Skeletal muscle oxidative capacity is an independent predictor of physical activity in smokers with and without COPD

Low physical activity level (PAL) is the strongest predictor of mortality in COPD. COPD is associated with skeletal muscle mitochondrial atrophy. We hypothesized that low muscle oxidative capacity is an independent predictor of PAL and daily steps in current and ex-smokers with and without COPD. Methods: 104 COPDGene participants volunteered: 43 with COPD (GOLD 1-4, n=13/14/8/8) and 61 without. PAL (total energy expenditure/basal metabolic rate) and daily steps were assessed from 5-7 day DynaPort accelerometry. Calf muscle oxidative capacity was assessed at rest from O 2 uptake recovery rate constant ( k ) by near-infrared spectroscopy: greater k reflects greater oxidative capacity. Demographics, anthropometry, spirometry, QCT, hypertension, smoking history, exacerbations, anemia, albumin, mMRC, HADS and SGRQ were entered. Univariate and multiple linear regression determined variables associated with PAL and steps. Results: k was less in COPD (1.5±0.6 min -1 ) than in those without (2.0±0.9 min -1 ; p 1 %pred, mMRC, gender, age, k , exacerbations, albumin and BMI. Multiple linear regression revealed age (β=.30), FEV 1 %pred (.28), mMRC (.27) and k (.18) were independent predictors of PAL (r 2 =.36; p 2 =.40; p Conclusions: Low muscle oxidative capacity is an independent predictor of inactivity in COPD. This highlights the integrative-systemic nature of the disease: therapies to target pulmonary and peripheral COPD pathologies are needed to increase physical activity and quality of life, and reduce comorbidities and mortality. Funding: NIH HL089856, HL089897; SNSF P3SMP3_151705/1.