Skeletal muscle area correlates with body surface area in healthy adults

Aim: Depletion of skeletal muscle mass (sarcopenia) predicts survival in patients with cancer or liver cirrhosis. Recently, many reports have used computed tomography (CT) to measure muscle area to define sarcopenia. However, the definition of sarcopenia using CT has not been fully determined. The aim of this study was to establish formulae to calculate the standard area of skeletal muscle. Methods: Forty-five healthy adults (24 men and 21 women, aged 21-66 years) who wished to donate part of their liver for transplantation underwent CT. Cross-sectional areas (cm²) of skeletal muscle were measured at the caudal end of the third lumbar vertebra. Regression analysis was performed to establish formulae to calculate the standard area of skeletal muscle. A validation conducted on 30 other healthy adults was performed to check the accuracy of formulae. Results: Men had a median skeletal muscle area of 155.0cm² (range, 114.0-203.0), compared with 111.7cm² (range, 89.8-139.3) in women (P<0.001). Furthermore, skeletal muscle area significantly correlated with body surface area (BSA) in men (P<0.0001, r²=0.60) and women (P<0.0001, r²=0.78). The formulae to calculate skeletal muscle area were 126.9×BSA-66.2 in men and 125.6×BSA-81.1 in women. The estimated muscle area significantly correlated with actual muscle area in men (P=0.003, r²=0.64) and women (P=0.0001, r²=0.70). Conclusion: Sarcopenia can be defined by the difference between measured data and calculated data using our new formulae.