INTRODUCTION Longitudinal validity (or external responsiveness) indicates the ability of a test to reflect changes in the reference criterion. The Yo-Yo Intermittent Recovery Test Level 1 (YO1) is the most valid soccer endurance test; its validity has been showed by its correlations with high-intensity running (HIR) during the match, also it discriminates between competitive levels and playing positions(1). To our knowledge the longitudinal validity of YO1 has been assessed only in referees. A sub-maximal version of YO1 (YO1sub), ending at the 6thmin., has been proposed for some “special” population such as injured players during rehabilitation. The aim of this study was to examine the longitudinal validity of YO1 and YO1sub in soccer players. METHODS Eleven players (age 24.8±6.3yrs; height 176±6.1cm; weight 73.6±7.2kg) participated in the study. A friendly match, the YO1 and YO1sub were completed in preseason (PRE) and after 15-17 weeks of training (POST). HIR was measured as the distance covered higher to 15 km/h, using a GPS system (SPIProX, 15Hz). Distance covered and percentage of heart rate max at 6th min (HR6) were considered as outcomes in YO1 and YO1sub, respectively. External responsiveness was measured with correlations between changes scores in YO1 and YO1sub with HIR. RESULTS Distance in YO1 (1694±243m PRE to 2385±411m POST, p<0.0001) and HIR (1202±388m PRE to 1631±466m POST, p=0.002) increased after training. HR6 showed no changes (86.2±3.9% PRE and 85.4±3.8% POST, p=0.27). Correlations between YO1 and HIR in PRE and POST were r=0.68 (CI90% 0.12 to 0.86) and r=0.59 (CI90% 0.10 to 0.85), respectively. Correlations between YO1sub and HIR in PRE and POST were r=0.32 (CI90% -0.19 to 0.69) and r=0.34 (CI90% -0.16 to 0.71). PRE-POST changes were 40% (CI90% 31 to 50), -0.9% (CI90% -2.3 to 0.5) and 37.2% (CI90% 19 to 57) in YO1, YO1sub and HIR, respectively. Correlations between changes in HIR vs.YO1 and vs. YO1sub were r=0.69 (CI90% 0.27 to 0.89) and r=-0.31(CI90%-0.72 to 0.26), respectively. DISCUSSION Similar to previous studies, significant and large correlations between YO1 and HIR were found in both PRE and POST tests. The correlation between changes scores in YO1 and HIR showed that an increase in the test reflected improvements in the HIR during matches, confirming its longitudinal validity. On the other hand, our data did not support the usefulness of YO1sub in detecting changes in the HIR
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