The associations of body mass index, bioimpedance spectroscopy-based calf intracellular resistance, single-frequency bioimpedance analysis and physical performance of older people

BACKGROUND: Bioimpedance skeletal muscle indices (SMI) are used as a surrogate for skeletal muscle mass, but their associations with physical functioning and obesity need further evaluation. AIMS: To compare the associations of body mass index (BMI), bioimpedance spectroscopy-based calf intracellular resistance (Cri-SMI), and single-frequency bioimpedance analysis (SF-SMI) indices with physical performance and the functioning of community-dwelling older people at risk of or already suffering from sarcopenia. METHODS: Pre-intervention measurements of the screened subjects and the participants of the Porvoo sarcopenia trial (N = 428) were taken. Cri-SMI, whole-body SF-SMI, and BMI were related to hand-grip strength, walking speed, short physical performance battery (SPPB), and the physical component of the RAND-36. RESULTS: Among the older people (aged 75–96), Cri-SMI correlated inversely with age (men r = - 0.113, p < 0.001; women r = - 0.287, p < 0.001), but positively with SPPB (r = 0.241, p < 0.001) and the physical component of the RAND-36 (r = 0.114, p = 0.024), whereas BMI was inversely associated with SPPB (r = - 0.133, p < 0.001) and RAND-36 (r = - 0.286, p < 0.001). After controlling for age, gender, and comorbidity, one unit of Cri-SMI (cm(2)/Ω) was associated with a 3.3-fold probability of good physical performance (SPPB ≥ 9 points, OR = 3.28, p < 0.001) and one unit of BMI (kg/m(2)) decreased the respective probability 4% (OR= 0.96, p = 0.065). Physical inactivity partly explained the negative association of BMI. When Cri-SMI and BMI were controlled for, a 1% difference in Cri-SMI was associated with a 0.7% (p < 0.001) higher probability of good performance, the respective figure being - 2.2% (p = 0.004) for BMI. The associations of SF-SMI with physical functioning indices were insignificant. CONCLUSIONS: Independent of each other, Cri-SMI was positively and BMI was inversely associated with the physical performance and functioning of community-dwelling older people who were at risk of or already suffering from sarcopenia. We found no association between SF-SMI and physical functioning.