Ten trained male team-sport athletes completed 3 sets of repeated sprints ( 9 4 s ) on a nonmotorized treadmill at sea level and at simulated altitudes of 2000 , 3000 , and 4000 m. Participants completed 4 trials in a random order over 4 wk , with mean power output ( MPO ) , peak power output ( PPO ) , blood lactate concentration ( Bla ) , and oxygen saturation ( SaO2 ) recorded after each set .