ABSTRACT
The Yo-Yo intermittent recovery level 2 test (Yo-Yo IR2) is widely utilized to evaluate high-intensity intermittent endurance in high-level soccer players (Randerset al., 2009). Yo-Yo IR2 results improve with age during adolescence. According to Bangsbo et al. (2008), the Yo-Yo IR2 applies a heavy load to both the aerobic and anaerobic energy systems of players. Adolescent development in aerobic and anaerobic fitness occurs at different timings and tempos (Chuman et al, 2009; Malina and Bouchard, 1991). In general, anaerobic fitness improves gradually with age during adolescence (Malina and Bouchard, 1991) and young soccer players aged 12–13 years have already achieved aerobic fitness equivalent to that of professional players (Chuman et al., 2009). Both Yo-Yo IR2 and anaerobic fitness are closely correlated to age (Chuman et al., 2009), but aerobic fitness may not be. Therefore, improvement in Yo-Yo IR2 results in young soccer players seems due mainly to the development of anaerobic fitness. However, whether anaerobic fitness is more important than aerobic fitness for Yo-Yo IR2 performance after taking the age factor into account is unknown. We hypothesized that Yo-Yo IR2 performance in youth soccer players (U-13 to U-18) was affected by anaerobic fitness rather than aerobic fitness, and was affected by aerobic fitness even after taking the player age into account (Figure 1). The purpose of this study was to confirm the hypothetical models.
