Which Is A Better Skeletal Muscle Mass Index For The Evaluation Of Physical Abilities: The Present Height Or Maximum Height?

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 (Delta SMI) (mSMI-SMI) were calculated.Results Age and body mass index (BMI)-adjusted regression analyses showed that the SMI (beta=0.30, p<0.001 and beta=0.14, p=0.034) and mSMI (beta=0.40, p<0.001 and beta=0.29, p<0.001) were positively associated while the Delta SMI was negatively associated with the grip strength and gait speed (beta=-0.15, p<0.001 and beta=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/m(2)) 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.