Influence of Chronological Age, Anthropometric Characteristics and Biological Maturity on Eccentric Knee Flexion Strength During the Nordic Hamstring Exercise in Female International Youth Soccer Players.

This study aimed to investigate the influence of chronological age, anthropometric characteristics and biological maturity on eccentric knee flexion strength during the Nordic hamstring exercise in female international youth soccer players. We included 50 under-15-year-old (chronological age = 14.1 ± 0.4 years) and 31 under-16-year-old (chronological age = 15.0 ± 0.5 years) female international youth soccer players as participants in this study. We measured each participant's body mass, height and biological maturity expressed as the percentage of predicted adult height (PAH%). Each participant performed three maximal effort repetitions of the Nordic hamstring exercise on a field-based testing device (NordBord, VALD Performance, Brisbane, Australia) to measure their eccentric knee flexion strength. We used linear regression to investigate individual associations between eccentric knee flexion strength and each predictor variable (body mass, height, chronological age and PAH%). In addition, a partial least squares (PLS) regression model was developed to predict the average eccentric knee flexion strength. Eccentric knee flexion strength had statistically significant associations with body mass (p < 0.01 and R2 = 0.34), PAH% (p < 0.01 and R2 = 0.18) and chronological age (p = 0.03 and R2 = 0.06) but not with height (p = 0.11 and R2 = 0.03). The 2-component PLS model explained 36% of variance in eccentric knee flexion strength, with body mass and PAH% the most influential predictors. Body mass and biological maturation status should be considered when interpreting eccentric knee flexion strength testing results during the Nordic hamstring exercise in female youth soccer players as these factors appear more influential than chronological age or height in determining test performance.