Physiological Correlates of the Yo-Yo Intermittent Recovery Tests in Canadian Male Professional Soccer Players

This cross-sectional observational study examined associations between distance covered in the Yo-Yo Intermittent Recovery Test Level 1 (YYIRTL1) and Level 2 (YYIRTL2) and selected physical and physiological performance characteristics in Canadian male professional soccer players. A convenience sample of 29 players from one Canadian Premier League club completed YYIRTL1, YYIRTL2, VO₂max testing, the Cunningham-Faulkner Test (CFT), squat-jump-derived power, theoretical running-power index, maximal running velocity (Vmax), reactive strength index (RSI), and isometric mid-thigh pull (IMTP). Pearson correlations with 95% confidence intervals and Benjamini-Hochberg false-discovery-rate adjustment were calculated. Hypothesis-driven hierarchical regression models were limited to VO₂max and CFT. YYIRTL1 distance was positively correlated with VO₂max (r = 0.666) and CFT (r = 0.540), and was inversely correlated with squat-jump-derived power and theoretical running-power index (both r = -0.501). VO₂max explained 44.3% of YYIRTL1 variance; adding CFT increased explained variance to 52.9%. YYIRTL2 distance was positively correlated with CFT (r = 0.740) and VO₂max (r = 0.684). CFT explained 54.8% of YYIRTL2 variance; adding VO₂max increased explained variance to 72.2%. These findings suggest that VO₂max and CFT performance are associated with YYIRT performance in this single-club professional cohort. Because the sample was small and externally unvalidated, the regression models should be interpreted as exploratory explanatory models rather than prospective prediction tools.