Usefulness of the bioimpedance phase angle in identifying older adults with poor muscle properties: The Shizuoka study

Abstract

Background & aims: The bioimpedance phase angle (PhA) was suggested to represent muscle deterioration. This study investigated whether segmental PhA was superior to whole-body PhA in the association with physical performance measures and whether it was useful for identifying older adults with poor muscle characteristics.

Methods: This cross-sectional study included 1779 community-dwelling individuals aged 65 years or older. Segmental PhA was measured by bioelectrical impedance analysis. Physical performance was assessed using handgrip strength, gait speed, and the five-times chair-stand test. We used computed tomography images at the midthigh to assess skeletal muscle mass and fat infiltration into the muscle.

Results: Leg PhA was significantly associated with conventional physical performance measures compared with the PhA of other body segments. Among participants with low leg PhA (<4.5° in men, <4.0° in women), 64 % had a normal physical performance. Participants were then divided into four groups according to low leg PhA and low physical performance, revealing that the mid-thigh skeletal muscle cross-sectional area (representative of muscle mass) was significantly lower in groups with low physical performance (β = -0.12, P < 0.001), low leg PhA (β = -0.10, P < 0.001), and both (β = -0.17, P < 0.001). In contrast, the mean attenuation value, representing fat infiltration into the muscle, decreased in groups with low leg PhA (β = -0.22, P < 0.001) and both low leg PhA and low physical performance (β = -0.19, P < 0.001), but not in the group with only low physical performance (β = -0.03, P = 0.330).

Conclusions: Leg PhA may help identify individuals with reduced skeletal muscle mass and increased fat infiltration into the muscle who were overlooked by conventional physical performance assessments alone.

Keywords: Bioimpedance analysis; Older adults; Phase angle; Physical performance; Skeletal muscle mass.