Identifying physical activity patterns in chronic fatigue syndrome using actigraphic assessment
Introduction
Patients with chronic fatigue syndrome (CFS) often describe themselves as being profoundly less physically active and unable to reach similar physical activity levels as compared to before the onset of their illness. Many CFS patients report that even minor physical exertion results in a significant increase in fatigue- and CFS-related symptoms. There is evidence that many CFS patients cope with their illness by resting or avoiding physical activity [1], [2], [3]. In cognitive behaviour models of CFS, it has been hypothesised that pervasive avoidance of physical activity decreases the tolerance for physical exertion, and as such can perpetuate the CFS-related symptoms [4].
Clinical observations and especially patients' self-reports suggest that the lifestyles of some other CFS patients are characterised by very active periods, followed by abnormally long periods of inactivity. Some authors have suggested that in CFS, the periods of rest are interrupted by short periods of marked activity during which patients perform at “normal” levels [5]. These short periods of high physical activity may have detrimental effects and cause fatigue in patients with a low overall physical activity level. However, until now no empirical data are available to test this assumption.
Since changes in physical activity patterns are supposed to play an important role in maintaining symptoms and subsequently many therapeutic interventions have emphasised on activity regulation, it is crucial to identify abnormal activity patterns in a valid and reliable way. In earlier studies of our research group, actual motor activity has been recorded with an ankle-worn motion-sensing device (actometer) in conjunction with self-report measures of physical activity [6], [7]. The data of these studies suggest that self-report measures of activity reflect the patients' view about their physical activity and may have been biased by cognitions concerning illness and disability.
In clinical practice, it has been observed that part of the CFS patients are characterised by profound physical inactivity, while other patients are far more active but nevertheless judge themselves as rather inactive. Both, research results and clinical impressions, indicate that it is important to test whether patients' self-report concerning long-term inactivity after exertion, large day-to-day fluctuations in activity, and pervasive inactivity, can be substantiated by a behavioural measure of activity.
In this study, physical activity was measured with an actometer over 12 consecutive days in both healthy controls and CFS patients. The general activity scores that were used in previous studies provided little information about intraindividual differences and might have obscured large fluctuations in daily activity scores. Therefore, parameters were developed to describe changes in physical activity in more detail. Specific attention was paid to periods of high activity and subsequent rest periods. Furthermore, it was tested whether the CFS sample was characterised by many large day-to-day fluctuations in physical activity. The actometer measurements were also used to subtype activity patterns in CFS in order to identify pervasively passive patients.
Previous studies found that part of the CFS patients had elevated depression scores. Since physical inactivity could be a symptom of depression, one might hypothesise that, in particular, pervasively passive patients would be characterised by increased levels of psychological distress. Therefore, it was tested whether levels of fatigue, psychological distress, and functional impairment were elevated in pervasively passive CFS patients, as compared to more physically active CFS patients.
Section snippets
Subjects
All patients with a major complaint of fatigue, referred to the outpatient clinics of internal medicine of the University Medical Centre Nijmegen and the University Hospital Maastricht between October 1996 and December 1998 were assessed by means of detailed history, physical examination, and questionnaires. Patients had to fulfil the CDC criteria for CFS [8]. Additional criteria were age between 18 and 60 years, no previous or current engagement in CFS research, not pregnant or engaged in
Results
The group characteristics of the CFS patients and healthy controls are displayed in Table 1. The CFS sample had significantly more females but the groups were comparable concerning their average age. Table 2, Table 3 show that the general physical activity was significantly higher for the controls and that in both groups, men had higher general activity scores compared to women.
Discussion
Previous studies showed that CFS patients were as a group less physically active compared to healthy controls. Nevertheless, quite large variations in actometer scores suggested considerable individual differences. Earlier studies also indicated that self-report measures of physical activity and actual measurement of activity were not highly correlated. Furthermore, our clinical observations strengthened our belief that by merely comparing overall levels of physical activity important
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