Determinants Of Exercise In Cancer Survivors

Given the low exercise participation rates in many cancer survivor groups both during and after treatments, researchers have turned their attention to understanding the determinants of exercise in cancer survivors. Most early research was descriptive and atheoretical, selecting various demographic, medical, and psychosocial constructs to test as correlates and predictors of exercise behavior. Most recent research has applied one of the currently validated social cognitive models of human motivation and behavior to facilitate understanding. The two models that have been applied most often to exercise in cancer survivors have been the theory of planned behavior19 and social cognitive theory.20

3.1. Social Cognitive Models Applied to Exercise in Cancer Survivors

Bandura's social cognitive theory (SCT)20 is based on the concept of reciprocal determinism among behavior, the person, and the environment. Self-efficacy is considered the key organizing construct within SCT and is defined as "beliefs in one's capabilities to organize and execute the courses of action required to produce given levels of attainment" (p. 300).21 Self-efficacy is theorized to influence the activities that individuals choose to approach, the effort expended on such activities, and the degree of persistence in the face of failure or obstacles.22

Another important construct in SCT is outcome expectation, which refers to the expected outcomes associated with the performance of a behavior. Outcome expectations serve as incentives or disincentives depending on whether the anticipated outcomes are positive or negative. Bandura21 describes three main categories of outcome expectations labeled physical, social, and self-evaluative. Physical outcome expectations include the physical effects of a behavior such as pain, injury, and disease risk. Social outcomes include anticipated social reactions toward the behavior such as disapproval. Self-evaluative outcome expectations focus on one's own reaction to performing a given behavior (e.g., guilty, proud, embarrassed).

Ajzen's theory of planned behavior (TPB)19 proposes that a person's intention is the immediate determinant of a behavior because it reflects a conscious decision to perform or not perform the behavior. Intention is hypothesized to be determined by attitude, subjective norm, and perceived behavioral control (PBC). Perceived behavioral control is the perceived ease or difficulty of performing the behavior and may directly predict the behavior if it is an accurate reflection of the person's actual control over the behavior. Attitude is a positive or negative evaluation of performing the behavior that includes both instrumental (e.g., harmful/beneficial, useless/useful) and affective (unenjoyable/enjoyable, boring/fun) components. Subjective norm reflects the perceived social pressure that individuals feel to perform or not perform the behavior and includes both injunctive (what others think) and descriptive (what others do) component. The primary propositions of the TPB are: (a) people will perform a behavior when they are motivated to do so and have the opportunity to do so and (b) people will be motivated to perform a behavior when they evaluate it positively, believe it will be enjoyable, perceive that others approve and also perform the behavior, and believe that the behavior is under their control and that they are capable of performing it.

The TPB also proposes that attitude, subjective norm, and PBC are comprised of underlying accessible beliefs in an expectancy-value formulation.19 Attitude is a function of behavioral beliefs, which refer to the perceived advantages and disadvantages of performing the behavior. Subjective norm is a function of normative beliefs, which focus on the specific individuals or groups important to the individual who may or may not approve of the behavior. Finally, control beliefs underlie PBC and represent the opportunities and resources available to the individual for performing the behavior and their ability to influence the behavior.

3.2. Literature Review of Exercise Determinants in Cancer Survivors

Seventeen studies to date have examined social cognitive determinants of exercise in cancer survivors using a validated theoretical model (Table 1). Fourteen (82%)

Table 1. Summary of Theoretical Studies Examining Social Cognitive Determinants of Exercise in Cancer Survivors

Authors

Sample

Design

Results

Theory of Planned Behavior

110 colorectal cancer survivors receiving treatment

Courneya and

Friedenreich28 Courneya and

Friedenreich29 Courneya et al?

Courneya et. al

Courneya et. al2

Blanchard et al41

Courneya et al

Rhodes and

Courneya43 Courneya et al4

Courneya et al

164 breast cancer survivors receiving treatment 66 colorectal cancer survivors with 73% receiving treatment 37 mixed cancer survivors receiving high-dose treatment 24 posttreatment breast cancer survivors training for dragon boat racing 83 posttreatment breast cancer survivors and 46 posttreatment prostate cancer survivors 51 mixed cancer survivors randomized to a 10-week home-based exercise program 272 posttreatment mixed cancer survivors 62 colorectal cancer survivors randomized to a 16-week home-based exercise program 82 prostate cancer survivors randomized to a 12-week supervised exercise program

Retrospective Retrospective Prospective Prospective

Prospective

Cross-sectional

Prospective as part of an RCT

Cross-sectional

Prospective as part of an RCT

Prospective as part of an RCT

Intention and perceived behavioral control (PBC) were independent correlates of behavior (R2 = 0.22) and attitude was an independent correlate of intention (-R2 = 0.31).

Intention and PBC were independent correlates of behavior (.R2 = 0.14) and attitude and subjective norm were independent correlates of intention (-R2 = 0.23).

Intention was an independent predictor of behavior (-R2 = 0.30) and attitude was an independent correlate of intention (.R2 = 0.23).

Intention was an independent predictor of behavior (-R2 = 0.14) and attitude and PBC were independent correlates of intention (-R2 = 0.68).

Intention was an independent predictor of behavior (.R2 = 0.35) and subjective norm was an independent correlate of intention (-R2 = 0.49).

In breast cancer survivors, intention was an independent correlate of behavior (-R2 = 0.32) and attitude and PBC were independent correlates of intention (-R2 = 0.45). In prostate cancer survivors, intention was an independent correlate of behavior (-R2 = 0.37) and PBC was an independent correlate of intention (.R2 = 0.36).

Independent predictors of exercise adherence were sex (male), extraversión, normative beliefs (-), and PBC (Í2 = 0.42).

Intention and PBC were independent correlates of behavior (.R2 = 0.34) and affective attitude, subjective norm, and PBC were independent correlates of intention (-R2 = 0.46). Independent predictors of exercise adherence were exercise stage of change, employment status, treatment protocol, and PBC (R2 = 0.40).

Independent predictors of exercise adherence were exercise stage of change, age (-), and intention (R2 = 0.20).

Courneya et ai31 399 posttreatment Cross-sectional non-Hodgkins lymphoma survivors

Jones et al46 70 posttreatment multiple Cross-sectional myeloma survivors

Karvinen et al.26 354 posttreatment endometrial Cross-sectional cancer survivors

Keats et al4"7 118 adolescent cancer survivors Cross-sectional

Social Cognitive Theory

Rogers et al.23 21 breast cancer survivors Cross-sectional undergoing treatment

Five Factor Model

Rhodes et al41, 175 non-metastatic breast Retrospective cancer survivors

Attribution Theory

Courneya et al24 46 mixed cancer survivors at Prospective the 5-week follow-up who had participated in the exercise arm of a 10-week long randomized controlled trial

Affective attitude, subjective norm, and PBC were independent correlates of intention (F2 = 0.55).

Affective attitude, instrumental attitude, and PBC were independent correlates of intention (R2 = 0.43).

Intention was an independent correlate of behavior (-R2 = 0.24) and affective attitude and self-efficacy were independent correlates of intention (.R2 = 0.38). Intention and self-efficacy were independent correlates of behavior (.R2 = 0.29) and affective attitude and instrumental attitude were independent correlates of intention (-R2 = 0.34).

Higher average of steps per day was significantly associated with having a breast cancer exercise role model (r = 0.56) and higher annual income (r = 0.61). Higher daily energy expenditure was significantly associated with higher barrier self-efficacy (r = 0.62), higher task self-efficacy (r = 0.77), having an exercise partner (r = 0.71), and having a breast cancer exercise role model (r = 0.74).

During cancer treatment, contemplators were significantly higher in neuroticism than those p?

in action/maintenance and preparers were significantly higher in extraversión than ^ contemplators. At posttreatment, neuroticism was lower for those in action/maintenance compared to contemplators and preparers, extraversión and conscientiousness were g significantly higher for those in the action/maintenance stage compared to those in o contemplation and preparation. «3*

o" E3

Perceived success and program exercise frequency were independent predictors of postprogram exercise frequency (-R2 = 0.46). Program exercise minutes was an g &

independent predictor of postprogram minutes. Sd rc sr

sr g

ft of these studies tested Ajzen's TPB.19 Of these studies, two used a retrospective design, six used a cross-sectional design, three used a prospective observational design, and three were prospective as part of a randomized controlled trial. Three studies examined colorectal cancer survivors, three examined breast cancer survivors, three involved mixed cancer survivors, and two focused on prostate cancer survivors. Single studies have examined NHL survivors, multiple myeloma survivors, adolescent cancer survivors, and endometrial cancer survivors. Results indicated that between 14 and 37% of the variance in exercise behavior was accounted for by intention and PBC, and between 23 and 68% of the variability in exercise intention was influenced by attitude, subjective norm, and PBC. All studies found support for the TPB as a theoretical framework for understanding exercise behavior in cancer survivors, however, the constructs that made the most important contributions to predicting exercise behavior and intention varied by cancer survivor group.

Three studies to date have used other models as a theoretical basis for understanding correlates of exercise motivation in cancer survivors. One study used SCT,23 one used attribution theory,24 and one used the Five Factor Model of Personality.16 Two studies involved breast cancer survivors and one examined mixed cancer survivors. Results suggested several important correlates of exercise participation including self-efficacy, the influence of others, personality, and perceived success.

One of the early prospective studies examined predictors of exercise behavior in 66 postsurgical colorectal cancer survivors.7 Participants completed a baseline questionnaire that assessed the TPB, demographic and medical variables, and pre-diagnosis exercise. Exercise was monitored over a 4-month period by self-report and reported monthly by telephone. Hierarchical regression procedures indicated that intention and prediagnosis exercise were the key predictors of exercise behavior, and that attitude was the most important determinant of exercise intention. The authors concluded that the TPB was a useful framework for understanding determinants of exercise in this sample.

One of the first studies to examine predictors of an objective measure of exercise adherence focused on 24 breast cancer survivors attending a twice weekly 12-week training program for dragon boat racing.25 At baseline, participants completed a questionnaire that assessed TPB constructs, past exercise, and demographic and medical variables. Exercise adherence was measured using objective attendance records. Multiple regression analyses indicated that intention was the key determinant of adherence to the exercise program, and that subjective norm was the sole independent determinant of intention. The authors concluded that the TPB may be an effective framework for use in the design of exercise interventions for breast cancer survivors.

One of the largest studies to date was a cross-sectional study of 354 endometrial cancer survivors.26 Participants in this study completed a questionnaire that assessed the TPB, exercise participation, and demographic and medical variables. Multiple regression analyses indicated that intention was the sole independent correlate of exercise behavior, and self-efficacy and affective attitude were the key correlates of intention. Age was found to interact with intention and perceived control in the behavioral analyses. Intention was positively associated with behavior only in survivors under the age of 70 years, and perceived control was only associated with behavior in survivors over the age of 70 years. Additionally, BMI was found to interact with instrumental attitude and self-efficacy in the intention analysis. Instrumental attitude was positively associated with intention only in normal weight survivors, while self-efficacy was only associated with intention in obese survivors. The authors concluded that the TPB may be a useful framework for understanding correlates of exercise motivation and behavior in endometrial cancer survivors.

3.3. Exercise Motives and Barriers in Cancer Survivors

Early research into the specific exercise motives and barriers of cancer survivors reported that some exercise motives and barriers were unique to the cancer experience while others were common to other populations.27-30 For example, Courneya and Friedenreich28,29 asked breast and colorectal cancer survivors to recall the major benefits and barriers to exercise during their treatments. The main benefits of exercise that were reported were: (a) get mind off cancer and treatment, (b) feel better and improve well-being, (c) maintain a normal lifestyle, (d) cope with the stress of cancer and treatment, (e) gain control over cancer and life, (f) recover from surgery and treatment, and (g) control weight. The main exercise barriers in this group were: (a) nausea, (b) fatigue/tiredness, (c) no time to exercise, (d) no support for exercise, (e) pain or soreness, (f) no counseling for exercise, and (g) working at a regular job. These results indicate many unique exercise motives and barriers that are based on the cancer experience.

More recent research has examined larger and less-studied groups of cancer survivors.26,31 For example, Courneya and colleagues31 surveyed 399 NHL survivors. Participants were asked to list what they believed were the main advantages of exercise after their cancer diagnosis and the main factors that made it easier or more difficult for them to exercise during their cancer care. The seven most common perceived advantages of exercise were that it leads to: (a) a positive mental attitude, (b) muscular strength and tone, (c) aerobic fitness/endurance, (d) a sense of well-being, (e) increased energy, (f) improved circulation, and (g) stress relief. The seven most common perceived barriers to exercise were: (a) a lack of energy/fatigue, (b) being too deconditioned/tooweak, (c) nausea, (d) pain, (e) feeling ill, (f) a lack of motivation/laziness, and (g) depression. The finding that deconditioning/weakness was the second most commonly identified barrier in NHL survivors is consistent with clinical observations of this population.

Similarly, Karvinen et al.26 surveyed 354 endometrial cancer survivors. Participants were asked to list: (1) "... the main advantages of participating in regular exercise" (motives) and (2) the factors that "... make it difficult for you to exercise regularly" (barriers). The most common motives were: (a) lose weight, (b) feel better about one's self, (c) keep in shape, (d) improve strength/tone muscles, and (e) improve cardiovascular health. The five most frequently reported barriers were: (a) poor health, (b) lack of time, (c) poor weather conditions, (d) injury, and (e) fatigue/lack of energy. The finding that weight loss is the most commonly reported benefit of exercise is consistent with the obesity rate in this population.

Courneya, Jones, Mackey, and Fairey32 examined the motives and barriers of 52 breast cancer survivors prior to participating in a randomized controlled trial. Over 90% of participants felt that it was quite or extremely likely that exercise would improve their energy level and their well-being, 70-80% felt that it would reduce their stress and improve their immune function, and 40-45% felt that it would reduce their risk of a recurrence and help them maintain a normal lifestyle. In terms of overcoming barriers, over 75% were quite or extremely confident they could exercise if the weather was bad, they had limited time, or they became tired or fatigued. They were less confident, however, that they could exercise if they experienced pain or additional family responsibilities and especially if they experienced a recurrence of their cancer or other medical/health problems.

In the only prospective study to date, Courneya and colleagues33 examined the barriers to weekly exercise in 69 colorectal cancer survivors. In the trial, participants randomized to the exercise group were asked to report their exercise on a weekly basis by telephone. Those participants not achieving the minimum weekly exercise prescription (i.e., 3 times/week for 30 minutes) were asked for a primary exercise barrier. The most common barriers to exercise reported in this sample were lack of time/too busy (reported 65 times by 22 different participants), nonspecific treatment side effects (reported 51 times by 17 different participants), and fatigue (reported 44 times by 16 different participants). These three barriers accounted for 45% of all missed exercise weeks. The top seven barriers (including surgical complications, work responsibilities, progressing toward the exercise prescription, and getting enough activity elsewhere) accounted for 70% of all missed weeks and the top 10 barriers (including diarrhea, the flu, and nausea) accounted for almost 80% of all missed exercise weeks.

Overall, these studies indicate that cancer survivors have diverse motives and barriers to exercise, some of which are unique to the cancer experience and some of which are common to other populations. Not surprisingly, motives and barriers vary by treatment status. Barriers to exercise during treatment often reflect the well-known side effects of treatments (e.g., nausea, diarrhea, fatigue, depression) whereas barriers to exercise after treatments tend to realign with barriers in the general population (e.g., lack of time, too busy). It is also apparent that exercise motives and barriers vary by cancer survivor group reflecting the unique profile of the particular disease. For example, weight loss is the most common exercise motive in endometrial cancer survivors and deconditioning is a major exercise barrier in NHL survivors.

3.4. Exercise Preferences in Cancer Survivors

Although a number of studies have successfully explored social cognitive correlates of exercise motivation, relatively little is known about the exercise programming and counseling preferences of cancer survivors—factors that would also presumably influence exercise participation. Four studies to date have examined exercise preferences in cancer survivors.17,34-36

Vallance et al.35 found, in a cross-sectional survey of 431 NHL survivors, that the majority of participants indicated that they were interested (81%) and able (85%) to participate in an exercise program for NHL survivors. Participants most commonly reported walking as the activity of choice (55%) and moderate level exercise as the preferred intensity (62%). More than half of participants (56%) indicated they would have preferred to start an exercise program at least 3 months after treatment. Equal proportions of participants indicated that they preferred to exercise alone (31%) or with others (35%).

Another cross-sectional study involving 386 endometrial cancer survivors reported similar findings.36 In this study, the majority of participants also indicated that they would have preferred exercise counseling at some point after their diagnosis (75.7%) and felt able (81.7%) and interested (76.9%) in doing an exercise program. Participants also indicated that walking was the most commonly preferred activity (76.9%), most preferred moderate intensity exercise (61.1%), the most common preference for initiation of an exercise program was 3-6 months posttreatment

(39.3%), and participants were equally distributed among the desire to exercise alone (23.8%), with others (22.6%), or no preference (23.8%).

In an earlier cross-sectional study of 307 breast, prostate, lung, and colorectal cancer survivors, Jones and Courneya17 found that the majority of participants (84%) would have, or possibly would have, been interested in exercise counseling at some point after diagnosis, preferred face-to-face exercise counseling (85%), and to receive counseling from an exercise specialist affiliated with a cancer center (77%). Walking was the preferred modality (81%), almost all preferred recreational activities (98%), half indicated a preference for moderate intensity exercise (56%), and before treatment was the time period most selected for the initiation of an exercise program (32%). The results of these studies suggest that cancer survivors may be interested in receiving exercise counseling and programming services; however, individual variation in the types of activities, intensity, partners, and structure do exist and need to be considered.

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