Insulin resistance is associated with skeletal muscle weakness in COPD.

BACKGROUND AND

OBJECTIVE

Quadriceps weakness is seen across all GOLD stages of COPD and is associated with increased morbidity and mortality. As quadriceps weakness is only weakly associated with FEV1 , mechanisms other than airflow obstruction are implicated. We tested the hypothesis that insulin resistance contributes to skeletal muscle weakness in people with stable COPD.

METHODS

Fifty-one COPD patients (no exacerbations preceding 6 weeks, no rehabilitation preceding 3 months) without known diabetes mellitus underwent assessment of skeletal muscle, including measurement of quadriceps maximal voluntary contraction (QMVC). Physical activity was measured for 7 days using a multisensory biaxial accelerometer armband. Insulin resistance (HOMA2 IR) was calculated from fasting blood glucose and insulin concentrations.

RESULTS

QMVC was 30 ± 13 kg (74 ± 25% predicted) and 16 (31%) participants had quadriceps weakness. There was a negative univariate correlation between HOMA2 IR and QMVC (r = -0.446, P = 0.002). HOMA2 IR was greater in people with quadriceps weakness (1.59 ± 0.99) than in those without (1.11 ± 0.55, P = 0.032). On multivariate analysis, with age, sex, weight, BODE index and step count per day included in the model, a one-unit increase in insulin resistance was associated with a 5.9 (2.0-9.8)-kg decrease in QMVC (P = 0.004) and a 4.2 (1.3-14.3)-fold increased risk of quadriceps weakness (P = 0.02).

CONCLUSION

Insulin resistance is associated with skeletal muscle weakness in COPD, independent of potential confounders. Further studies are required to explore underlying mechanisms and determine whether insulin-sensitizing drugs could augment pulmonary rehabilitation in building skeletal muscle strength in COPD.