Objective Sarcopenia and osteoporosis often coexist in older adults. Sarcopenia is diagnosed using the skeletal muscle mass index (SMI), which is calculated as the appendicular skeletal muscle mass (ASM)/(present height)2, although patients with osteoporosis frequently have a loss of body height. We therefore investigated whether the present height or maximum height is more useful for calculating the SMI in the evaluation of physical abilities. Methods We conducted a cross-sectional study to investigate the association of the SMI with physical abilities, such as the grip strength and gait speed, in 587 postmenopausal women. The SMI was evaluated using whole-body dual-energy X-ray absorptiometry (DXA). The SMI [(ASM)/(present height)2], modified SMI (mSMI) [(ASM)/(maximum height)2], and SMI difference (ΔSMI) (mSMI-SMI) were calculated. Results Age and body mass index (BMI)-adjusted regression analyses showed that the SMI (β=0.30, p<0.001 and β=0.14, p=0.034) and mSMI (β=0.40, p<0.001 and β=0.29, p<0.001) were positively associated while the ΔSMI was negatively associated with the grip strength and gait speed (β=-0.15, p<0.001 and β=-0.24, p<0.001, respectively). Furthermore, the age, BMI, and presence of osteoporotic fractures-adjusted logistic regression analyses showed that a low mSMI (<5.4 kg/m2) was significantly associated with a low grip strength (<18 kg) and slow gait speed (1.0 m/s) [odds ratio (OR) =2.45, 95% confidence interval (CI) =1.52-3.95 per SD increase, p<0.001; and OR=1.73, 95% CI=1.01-2.96, p=0.042, respectively], although a low SMI showed no such relationship (p=0.052 and p=0.813, respectively). Conclusion The mSMI using the maximum height is more useful for evaluating physical abilities than conventional SMI estimation in postmenopausal women.
Keywords: gait speed; grip strength; maximum height; physical ability; sarcopenia; skeletal muscle mass index.