High muscle-to-fat ratio predicts slow muscle strength decline in middle-aged and older adults: Longitudinal aging study of Taipei

BACKGROUND: Handgrip strength is a vital marker of muscle function and predictor of health outcomes in older adults. This study investigated the relationship between the muscle-to-fat ratio and 3-year decrease in handgrip strength in community-dwelling adults aged ≥50 years. METHODS: Data were obtained from the Longitudinal Aging Study of Taipei (LAST), a cohort study of adults aged 50 years and older. Measurements from two waves, 3 years apart, were analyzed. Demographics, laboratory data, and handgrip strength data were collected. Appendicular skeletal muscle mass was assessed using bioimpedance analysis, and the relative appendicular skeletal muscle mass index was calculated by dividing appendicular muscle mass by height squared. The muscle-to-fat ratio was derived by dividing appendicular muscle mass by total body fat. Handgrip strength decrease was divided into quartiles; slow decliners experienced the smallest decrease, whereas rapid decliners had the greatest decrease. Associations between the muscle-to-fat ratio and other risk factors were analyzed. RESULTS: Over 3 years, the Charlson Comorbidity Index, medication use, waist-to-hip ratio, and fat percentage increased, whereas skeletal muscle mass, the muscle-to-fat ratio, and handgrip strength decreased. Rapid decliners were less likely to be male (21.6% vs 33.3%, p = 0.008) or alcohol drinkers (53.8% vs 66.2%, p = 0.01) and had lower skeletal muscle mass (6.3 ± 0.9 vs 6.6 ± 1.0, p = 0.006) and muscle-to-fat ratios (1.0 ± 0.4 vs 1.1 ± 0.5, p = 0.004) but greater fat percentages (30.4 ± 6.6 vs 29.0 ± 7.6, p = 0.045). A greater muscle-to-fat ratio (odds ratio [OR] = 3.751, p = 0.047), greater physical activity (OR = 1.694, p = 0.04), and lower glycated hemoglobin (HbA1c; OR = 0.61, p = 0.008) reduced the risk of rapid decline. CONCLUSION: The muscle-to-fat ratio, together with physical activity and glycemic control, predicts a decrease in handgrip strength, highlighting its potential as a biomarker of intrinsic capacity and muscle-fat interplay. Further research is needed to explore the underlying biological mechanisms involved.