Differences and commonalities in risk factors for dynapenia and sarcopenia in elderly patients as shown by higher body mass index and bioelectrical impedance-derived phase angle in dynapenia and predominance of osteoporosis in sarcopenia: a retrospective observational study

Abstract Background: Decreased physical function is divided into two categories: dynapenia with retained muscle mass and sarcopenia with loss of muscle mass. The differences in the characteristics of dynapenia and sarcopenia remain unclear. This study was performed to clarify the characteristics and risk factors of dynapenia and sarcopenia in elderly patients. Methods: This study involved 267 patients aged ≥ 65 years (111 men, 156 women). All patients underwent measurement of the (a) skeletal muscle index by bioelectrical impedance, (b) grip strength (index of muscle strength), and (c) walking speed (index of physical ability). Based on the Asian Working Group for Sarcopenia criteria, the patients were categorized into three groups: the control (C) group (n = 77), who had normal (b) and (c) regardless of (a); the dynapenia (D) group (n = 61), who had normal (a) with decreased (b) and/or (c); and the sarcopenia (S) group (n = 129), who had decreased (a) with decreased (b) and/or (c). The characteristics and risk factors in the C, D, and S groups were statistically analyzed. Results: The logistic analysis adjusted for age, sex, and body mass index (BMI) showed that the complication of diabetes, a stroke history, and a fracture history were significant risk factors in both the D and S groups compared with the C group. An osteoporosis-equivalent BMD of the femoral neck or lumbar spine (i.e., BMD of < 70% of the young adult mean) was a risk factor only in the S group, but not in the D group. In the three-group comparison by the Kruskal–Wallis test, the BMI was significantly higher in the D group than in the S group. The phase angle as measured by bioelectrical impedance was higher in the D group than in the S group. Conclusion: The complication of diabetes, a history of stroke, and a history of fracture are common risk factors for dynapenia and sarcopenia. The higher BMI and phase angle in the D group and the predominance of osteoporosis diagnosed by BMD < 70% in the S group suggest qualitative differences between dynapenia and sarcopenia.