Literature Review
The authors performed searches in PubMed and Google Scholar up to July 2013 using the following key words interchangeably: physical activity, cancer, exercise, cancer survivors, and health.
After reviewing the literature related to physical activity among cancer survivors, the authors identified several areas of research that could aid in the promotion of physical activity among this population. Where appropriate, findings were summarized from review studies, as opposed to single empirical studies.
Physical Activity Before and During Cancer Treatment
Loprinzi & Cardinal (2012a) reviewed the extant literature related to the effects of physical activity on side effects associated with cancer treatment. Their review of exercise interventions showed that physical activity during cancer treatment may help to mitigate many of the side effects associated with cancer treatment, including fatigue, depression, decreased muscular strength, decreased aerobic capacity, weight gain, and impaired quality of life. In addition, some studies suggested that physical activity participation may increase the rate of completion of cancer treatment (Courneya et al., 2007). Emerging research indicated that high levels of physical activity preoperatively may reduce the risk of postoperative complications (Tatematsu, Park, Tanaka, Sakai, & Tsuboyama, 2013). Brown, Loprinzi, Brosky, and Topp (2014) have shown that prehabilitation exercise (i.e., exercise before treatment or surgery) may influence psychological constructs, such as outcome expectations, which may help facilitate the rehabilitation process.
Biologic Markers
Löf et al. (2012) and Ballard-Barbash et al. (2012) published review studies examining the effects of physical activity on biomarkers in cancer survivors. Löf et al. (2012) evaluated nine randomized, controlled trials and results, although mixed, showed that physical activity was associated with insulin, insulin-like growth factor (IGF)-I, IGF-II, insulin-like growth factor binding protein (IGFBP)-3, and C-reactive protein (CRP) in breast cancer survivors, with no associations occurring for interleukins. Ballard-Barbash et al. (2012) reviewed four epidemiologic studies and found that self-reported physical activity was inversely associated with leptin, IGF-I, and CRP, with no associations found for C-peptide, IGFBP-3, the ratio of IGF-I to IGFBP-3, or serum amyoid A. Although findings are mixed, these results suggest that physical activity is favorably linked with biomarkers associated with cancer recurrence among cancer survivors.
In an empirical study, Järvelä et al. (2013) showed that among long-term survivors of childhood acute lymphoblastic leukemia, physical activity may alleviate excess burden of cardiovascular disease morbidity by improving endothelial function. Showing similar beneficial effects, Elme et al. (2013) demonstrated in an empirical study that among breast cancer survivors, self-reported physical activity was inversely associated with waist circumference, triglyceride, insulin, and metabolic syndrome, but positively associated with high-density lipoprotein (HDL) cholesterol. However, in a randomized, controlled trial among postmenopausal breast cancer survivors, Jones et al. (2013) did not find an effect between the intervention and control groups for tumor necrosis factor (TNF)-alpha, interleukin-6 (IL-6), or CRP; however, participants who reached 80% of the intervention goal had lower IL-6 levels, which suggests that higher physical activity levels may help to reduce biomarkers associated with cancer development.
To the authors' knowledge, only one nationally representative study of U.S. cancer survivors used an objective measure of physical activity and examined its association with biomarkers (Lynch et al., 2010). However, in that study, the only biomarker investigated was adiposity (i.e., waist circumference and body mass index [BMI]), with the results showing an inverse association between adiposity and physical activity among breast cancer survivors.
Health Outcomes
Fong et al. (2012) published a meta-analysis of randomized, controlled trials and reported that, among cancer survivors, physical activity is associated with improvements in bench press, leg press, fatigue, depression, BMI, peak oxygen consumption, peak power output, distance walked in six minutes, handgrip strength, and quality of life. Similar results were found in a systematic review and meta-analysis by Craft, Vaniterson, Helenowski, Rademaker, and Courneya (2012) that reported that physical activity has a modest positive effect on depression symptoms and is associated with reduced pain, fatigue, and improved quality of life. Inoue-Choi, Lazovich, Prizment, and Robien (2013) and McClellan (2013) also demonstrated a positive effect of physical activity on physical functioning and quality of life.
Cancer Recurrence and Mortality
Loprinzi, Cardinal, Winters-Stone, et al. (2012) reviewed the literature and reported six studies examining the influence of physical activity on breast cancer-related mortality, with two of those studies also examining breast cancer recurrence. Findings showed that four of the six studies demonstrated a protective effect of physical activity on breast cancer-related mortality, and the two breast cancer recurrence studies reported nonsignificant risk reductions. Fontein et al. (2013) identified 12 studies that examined the association between physical activity and breast cancer-related mortality and showed that eight of those studies found a protective effect of physical activity in reducing death from breast cancer. Although likely complex, the mechanism through which physical activity could have a protective effect on cancer recurrence and cancer-related mortality may be found in its influence on body weight (Davies, Batehup, & Thomas, 2011), with excess body weight being a strong risk factor for cancer recurrence and death (Ligibel, 2012). Other potential mechanisms include physical activity-induced changes in hormones, markers of insulin resistance, and inflammation (Loprinzi, Cardinal, Smit, et al., 2012), with emerging research also suggesting that physical activity may help to reduce breast and prostate cancer risk and recurrence through suppression of vasoactive intestinal peptide (VIP) by increasing anti-VIP antibodies (Veljkovic et al., 2011).
Physical Activity Levels
In general, cancer survivors engage in less physical activity than people who were never diagnosed with cancer (Smith, Nolan, Robison, Hudson, & Ness, 2011), with one estimate showing that about 32% of cancer survivors report no leisure-time physical activity (Underwood et al., 2012). Loprinzi, Lee, and Cardinal (2013) described the accelerometer-determined activity patterns of U.S. cancer survivors and reported that only 13% were sufficiently active (i.e., engage in at least 150 minutes per week of moderate-intensity or at least 75 minutes per week of vigorous-intensity physical activity). In addition, obese cancer survivors, when compared to nonobese survivors, engaged in less moderate-to-vigorous physical activity. Mason et al. (2013) demonstrated that physical activity levels tend to decline with age among breast cancer survivors.
Physical Activity Preferences
In a population-based sample of kidney cancer survivors, Trinh, Plotnikoff, Rhodes, North, and Courneya (2012) described physical activity preferences. Encouragingly, more than 80% felt they were able to participate in physical activity, and more than 70% indicated that they were interested in doing so. To help inform the development of physical activity interventions, those cancer survivors indicated that they wanted to receive physical activity-related information from fitness experts at the cancer center (56%), receive printed information (50%), exercise at home (52%), and walk in the summer (64%) and winter (48%).
Strategies to Promote Physical Activity
Several studies have demonstrated use of the social cognitive theory (SCT) for promoting physical activity behavior among cancer survivors (Brunet & Sabiston, 2011; Phillips & McAuley, 2013; Short, James, & Plotnikoff, 2013). SCT postulates a reciprocal association between cognition, behavior, and environmental influences, with behavior affected by the interactions. Key constructs from SCT (e.g., self-efficacy, outcome expectations, social support) play an important role in influencing the activity behavior of cancer survivors. In addition to SCT, key constructs from the theory of planned behavior, including individual, normative, and control beliefs, have been associated with physical activity among breast cancer survivors (Bélanger, Plotnikoff, Clark, & Courneya, 2012; Vallance, Lavallee, Culos-Reed, & Trudeau, 2012). The parameters of the theory of planned behavior influence an individual's behavioral intention, ultimately affecting behavioral engagement. The transtheoretical model is a stage-matched framework that examines an individual's readiness to change behavior, which has been used effectively to promote physical activity among cancer survivors (Husebo, Dyrstad, Soreide, & Bru, 2013).
Evidence exists among older colorectal cancer survivors that participating in physical activity in a social setting may be particularly important for improving or maintaining mental health (Thraen-Borowski, Trentham-Dietz, Edwards, Koltyn, & Colbert, 2013), with the act of attending community-based wellness workshops also likely to have beneficial effects on physical activity and health-related quality of life (Spector, Battaglini, Alsobrooks, Owen, & Groff, 2012). Proper physical activity promotion among older adult cancer survivors appears to be safe and feasible (Klepin, Mohile, & Mihalko, 2013; Rajotte et al., 2012), with findings, although limited, also showing that physical activity may be safe and effective among patients with advanced-stage cancer (Albrecht & Taylor, 2012). However, healthcare providers should refer to other sources (Burr, Shephard, & Jones, 2012) for clinical risk assessment before recommending physical activity to cancer survivors.
In addition to tailoring a physical activity program to enhance psychosocial constructs, healthcare providers should understand physical activity-related barriers that cancer survivors may encounter. Cancer treatment may influence a patient's perceptions, beliefs, and attitudes toward his or her body, which in turn may influence his or her desire or motivation to engage in physical activity. Research has shown that, among breast cancer survivors, regular engagement in physical activity may help to restore positive body-related perceptions (Brunet, Sabiston, & Burke, 2013) and help regain control and reduce distress associated with cancer (Maley, Warren, & Devine, 2013). Other common physical activity-related barriers and concerns include fear of movement and perceived risk of injury, which may negatively influence mental health outcomes (e.g., depression) among cancer survivors (Velthuis et al., 2012). Another reported barrier is pain associated with movement (Prinsloo, Gabel, Lyle, & Cohen, 2013; Sabiston, Brunet, & Burke, 2012). A study by Sabiston et al. (2012) demonstrated that physical activity may mediate the relationship between pain and depression among cancer survivors, suggesting that physical activity may serve as a therapeutic strategy to manage and treat pain and depression. An emerging area of research has focused on the neuromodulation of cancer pain (Prinsloo et al., 2013), with initial research showing that brain-based learning may influence neuroplasticity (i.e., changes in neural pathways and synapses) and alter perceptions of pain. Although additional research is needed in this emerging area of research, physical activity participation may alter perceptions of pain through its established neuroplasticity effects (Hötting & Röder, 2013).
Those findings demonstrate that healthcare providers can effectively promote physical activity to cancer survivors by employing evidence-based strategies with the use of established theoretical models. For example, teaching cancer survivors how to enlist social support, use behavioral and cognitive skills, and enhance their perceptions of self-efficacy may serve as effective strategies to promote physical activity. Healthcare providers may want to employ those strategies in person; however, evidence indicates that web-based physical activity interventions may be feasible and acceptable among younger cancer survivors (Rabin, Dunsiger, Ness, & Marcus, 2011). Future research investigating feasible methods for physical activity promotion is needed because patients with cancer are the least likely to be advised by their physicians to exercise, when compared to healthy patients, overweight patients, or patients with other chronic diseases (e.g., diabetes) (Barnes & Schoenborn, 2012). Although speculative, healthcare providers may selectively promote physical activity based on their perception of whether they think the patient would be successful in losing weight and adhering to a physical activity program. However, a sensible strategy would be for healthcare providers to promote physical activity to all patients when feasible, as research indicates that some healthcare providers have limited accuracy in predicting which patients will improve weight and physical activity levels (Chisholm, Hart, Mann, Harkness, & Peters, 2012; Pollak et al., 2012).
Healthcare providers should use caution when promoting physical activity to certain subgroups of cancer survivors. Specific precautions for cancer survivors include delaying exercise for those with severe anemia, avoiding public gyms and public pools for those with compromised immune function, avoiding chlorine exposure to irradiated skin for those undergoing radiation, and avoiding pools for those with indwelling catheters or feeding tubes (Rock et al., 2012). In addition, those with significant peripheral neuropathies or ataxia may wish to use a stationary reclining bicycle instead of walking on a treadmill.