Examining the relationship between D3Cr muscle mass, physical performance, and functional limitation in postmenopausal women.

BACKGROUND: The D3-creatine (D3Cr) dilution method provides a non-invasive and accurate assessment of muscle mass. Our objective was to examine the relationship between D3Cr muscle mass, objective measures of physical performance, and self-report physical function postmenopausal women. METHODS: We enrolled 2382 women from the Women's Health Initiative (WHI) cohort to complete the D3Cr dilution protocol. The primary exposure variable is D3Cr muscle mass, examined as an absolute value in kilograms (kg) and relative to total body weight (D3Cr muscle mass/body mass in kg). Tertiles of absolute D3Cr muscle mass and D3Cr muscle mass/body mass were examined. The primary outcomes were objective measures of physical performance, including balance, gait speed, chair stands, and hand grip strength. The short physical performance battery (SPPB) provided an overall measure of physical performance. Physical function and functional limitation were assessed via self-report questionnaire. The association between D3Cr muscle mass/kg (in tertiles) and functional limitation was assessed in multivariate logistic regression analyses. RESULTS: The mean age of the study sample was 84.5 years. Average D3Cr muscle mass in the study population was 17.6 kg (SD = 4.0) and 26.1% (SD = 5.8). Mean SPPB scores were higher across higher tertiles of D3Cr muscle mass (7.0 in T1, 7.8 in T3). Women with low muscle mass were more likely to self-report prevalent limitation in physical function. CONCLUSION: In this large cross-sectional study of older women, there was a strong relationship between low D3Cr muscle mass, physical performance, and functional limitation.