Introduction
Patients with Parkinson’s disease (PD) are likely to experience a decrease in their daily physical activity, because of physical impairments, fatigue, and apathy. Such a sedentary lifestyle is undesirable, because physical inactivity is a risk factor for cardiovascular disease, diabetes mellitus, cognitive impairment, osteoporosis, and depression [
40]. Moreover, physical inactivity may worsen various nonmotor symptoms, such as insomnia and constipation.
Thus far, only a few studies have examined physical activity in PD, and the results were inconsistent. Several studies found reduced levels of physical activity, but activity levels were not assessed optimally (either indirectly using visual analogous scales [
12], or using activity monitors mounted at the wrist, rather than the leg [
37]), or studies were very small [
5,
35]. Unexpectedly, two studies found that patients and controls spent comparable amounts of time being active [
7,
29].
The determinants of physical activity in PD remain incompletely understood [
11]. Generic factors such as age [
16], gender [
6,
16], and health status [
16] are associated with the level of physical activity in healthy adults. Furthermore, depression is a risk factor for developing a sedentary lifestyle [
30]. Such factors may also affect exercise behavior in patients with PD. Identifying the determinants of physical activity may help to structure new exercise interventions.
Here, we quantified daily physical activities in a large group of PD patients and analyze the associated determinants, using data from the ParkinsonNet trial (699 patients) [
24,
25] and the population-based LASA study (1,959 controls) [
10].
Discussion
Patients with PD are widely presumed to follow a sedentary lifestyle, due to their physical, cognitive, and emotional impairments. We now provide new evidence to underpin this assumption, based on analyses of time spent on daily physical activity in a large cohort of PD patients and another large cohort of controls. The loss of time spent on activities was most obvious in patients with greater disease severity.
Our results showed that PD patients were 29% less active compared to controls. In a previous study of 24,000 subjects aged 65 years and older, similarly reduced activity levels (by about 23%) were found for patients with a chronic disease such as musculoskeletal disorders and vascular or heart diseases [
2]. The 29% reduction observed for PD patients in the present study might even be greater in comparison with healthy controls since our cohort did not include severely affected PD patients [
24]. Moreover, the LASA study, which we used as a control group, showed that about 60% of the population had a chronic disease [
39]. Direct comparison for comorbidity between the two groups was not possible as the LASA study only recorded broad categories and did not subdivide in specific disorders. Although it would be interesting incorporating fall histories in the analysis, data of fall history was not available for the control group. Future studies are required to investigate the influence of these factors.
It is important to consider the methods used to assess physical activity in the present and other studies. We used a validated interview-based physical activity questionnaire [
33], which is a subjective method of measuring physical activity. This might have resulted in an overestimation of the reported physical activity. However, this possible overestimation likely applies equally to both patients and controls, so it is unlikely that this influenced our results. Another possibility is that patients underestimated their activity due to memory problems. However, patients with severe cognitive impairment (MMSE < 24) were excluded, so this is unlikely to explain the physical inactivity observed in PD patients. Other studies circumvented such problems by using objective measures of physical activity; these studies did not find differences between patients and controls [
7,
11,
37]. Although these activity monitors have been well validated and shown to be reliable for a range of activities, some specific activities such as gardening and cycling are difficult to quantify [
9,
20,
41]. This may be one reason for the discrepancy with our results.
We also investigated the determinants associated with daily physical activity in PD patients. One factor was gender. Univariate regression analysis showed that women with PD were 80% more active than men. This is in contrast with observations in non-PD populations [
16]. The LAPAQ assessed a broad range of activities, including walking outside, cycling, gardening, light and heavy household activities, and a maximum of two sport activities. When we removed the household activities from the total activity score, men appeared to be more physically active than women (
p < 0.01). The same effect was found in the control group. This suggests that women spent more time to daily activities because the LAPAQ records household activities. Another study found comparable results for older women: two-thirds of them reached recommended levels of physical activity when domestic activities were included in the assessment, but only 21% when these domestic activities were excluded [
19].
We also found several additional determinants associated with daily physical activity. Specifically, inactivity in PD was associated with worse walking performance, more disability in daily life, and greater disease severity. These factors identified in this study for PD are comparable to other studies that investigated the determinants of physical inactivity in older persons [
2,
6,
32].
Our results concerning the determinants of daily physical activity in PD have to be interpreted with some caution for several reasons. First, the final model was not unique, because various different combinations of determinants yielded almost the same percentage of explained variance. A model with two dimensions (i.e., walking performance and disability in daily life) was as good as a model with three dimensions (additionally including either disease severity, fear of falling, anxiety and depression, or faller status).
Second, in all models, the unexplained variance remained large. Our final model explained 24% of the variance. Adding more variables into the model did not increase the explained variance. This suggests that additional factors are responsible for the variability in LAPAQ scores in PD. Because we secondarily analyzed data from two previous trials, various factors were not investigated. One such factor is fatigue, which may be an independent contributor to physical inactivity in PD [
11]. Moreover, social cognitive theories propose that behavioral factors are associated with physical activity [
28,
32]. Earlier work showed that a model which included self-efficacy and outcome expectations, explained 64% of the variance in exercise behavior in older adults [
28]. Other studies found that (lack of) interest in physical activity, knowledge about the benefits of exercise, and social supports also predicted exercise behavior [
8,
28,
32]. In the literature, many other possible determinants have been suggested, ranging from income and socioeconomic status up to seasonal effects [
30,
31,
36]. Further work, therefore, remains necessary to identify ‘all’ determinants, as a basis for future therapeutic interventions.
Although we showed that physical inactivity was most obvious in patients with greater disease severity, not all PD patients with advanced disease were completely sedentary. This suggests that even PD patients in later stages of the disease might be stimulated to become more active. Participating in regular physical activity would be particularly useful for PD patients, because exercise may help to prevent cardiovascular events, diabetes mellitus, and osteoporosis [
40]. Moreover, in older subjects, physical activity was reported to suppress typical PD symptoms such as depression and cognitive decline [
4,
18]. In addition, preclinical evidence in animals with experimental parkinsonism suggests that exercise may directly alter the neurodegenerative process in PD [
27]. A meta-analysis found exercise to be effective at improving physical functioning, health-related quality of life, strength, balance, and gait speed for people with PD [
15]. It is, therefore, important for PD patients to avoid a sedentary lifestyle. Simply informing people about the health benefits of physical activity is likely insufficient to attain a sustained behavioral change. Motivational aspects are especially important because such behavioral interventions could target motivation to increase levels of physical activity. We are now testing this in the ParkFit trial, a large exercise study involving 586 PD patients randomized to receive a behavioral change program aimed to increase daily physical activity levels. The ParkFit trial uses motivational strategies and personal health coaches to induce a lasting increase in exercise behavior for patients with PD; the first results are expected in 2012 [
38].
Acknowledgments
The ParkinsonNet trial was supported by ZonMw (947-04-357), the Netherlands Organization for Scientific Research, the Dutch Parkinson’s Disease Society, the National Parkinson Foundation, and De Stichting Robuust. The Longitudinal Aging Study Amsterdam is largely supported by a grant from the Netherlands Ministry of Health Welfare and Sports, Directorate of Nursing Care and Older persons. This study was sponsored by the MJ Fox Foundation and the National Parkinson Foundation. All sources of funding had no further involvement.