Objective To evaluate the effects of repeated sprint (RS) training in hypoxia on aerobic performance, repeated sprint ability (RSA), and muscle oxygenation in Rugby Sevens. Methods Fourteen Rugby Sevens players were randomly allocated into hypoxic (RSH, FIO2 = 14.5%, n = 7) or normoxic (RSN, FIO2 = 20.9%, n = 7) groups. Both groups underwent RS training consisting of 3 sets of 6-s × 10 sprints at 140% of velocity at peak oxygen uptake (vVO2peak) on a motorized treadmill, 3 days/week for 6 weeks in addition to usual training. Hematological variables, hypoxia-inducible factor-1 alpha (HIF-1a), and vascular endothelial growth factor (VEGF) concentrations were measured. Aerobic performance, RSA, and muscle oxygenation during the running-based anaerobic sprint (RAS) test were analyzed. Results RSH caused no changes in hemoglobin concentration and hematocrit but significant improvements in VO2peak (7.5%, p = 0.03, ES = 1.07), time to exhaustion (17.6%, p = 0.05, ES = 0.92), and fatigue index (FI, - 12.3%, p = 0.01, ES = 1.39) during the RSA test compared to baseline but not RSN. While "delta"-deoxygenated hemoglobin was significantly increased both after RSH and RSN (p < 0.05), "delta"-tissue saturation index (- 56.1%, p = 0.01, ES = 1.35) and "delta"-oxygenated hemoglobin (- 54.7%, p = 0.04, ES = 0.97) were significantly decreased after RSH. These changes were concomitant with increased levels of HIF-1a and VEGF in serum after RSH with a strong negative correlation between "delta"-FI and "delta"-deoxygenated hemoglobin after RSH (r = - 0.81, p = 0.03). Conclusion There was minimal benefit from adding RSH to standard Rugby Sevens training, in eliciting improvements in aerobic performance and resistance to fatigue, possibly by enhanced muscle deoxygenation and increased serum HIF-1alpha and VEGF concentrations.
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