This study demonstrates that the Yo-Yo IR2 test is reproducible and can be used to evaluate an athlete's ability to perform intense intermittent exercise with a high rate of aerobic and anaerobic energy turnover. Specifically, the Yo-Yo IR2 test was shown to be a sensitive tool to differentiate between intermittent exercise performance of soccer players in different seasonal periods and at different competitive levels and playing positions.

The purpose was to examine the fatigue pattern of elite female soccer players after competitive games. Soccer players (n = 23) from the Danish women Premier League performed a countermovement vertical jump test, a repeated 30-m sprint test, and the Yo-Yo intermittent endurance level 2 (Yo-Yo IE2) test at rested state and after a competitive game. Average heart rate during the game was 86 +/- 1% of maximal heart rate with no differences between halves. Blood lactate was 5.1 +/- 0.5 mmol.L after the first half, which was higher (p < 0.05) than after the second half (2.7 +/- 0.4 mmol.L). Yo-Yo IE2 performance was 484 +/- 50 m after the game, which was 62% lower (p < 0.05) than at rested state (1,265 +/- 133 m). Average sprinting time of three 30-m sprints was 5.06 +/- 0.06 seconds after the game, which was 4% slower (p < 0.05) than at rest (4.86 +/- 0.06 seconds). No game-induced effect was observed on vertical jump performance. Significant inverse correlations were observed between Yo-Yo IE2 test performance and fatigue index during the repeated sprint test both at rest (r = -0.76, p < 0.05) and after the game (r = -0.66, p < 0.05). The study demonstrates that the type of fatigue that occurs after a female soccer game does cause marked impairment in intense intermittent exercise and repeated sprint performance but does not affect vertical jump performance. These findings support the notion that decrements in distance covered by sprinting and high-speed running toward the end of elite female games are caused by fatigue.