Effect of Sex and Age on Knee Strength in Young Athletes: A Systematic Review and Meta-analysis.

The purpose was to summarize the studies examining knee strength in young athletes and provide valuable insights into the magnitude of changes in knee flexion and extension strength during the transition from pre-puberty to puberty among male and female athletes. The literature search was conducted through Cochrane Library, Embase, PubMed, Web of Science. Cohen's effect size (ES) and 95% confidence intervals (CIs) were computed using a random effects model. While comparing males and females, as well as pre-puberty and puberty stages, we conducted subgroup analyses for pre-puberty versus puberty and for males versus females respectively. Thirteen studies published between 2003 and 2021 were included in the analysis. In the pre-puberty stage, no statistical difference was observed on knee extensors or flexors between male athletes and female athletes (=0.695, 0.138); In the puberty stage, males exhibited higher strength relative to weight compared to females for both knee extensors and flexors (SMD=1.36, 1.25). From pre-puberty to puberty, the strength of knee extensors and flexors relative to weight vastly increased for males (SMD=-1.71, -1.86), while no significant change was found for females (=0.436, 0.071). There were no discernible sex- or age-related differences in the hamstring-quadricep (HQ) ratio (=0.590, 0.834). The validity of the HQ ratio as a parameter for predicting injury risks was brought into question by the findings of this study. Strength of male athletes started to grow in puberty while the increase in strength for female athletes was not significant, which indicated that more sex-specific training and injury reduction program should be accomplished.