Muscle Strength and Fasting Insulin Levels Following a Combined Exercise Intervention in Breast Cancer Survivors

Abstract

PURPOSE: Breast cancer treatments may lead to elevated fasting insulin levels and gains in fat mass causing insulin resistance in skeletal muscle and subsequent reductions in muscle strength (MST). Exercise is a non-pharmacologic strategy to improve elevated insulin and reduced MST. In particular, combined aerobic and resistance exercise (CE) reduces insulin levels and improves MST, and has been shown to be superior to resistance or aerobic exercise alone at reducing insulin resistance in patients with type 2 diabetes. The purpose of this study was to determine whether fasting insulin levels and muscle strength (MST) can be improved following a 16-week supervised CE intervention in overweight and obese breast cancer survivors (BCS). We further sought to determine whether exercise-induced changes in fasting insulin are associated with changes in MST. METHODS: Sedentary, overweight/obese (BMI >25 kg/m2) BCS (Stage I-III) were randomized to the Control (CON) or the Exercise (EX) groups. EX underwent supervised CE sessions 3 times per week for 16 weeks. CON was asked to maintain their current level of activity. Fasting serum insulin was measured using enzyme-linked immunoabsorbent assays. MST was assessed from 10-RM (repetition maximum) tests of the leg extension (LE) and chest press (CP) to estimate 1-RM values. Repeated measures ANOVA was used to examine the effects of exercise on MST and insulin. Pearson’s correlations were performed to examine the association between MST changes for each exercise and insulin. RESULTS: At baseline, EX (n=48) and CON (n=46) did not differ by age (53.0 ± 10.4 yr), insulin (35.2 ± 15.4 pmol/L), or BMI (33.5 ± 5.5 kg/m2). Post-intervention, insulin was significantly reduced (-13.5 ± 3.1%) and all MST measures (35.9 ± 6.7%) significantly increased in EX compared to CON (P<0.01). Significant correlations were found between reduced insulin and improved MST for LE (r=-0.67, p=0.001) and CP (r=-0.81, p=0.01) in EX. CONCLUSION: A 16-week supervised CE intervention is an effective approach to reduce insulin, and increase MST, and reductions in insulin are associated with improved muscle strength in BCS. Collectively, this supports the utilization of aerobic and resistance exercise as vital components of cancer rehabilitation following completion of cancer treatment.