16-week Combined Exercise Training Improves Muscle Quality In Breast Cancer Survivors

Abstract

Cancer treatment is associated with skeletal muscle loss, leading to reductions in muscular strength and functional capacity. Exercise training can improve muscular strength in breast cancer survivors (BCS), even without skeletal muscle hypertrophy. Factors such as improved muscle quality (MQ) may contribute to improved function but limited data are available in BCS. PURPOSE: To investigate the effects of exercise training in BCS and healthy controls (HC) on MQ, cross-sectional area (CSA), muscular strength, and physical function and to examine associations between these measures. METHODS: BCS (n = 31, 54 [11] y, 27.5 [5.0] kg/m2) and HC (n = 15, 54 [8] y, 29.3 [4.9] kg/m2) underwent a 16-week combined aerobic and strength training intervention 3x/week for one-hour at a community-based exercise program for BCS. Isokinetic peak torque and maximal voluntary isometric contraction (MVIC) were assessed in the knee extensor muscles. Ultrasound was used to determine muscle CSA and echo intensity of the vastus lateralis. Functional parameters included 6-minute walk (6MWT) and timed up and go (TUG). All measures were taken pre- and post-intervention and were analyzed using a 2x2 repeated measures ANOVA and Pearson’s correlations. Data are mean change [SD]. RESULTS: Echo intensity decreased with training overall (-5.4 [24.6], p = .046), indicating higher MQ, with no change in CSA. A time x group interaction for MVIC showed increased strength after training in BCS (+11.0 [17.2] N·m, p = .001) but not HC (-2.6 [23.7] N·m, p = .673). Physical function improved in both groups (TUG -0.5 [0.9] sec, p < .000; 6 MWT 35.5 [45.0] m, p < .001). At baseline, echo intensity was inversely correlated with MVIC, TUG and 6 MWT in HC only (r = -0.451-0.490, all p < 0.05). No associations in the changes of these variables were observed with training. CONCLUSION: A 16-week exercise intervention improved MQ and functional measures in both BCS and HC, while MVIC increased only in BCS. MQ was moderately correlated with functional and strength measures at baseline in HC but not in BCS. The lack of correlations in BCS suggest that other factors, possibly neural adaptations, may be responsible for the improvements in muscular strength and functional measures seen after an exercise intervention rather than improvements in MQ and CSA.