LAUSR

BACKGROUND The Yo-Yo Intermittent Recovery Test Level 1 (YYIR1) is often utilized to indirectly assess the cardiorespiratory fitness of team-sport athletes due to its proposed association with match-play high-speed running performance and predicted maximal oxygen uptake. No previous research has investigated the relationships between YYIR1 performances, actual oxygen uptake recorded during the YYIR1, and true all-out sprint kinetics (eg, maximal sprint speed, maximal force capacity, and maximal power output), which therefore served as the primary objective of this study. OBJECTIVES To assess the true physiological kinetics (V˙O2 and heart-rate responses) during the YYIR1 and to evaluate the correlations between the physiological kinetics, sprint kinetics, and YYIR1 performance parameters. METHODS A total of 23 amateur male soccer players were recruited for the study (age 22.52 [2.86] y; height 1.75 [0.06] m; body mass 65.61 [8.43] kg). Each participant completed a YYIR1 and 2 all-out sprint tests. RESULTS Significant differences were observed between actual and predicted maximal oxygen-uptake values (Mdiff = 17.57 mL·kg-1·min-1, P < .001, r = .63). Shuttle distances showed statistically significant correlations with maximal sprint speed (r = .42, P = .044) and theoretic maximal speed (r = .44, P = .035). However, no other correlations with sprint kinetic parameters (eg, maximal force or power output) were observed. CONCLUSION Practitioners should carefully consider the outcomes and utilities of the parameters derived from the YYIR1. The estimations of maximal oxygen uptake from shuttle performances as a proxy for cardiorespiratory fitness are not adequate. However, shuttle distances appear to be positively associated with all-out sprinting capacities.