## 4 Discussion  
From the results, a moderate positive correlation was observed between the \(\mathrm{vVO_{2 max}}\) of the laboratory test and the distance in the YYIR1 and estimated \(\mathrm{VO_{2 max}}\) using the YYIR1 test. Among the anthropometric characteristics, only height and weight were negatively correlated with \(\mathrm{LVO_{2 max}}\). Lastly, no differences were observed between playing positions in any variable. [PERSON] et al. (2005) [15] in their study did not observe correlations between the \(\mathrm{VO_{2 max}}\) measured on the treadmill and the \(\mathrm{VO_{2 max}}\) measured with the Yo-Yo intermittent endurance test. Similar findings are reported by other researchers who used the YYIR1 test [33]. According to the researchers, the lack of correlations indicates the difference between the two tests. Specifically, the laboratory test was designed to measure the participant's aerobic capacity (\(\mathrm{VO_{2 max}}\)) and is a continuous test. In contrast, the YYIE was designed to assess the participant's ability to perform repeated efforts with intervals [35] and not to measure \(\mathrm{VO_{2 max}}\). In a subsequent study [17], the researchers observed moderate correlations of \(\mathrm{VO_{2 max}}\) with the distances covered by football players in the YYIR1 and YYIR2 tests and weak correlations with the distance in the YYET. The literature also includes studies on football players that found strong correlations. Specifically, [PERSON] et al. (2003) [36] in their study examining the physiological response of YYIR tests, found, among other things, a strong positive correlation of \(\mathrm{VO_{2 max}}\) with the distance in the YYIR1 test (r = 0.71), as did [PERSON] et al. (2010) [37] a few years later (r = 0.74). From the presentation of the results of the above studies, it appears that the relationship between \(\mathrm{VO_{2 max}}\) and the YYIR1 field test is not clear. These differences between the studies may be due to the characteristics of the participants. Such characteristics may include age and level. We observed high correlations in studies involving adults and professional football players [36; 37]. Another variable to consider when evaluating the results of studies with correlations is the sample size of each study. In the present study, 27 young football players participated; in the study  
Figure 3: (**A**) Differences in \(\mathrm{VO_{2 max}}\) measured with laboratory test. (**B**) Differences in velocity of \(\mathrm{VO_{2 max}}\) measured with laboratory test. (**C**) Differences in performance on Yo-Yo intermittent recovery test level 1. (**D**) Differences in \(\mathrm{VO_{2 max}}\) predicted from the performance of Yo-Yo intermittent recovery test level 1.  
of [PERSON] et al., [15] 21 young football players from a U18 team participated; in the study of [PERSON] et al. [33] 24 adult football players took part; in the study of [PERSON] et al. [17] there were 12 young football players under 15; in the study of [PERSON] et al. [36] there were 17 adults and 37 professional football players; and in the study of [PERSON] et al. [37] 13 professional football players. These differences make it difficult to generalize the results. Previous studies report that a lack of correlations between tests leads to the conclusion that the tests have different physiological demands. However, this conclusion is not confirmed by studies showing large correlations. As mentioned above, of the anthropometric characteristics, only height and weight were negatively correlated with \(\text{LVO}_{\text{2 max}}\). In the football players of the present study, it was observed that the value of \(\text{VO}_{\text{2 max}}\) decreased as the weight or height of the athletes increased. In a recent review study [38], a moderate negative correlation of \(\text{VO}_{\text{2 max}}\) with body mass was reported. In an earlier study [18] conducted on professional football players, a negative moderate correlation was observed between body fat and the distance covered in the multistage test.