The Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo IR1)

The Yo-Yo IR1 was conducted as described by Krustrup et al. (2003). The reliability of the test has been established with a coefficient of variation of 3.6% and an intraclass correlation (ICC) coefficient of 0.94 (Krustrup et al., 2003). A standardized warm up comprised 5 min of low-intensity running. Then, participants completed 20 m shuttle runs at increasing velocities until exhaustion, with 10 s of active recovery (2 m × 5 m of jogging) between each 20 m. If participants failed twice to reach the line in time (objective criterion) and/or felt unable to complete another shuttle at the required speed (subjective criterion), their test was terminated. The total distance covered was considered as the test score.