Quadriceps muscle phenotype varies widely between patients with chronic obstructive pulmonary disease (COPD) and cannot be determined without muscle biopsy. We hypothesised that measures of skeletal muscle adiposity could provide noninvasive biomarkers of muscle quality in this population.In 101 patients and 10 age-matched healthy controls, mid-thigh cross-sectional area, percentage intramuscular fat and skeletal muscle attenuation were calculated using computed tomography images and standard tissue attenuation ranges: fat -190– -30 HU; skeletal muscle -29–150 HU.Mean±sd percentage intramuscular fat was higher in the patient group (6.7±3.5% versus 4.3±1.2%, p = 0.03). Both percentage intramuscular fat and skeletal muscle attenuation were associated with physical activity level, exercise capacity and type I fibre proportion, independent of age, mid-thigh cross-sectional area and quadriceps strength. Combined with transfer factor of the lung for carbon monoxide, these variables could identify >80% of patients with fibre type shift with >65% specificity (area under the curve 0.83, 95% CI 0.72–0.95).Skeletal muscle adiposity assessed by computed tomography reflects multiple aspects of COPD related muscle dysfunction and may help to identify patients for trials of interventions targeted at specific muscle phenotypes.

There is insufficient evidence to determine the safety and effectiveness of exercise for patients with cancer cachexia. Randomised controlled trials (i.e., preferably parallel-group or cluster-randomised trials) are required to test the effectiveness of exercise in this group. There are ongoing studies on the topic, so we will update this review to incorporate the findings.

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Introduction Quadriceps muscle impairment is an important complication of COPD occurring in mild as well as more advanced disease 1 . This is driven by physical inactivity and can include muscle atrophy and/or a shift towards a less aerobic phenotype with reduced Type I fibre proportions and a reduction in capillarity and oxidative enzymes. 2 We hypothesised that physical inactivity in COPD patients would be associated with intramuscular fat and that this could potentially be a non-invasive and non-volitional marker of muscle quality. Methods Mid-thigh cross-sectional area (MT CSA ), percentage intramuscular fat and skeletal muscle attenuation (Hounsfield units [HU]) were assessed using computed tomography (CT) image analysis. Tissues were differentiated using standard attenuation ranges; fat: -190 to -30HU and skeletal muscle: -29 to 150HU Quadriceps isometric maximal voluntary contraction (QMVC) was measured using a strain gauge. Fat-free mass index (FFMI) and the impedance ratio (Z 200 /Z 5 ) were determined by bioelectrical impedance analysis. Daily step count and physical activity level (PAL) were recorded over 6 days using a multisensory biaxial armband accelerometer (SenseWear, Bodymedia; Pittsburgh, US). Results 69 patients (mean (SD), 65(8) years, FEV 1 44(21)% predicted, 54% male) participated in the study. Mean (SD) daily step count was 4502 (3274) steps; physical activity level 1.4 (0.2); QMVC 25.2 (5.9) kg; FFMI 17.3 (2.3)kg/m 2 , MT CSA 178 (43)cm 2 . Using a stepwise regression model incorporating MT CSA , intramuscular fat, skeletal muscle attenuation, QMVC, and FFMI as independent variables, only skeletal muscle attenuation (HU) was retained as an independent correlate of daily step count (r=0.34, p=0.006). In a similar model, percentage intramuscular fat was the only independent predictor of physical activity level (r=0.37, p=0.002). The bioelectrical impedance ratio (Z 200 /Z 5 ) was also associated with skeletal muscle attenuation (r=0.40, p<0.001) in this cohort. Conclusion These data suggest that muscle "quality" assessed using CT is independently associated with daily physical activity and may therefore have potential as a biomarker in this area.1. Shrikrishna D et al. Quadriceps wasting and physical inactivity in patients with COPD.