Ultrasound assessment of lower limb muscle mass in response to resistance training in COPD

Background: Quantifying the improvements in lower limb or quadriceps muscle mass following resistance training (RT), is an important outcome measure in COPD. Ultrasound is a portable, radiation free imaging technique that can measure the size of superficial muscles belonging to the quadriceps group such as the rectus femoris, but has not been previously used in COPD patients following RT. We compared the responsiveness of ultrasound derived measures of quadriceps mass against dual energy x-ray absorptiometry (DEXA), in patients with COPD and healthy controls following a programme of high intensity knee extensor RT. Methods: Portable ultrasound was used to assess the size of the dominant quadriceps in 45 COPD patients and 19 healthy controls-before, during, and after 8 weeks of bilateral high intensity isokinetic knee extensor RT. Scanning was performed at the mid-thigh region, and 2 indices of quadriceps mass were measured-rectus femoris cross-sectional area (RFcsa) and quadriceps muscle thickness (Q(t)). Thigh lean mass (T-dexa) was determined by DEXA. Results: Training resulted in a significant increase in T-dexa, RFcsa and Q(t) in COPD patients [5.7%, 21.8%, 12.1% respectively] and healthy controls [5.4%, 19.5%, 10.9 respectively]. The effect size for the changes in RFcsa (COPD=0.77; Healthy=0.83) and Q(t) (COPD=0.36; Healthy=0.78) were greater than the changes in T-dexa (COPD=0.19; Healthy=0.26) following RT. Conclusions: Serial ultrasound measurements of the quadriceps can detect changes in muscle mass in response to RT in COPD. The technique has good reproducibility, and may be more sensitive to changes in muscle mass when compared to DEXA.