Taking steps to improve quality of life after cancer: the role of physical activity

The past two decades have generated a convincing body of research describing the benefits of moderate–vigorous physical activity after a cancer diagnosis. Physical activity after a diagnosis of breast or colorectal cancer, in particular, is associated with a reduced risk of disease-specific mortality. A recent meta-analysis estimated these effects as a 28% risk reduction (95% confidence interval [CI]: 0.60–0.85) for breast cancer mortality and a 39% risk reduction (95% CI: 0.40–0.92) for colorectal cancer mortality [1]. Survival benefits of this magnitude are comparable with the reductions in diseasespecific mortality attributed to chemotherapy [2]. Post-diagnosis moderate–vigorous physical activity has been associated with diminished treatment side effects, especially fatigue, and enhanced quality of life [3,4]. Physical activity is also an effective strategy for attenuating the increased risk of comorbid chronic disease that cancer survivors face [5]. The broad range of health benefits for cancer survivors associated with physical activity is widely acknowledged. Most government and nongovernment cancer agencies recommend that, barring some clinical precautions, cancer survivors should engage in the same levels of physical activity that are currently recommended for the general population, i.e. at least 30 min of moderate–vigorous physical activity on most days of the week (e.g. Ref. [6,7]). Despite the compelling benefits associated with physical activity, few cancer survivors are sufficiently active. Various studies have estimated that 22–54% of breast cancer survivors [8] and 26–52% of colorectal cancer survivors [9] accumulate the recommended amount of physical activity each week. However, these estimates are derived from self-report measures, which tend to generate inflated estimates of physical activity among cancer survivors [10]. More recent studies have used accelerometry to characterize the physical activity of cancer survivors. Use of accelerometers to measure physical activity among cancer survivors has demonstrated the very small fraction of the day that is comprised of moderate–vigorous physical activity. Studies of breast cancer survivors have reported approximately 4% [8] and 2% [11] of accelerometer wear time (waking hours of the day) accounts for moderate–vigorous physical activity, while approximately 3% of colon cancer survivors’ time is spent in moderate–vigorous physical activity [9]. Accelerometer studies have also highlighted the large volumes on time spent in sedentary behavior (sitting): between 56% [8] and 78% [11] of the day for breast cancer survivors and 61% of the day for colon cancer survivors [9]. Changing cancer survivors’ physical activity levels is challenging. Behavioral interventions – delivered in person or via telephone or written materials – can achieve modest increases in moderate–vigorous physical activity; however, these are often short lived and diminish post-intervention [12]. Most interventions delivered to cancer survivors focus on increasing moderate–vigorous aerobic activity [13] although there is also a comprehensive body of literature pertaining to strength training, particularly among breast and prostate cancer survivors [14]. Numerous studies examining the effects of yoga on health outcomes in cancer survivors have been conducted, with a systematic review and meta-analysis concluding that this mode of physical activity improves psychological health outcomes and reduces fatigue [15]. Research focused on other components of the physical activity spectrum is emerging. For example, high-intensity interval training (HIIT) has been administered to cancer survivors with promising results [16]. This type of exercise training has specific benefits for cardiorespiratory fitness and body composition, both of which are adversely affected by cancer therapies. Reducing sedentary behavior may be another strategy for improving health outcomes in cancer survivors. It has been suggested that targeting sedentary behavior may be a more feasible and appropriate approach for cancer survivors, including those for whom moderate–vigorous physical activity is contraindicated [17]. It is important that future research continues to examine the potential benefits provided by physical activity across the full spectrum, from reducing sedentary behavior through to HIIT training. Such research will help guide health care providers to tailor advice about physical activity to their clients, according to their needs. The personal preferences of cancer survivors must also be taken into consideration when providing guidance in relation to becoming more physically active. Enabling cancer survivors to be actively involved in this element of their rehabilitation is essential for long-term maintenance of behavioral change. Finally, it has been highlighted by others that there is a role to be played by health care providers, family members, community-based organizations,