Weight-Independent Cardioprotective Effects of Physical Activity in Patients with Myocardial Infarction

Background: Physical activity is a key modifiable determinant of cardiovascular risk, yet whether its protective association with coronary artery disease (CAD) severity in patients with myocardial infarction (MI) is mediated by body mass index (BMI) remains uncertain. Methods: This cross-sectional study included 294 adults admitted with MI and angiographically confirmed MI. Daily preadmission physical activity, as a score, BMI, cardiovascular risk factors and angiographic CAD extent (single-, double-, or triple-vessel disease) were analyzed. Multivariable ordinal logistic regression assessed independent associations of preadmission physical activity with CAD severity. Mediation analysis evaluated BMI as an intermediary using non-parametric bootstrap resampling with 2000 iterations and 95% confidence intervals (CIs). Results: Higher preadmission physical activity was independently associated with lower CAD severity after adjustment for age, sex, smoking, hypertension, diabetes, hyperlipidemia and BMI (β = −0.54, p < 0.001). BMI showed no independent association with CAD severity (β = 0.009, p = 0.76). Bootstrapped mediation analysis demonstrated no significant indirect effect through BMI (mean indirect effect 0.00044; 95% CI −0.00184 to 0.00360). Conclusions: In patients with MI, the inverse relationship between physical activity and CAD severity appears independent of BMI, suggesting weight-independent cardioprotective mechanisms. Promotion of habitual physical activity should remain a central component of secondary cardiovascular prevention regardless of body weight.