Five of the 11 studies examined early-stage breast cancer patients receiving chemotherapy, and three studies examined mixed cancer patients after high-dose chemotherapy and bone marrow/stem cell transplantation. One study each examined breast cancer patients receiving radiation therapy, prostate cancer patients on hormone therapy, and mixed cancer patients experiencing severe fatigue on mixed treatments. Study designs consisted of four randomized clinical trials (RCTs) with usual-care or wait-list controls, two RCTs with placebo (i.e., stretching) and usual-care controls, one RCT comparing two exercise frequencies (i.e., 3 versus 5 d per week) with usual-care controls, one pretest-posttest design with two matched controls (i.e., nonexercising cancer patients and exercising healthy persons), and three pretest-posttest designs with no controls. The sample sizes ranged from 5 to 70 with a mean of 33. Supervised exercise programs were reported in nine studies, whereas two studies reported unsupervised, home-based exercise programs. Nine studies tested an aerobic exercise intervention (six cycling, two walking, and one self-selected), whereas two studies examined resistance training. All studies followed traditional exercise prescription guidelines in terms of frequency, intensity, and duration of exercise, but the length of the intervention was ≤12 wk in all of the studies and < 10 wk in six of the studies. The studies examined a wide variety of biopsychosocial outcomes, with the most common being functional capacity (seven studies). Three studies each examined body composition, mood states, and fatigue.
Overall, the results of these studies consistently demonstrate that an exercise intervention during cancer treatment has many positive effects. In fact, all 11 studies showed statistically significant results in favor of the hypothesis despite small sample sizes. The physical and functional benefits that have been demonstrated include improvements in functional capacity, muscular strength, body composition, hematological indices, sleep patterns, nausea, fatigue, pain, and diarrhea. The psychological and emotional benefits that have been demonstrated include positive changes in personality functioning, body satisfaction, mood states (including anxiety, anger, and depression), and general QOL.
Results of the reviewed studies are promising and suggest that exercise during cancer treatment may improve many biopsychosocial outcomes. The primary foci of these studies, however, has been on the biologic mechanisms that may underlie improved QOL (e.g., physiological and functional fitness), actual symptom occurrence (e.g., fatigue, pain, sleep), and psychological distress (e.g., depression, anxiety). Very little research has addressed the possible psychosocial mechanisms by which exercise might improve QOL (e.g., self-efficacy, distraction, sense of accomplishment), the impact of symptom occurrence on functional and social well-being, positive indicators of psychological well-being (e.g., energy, pride, hope), or actual QOL itself. Moreover, the few studies that did assess multiple outcomes (e.g., biologic mechanisms, symptom occurrence, psychological distress) did not examine the interrelationships among the outcomes and, consequently, can be considered descriptive or atheoretical. In such studies, it is not clear whether changes in the biologic mechanisms were responsible for the changes in symptom occurrence and, in turn, whether changes in symptom occurrence were responsible for changes in psychological distress. Future studies should adopt a theoretical framework for determining the effects of exercise on QOL during cancer treatment.
Methodologically, the studies were generally rigorous, consisting of RCTs with appropriate controls, supervised exercise sessions, an appropriate exercise stimulus, objective fitness indicators, and validated psychometric scales. The primary methodological limitations of the current research, however, include (a) small convenience samples, which restrict the generalizability of the findings; (b) relatively short exercise interventions that did not coincide with the medical treatment in its entirety; and (c) limited follow-up.
Despite the descriptive nature and methodological limitations of the current research, the major concern at this time is simply the nascency of the field. That is, research has just begun on this issue and much more remains to be done. One important future research direction is to extend the research beyond breast cancer to other major cancers (e.g., prostate, colorectal, lung) and beyond chemotherapy to other major cancer treatments (e.g., radiation therapy, hormone therapy). Each cancer/treatment combination is unique based on a different demographic profile of the patients, pathophysiology of the disease, treatment protocol, and side effects. Consequently, it would be unwise to generalize the benefits of exercise found for one particular cancer/treatment combination to another.
A second important future direction is to initiate “second-generation” studies in the one area where sufficient research has demonstrated reliable results—early-stage breast cancer patients receiving chemotherapy. The studies reviewed here may be thought of as first-generation studies because they have compared a single exercise intervention with nothing at all. Second-generation studies are needed to determine the optimal type (e.g., aerobic versus resistance exercise training), volume (e.g., moderate versus high intensity), and context (e.g., individual versus group based) of exercise for enhancing QOL in early-stage breast cancer patients receiving chemotherapy. Moreover, second-generation studies are also needed to compare and integrate exercise with other currently accepted QOL interventions (e.g., group therapy, diet, social support) to determine whether exercise is complementary or redundant with these interventions in such patients.
A third important, although controversial, future direction is to determine whether exercise after the diagnosis may influence tumor growth, disease progression, recurrence, and/or survival from cancer. From a primary prevention perspective, exercise has been shown to reduce the risk of certain cancers (e.g., colon, breast), and the mechanisms thought to confer this reduced risk (e.g., hormonal changes, immune function, obesity) may also operate in the secondary prevention of cancer. Moreover, additional mechanisms may operate after the diagnosis, such as highly fit individuals being able to complete more dose-intensive cancer treatments.
Finally, the effectiveness of exercise as a QOL intervention during cancer treatment will depend to a large extent on the motivation and ability of participants to adhere to such a program. Exercise adherence is a major challenge for health professionals regardless of the demographic profile of the group or the purpose of the exercise. The significant complications caused by cancer and its treatments make it likely that exercise adherence is even more difficult for cancer patients. Consequently, understanding the demographic, disease/medical, and social cognitive determinants of recruitment and adherence to various types of exercise programs in cancer patients is an important adjunct to this line of research. Similar to outcomes research, however, it is likely that different determinants of exercise will emerge for the different combinations of cancers and treatments.
SUMMARY AND CONCLUSION
More than 8 million Americans are alive today who have been through the cancer experience, and this number is increasing. Moreover, cancer treatments are intensive and cause significant complications that result in acute reductions in many QOL-related outcomes. Based on a review of 11 methodologically sound studies, it was concluded that exercise during cancer treatment is likely to be beneficial to cancer patients. Future research is needed, however, because this field is only beginning to take shape.
Dr. Courneya’s research program is supported by the National Cancer Institute of Canada (NCIC) with funds from the Canadian Cancer Society (CCS) and the CCS/NCIC Sociobehavioral Cancer Research Network.
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Keywords:© 2001 American College of Sports Medicine
coping; rehabilitation; chemotherapy; radiation therapy; disease; quality of life; physical activity; cancer epidemiology