Date of Award

2014

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Exercise and Health Sciences

Faculty

Health, Engineering and Science

First Advisor

Professor Robert U Newton

Second Advisor

Professor Kenneth M Greenwood

Abstract

Cancer survivors are more than twice as likely as the general population to suffer the debilitating effects of depression. This comorbid condition is associated with several negative consequences, such as reduction in compliance with cancer treatments, and hastened mortality. Recent research has examined the therapeutic effect of exercise on depression and reported excellent results of similar magnitude to those achieved with pharmacotherapy or psychological intervention. However, no research, to date, has examined the effectiveness of exercise on reducing depression in depressed cancer survivors. In order to address this important question this thesis reviewed previous literature in the area of cancer and depression, explored the exercise preferences of depressed cancer survivors living in Australia, and completed the first exercise intervention with a cohort of depressed cancer survivors.

Two descriptive reviews provided background information about the types of exercise programs that have been prescribed for cancer survivors as well as the exercise preferences of many cancer survivors. These reviews identified that there was a lack of available information relating to the optimal exercise program to improve depression and, further, that no information was available to determine the preferred exercise options of depressed cancer survivors and whether this group would be interested in engaging in exercise.

The first research study was a cross-sectional comparison of the physical activity habits and exercise preferences of depressed (n = 158) and non-depressed (n = 650) Australian cancer survivors. It was found that depressed survivors were less active (-48 mins/wk; p < .05), yet a greater number of depressed cancer survivors (78.5% vs 71.6%) expressed a desire to participate in an exercise program (p = .044). Contrary to expectations, depressed survivors were more interested in supervised sessions (p < .001), and were also more willing to attend their local fitness centre (p = .049). These findings suggest that being depressed does influence the preferred exercise program and that these differences should be considered before prescribing exercise to cancer survivors.

Secondary analysis of the dataset was conducted to examine the differences between metropolitan and regional cancer survivors, living in New South Wales, Australia. The role of exercise may be even more important for isolated regional survivors who lack access to traditional form of psychological support and service providers. Results obtained from 366 participants revealed that the incidence of depression (~21%) was not related to location of residence. There was no difference in physical activity participation between metropolitan (n = 236) and regional (n = 130) survivors, with only 40% of all participants being sufficiently active. No differences were found for the primary perceived benefits of improving aerobic fitness, controlling weight, and improving overall health. However, metropolitan residents were more interested in the performing exercise that elicited strength and functional improvements (p = .041). Furthermore, there were no differences in barriers to exercise. These findings indicate that many cancer survivors, including those living in regional locations, are familiar with health benefits of exercise, yet remain insufficiently active to obtain these positive outcomes.

The final study was a longitudinal controlled trial that aimed to examine whether exercise was indeed able to produce an antidepressant effect in depressed cancer survivors. Eligible participants were allocated to a clinic-based, supervised exercise group (n = 10), an unsupervised, home-based exercise group (n = 8), or a usual care control group (n = 14). The supervised exercise group completed two sessions of combined resistance and aerobic training per week for the duration of the 12-week program. The home-based group were provided with printed material about the benefits of exercise and were encouraged to complete 150 minutes of exercise per week, but received no specific prescriptive information about the form of exercise they should undertake. The control group received no exercise or printed material, and were encouraged not to alter their usual activity. Intention-to-treat analysis, with the last response carried forward, found that both exercise groups improved depression, with a greater response seen in the supervised program (-56%; p = .002) compared to the home-based group (-48%; p = .016). No significant differences were found when comparing the results between the two exercise groups. When per-protocol analysis was used to examine the responses in depression, it was found that the home-based group decrease depression more rapidly, measured at week 6, and to a greater extent, than the supervised group (d = 0.50). At the final assessment (week 12) the home-based group and supervised group produced a similar response for a reduction in depression. These findings are the first to indicate the antidepressant effect of exercise in depressed cancer patients and the outcomes match those previously reported for people living with depression. Combined with the fact that no adverse effects were reported, the results should be used to promote exercise as a therapeutic treatment option for cancer survivors experiencing comorbid depression.

In summary, this research has demonstrated that depressed cancer survivors are able to obtain antidepressant benefits from commencing a well-designed, structured, and supervised exercise program. Despite willingness to engage in exercise, and knowledge of the perceived benefits, almost 60% of depressed cancer survivors are not performing enough physical activity. Therefore, there is need for future research to examine how to increase the uptake of exercise. Engagement is likely to increase if recommendations to commence exercise are made by the survivors’ referring specialist, and, therefore, it is suggested that referral for specialised exercise should be included within best practice cancer care, to remediate comorbid depression.

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