Is the chronic fatigue syndrome an exercise phobia? A case control study

OBJECTIVE: The aim of this study was to test whether patients with chronic fatigue syndrome (CFS) have an exercise phobia, by measuring anxiety-related physiological and psychological reactions to ordinary activity and exercise. METHODS: Patients and healthy but sedentary controls were assessed over 8 h of an ordinary day, and before, during and after an incremental exercise test on a motorised treadmill. To avoid confounding effects, those with a comorbid psychiatric disorder were excluded. Heart rate, galvanic skin resistance (GSR) and the amount of activity undertaken were measured, along with state and trait measures of anxiety. RESULTS: Patients with CFS were more fatigued and sleep disturbed than were the controls and noted greater effort during the exercise test. No statistically significant differences were found in either heart rate or GSR both during a normal day and before, during and after the exercise test. Patients with CFS were more symptomatically anxious at all times, but this did not increase with exercise. CONCLUSION: The data suggest that CFS patients without a comorbid psychiatric disorder do not have an exercise phobia.     

Fatigue after breast cancer and in chronic fatigue syndrome: Similarities and differences

Objective: Fatigue is investigated in 57 severely fatigued disease-free breast cancer patients and in 57 gender- and age-matched patients with chronic fatigue syndrome (CFS) using multidimensional and multimethod assessment. A comparison between these groups of patients is important to determine whether a cognitive behavioural intervention to reduce fatigue in CFS patients would be appropriate as well for severely fatigued disease-free breast cancer patients. Methods: Measurement included computerised questionnaires and a standardised neuropsychological test. Furthermore, patients filled out a daily Self-Observation List (SOL) and wore an actometer during a period of 12 days. Results: In comparison to severely fatigued disease-free breast cancer patients, CFS patients score more problematic with regard to the level of fatigue, functional impairment, physical activity, pain and self-efficacy. However, a subgroup of severely fatigued disease-free breast cancer patients reports the same amount of problems as CFS patients with regard to psychological well-being, sleep and concentration. Finally, CFS patients and severely fatigued breast cancer patients score equal on measures of social support. Conclusion: There seem to be some similarities but also many differences between severely fatigued breast cancer survivors and females with CFS. Therefore, cognitive behaviour therapy (CBT) to reduce fatigue after treatment for cancer should also differ in certain aspects from cognitive behaviour therapy as it has been developed for patients with CFS.     

Fatigue after breast cancer and in chronic fatigue syndrome: similarities and differences

Objective: Fatigue is investigated in 57 severely fatigued disease-free breast cancer patients and in 57 gender- and age-matched patients with chronic fatigue syndrome (CFS) using multidimensional and multimethod assessment. A comparison between these groups of patients is important to determine whether a cognitive behavioural intervention to reduce fatigue in CFS patients would be appropriate as well for severely fatigued disease-free breast cancer patients. Methods: Measurement included computerised questionnaires and a standardised neuropsychological test. Furthermore, patients filled out a daily Self-Observation List (SOL) and wore an actometer during a period of 12 days. Results: In comparison to severely fatigued disease-free breast cancer patients, CFS patients score more problematic with regard to the level of fatigue, functional impairment, physical activity, pain and self-efficacy. However, a subgroup of severely fatigued disease-free breast cancer patients reports the same amount of problems as CFS patients with regard to psychological well-being, sleep and concentration. Finally, CFS patients and severely fatigued breast cancer patients score equal on measures of social support. Conclusion: There seem to be some similarities but also many differences between severely fatigued breast cancer survivors and females with CFS. Therefore, cognitive behaviour therapy (CBT) to reduce fatigue after treatment for cancer should also differ in certain aspects from cognitive behaviour therapy as it has been developed for patients with CFS.     

Strength and physiological response to exercise in patients with chronic fatigue syndrome

OBJECTIVE: To measure strength, aerobic exercise capacity and efficiency, and functional incapacity in patients with chronic fatigue syndrome (CFS) who do not have a current psychiatric disorder. METHODS: Sixty six patients with CFS without a current psychiatric disorder, 30 healthy but sedentary controls, and 15 patients with a current major depressive disorder were recruited into the study. Exercise capacity and efficiency were assessed by monitoring peak and submaximal oxygen uptake, heart rate, blood lactate, duration of exercise, and perceived exertion during a treadmill walking test. Strength was measured using twitch interpolated voluntary isometric quadriceps contractions. Symptomatic measures included physical and mental fatigue, mood, sleep, somatic amplification, and functional incapacity. RESULTS: Compared with sedentary controls, patients with CFS were physically weaker, had a significantly reduced exercise capacity, and perceived greater effort during exercise, but were equally unfit. Compared with depressed controls, patients with CFS had significantly higher submaximal oxygen uptakes during exercise, were weaker, and perceived greater physical fatigue and incapacity. Multiple regression models suggested that exercise incapacity in CFS was related to quadriceps muscle weakness, increased cardiovascular response to exercise, and body mass index. The best model of the increased exercise capacity found after graded exercise therapy consisted of a reduction in submaximal heart rate response to exercise. CONCLUSIONS: Patients with CFS were weaker than sedentary and depressed controls and as unfit as sedentary controls. Low exercise capacity in patients with CFS was related to quadriceps muscle weakness, low physical fitness, and a high body mass ratio. Improved physical fitness after treatment was associated with increased exercise capacity. These data imply that physical deconditioning helps to maintain physical disability in CFS and that a treatment designed to reverse deconditioning helps to improve physical function.     

The development of a model of fatigue in neuromuscular disorders: a longitudinal study

BACKGROUND: Severe fatigue is reported by the majority of patients with three relatively common types of neuromuscular disorders. OBJECTIVE: This study aimed to identify predictors of fatigue in a longitudinal study and to develop a model of fatigue in patients with three neuromuscular disorders. METHODS: One hundred ninety-eight patients [60 facioscapulohumeral muscular dystrophy (FSHD), 70 adult-onset myotonic dystrophy (MD), and 68 hereditary motor and sensory neuropathy type I (HMSN-I) patients] were studied twice during an 18-month period. Fatigue severity was assessed by the Checklist Individual Strength. A multidimensional assessment method was used, including self-report questionnaires, a daily Self-Observation List, and physical activity (actometer). Muscle strength was determined using the Medical Research Council scale. Structural equation modeling was used to develop and test a model of factors contributing to the persistence of experienced fatigue. RESULTS: Muscle strength, self-reported physical activity, sleep disturbances, and pain at baseline contributed directly or indirectly to fatigue and impairment at follow-up. Lower muscle strength contributed to lower levels of physical activity, which, in turn, contributed to fatigue severity. The model showed excellent fit for the whole group of neuromuscular disorders. In FSHD, pain also contributed to physical activity. A model with the actometer as measurement for actual physical activity instead of self-report showed an excellent model fit in FSHD and HMSN but an insufficient fit in MD. CONCLUSION: The model of perpetuating factors for fatigue in FSHD and HMSN is different from the model in MD. The main difference is in physical (in)activity. These differences have implications for interventions based on these models.     

Deviations in daily physical activity patterns in patients with the chronic fatigue syndrome: a case control study

Objectives

Deviations in daily physical activity patterns may play an important role in the development and maintenance of fatigue in the chronic fatigue syndrome (CFS). The aim of this study is to gain insight into the objective daily physical activity pattern of patients with CFS in comparison with healthy controls. The secondary objective is studying the awareness in performing physical activities.

Methods

The objective daily physical activity pattern was measured with a tri-axial accelerometer in 35 patients with CFS and in 35 age- and gender-matched healthy controls. The objective daily physical activity level and distribution of physical activities at low, medium and high intensity levels during the day were measured. Moreover, variability in performing physical activities within and between subjects was computed. Subjective ratings of self-reported daily physical activity levels were assessed at a visual analog scale.

Results

CFS patients were significantly less physically active in the afternoon and evening, and spent fewer activities at high intensity levels and more at low intensity levels. Moreover, CFS patients showed more variability in their own physical activity pattern during the afternoon. The heterogeneity in the physical activity pattern between subjects within the CFS and control group did not differ. Finally, CFS patients were more aware about their daily physical activity level than healthy controls.

Conclusion

CFS patients showed deviations in the objectively measured daily physical activity pattern. Future research should elucidate the relation between impaired balances in daily physical activity patterns and fatigue severity in CFS.     

Hormonal responses to exercise in chronic fatigue syndrome

Chronic fatigue syndrome (CFS) is a debilitating disease characterized by severe, unexplained fatigue and postexertional exacerbation of symptoms. We examined basal endocrine function in a group of CFS patients and a carefully matched group of sedentary controls. The subjects then completed a graded, maximal exercise test on a treadmill, and additional blood samples were drawn 4 min and a day after the end of exercise. There were no differences in basal hormone levels before exercise. Plasma adrenocorticotropin, epinephrine, prolactin and thyrotropin responses 4 min after exercise were lower in the CFS group, but the growth hormone response may have been exaggerated, and the plasma norepinephrine response was similar to that in controls. The next day, there were no differences in hormone levels between the groups, which suggests that long-term changes in endocrine function are unlikely to be a cause of the prolonged fatigue that occurs in CFS patients after a bout of exertion.     

Stress-induced changes in LPS-induced pro-inflammatory cytokine production in chronic fatigue syndrome

OBJECTIVE: It has been suggested that a hypofunctional hypothalamic-pituitary-adrenal (HPA) axis in chronic fatigue syndrome could result in an exaggerated release of pro-inflammatory cytokines during stress. As pro-inflammatory cytokines are involved in the induction of sickness behavior and thus constitute a potential physiological correlate of stress-induced symptom exacerbation in chronic fatigue syndrome, we set out to evaluate the LPS-induced production of pro-inflammatory cytokines during psychosocial stress in CFS and healthy controls. METHOD: Twenty-one CFS patients and 20 healthy controls matched for age and gender underwent a standardized psychosocial stress test (Trier social stress test, TSST). Adrenocorticotropine hormone (ACTH), salivary cortisol and plasma cortisol levels were measured before and repeatedly following exposure to the stressor. Lipopolysaccharide-stimulated production of interleukin-6 and tumor necrosis factor-alpha were assessed at baseline as well as 10 and 60 min after the stress test. RESULTS: CFS patients showed an inverse stress-induced response pattern of LPS-stimulated cytokines responses in comparison to healthy controls, i.e. stimulated cytokine production decreased shortly after stress in CFS patients, while it increased in controls. Fatigue scores and basal LPS-induced cytokine levels were significantly associated for TNF-alpha in controls and for both cytokines in CFS patients. Stress-induced changes in stimulated cytokine production were not associated with general fatigue scores in the control group, whereas in the CFS group, fatigue scores were significantly correlated with integrated levels of LPS-induced cytokines. However, partial correlations revealed that these results were due to the high correlations with basal LPS-induced cytokine levels. CONCLUSION: CFS patients do not show an exaggerated secretion of LPS-induced cytokines. Although cortisol responses to stress were normal, pro-inflammatory cytokine levels in CFS patients were significantly attenuated. Possible intracellular mechanisms, such as for example an enhanced sensitivity to inhibitory effects of glucocorticoids, a diminished responsivity to catecholaminergic stimulation, and a disruption of intracellular activation are discussed. Basal levels of stimulated pro-inflammatory Il-6 levels are generally related to fatigue scores. However, in CFS patients this association is of greater magnitude and can also be observed for TNF-alpha.     

Determinants of health care use in chronic fatigue syndrome patients: a cross-sectional study

BACKGROUND: Chronic fatigue syndrome (CFS) is associated with a high use of health care services. To reduce the related costs for patients and society, it will be useful to know which factors determine CFS patients' amount of health care use. Little is known, however, about these factors. METHOD: The present study retrospectively performed a cross-sectional analysis to investigate the possible factors determining CFS patients' health care use. A total of 263 CFS patients, derived from two subgroups (149 from tertiary care and 114 from primary/secondary care), participated. Health care use was measured with a questionnaire asking details on consumption over the past 6 months. Fatigue severity and physical functioning were measured with the subscale Experienced Fatigue of the Checklist Individual Strength (CIS-20) and the subscale Physical Functioning of the SF-36, respectively. Multiple regression analysis, T-tests, and chi(2) tests were performed. RESULTS: The regression analysis revealed that, after controlling for patient characteristics (explaining 13%), fatigue factors added 4% predictive value and certain perpetuating factors of fatigue, including focus on bodily symptoms and attributions of fatigue, added another 5%. The analysis of subgroups revealed that, compared to the tertiary care population, fewer patients from primary/secondary care had visited a medical specialist (50% vs. 71%), used antidepressants (16% vs. 25%) and tranquilizers (3% vs. 18%), and had spent a night in hospital (7% vs. 10%). However, overall costs of health care between these subgroups did not differ. CONCLUSIONS: This study showed that illness duration, physical impairment due to fatigue, and psychological perpetuating factors of fatigue do determine the variance in CFS patients' health care use. These results give clear directions for treating CFS patients and managing health care for CFS.     

Reduced oxidative muscle metabolism in chronic fatigue syndrome

The purpose of this study was to determine if chronic fatigue syndrome (CSF) is characterized by abnormalities in oxidative muscle metabolism. Patients with CFS according to Centers for Disease Control (CDC) criteria (n = 22) were compared to normal sedentary subjects (n = 15). CFS patients were also tested before and 2 days after a maximal treadmill test. Muscle oxidative capacity was measured as the maximal rate of postexercise phosphocreatine (PCr) resynthesis using the ADP model (V_max) in the calf muscles using ³¹P magnetic resonance spectroscopy. V_max was significantly reduced in CFS patients (39.6 ± 2.8 mmol/L/min, mean ± SE) compared to controls (53.8 ± 2.8 mmol/L/min). Two days postexercise there was no change in resting inorganic phosphate (Pi)/PCr or V_max in the CFS patients (n = 14). In conclusion, oxidative metabolism is reduced in CFS patients compared to sedentary controls. In addition, a single bout of strenuous exercise did not cause a further reduction in oxidative metabolism, or alter resting Pi/PCr ratios. © 1996 John Wiley & Sons, Inc.     

Psychological correlates of functional status in chronic fatigue syndrome

Background: The present study was designed to test a cognitive model of impairment in chronic fatigue syndrome (CFS) in which disability is a function of severity of fatigue and depressive symptoms, generalized somatic symptom attributions and generalized illness worry. Methods: We compared 45 CFS and 40 multiple sclerosis (MS) outpatients on measures of functional ability, fatigue severity, depressive symptoms, somatic symptom attribution and illness worry. Results: The results confirmed previous findings of lower levels of functional status and greater fatigue among CFS patients compared to a group of patients with MS. Fatigue severity was found to be a significant predictor of physical functioning but not of psychosocial functioning in both groups. In CFS, when level of fatigue was controlled, making more somatic attributions was associated with worse physical functioning, and both illness worry and depressive symptoms were associated with worse psychosocial functioning. Conclusions: Our findings support the role of depression and illness cognitions in disability in CFS sufferers. Different cognitive factors account for physical and psychosocial disability in CFS and MS. The SF-36 may be sensitive to symptom attributions, suggesting caution in its interpretation when used with patients with ill-defined medical conditions.     

Cognitive behavior therapy for chronic fatigue syndrome: a case study

The case of a 26-year old woman with Chronic Fatigue Syndrome (CFS) is presented. Multidimensional assessment showing severe debilitating fatigue and considerable psychological, social and occupational impairment confirmed the diagnosis. Cognitive behavior therapy (CBT) was based on a tested causal model of CFS and individual behavioral analyses. Key elements in CBT were process variables from the CFS model, like sense of control, causal attributions, physical activity and focusing on bodily functions. Goals were recovery from fatigue, returning to work and relapse prevention. The course of therapy is described in detail to illustrate difficulties in treating CFS. Assessments were made five times, at baseline and at 8, 14, 21 and 33 months. Comparison of the pretest, post-test and follow-up scores of the outcome variables, fatigue and functional impairment and of the process variables showed clinically significant improvement from the range of CFS patients to the range of healthy controls.     

Exercise performance and fatiguability in patients with chronic fatigue syndrome.

To examine the role of delay in recovery of peripheral muscle function following exercise in the fatigue experienced by patients with the chronic fatigue syndrome (CFS) and to examine the influence of effort perception in limiting exercise performance in these patients, a study was carried out on a group of twelve patients with chronic fatigue syndrome and 12 sex and age-matched sedentary control subjects. Symptom limited incremental cycle exercise tests including measurements of perceived exertion were performed followed by examination of the contractile properties of the quadriceps muscle group for up to 48 hours. Muscle function was assessed by percutaneous electrical stimulation and maximum voluntary contractions. Muscle function at rest and during recovery was normal in CFS patients as assessed by maximum isometric voluntary contraction, 20:50 Hz tetanic force ratio and maximum relaxation rate. Exercise duration and the relationship between heart rate and work rate during exercise were similar in both groups. CFS patients had higher perceived exertion scores in relation to heart rate during exercise representing a reduced effort sensation threshold of 3.2 units on an unmodified Borg scale in CFS patients. Patients with chronic fatigue syndrome show normal muscle physiology before and after exercise. Raised perceived exertion scores during exercise suggest that central factors are limiting exercise capacity in these patients.     

Exacerbated physical fatigue and mental fatigue in Parkinson's disease.

OBJECTIVE: To characterize fatigue in Parkinson's disease (PD). BACKGROUND: Fatigue is a recognized problem in PD. Fatigue can be in the physical realm or in the mental realm. Fatigue has not been characterized in PD. METHODS: We characterized fatigue in 39 PD patients and 32 age-matched normal controls using five questionnaires: A. The Multidimensional Fatigue Inventory (MFI), which measures five dimensions of fatigue independently including general fatigue, physical fatigue, reduced motivation, reduced activity, and mental fatigue. B. The Fatigue Severity Inventory (FSI), which quantifies fatigue in general. C. The Profile of Mood States (POMS), which assesses six subjective subscales: tension-anxiety, depression-dejection, anger-hostility, fatigue-inertia, vigor-activity, and confusion-bewilderment. D. Center for Epidemiological Studies-Depression Scale (CES-D). E. Visual Analog linear scale of energy (VA-E). RESULTS: PD patients scored higher in all of the five dimensions of fatigue in the MFI including general fatigue, physical fatigue, reduced motivation, reduced activity, and mental fatigue (P < 0.001 except for mental fatigue P = 0.005). The severity of physical fatigue did not correlate with that of mental fatigue. PD patients scored higher on the FSI, POMS, CES-D, and scored lower on the VA-E. The scores in the FSI correlated with general fatigue, physical fatigue, reduced activity, and reduced motivation but not with mental fatigue in the MFI. Depression correlated with all dimensions of fatigue except physical fatigue in the MFI. Disease severity, as measured by Modified Hoehn and Yahr staging, did not correlate with any of the measures. CONCLUSIONS: PD patients have increased physical fatigue and mental fatigue compared to normals. Physical fatigue and mental fatigue are independent symptoms in PD that need to be assessed and treated separately.     

Fatigue and daytime sleepiness rating scales in myotonic dystrophy: a study of reliability

OBJECTIVES: To assess the reliability of the Epworth Sleepiness Scale (ESS), Daytime Sleepiness Scale (DSS), Chalder Fatigue Scale (CFS), and Krupp's Fatigue Severity Scale (KFSS) in patients with myotonic dystrophy type 1 (DM1). METHODS: In total, 27 patients with DM1 were administered the questionnaires on two occasions, with a 2 week interval. Internal consistency and test retest reliability were measured using intraclass correlation coefficients (ICCs), and Cronbach's alpha, Cohen's kappa, and Goodman-Kruskal's gamma coefficients. RESULTS: Internal consistency of the CFS and KFSS were adequate (alpha > 0.70) but that of the ESS was weak (alpha = 0.24). Both daytime sleepiness and fatigue rating scales showed significant test retest reliability. Test retest reliability for individual items revealed inconsistencies for some ESS and CFS items. CONCLUSIONS: Reliability of the CFS, DSS, and KFSS was high, allowing their use for individual patients with DM1, but that of the ESS was lower, rendering its current usage in DM1 questionable. Fatigue rating scales such as the KFSS, which are based on the behavioural consequences of fatigue, may constitute a more accurate and comprehensive measure of fatigue severity in the DM1 population.     

Influence of repeated maximal exercise testing on biomarkers and fatigue in sarcoidosis

Fatigue in the immune mediated inflammatory disease sarcoidosis is thought to be associated with impaired exercise tolerance. This prospective study assessed fatigue and recuperative capacity after repeated exercise, and examined whether changing concentrations in biomarkers upon exercise are associated with fatigue.Twenty sarcoidosis patients and 10 healthy volunteers performed maximal cardiopulmonary exercise tests on two successive days. Concentrations of cytokines, stress hormones, ACE and CK were assessed before and after the two exercise tests, and 3 days thereafter. All participants completed a sleep diary.Severely fatigued patients showed significant lower VO₂ max (p = 0.038, p = 0.022) and maximal workload (p = 0.034, p = 0.028) on both exercise tests compared to healthy controls. No impairment of maximal exercise testing was demonstrated during the second cycling test in any group. Fatigue was not correlated with changes in concentrations of biomarkers upon exercise. Severely fatigued patients rated both tests as significantly more fatiguing, and reported significant lower mean subjective night sleeping time during the testing period.Fatigue in sarcoidosis patients cannot be objectified by reduction of exercise capacity after repeated maximal exercise testing, and is not correlated with significant changes in biomarkers. Severe fatigue is only and consistently featured by patient reported outcomes.     

The role of fear of physical movement and activity in chronic fatigue syndrome

Objective: To examine beliefs in relation to avoidance of activity in chronic fatigue syndrome (CFS) patients. Methods: The first phase consisted of modifying an existing chronic pain measure of kinesiophobia—fear of physical movement and activity—and validating it on the CFS population [Tampa Scale of Kinesiophobia-Fatigue (TSK-F); n=129; test–retest: r=.89, P<.001; =.68]. Subscales of Illness Beliefs (=.78) and Beliefs about Activity (=.70) were identified. The second phase consisted of evaluating whether behavioural persistence was predicted by the TSK-F (n=33). Participants were asked to ride an exercise bike for as long as they felt able. Results: Analyses indicated that behavioural persistence did not correlate with maximal heart rate or resting heart rate, level of tiredness, symptom severity, illness identity or emotional distress. However, the TSK-F did correlate highly with distance travelled and added a significant 15% of the variance in distance after adjustments for gender and physical functioning (PF). The TSK-F Beliefs about Activity subscale appears to be the predictive factor, explaining 12% of the variance in excise performance or rather 12% of the avoidance of exercise. Conclusion: Beliefs about Activity appear to be an important variable in predicting behaviour and avoidance of exercise. As avoidance has been suggested as a key to the maintenance of symptoms, disability and distress in CFS patients, this research has important theoretical, clinical and research implications.     

Cerebral and Systemic Hemodynamics Changes During Upright Tilt in Chronic Fatigue Syndrome

BACKGROUND AND PURPOSE: During head-up tilt (HUT), patients with chronic fatigue syndrome (CFS) have higher rates of neurally mediated hypotension (NMH) and postural tachycardia syndrome (POTS) than healthy controls. The authors studied whether patients with CFS were also more likely to have abnormal cerebral blood flow velocity (CBFV) compared with controls in response to orthostatic stress. METHODS: Transcranial Doppler monitoring of middle cerebral artery (MCA) CBFV was performed during 3-stage HUT prospectively in 26 patients with CFS and 23 healthy controls. At the same time, continuous monitoring of arterial blood pressure (BP), heart rate (HR), endtidal CO2 (ET-CO2) were performed. Results are reported as mean +/- SD. RESULTS: NMH developed in 21 patients with CFS and in 14 controls (P = .22). POTS was present in 9 CFS patients and 7 controls (P = .76). Supine HR was higher in CFS patients, but all other hemodynamics and CBFV measures were similar at baseline. The median time to hypotension did not differ, but the median time to onset of orthostatic symptoms was shorter in those with CFS (P < .001). The CBFV did not differ between groups in the supine posture, at 1 or 5 minutes after upright tilt, at 5 or 1 minute before the end of the test, or at termination of the test. Mean CBFV fell at termination of tilt testing in those with CFS and controls. ET-CO2 was lower at termination of the test in those with CFS versus controls (P = .002). CONCLUSIONS: The results of this study are not consistent with the hypothesis that patients with CFS have a distinctive pattern of MCA CBFV changes in response to orthostatic stress.     

Physical activity in chronic fatigue syndrome: Assessment and its role in fatigue

This paper describes the assessment of physical activity in chronic fatigue syndrome (CFS) and investigated the following questions: Do patients with CFS have low levels of physical activity; is there a relationship between actual level of physical activity and fatigue: can self-report measures adequately assess actual level of physical activity; what is the role of cognitions with respect to physical activity; and are results with respect to physical activity specific to CFS? Three different types of activity measures were used: self-report questionnaires, a 12-day self-observation list, and a motion-sensing device (Actometer) which was used as a reference for actual activity level. Fifty-one patients with CFS, 50 fatigued patients with multiple sclerosis (MS), and 53 healthy subjects participated in this study. Although none of the self-report questionnaires showed high correlations with the Actometer, questionnaires that require simple ratings of specified activities were related to the Actometer and can be used as acceptable substitutes, in contrast to instruments that require general subjective interpretations of activity that had low or non-significant correlations with the Actometer. Actometer results showed that CFS patients and MS patients had similar activity levels and both groups were significantly less active than healthy subjects. Compared to MS patients, CFS patients were more likely to indicate that they had been less active than other persons they knew. Activities which patients expected to result in higher fatigue levels were less frequently performed. Patients with CFS had significantly higher scores on this measure than MS patients and healthy subjects. Low levels of physical activity were related to severe fatigue in CFS but not in MS. In conclusion, although CFS patients have similar low activity levels than MS patients, there are also important differences between both groups: in CFS cognitive factors are more prominently involved in producing the low activity levels than in MS and in CFS patients activity level is related to fatigue but not in MS.