCO2 was not significantly different between the trials (main effect of trial, P=0.65). CONCLUSION: No apparent difference in muscle oxygenation kinetics during maximal sprint exercise was found between hypoxic and normoxic conditions. However, exercise-induced elevations of muscle deoxygenation (deoxy-Hb) tended to be augmented under hypoxic condition.