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

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.