Introduction
Fatigue is a common and debilitating side effect of cancer and its treatment that often persists well beyond active cancer treatment [
1,
2]. Chronic cancer-related fatigue (CCRF) prevents patients to have “a normal life” [
3] and hampers in performing daily activities [
4].
The role of physical activity in the context of chronic cancer-related fatigue is neither straightforward nor evident. For example, inactivity has been proposed as a result as well as a cause of fatigue. Lower physical activity was associated with fatigue before initiation of treatment [
5] and with persistence of fatigue [
1]. However, a large cohort study of Neil et al. [
6] showed no difference in inactivity between cancer survivors and individuals with no history of cancer, and another study showed that self-reported physical activity was no predictor for fatigue before and after chemotherapy [
7].
Behavioral interventions that try to reduce fatigue usually aim at increasing level of physical activity by means of exercise or graded activity [
8‐
11]. These interventions are generally effective in reducing fatigue [
8‐
12]. Such interventions should be adapted to individual physiological differences [
13] to be fully appreciated. Presumably, effective interventions correspondingly depend on the individual’s starting point in terms of physical behavior. Therefore, it is needed to consider the heterogeneity of patients’ physical behavior and to explore what patient characteristics relate to these behaviors.
In fact, heterogeneity in physical behavior has been scarcely considered in behavioral intervention studies. One example is a study by Van der Werf et al. who aimed to reveal heterogeneity of physical behavior in non-cancer patients who suffer from chronic fatigue syndrome [
14]. Patients were labeled pervasively passive, active, or moderately active based on their total amounts of physical activity. Such “sub-typing” can help to personalize interventions and define helpful and realistic treatment goals.
Other, more specific physical behavior measures than total amounts of physical activity are increasingly acknowledged as important and clinically relevant. Firstly, benefits of exercising or performing higher intensity activities are substantiated for cancer survivors [
10]. Secondly, deteriorating effects of high amounts of sedentary behavior are increasingly acknowledged [
15,
16] and addressed in many guidelines for cancer survivors [
13]. Thirdly, measures that quantify distributions of these behaviors over time [
17‐
19] were able to differentiate patients with chronic health conditions comparable to CCRF from healthy subjects independently of the total amounts of these physical behaviors. Consequently, focusing solely on total amounts of physical activity is probably too generic.
To acknowledge the relevance of different measures of physical behavior, Thompson et al. advocate to use profiles to describe physical activity of individuals [
20]. This inherently leads to the research question in the current paper: What physical behavior profiles are prominent in persons who suffer from CCRF? This paper explicitly focusses on the interrelatedness of a range of physical behavior measures, which is novel in this field.
Secondly, this paper explores if the physical behavior profiles are related to participant characteristics. Therefore, demographic and clinical factors (age, sex, education, body mass index (BMI), working hours, cancer treatment types, time since last cancer treatment, and limitations due to pain or comorbidities), as well as fatigue, distress, and perceived work ability are studied for their relation with the physical behavior profiles.
Discussion
In this study, multiple physical behavior measures were collected to exhibit heterogeneity of patients who suffer from CCRF by means of physical behavior profiles. Three profiles were distinguished: a sedentary, active, and average profile. Furthermore, we investigated participant characteristics as covariates of these profiles, to increase knowledge on and enhance personalization of interventions that somehow target physical behavior in this population.
The three profiles were mostly distinguished by the measures PAL and MVPA time. Compared to the sedentary profile, participants in the active profile were roughly twice as active in terms of PAL and spent almost seven times longer on prolonged MVPA. Time spent in prolonged bouts of SB also differed between profiles: means were 4 h and 15 min in the active profile, compared to 6 h and 31 min in the sedentary profile. The average profile had the lowest (almost no) decline of PAL between morning and afternoon. These results show that persons who suffer from CCRF form a very heterogeneous group in terms of physical behaviors, who require diverse intervention goals when focusing on physical behavior.
All three profiles provide potential focus for intervening on physical behavior in clinical practice. Obvious goals—and currently widely accepted [
13]—are increasing PAL and prolonged MVPA time, which apply to participants in the sedentary and average profile. However, in the active profile, increasing PAL is expected to be less effective compared to the other profiles. Patients who have an active profile might benefit from reducing the time of pronged SB or from better dividing physical activities throughout the day by energy conservation strategies [
38]. Indeed, a patient in the active profile may actually be helped by reducing PAL before increasing it gradually in order to match the patient’s physical behavior to his or her capacity. This assumption is supported by a study in breast cancer survivors in which self-reported physical activity measures showed that psychological outcomes were poor for the quartile of patients with the highest durations of physical activity [
39].
Boundaries between the physical behavior profiles are not strict, which hampers direct transfer to clinical practice; 88% of the participants were assigned to a profile with a probability above 80%. The distinct profiles can provide a direction for defining an effective physical behavior goal, but encourage to match the intervention goals to the patient’s perspective and individual wishes as well.
The second research question focused on covariates of these physical behavior profiles. Participants who reported stronger limitations by pain were more likely to have a sedentary profile compared to an active profile. This result highlights the relevance of pain management in the context of physical activity interventions as it could be a barrier for becoming more physically active and for staying physically active when professional guidance in the context of rehabilitation stops.
Additionally, older participants and participants who reported no or only weak limitations due to comorbid conditions were more likely to have a sedentary profile compared to an average profile. Studies on—not necessarily fatigued—breast cancer survivors support the results on the associations with age [
40]. The result on the association with limitations by comorbid conditions seems contradictory to the findings on limitations by pain. An explanation might be that comorbid conditions are perceived as less limiting for those who are engaged in a sedentary lifestyle, although it should be noted that the question that assesses limitations due to comorbid conditions do not explicitly mention physical activities.
Our sample is comparable to a sample of long-term colon cancer survivors [
25], in terms of prolonged MVPA. Fourteen percent compared to 15% in the current sample meets clinical guidelines, operationalized as spending 150 min per week on MVPA in bouts of 10 min or longer. However, MVPA time (6.2%) differed greatly from samples of breast cancer survivors: 1.9% [
16] and 1.1% [
15]. Also, SB time (78.4% in our sample) differed from breast cancer survivors (61.3% [
41], 66.3% [
15], and 78.2% [
16]) and from colon cancer survivors (60.7% [
25]). Prolonged SB differed even more: 152.9 min of prolonged SB [
25] versus 325.6 min in the current sample. Differences could relate to choices for cutoff values, as well as to clinical status; the comparison samples were not necessarily fatigued and homogeneous groups in terms of cancer diagnoses.
Our study has a number of limitations. Firstly, all participants were willing to follow an intervention in a trial called “Fitter after cancer” and were aware that physical activity was measured. Both properties could provide bias by overestimating PAL compared to the general population of CCRF. Secondly, generalizability might be hampered because our sample was diagnosed with various cancer types and received different treatments. Thirdly, evaluating 1-minute measurement intervals, although generally used [
42], causes real life data points to represent a mixture of behaviors. Therefore, absolute values of SB and MVPA measures should be interpreted cautiously. Finally, in order to come to the set of physical behavior measures, some measures and cutoff values for time or cpm lack evidence or were chosen arbitrarily. However, by describing these choices transparently, we presume that the results of this study are valuable nevertheless.
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