Yo-Yo intermittent recovery level 2 test in young soccer players from U-13 to U-18
Figure 4 shows effects of aerobic and anaerobic fitness on intermittent endurance when the age of young soccer players from U-13 to U-18 is taken into account. Here, the x2 was 1.013 (P value=0.314), GFI was 0.994, AGFI was 0.941, CFI was 1.000, NFI was 0.994, RFI was 0.965, and RMSEA was 0.012. Path coefficients
from age to Yo-Yo IR2, O2max and Wingate test were 0.79, 0.10 and 0.78, respectively. The path coefficients from age to Yo-Yo IR2 and Wingate test were significant. Path coefficients from O2max and Wingate test to Yo-Yo IR2 were 0.35 and 0.52, respectively. The path coefficient from O2max to Yo-Yo IR2 was significant. 4. DISCUSSION The model fitting indicators for the hypothetical models (Figure 1) showed significant values and these causal structural models were confirmed (Figure 3 and 4). Significant path coefficients from O2max and Wingate test result to Yo-Yo IR2 result were confirmed in one model (Figure 3). The Yo-Yo IR2 test does apply a heavy load to both the aerobic and anaerobic energy systems (Bangsbo et al., 2008). Both Yo-Yo IR2 and anaerobic fitness are closely correlated with age (Table 1), but young soccer players aged 12-13 years have already achieved a highlevel of O2max equivalent to professional soccer players (Chuman et al., 2009). These results suggest that intermittent endurance (Yo-Yo IR2 performance) is affected by anaerobic fitness (Wingate test performance) to a higher degree than aerobic fitness (O2max).