Table 1. Arterial oxygen saturation (SpO2) and rating of perceived exertion (RPE) measured in team-sport athletes before (SpO2), during, and immediately after performing the RSR444 (4 sets of 4, 4-s sprints) in normoxic (20.9%) and hypoxic (14.5%) conditions. Data are means (±SD). Variable Condition Baseline Pre-test Post-set 1 Post-set 2 Post-set 3 Post-set 4 SpO2 (%) Normoxia 97.3 (0.9) 97.7 (1.0) 95.0 (3.1) 95.0 (2.3) 94.1 (2.4) 94.2 (1.8) Hypoxia 98.0 (0.8) 91.2 (1.8)* 83.2 (2.9)* 80.6 (3.2)* 79.9 (3.7)* 79.4 (4.0)* RPE Normoxia - - 4.4 (1.1) 5.6 (1.2) 6.9 (0.9) 7.9 (1.1) Hypoxia - - 5.0 (1.2) 6.4 (1.1) 7.6 (1.2) 8.4 (0.9) *Different from normoxia (p < 0.05). Baseline measurements were obtained in normoxic conditions before the warm up. Pre-test measurements were performed in the environmental condition, after the warm up and immediately before the commencement of the RSR444