# 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

## TL;DR

This study shows that body mass and biological maturity are more important than age or height in determining hamstring strength in young female soccer players.

## Contribution

The study identifies body mass and biological maturity as key predictors of eccentric knee flexion strength in female youth soccer players.

## Key findings

- Body mass and biological maturity significantly influence eccentric knee flexion strength.
- Chronological age has a weaker impact compared to body mass and biological maturity.
- A PLS model explained 36% of the variance in strength, with body mass and PAH% as top predictors.

## Abstract

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 R
2 = 0.34), PAH% (p < 0.01 and R
2 = 0.18) and chronological age (p = 0.03 and R
2 = 0.06) but not with height (p = 0.11 and R
2 = 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.

Body mass and biological maturity should be considered when interpreting Nordic hamstring exercise strength testing results in female youth soccer playersDespite having a statistically significant association with eccentric knee flexion strength in this study, chronological age has less influence than body mass and biological maturity on Nordic hamstring exercise strength testing resultsOur findings highlight relevant participant characteristics to consider when interpreting Nordic hamstring exercise strength testing results in youth female soccer players

Body mass and biological maturity should be considered when interpreting Nordic hamstring exercise strength testing results in female youth soccer players

Despite having a statistically significant association with eccentric knee flexion strength in this study, chronological age has less influence than body mass and biological maturity on Nordic hamstring exercise strength testing results

Our findings highlight relevant participant characteristics to consider when interpreting Nordic hamstring exercise strength testing results in youth female soccer players