Associations between physical activity, physical fitness, and body composition in adults living in Germany: a cross-sectional replication study

Previous work showed that physical fitness (PF) is more strongly related to body composition (BC) than self-reported physical activity (PA) in adults. In this study, we provide post-COVID BC statistics and evaluate the reproducibility of previously observed associations between PA, PF, and BC. We analyzed cross-sectional data from 320 adults aged 34–82 years collected in 2025 and compared them with data from 2021. PA was assessed using a validated questionnaire. PF was measured through a standardized performance test battery and BC was obtained via bioelectrical impedance analysis. Associations between PA, PF, and BC were analyzed using sex-specific linear regression models. No significant differences in BC were found between 2021 and 2025. Participants had higher PA and muscular strength but lower coordination in 2025 compared to 2021. PF showed stronger associations with BC than PA. Muscular strength remained the most important predictor of BC and showed the strongest association with phase angle (males: β = 0.40, p < .001; females: β = 0.31, p = .002). The consistency of these associations across two independent samples from 2021 to 2025 indicates a robust pattern under different societal conditions and highlights the importance of PF for supporting healthy aging with regard to BC.