Cross-sectional associations between trunk muscle composition, back pain, and physical function in the health, aging and body composition study

Background. Associations between trunk muscle composition and physical function have not been examined previously in older adults. We hypothesized that lower trunk muscle area and attenuation (higher fat infiltration) are associated with decreased functional capacity. Methods. The study sample consisted of a biracial cohort of well functioning men (739) and women (788) aged 70-79 from the Pittsburgh site of the Health, Aging and Body Composition (Health ABC) study. Computed tomography was used to measure trunk muscle area (cm²) and muscle attenuation (Hounsfield Unit [HU]) of the following muscle groups: lumbar paraspinals, lateral abdominals, and rectus abdominis. An average score was calculated for both trunk area and attenuation. The Health ABC Physical Performance Battery (PPB) and its individual components (usual and narrow walk, chair stands, and standing balance) were used to measure functional capacity. Results. Linear regression analyses adjusting for demographic factors, height, body fat, thigh muscle composition, disease status, and low back pain (LBP) found that average trunk muscle area was not associated with any element of functional capacity (p > .10), whereas average trunk muscle attenuation was positively associated with the Health ABC Physical Performance Battery (p < .05) and chair stands (p < .001). Participants reporting higher LBP severity during the past year had lower muscle attenuation (p < .001 for trend), but there was no difference in average trunk muscle area according to LBP status. Conclusions. Findings suggest a link between trunk muscle composition and history of LBP as well as reduced functional capacity in older adults. Improving trunk muscle quality may lead to reduced LBP severity and improved functional status.