Muscle strength: A better index of low physical performance than muscle mass in older adults

Aim: The most appropriate muscle index for the definition of sarcopenia has not been agreed on. We aimed to investigate the associations of muscle mass and strength with 5-year mortality and low physical performance. Methods: We included 560 participants aged 65 years or older in the analysis. Muscle and fat mass were assessed by dual-energy X-ray absorptiometry. Leg muscle and grip strength were measured using dynamometers. The clinical outcomes were 5-year mortality and low physical performance (Short Physical Performance Battery score < 9) in 5 years. Associations between muscle indices and clinical outcomes were analyzed. A Cox proportional hazard model for mortality and a logistic regression model for physical performance were used. Results: Decreases in leg muscle and grip strength were significantly associated with 5-year mortality and low physical performance in both sexes. Total muscle mass in men and appendicular skeletal mass in both sexes were associated with mortality, but not with low physical performance. Lower leg muscle strength (OR 0.107; P = 0.020) was an independent predictor of low physical performance in women after adjusting for age, fat, cognition, and depression. Lower leg muscle (OR 0.123; P = 0.031) and lower grip strength (OR 0.950; P = 0.012) were independent predictors of low physical performance in men. Conclusions: Muscle strength is a better indicator of 5-year adverse clinical outcomes of mortality and low physical performance than muscle mass. Muscle strength was an independent predictor of low physical performance in 5 years.