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

Abstract

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 (Qt). Thigh lean mass (Tdexa) was determined by DEXA.

Results: Training resulted in a significant increase in Tdexa, RFcsa and Qt 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 Qt (COPD=0.36; Healthy=0.78) were greater than the changes in Tdexa (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.

Trial registration: http://www.controlled-trials.com (Identifier: ISRCTN22764439).

Figure 1

Ultrasound image of the quadriceps. Sample scan of a study participant showing (a) Image at mid-thigh region, (b) RF_csa, and (c) Q_t.

Figure 2

Baseline relationships between ultrasound and DEXA measured indices of quadriceps size (a) T_{dexa VS.} RF_csa and (b) T_dexa vs. Q_t.

Figure 3

Baseline relationships between quadriceps strength and ultrasound and DEXA measured indices of quadriceps mass (a) QMVC vs. RF_csa, (b) QMVC vs. Q_t, and (c) QMVC vs. T_dexa.

Figure 4

Percentage change from baseline in ultrasound and DEXA measured indices of quadriceps mass in (a) COPD, and (b) Healthy. Data presented as Means (SEM) RF_csa: Rectus femoris cross-sectional area measured by ultrasound, Q_t: Quadriceps muscle thickness measured by ultrasound, T_dexa: Thigh lean mass measured by DEXA, Wilcoxon Signed rank test: *** p ≤ 0.0001; ** p < 0.001; * p < 0.01, significantly different from baseline.

Figure 5

Relationships between training induced changes in quadriceps strength (ΔQMVC) and (a) ΔRF_csa, (b) ΔQ_t, and (c) ΔT_dexa.

Figure 6

The relationship between training-induced changes in ultrasound and DEXA indices of quadriceps mass (a) ΔT_dexavs. ΔRF_csa, and (b) ΔT_dexavs. ΔQ_t.

Figure 7

Bland-Altman plots of the inter-occasion reproducibility of ultrasound measurements (a) RF_csaand (b) Q_t.

Figure 8

Bland-Altman plots of the inter-operator reproducibility of ultrasound measurements (a) RF_csa: Operator A vs. Operator B, (b) Q_t: Operator A vs. Operator B, (c) RF_csa: Operator A vs. Operator C, and (d) Q_t: Operator A vs. Operator C.