Bioimpedance phase angle is independently associated with myosteatosis: The Shizuoka study

Phase angle (PhA) calculated from the resistance and reactance measured using a bioimpedance device was suggested to represent the degree of fat deposition in muscle (myosteatosis), though no direct evidence is available. We aimed to clarify the possible association between PhA and skeletal muscle myosteatosis in community-dwelling middle-aged to older adults.

Participants consisted of 424 Japanese (aged ≥50 years). Leg PhA and skeletal muscle mass index (SMI) were obtained by bioelectrical impedance analysis. The mean attenuation values and cross-sectional area of the mid-thigh skeletal muscle were calculated from computed tomography images and considered as indexes of myosteatosis and skeletal muscle mass, respectively.

Leg PhA was positively associated with SMI, and cross-sectional area and mean attenuation value at mid-thigh. Multiple regression analysis adjusted for possible covariates identified leg PhA (β = 0.214) and SMI (β = 0.260) as independent factors of mid-thigh muscle cross-sectional area (P < 0.001), while leg PhA (β = 0.349, P < 0.001) but not SMI (P = 0.645) was associated with mean attenuation value. Similar results were observed in the analysis in the older (≥65 years) subpopulation. The combination of low SMI and low leg PhA showed stepwise association with cross-sectional area, while only individuals with low leg PhA had lower mean attenuated value.

Leg PhA was independently associated with mean attenuated value of the mid-thigh skeletal muscle, suggesting that the assessment of PhA in combination with SMI could provide additional information for the evaluation of muscle properties.