Sex, anthropometric, behavioural, and socioeconomic disparities in physical strength of german children and adolescents

Background: Evidence suggests that sex, body composition, physical activ- ity (PA), and socioeconomic status (SES) significantly influence development of physical strength - a key factor for health - in youth. However most research has focused on isolated age groups or regions, limiting broader generalizability. This study aims to investigate sex, anthropometric, behavioral, and socioeconomic dis- parities in physical strength using representative data from Germany. Methods: We analysed a combination of cross-sectional and longitudinal data from 13,735 individuals (aged 4–31 years) assessed in three waves of the Motorik-Modul (MoMo) study (2003-2017). Physical strength was measured using standing long jump, sit-ups, and push-ups. Body fat percentage (BF%) was measured via bioelectrical impedance analysis and age, sex, SES, and PA were self-reported. A latent strength variable was calculated through confirmatory factor analy- sis based on the three strength tasks. Using Generalized Additive Models for Location and Scale with the Gaussian location-scale model family (GAMLSS) disparities based on sex, BF%, PA, and SES were estimated. Marginal effects (Cohen´s d for sex and Pearson’s r for BF%, PA, and SES) were calculated for the ages 10 and 18. Results: GAMLSS explained up to 74.6% of variance in strength-related measures. Sex disparities in physical strength emerged around puberty, with males showing performance increases while females stagnated or declined. By age 18, effect sizes ranged from d=.92 (push-ups and sit-ups) to d=2.22 (standing long jump), highlighting a widening performance gap. BF% had a strong effect, with performance differences widening by late adolescence. At age 18, marginal effects ranged from r=-.45 (sit-ups) to r=-.91 (standing long jump). PA disparities in physical strength increased with age as well, with marginal effects ranging from r=.31 (sit-ups) to r=.36 (push-ups) at age 18. SES had a minor impact, though higher SES was linked to slightly better per- formance, particularly after puberty. Marginal effects for SES at age 18 ranged from r=.11 (pus-ups and sit-ups) to r=.17 (standing long jump). Conclusion: Our findings highlight the importance of addressing sex, anthropometric, and behavioral disparities in youth strength development, especially during puberty. Future research should explore nutritional and psychological factors, alongside detailed body composition and physical activity intensity measures