With survival rates improving dramatically, attention must be paid to managing the late effects of cancer and the consequences of treatment. Physical activity and specifically designed exercise programs are an important, albeit underutilized, tool that may improve health and quality of life in cancer survivors. However, our results make it apparent that very few survivors are taking advantage of the potential benefits of physical activity. A very low proportion of survivors meet the CDC guidelines for physical activity, and presumably, even fewer engage in formal exercise programs. Our results indicate that not only do cancer survivors engage in less physical activity than the general population, but also that co-morbid medical conditions, race/ethnicity, sex, age, income, and educational attainment influence their participation rates.
The results of our analyses are in agreement with previous reports that indicate that most adults in the United States do not participate in adequate levels of physical activity [24
]. In addition, our reported associations between co morbid conditions, race, sex, income, age, educational attainment, obesity, and physical inactivity concur with existing literature describing these associations [24
]. As expected, our results support the analysis of Troiano et al, who used the same 2003-2004 cohort and accelerometer recorded data to evaluate physical activity in the entire U.S. population [22
]. Accelerometer recorded data suggest that Americans are much less physically active than previously thought. Previous investigations, based on self-report, estimated that 26.2% of Americans participate in recommended amounts of physical activity [24
], whereas our analyses, based on accelerometer recorded data, estimated that only 12.7% of Americans actually meet the CDC guidelines for physical activity.
Our results also concur with previously published research reporting low physical activity levels in cancer survivors [31
]. However, there are some key differences. Our findings expand on those of Coups et al [32
] and Bellizini et al [31
], who reported that cancer survivors were less likely to meet the recommend levels of physical activity (25.2%, 33.0%) compared to those with no cancer history (30.8%, 35.3%). Their analyses identified this association only among survivors between 40 to 64 years of age and not among those 18 to 40 years or age. Our study showed a difference across all age groups with a linear increase in risk of not meeting the CDC guidelines with each ten year increase in age. These discrepancies can at least partially be explained by differences in population selection and study design. Approximately half of the participants in the Coups et al [32
] and Bellizini et al [31
] reports were less than five year cancer survivors. Our analysis excluded these individuals because of the likelihood they could still be undergoing active treatment. Acute side effects of cancer treatment modalities may influence both ability and desire to participate in physical activity. Patients receiving treatment are likely to differ from survivors who are done with the acute phase of therapy by both health concern and motivation. Therefore, we felt it important to limit our analyses to those most likely through with the acute phase of curative intervention.
Our findings are in contrast to two other studies, Eakin et al[34
] and Courneya et al [33
], who reported that physical activity levels did not differ among adult cancer survivors and the general populations in Australia and Canada, respectively. Both of these manuscripts included individuals with acute cancer diagnoses, and again used self-report data to estimate physical activity. Self-report data is likely less precise than measured physical activity data, and may have influenced their abilities to correctly classify activity levels in their populations.
Previous studies have reported higher rates of physical disability [11
] and chronic conditions [1
] among cancer survivors when compared to healthy populations, so we evaluated the potential contributions of these impairments to low levels of physical activity among cancer survivors. As in previous investigations by other authors, we found that cancer survivors were more likely to report physical limitations, cardiovascular disease, diabetes, or arthritis than were members of the general population, and that comorbid conditions were associated with low levels of physical activity. However, in our multivariate analysis, physical limitations were not associated with inactivity independent of other co-morbid conditions and body mass index. This is likely because physical disability is directly influenced by or related to other co-morbid conditions.
In our analyses, individuals who identified themselves as black were more likely to be inactive than those who reported white or Hispanic race/ethnicity. These findings are in agreement with previous reports evaluating the influence of race/ethnicity on physical activity in the general population [29
] and among cancer survivors [11
]. Our finding that female sex was associated with inactivity is also in agreement with previous reports of low activity levels among females when compared to males in the both the general [28
] and cancer survivor populations [33
Educational attainment and household income were also significant predictors of physical activity status. Those with annual incomes less than $20,000, and those who did not get education past high school were at greater risk compared to those with annual incomes of $20,000 or more, and those who had education beyond high school to be at risk for physical inactivity. Although previous publications among cancer survivors have acknowledged and adjusted for both educational attainment and income level when examining physical activity, none have specifically reported the impact on physical activity levels in cancer survivors. Associations between income and physical activity and between educational attainment and physical activity are well established in the literature describing the general US population [36
]. Our data confirm that these associations do not disappear with a cancer diagnosis.
Historically, physical activity assessment was largely measured by self-report. Accelerometers offer the chance to objectively assess physical activity levels. However with all of the promise this tool offers, there are some limitations. First, this is a waist mounted device that records only linear acceleration. It is unable to record activities with horizontal displacement movements (i.e. swimming, cycling, etc.). If an individual's usual routine is composed of these types of activities, their total recorded minutes of physical activity would be underestimated. A second limitation of accelerometer technology is the need to use established cut points to determine the intensity of the physical activity. These cut points are based on a small number of studies in limited healthy populations [23
], which may be inaccurate approximations of metabolic equivalents in older individuals and/or those with mechanical or physiological adaptations (i.e. abnormal gait or decreased exercise capacity). Finally, we did use a liberal interpretation of the CDC guidelines in defining whether a person accomplished the recommended amount of physical activity. When determining the number of minutes of moderate/vigorous activity per day or week, we used “minimum 1 minute bouts” instead of “activity bouts (8 out of 10 minutes)” so we could capture both formal exercise and informal activities such as taking the stairs. Also, we credited a participant with completing “moderate” activity if 1.5 × total minutes of vigorous activity + total minutes of moderate activity was greater than or equal to 30 minutes. Though not a strict interpretation of the guidelines, we feel these modifications do not introduce bias, and more accurately represent the activity levels of most Americans.