Resistance Exercise Trims the Fat and Puts Some Muscle into Cancer Survivorship

Abstract

Elucidating the mechanisms through which exercise improves how patients with cancer feel, function, and survive is one of oncology’s most provocative unanswered questions. Observational studies have reported that survivors of cancer who lose muscle mass or gain adipose tissue report poorer quality of life and are at an elevated risk for physical impairment, treatment-related toxicity, disease recurrence or progression, and death [1]. Skeletal muscle and adipose tissue influence myriad aspects of whole-body metabolism, supporting the hypothesis that these tissues may have a causal effect on clinically relevant outcomes in survivors of cancer [2]. However, the degree to which resistance exercise can meaningfully remodel body composition in survivors of cancer during and after treatment has been inconsistent in the literature. In this issue of Sports Medicine, Clifford et al. [3] report the results of a systematic review and meta-analysis of the effect of resistance training on body composition during and after cancer treatment. Their review identified 15 randomized trials that compared resistance training and a non-exercise control group in 1368 survivors of cancer. All studies used dual-energy X-ray absorptiometry to quantify changes in body composition. Among the studies that reported sufficient detail, the average exercise program was 2.5 days per week and prescribed five to ten resistance training exercises, with 2.5 sets of ten repetitions of each exercise at an intensity of 70% of the 1-repetition maximum; the average program length was 32.7 weeks. These exercise prescription program variables are generally consistent with the American College of Sports Medicine recommendations for promoting muscle hypertrophy in healthy adults [4]. During cancer treatment, the resistance training group, as compared with the control group, did not statistically significantly change lean mass (+ 0.71 kg; 95% confidence interval [CI] − 0.04 to 1.45; I2 = 0.0%) or fat mass (0.00 kg; 95% CI − 5.31 to 5.30; I2 = 0.0%). The authors concluded that this evidence was of low certainty because of the risk of bias and the small sample size (three studies for lean mass [n = 200] and two studies for fat mass [n = 160]). After cancer treatment, the resistance training group, as compared with the control group, statistically significantly increased lean mass (+ 0.41 kg; 95% CI 0.05–0.76; I2 = 47.1%) and decreased fat mass (− 0.59 kg; 95% CI − 1.05 to − 0.12; I2 = 69.1%). The authors concluded that this evidence was of low certainty because of the risk of bias and treatment effect heterogeneity. Perhaps the most critical finding of this systematic review and meta-analysis is the modest resistance traininginduced changes to lean and fat mass. The magnitude of the observed changes in the body composition of survivors of cancer appears smaller than that in meta-analyses of resistance training conducted in other populations, such as older adults, despite having similar resistance training exercise prescriptions [5]. Randomized trials have demonstrated that resistance training improves the quality of life and preserves the physical function of survivors of cancer [6]. However, whether the magnitude of the reported change in lean and fat mass is sufficiently large to confer benefits on objectively measured clinical endpoints, such as treatment completion, disease recurrence, or death, remains unknown. Clifford et al. [3] attribute the modest lean and fat mass changes to a blunted anabolic response to resistance training in survivors of cancer. The authors raise the possibility that survivors of cancer may require an exercise prescription of resistance This comment refers to the article available at https:// doi. org/ 10. 1007/ s4027902101542-6.