Purpose: Midthigh intramuscular fat (IF), a feature of reduced muscle quality, is an important predictor of self-reported mobility loss in the elderly. This study compared measures of muscle strength, mass, IF, and mobility in patients with chronic obstructive pulmonary disease (COPD) and healthy subjects. Associations between measures of muscle strength, mass, IF, and mobility were explored.
Methods: Knee extensor muscle strength was assessed with an isokinetic dynamometer. Cross-sectional area and IF of the thigh muscles were measured with computerized tomography. Mobility was assessed with the repetitive sit-to-stand, self-selected gait speed, and 6-minute walk tests.
Results: Patients with COPD (n = 21, age 71.3 ± 8.1 years, and a percentage predicted force expiratory volume in 1 second of 47.2 ± 12.9) and 21 healthy subjects matched for age (67.4 ± 8.6 years), gender, and body mass participated in the study. Patients with COPD showed reduced average knee extensor strength (29%, P = .016) cross-sectional area of the thigh muscles (17%, P = .007) and mobility measures (~23%, P ≤ .001). Knee extensor and flexor IF was 2-folds greater in people with COPD (P ≤ .005). Measures of knee extensor muscle strength, mass, and IF were not associated with mobility measures.
Conclusions: Compared with healthy controls, patients with moderate to severe COPD show marked deficits in muscle strength, mass, quality, and mobility. More studies with larger sample size are required to elucidate whether any of these muscle deficits can explain mobility impairments in COPD.