HBF report part 4: Discussion

The primary finding of this study is that intervention participants improved on all measures and maintained all improvements. The intervention group made significantly greater gains than the control group on body composition and cardiopulmonary fitness, and trended toward greater gains in flexibility and muscular endurance and strength. There were no significant differences between cancer types on any of the outcome measures, indicating that the intervention was equally successful for both breast and prostate cancer survivors.

            Intervention participants improved their body composition, going from overweight to normal weight. A reduction of 4% body fat will lead to a significant reduction in all cause mortality risk, reoccurrence or new incidence of cancer, and development of secondary diseases.^17,66,79 The reduction seen in this study is a better result than many other studies have shown.^25,35,38 Possible reasons for this include the balance of aerobic and resistance exercises and the variety of exercises.^3,79

            Additionally, the intervention group improved their cardiopulmonary function by almost a full MET. An improvement of a full MET was found to confer a 12% reduction in risk of death from cancer.⁴² Amongst healthy adults, VO₂peak will begin to decrease at a rate of 0.5-1 MET per year in old age (over 75 years).⁵ In cancer survivors, this decline will likely happen earlier in life and at a greater rate unless they maintain an exercise regime.⁷⁶ This is especially true for cancer patients who undergo anthracycline chemotherapy, as it has been shown to cause cardiotoxicity and myocardial damage in some cases.^18,82 The two year mortality rate for cancer survivors who suffer chemotherapy induced cardiotoxicity (CIC) is 60%.⁸² While no study has yet determined if exercise can reverse or attenuate CIC once it develops, studies have shown that cancer survivors suffering CIC can still improve their VO₂peak, which will still improve all cause survival.⁸² 

Here it is important to highlight the findings of Hamer and colleagues.²⁹ They performed an analysis of the associations between physical activity levels and all cause mortality in a mixed group of cancer survivors. Half of the sample were breast cancer survivors, but prostate, bowel, and bladder cancer were highly represented amongst the participants. Their analysis found that “light and moderate activity such as domestic activity and regular walking did not confer protection.” Only vigorous exercise reduced the risk of death, by 52%. They estimated that if the cancer survivors performed vigorous exercise, the volume required was only 3 days per week, 20 minutes per day. Many other epidemiological studies support that a large total volume of exercise is not sufficient to reduce exercise if it is only performed at light to moderate intensity, but that vigorous intensity exercise is the key to improving cancer survival.^{9,23,24,27,31,42,81}

The intervention group made significant improvements in all areas of muscular endurance and strength. These improvements in lean muscle contributed to the reduction in body fat. Having a greater proportion of lean muscle mass and less fat mass will likely improve their metabolism and greatly reduce the risk of cardiovascular disease and diabetes.^29,39,43 Improvements in muscular endurance and strength make performing functional tasks and activities of daily living easier. Better functional performance will allow people to live independently longer, and in old age, decrease their risk of falling. Additionally, the performance of resistance exercises to improve muscular endurance and strength will maintain or increase bone mineral density and help prevent osteoporosis.^38,77,80 This is especially important for cancer survivors who underwent hormone therapy, as a common side effect of these treatments is the loss of bone mineral density.

Both groups made clinically meaningful improvements in QOL. The intervention group maintained the QOL level they achieved at the end of the intervention. A high level of QOL is a worthy accomplishment on its own. A meta-analysis showed a positive relationship between increasing exercise and improving QOL.²³ Like with the survival statistics, this relationship was stronger based upon intensity of exercise performed. While there is not as much evidence at this time, this trend is likely to be found as strong as the link between exercise intensity and survival. All together, the evidence shows that cancer survivors must perform vigorous intensity exercise, and that if they are doing so, it may require as little as three 20 minute sessions per week.

The intervention group made a statistically significant improvement in their fatigue score, but this change was not clinically meaningful because the average fatigue score was below the threshold for participants to be considered fatigued. Fatigue is an almost omnipresent side effect of cancer and its treatment, but for most people it resolves naturally within a year of treatment. As this sample was on average a year or further out from treatment, this explains why the fatigue levels are so low. However, research has documented the phenomena of cancer related fatigue (CRF), which is a direct side effect of treatment, and is increased with more doses or prolonged treatments.^26,73 The difference between regular fatigue and CRF is that CRF will not naturally resolve with time. Fortunately, exercise has been shown to be one of the most potent relievers of CRF.^19,33,44 Therefore, while certain modifications may need to be made to an exercise program to accommodate someone suffering CRF, all cancer survivors should be encouraged to exercise after treatment to help relieve their symptoms and regain their health.

The intervention was highly successful at motivating participants to continue their exercise after completing the program. Amongst intervention participants, only 30% reduced their physical activity levels from baseline to follow up. Of those people who reduced their activity, 53% were still surpassing the recommended weekly activity level.⁵⁷ This rate of behaviour maintenance greatly exceeds the normal rate of 70% reduction in physical activity levels after cancer treatment.^6,55

            Amongst this sample, the control group was very active, exceeding the weekly activity levels of the intervention participants. Anecdotally, many of the control participants commented that participating in the baseline assessment encouraged them to increase their physical activity levels. This high level of activity explains why the control group made significant improvements on most measures. A surprising outcome from this study is that there was not a difference between the control and intervention groups for QOL. A hypothesis of this study was that the SGP and group interaction in the intervention would have increased the psychological and social dimensions of QOL, therefore improving total QOL more than if the participants had just exercised. This hypothesis was generated from the results of Naumann et al.,⁵⁰ who showed that combining exercise and counselling provided a more-than-additive improvement to QOL than either component alone. It is unknown to what extent control group participants sought out psychological and/or social support on their own to meet their needs.

Of the entire sample, only 22% were not meeting the recommended weekly activity level at baseline, with 73% of those people participating in the intervention. These statistics lend support to a belief held amongst some researchers: the people who would benefit most from participating in a research intervention, i.e. people who are unfit and unmotivated to exercise, do not volunteer for these kind of projects.

A plethora of research has described the barriers and facilitators toward exercise.^7,20,54,64 Other research has observed increases in motivation amongst Western Australian cancer survivors to exercise after participating in a structured exercise program.⁴⁷ However, what is still lacking is research showing an effective way of encouraging people, who would normally not enrol in an exercise program or start exercise on their own, to take that first step. It is likely that the focus point of any efforts on this front will need to be through general practitioners and oncologists, as they make the first point of contact with these patients.

One precaution that should be taking when interpreting these results is their application to survivors of other cancers besides breast and prostate. While other research has shown that exercise, including vigorous exercise, is safe and beneficial for people suffering from other solid tumour cancers (e.g. colon or bowel cancer), these studies have also shown that haematological cancer survivors (e.g. leukemias and lymphomas) and brain tumour survivors may have adverse responses to exercise.^42,60 These adverse effects range from mild (needing more rest time or having to halt exercise early) to severe (suffering a stroke). More research is needed in these populations to determine appropriate exercise guidelines.