Among 5,255 Chinese adults aged 45+ followed for nine years, each 1-MET increment in estimated cardiorespiratory fitness (eCRF) was associated with an 18.9% reduction in cardiometabolic multimorbidity (CMM) risk — the co-occurrence of conditions like type 2 diabetes, hypertension, and cardiovascular disease. The dose-response was striking: compared to the lowest fitness quartile, risk fell 25.5% in Q2, 46.5% in Q3, and 61.0% in Q4, with a confirmed linear relationship. Skeletal muscle mass partially mediated this association, explaining roughly 23–41% of the protective effect depending on the muscle metric used.
This finding is noteworthy for several reasons. CRF is increasingly recognized as a stronger mortality predictor than most conventional risk factors, yet its relationship to multimorbidity accumulation — rather than single-disease endpoints — has been understudied. The mediation through skeletal muscle mass adds mechanistic plausibility: aerobic fitness preserves muscle, which in turn improves insulin sensitivity, reduces systemic inflammation, and lowers cardiometabolic burden. For adults in midlife and beyond, this reinforces the dual value of building both aerobic capacity and muscle mass simultaneously.
Limitations are meaningful: eCRF was derived from BMI-based sex-specific models rather than measured directly, introducing estimation error. The cohort is exclusively Chinese, limiting generalizability. As an observational study, reverse causation cannot be excluded — less fit participants may already harbor subclinical disease. Still, the linear dose-response, large effect sizes, and 9-year follow-up make this an important confirmatory signal for fitness-focused preventive strategies.
