Association between metabolic heterogeneity of obesity and the progression of muscle strength decline: a prospective cohort study

BACKGROUND: Obesity exhibits metabolic heterogeneity, but its impact on muscle strength decline remains unclear. METHODS: Based on 7772 participants from the China Health and Retirement Longitudinal Study, individuals were classified into 4 body mass index (BMI)-metabolic phenotypes (metabolically healthy normal weight [MHNW], metabolically unhealthy normal weight [MUNW], metabolically healthy overweight/obesity [MHOO], metabolically unhealthy overweight/obesity [MUOO]). Grip strength was used to assess muscle strength, and linear mixed-effects models examined phenotype-specific associations with muscle decline. RESULTS: Baseline muscle strength was significantly lower in the MUOO group compared to MHNW. Longitudinal analysis showed accelerated muscle loss in the MUOO group across low (β = -0.0164), medium (β = -0.0091), and high (β = -0.0159) muscle strength levels (p < .05). Transition analysis showed that participants transitioning from MUOO to MHNW demonstrated an additional annual decrease in muscle strength of 0.0465 (95% confidence interval [CI] = -0.0612 to -0.0318), compared with those maintaining stable MHNW. In the low muscle strength group, the stable MUNW (β = -0.0140), MHOO (β = -0.0195), and MUOO (β = -0.0263) groups all delayed recovery (all p < .05). In the medium muscle strength group, stable MUOO accelerated decline (β = -0.0091, 95% CI: -0.0182 to -0.0000), whereas decline was significantly slowed in those transitioning from MUOO to MUNW (β = 0.0329, 95% CI = 0.0135 to 0.0523). CONCLUSIONS: Both BMI and metabolic status influence muscle strength trajectories. Maintaining normal weight and metabolic health is essential for recovery in low-strength individuals, while weight loss may help mitigate decline in those with medium strength.