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Although physical activity may modify the late effects of childhood cancer treatment, 20%-52% of adult survivors are sedentary. We sought to identify modifiable factors that influence survivors' participation in physical activity.
Structural equation modeling of data from the Childhood Cancer Survivors Study of adult survivors (current mean age, 30.98 years; mean years since diagnosis, 23.74; mean age at diagnosis, 9.25 years) diagnosed between 1970 and 1986.
Forty percent of the variance in male survivors' recent participation vs. nonparticipation in physical activity was explained directly and/or indirectly by self-reported health fears (P=0.01), perceived primary-care physician (PCP) expertise (P=0.01), baseline exercise frequency (P=<0.001), education level (P=0.01), self-reported stamina (P=0.01), cancer-related pain (P=<0.001), fatigue (P=<0.001), age at diagnosis (P=0.01), cancer-related anxiety (P=<0.001), motivation (P=0.01), affect (P=0.01), and discussion of subsequent cancer risk with the PCP (P=<0.001) (N=256; X2=53.38, df=51, P=0.38, CFI=1.000, TLI=1.000, RMSEA=0.014,WRMR=0.76). Thirty-one percent of the variance in females' recent physical activity participation was explained directly and/or indirectly by self-reported stamina (P=<0.001), fatigue (P=0.01), baseline exercise frequency (P=0.01), cancer-related pain (P=<0.001), cancer-related anxiety (P=0.01), recency of visits with PCP (<0.001), quality of interaction with the PCP (P=0.01), and motivation (P=<0.001) (N=366; X2=67.52 df=55, P=0.12, CFI=0.98, TLI=0.98, RMSEA=0.025, WRMR=0.76).
Gender-tailored intervention strategies in which providers specifically target motivation, fear, and affect may support physical activity in childhood cancer survivors.
Increases in childhood cancer survival have shifted the care paradigm from one of cure to a long-term emphasis on treatment-related morbidity and quality of life. Among the potential consequences of cancer therapy are pain, fatigue, obesity, osteoporosis, cardiomyopathy, and neuromusculoskeletal complications [1-4]. Lifelong physical activity initiated during cancer therapy is essential to modify or prevent these late effects [5-8].
Recent reports indicate that 20% to 52% of adult survivors of childhood cancer are sedentary, despite their risk of late effects [9-12]; this rate is similar to that in the general population [13, 14]. However, survivors of acute lymphoblastic leukemia (ALL), the most common pediatric cancer, were more likely than members of the general population to report no leisure-time physical activity (OR, 1.74; 95% CI, 1.56-1.94) . Survivors treated with more than 20 Gy of cranial radiotherapy were at particular risk. When the comparison was adjusted for age, race, and ethnicity, ALL survivors were substantially more likely than their healthy counterparts to be inactive (females: OR, 1.86; 95% CI, 1.50-2.31; males: OR, 1.84; 95% CI, 1.45-2.32).
Factors that positively or negatively influence childhood cancer survivors' physical activity have not been documented. To describe modifiable influences on survivors' physical activity participation, we selected a broad-based health behavior model adapted to childhood cancer survivors [14-16] to inform variable selection and relationships and structural equation modeling (SEM).
The Interaction Model of Client Health Behavior (IMCHB) [16-18], (Fig. 1), has been used [18-21] to identify survivor, provider, and contextual factors that can be targeted by interventions to modify the late effects of cancer therapy. The model comprises three broad elements: (1) the intrapersonal (affect, motivation, cognitive appraisal) and contextual (demographic/social influences, health history, resources) characteristics that uniquely define individuals relative to their health, disease, and treatment; (2) the therapeutic content and process between providers and patients that can support or impede behavior change; and (3) behaviorally related health outcomes. All variables within the data sets corresponding to the conceptual model [17, 18] were evaluated in preliminary models (Figure 1); only those variables that contributed significantly (p≤0.01) to the explained variance in the physical activity outcome were retained in the final models.
The Childhood Cancer Survivors Study (CCSS) was designed to enroll a cohort of survivors sufficiently large and diverse to allow meaningful analysis of the delayed effects of treatment. The surveys and sampling methods have been described in detail by Robison et al. and are available for review at http://www.stjude.org/ccss. In 1994, participants completed a baseline questionnaire that addressed demographic and health-related information; additionally, participating centers provided detailed abstracts of the medical records for consenting subjects. The original CCSS study contacted 20,346 eligible participants from 26 institutions across the United States and Canada who had survived five or more years after treatment for malignant disease diagnosed (before age 21) between 1970 and 1986. A subsequent ancillary study, the Health Care Needs Survey (HCNS), randomly sampled 1600 of approximately 12,872 subjects who remained alive; 978 (61%) completed and returned the survey and 838 (86%) of the 978 returned the total-cohort Follow-up 2 survey within the same data collection period. These 838 survivors were the subjects of this analysis.
Consistent with previous CCSS reports , physical activity participation was measured as a binary outcome derived from the Behavioral Risk Factor Surveillance Study . Survivors were asked (yes=1; no=2), “During the past month, did you participate in any physical activities or exercises such as running, calisthenics, golf, bicycling, swimming, wheelchair basketball, or walking for exercise?”
Eleven directly observed independent variables were significantly associated with recent physical activity as covariates in the final analytical models. All were self-reported by survivors: 1) their primary-care physician's (PCP's) familiarity with cancer-related problems (1= familiar, 2 = not familiar); 2) current pain resulting from cancer or its treatment (1= no pain; 5=excruciating pain); 3) frequency of fatigue(1= all the time; 6=none of the time); 4) whether survivors had discussed the risk of recurrent cancer with their PCP (1=yes, 2=no); 5) baseline frequency of aerobic exercise (defined as sufficient to induce sweating or breathing hard, lasting ≥20 min,) (0 days per week, 7 days per week); 6) age at diagnosis; 7) current anxiety as a result of cancer or its treatment (1=no anxiety, 5=extreme anxiety); 8) current highest school grade completed; and 9) whether the survivor had seen a primary care physician since cancer treatment ended (1=yes, 2=no); 10) modified from the Multidimensional Health Locus of Control Scales , for intrinsic motivation, survivors rated 4 items (e.g., “I am in control of my health”; “The main thing which affects my health is what I myself do”) on a 6-point Likert Scale (1=strongly disagree; 6=strongly agree) (α=0.79); 11) for extrinsic motivation, survivors rated 4 items (e.g., “Health professionals control my health”; “Regarding my health, I can only do what my doctor tells me to do”) on a 6-point Likert Scale (1=strongly disagree; 6=strongly agree) (α=0.80).
In structural equation modeling, latent variables (e.g., depression) are measured indirectly by using a set of observed variables . Our final analyses identified 4 latent measures that contributed (directly or indirectly) to the explained variance in physical activity participation. The strength of the latent measures (i.e., the cohesiveness and fit of their contributory observed variables) was assessed by confirmatory factor analysis. Four strong latent variables (factor score determinacy values >0.80) were derived from the observed variables: survivor-provider interaction (0.94), fear (0.98), affect (0.96), and stamina (0.98).
Derived from 5 observed items on the physical function measure of the SF-36 , survivors were asked to what extent their physical health limited their ability to climb several flights of stairs, climb 1 flight of stairs, walk more than 1 mile, walk several blocks, and walk 1 block (3=not limited at all, 2=limited a little, 1=limited a lot) (α= 0.924).
Three observed variables measured on a 5-point Likert Scale assessed the extent of survivors' fear (1=not at all concerned; 5=extremely concerned) about their future health, the return of their cancer, and the discovery of a health problem during a routine check-up (α=0.76).
Derived from 3 observed measures on the SF-36 Mental Health subscale  rated on a 6-point Likert Scale (1=all of the time; 6=none of the time), survivors assessed the frequency of feeling unhappy, downhearted and blue, and not cheerful (α=0.78).
Four items asked survivors to rate on a 5-point Likert Scale (1=not at all; 5=extremely) to what extent they believed that: their doctor took enough time to answer their questions; they could ask their doctor questions about cancer; their fears and concerns had been addressed by their doctor; and their PCP could handle cancer-related problems (α=0.78).
Structural equation models of the data were analyzed using Mplus 4.2 software . Male (N=256) and female (N=366) subsamples with complete data comprised the final sample for the SEM analysis. We chose to use samples with complete data rather than to use data imputation in order to avoid potentially distorting coefficients of association and correlation relating variables . A sample size >200 is considered large in SEM . The best-fitting model is one that is conceptually sound, has parameter estimates that significantly correspond to the hypothesized relationships, meets the established SEM fit criteria (Figures 2 and and3,3, Appendix 1), and offers the highest percentage of explained variance for the outcome.
There were no demographic or cancer-related differences between the total sample with missing data (N=838) and the SEM subsamples with no missing data (Table 1). Significant differences observed between the gender subsamples and the total sample (using Bonferonni correction factor) were observed in the subsamples with complete data: males reported higher income categories; females were more likely to have visited their PCP since completion of cancer treatment (Table 1). The typical respondent was representative of the entire CCSS cohort [22, 29, 30]: white, female, college graduate, earning $20,000-$60,000, and covered by health insurance(Table 1). Approximately 25% percent of respondents in the total sample reported no leisure-time physical activity; females in the SEM subsample were slightly more active (NS). Subsample females were more likely to be fearful of finding a problem at check-up than were subsample males. Subsample males and females reported less fatigue than the total sample, with males reporting less fatigue than females. Subsample females were less extrinically motivated than subsample males (Appendix 2). Because gender differences in physical activity are reported in the general population [31-34] and were observed in the study's independent variables (Appendix 2), we estimated separate models for male and female survivors rather than test model equivalency between genders.
The likelihood of male survivors' physical activity participation during the past month was predicted by the perception that their PCP was familiar with cancer-related problems, greater fear about future health, more education, and by greater baseline frequency of aerobic exercise (Fig. 2 and Appendix 1). Younger age at diagnosis, infrequent fatigue, little or no cancer pain, and infrequent negative affect predicted greater stamina. Less fear about future health, infrequent fatigue, and less anxiety about cancer predicted a more positive affect. Greater fear was predicted by more cancer pain, having discussed the risk of cancer in the future with their PCP, higher levels of extrinsic motivation, and lower levels of intrinsic motivation. Perceptions of less stamina, greater cancer anxiety, physical activity non-participation, and greater cancer pain predicted frequent fatigue. Greater fear about future health, greater cancer pain, and less intrinsic motivation predicted greater cancer anxiety (correlate of physical activity participation).
A greater likelihood that female survivors had recently participated in physical activity (Appendix 1 and Figure 3) was directly predicted by greater reported stamina, less fatigue, and more frequent baseline aerobic exercise. Higher levels of intrinsic motivation (P=0.01) was a significant indirect predictor of physical activity through their effect on stamina. Greater stamina was predicted by less fatigue, less cancer-related pain, more frequent exercise at baseline, and greater intrinsic motivation. Greater fear about health was associated with having seen a PCP since completion of cancer therapy, greater fatigue, and greater extrinsic motivation. A more positive perception of survivor-PCP interaction was predicted by less fear about future health and greater extrinsic motivation. Greater intrinsic motivation was predicted by more positive perceptions of interaction with the provider. Greater fatigue was predicted by greater cancer-related pain; greater anxiety was predicted by greater cancer-related pain and greater fear about future health.
While this study identified some of the same direct predictors (education, fatigue, fear, stamina) of physical activity participation as those reported for adult cancer survivors [35, 36], the impact of these variables were gender specific and they simultaneously indirectly predicted physical activity participation through their impact on other variables. A higher level of education  predicted physical activity among males. Perceptions of greater stamina predicted physical activity participation in female survivors, consistent with the hypothesis  that low exercise capacity directly accounts for a more sedentary lifestyle among survivors. As with survivors of adult cancer [39, 40], fatigue predicted less physical activity among females; conversely, physical activity participation predicted less fatigue in males.
Both males and females who reported more frequent exercise at baseline were more likely to report recent physical activity, suggesting that physical activity was a previously established behavior. For both genders, cancer-related pain, anxiety, fear, and fatigue were powerful indirect influences on physical activity participation. Pain contributed to increased fatigue and anxiety, and reduced stamina. Perceptions of decreased stamina reinforced perceptions of increased fatigue. Higher fear levels increased cancer-related anxiety.
In contrast to anxiety which is a negative influence on positive health behavior, fear and worry can support positive health behavior . Consistent with survivors of adult cancer, , greater fear about health predicted physical activity participation among male childhood cancer survivors.
Having discussed cancer recurrence with their PCP predicted men's greater fear. Males often view physician visits as necessary only in a crisis [30, 42, 43]; physician contact may therefore reflect specific problems that contribute to a more negative affect. In contrast, females tend to view interaction with their physician as supportive [44, 45].
Perceptions of survivor-provider interaction were relevant to recent physical activity in the female but not the male model; the provider's perceived competence was predictive in the male but not the female model. These findings further demonstrate significant sex differences in health-care expectations, in which males seek minimal physician input but value physician competence, whereas females rely on physician input for their health care decisions and value the quality of the relationship with the physician [30, 42-45].
Both models revealed complex relationships between fear, motivation, and affect. Males who were more extrinsically motivated had greater fear about their future health. Extrinsically motivated individuals are known to be more worried and fearful about their health, to see themselves as less in control of health matters, and to rely more on health professionals for direction [18, 19, 46]. Higher levels of intrinsic motivation, supported by positive perceptions of the survivor-provider relationship, predicted greater stamina in females, and indirectly predicted physical activity participation through stamina. Individuals with greater intrinsic motivation are more often self-reliant and self-directed, rather than provider-directed [19, 21], in their health behavior choices.
Regardless of the length of time since a survivor's cancer diagnosis and treatment [29, 47], primary care physicians are encouraged to specifically inquire about any treatment-related symptoms, particularly pain, fatigue, and anxiety. These symptoms may share common biological mechanisms [48, 49] and, until they are addressed, may remain significant barriers to physical activity in survivors. Physical activity programs have reduced fatigue and decreased depression and anxiety in survivors of adult cancer [6, 7, 50-52], and they may similarly affect childhood cancer survivors.
Pediatric cancer patients experience problems with pain, physical function, and fatigue throughout therapy [53-55]; as survivors, many must confront these persistent symptoms as well as the late effects of radiation and chemotherapy [56, 57]. In order to modify these late effects, it is important to introduce individually tailored physical activity during treatment and support survivors to maintain their physical activity throughout their lives. Exercise programs during treatment include passive range of motion exercises, progressing to strength and endurance activities [58-62]. The concurrent demands of treatment, together with the patient's physical, psychological, and motivational preparedness must be considered in tailoring physical activities .
As in the general population, sex should be considered in tailoring physical activity interventions to survivors of childhood cancer [64-74]. For some male survivors, personalized risk information conveyed by print, video, and web-based media [71, 74] may help to increase health concern and support motivation for physical activity in the absence of frequent physician interaction[69-71, 74]. In some female survivors, direct contact with the PCP may be more effective in supporting physical activity than would a media intervention. Finally, interventions that are individually tailored to the influence of fear, affect, and motivation [65, 67, 69] are more likely to be effective in supporting behavior change than are interventions that only address changing knowledge.
The study sample reflects a subset of the overall CCSS population - those who responded to the Health Care Needs and CCSS Follow-up 2 Surveys; therefore, survivors included in the current analysis may not be fully representative of the population from which they were derived. The physical activity outcome, as well as the independent measures, was based upon self-reported data.
Despite the study limitations, we are able to report three novel findings about factors that predict the likelihood of childhood cancer survivors' physical activity and suggestions for considering these factors in managing survivors' long-term care: (1) physical activity is influenced by pain, anxiety, fatigue, and stamina independent of gender; (2) the sexes differ in which factors predict physical activity and how they do so; (3) affect, fear, motivation, and survivor-physician interaction are modifiable predictors of the likelihood of physical activity. Interventions that consider these multiple factors have the potential to support positive behavior change in childhood cancer survivors.
The authors acknowledge the contributions of Sharon Naron and Vani Shanker (for editorial assistance), Deborah Sherrill-Mittleman, PhD (for assistance with data analysis), and Kelly Shempert and Dawn Silcott (for illustrations).
Support: NIH, NINR RO3 NR009203 (Cox, C.L., PI); Robert Wood Johnson Foundation (Oeffinger, K.C., PI); NIH NCI U24 CA55727 (Robison, L.L., PI); American Lebanese Syrian Associated Charities (ALSAC).
Prior presentation: Podium presentation at 4th Biennial Cancer Survivorship Research Conference, June 19, 2008