ABSTRACT

This chapter deals with the application of the Yo-Yo intermittent recovery (YY-IR) tests in soccer. The YY-IR test evaluates the players' ability to do repeated intense exercise and has two levels; the level 1 test (YY-IR1) is usually indicated for players with low or moderate fitness capacity, and level 2 (YY-IR2) for players with a high capacity. The physiological responses to the YY-IR tests have been investigated in depth through non-invasive, example heart rate monitoring, and invasive measurements, demonstrating that both tests stimulate the aerobic system maximally while the rate of the anaerobic energy contribution is different between the two tests. Performances in both the YY-IR1 and YY-IR2 tests do often decline in the final phase of the competitive season compared to starting and mid-season periods, which may be related to an insufficient level of aerobic and anaerobic training toward the end of the season.