Should resistance exercise be recommended during breast cancer treatment?

Epidemiological evidence has pointed to the benefits of physical activity in reducing breast cancer risk, which in turn has prompted the American Cancer Society (ACS) to make specific recommendations for adopting a life style of physical activity as a guideline for cancer protection. There is also evidence for benefits of physical activity during and after cancer treatments of chemotherapy and radiation therapy. The ACS recommendations for exercise as prevention and for exercise during/after cancer treatment are the same: "that adults engage in at least 30 min of moderate to vigorous physical activity, above usual activities, on 5 or more days of the week; 45-60 min of intentional physical activity are preferable." These recommendations suggest participation in aerobic types of physical activity (e.g. brisk walking, biking). Effects of resistance exercise were not addressed specifically by the ACS but have been found to increase lean body mass in patients undergoing cancer treatment. Also, many women preferred resistance exercise over aerobic exercise during breast cancer treatment. In response to strenuous resistance exercise, however, muscle satellite (progenitor) cells are activated to reenter the cell cycle and proliferate. Satellite cells can then contribute their nuclear material into the fiber to facilitate muscle repair, regeneration, and hypertrophy. Cancer therapy damages rapidly dividing cells and thus has the potential to target satellite cells that enter into the cell cycle. Although satellite cells are self-renewing, they are not completely replenished over the lifespan so losses in this progenitor population via resistance exercise and cancer therapy may impair the maintenance of muscle mass with aging. Before recommending resistance training during breast cancer treatment, we must have more information about cancer treatment effects on activated satellite cells in human studies.