Activity In Chronic Fatigue Syndrome Research Articles

Relationship Between Exercise-induced Oxidative Stress Changes and Parasympathetic Activity in Chronic Fatigue Syndrome: An Observational Study in Patients and Healthy Subjects

PurposeOxidative stress has been proposed as a contributor to pain in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). During incremental exercise in patients with ME/CFS, oxidative stress enhances sooner and antioxidant response is delayed. We explored whether oxidative stress is associated with pain symptoms or pain changes following exercise, and the possible relationships between oxidative stress and parasympathetic vagal nerve activity in patients with ME/CFS versus healthy, inactive controls. MethodsThe present study reports secondary outcomes from a previous work. Data from 36 participants were studied (women with ME/CFS and healthy controls). Subjects performed a submaximal exercise test with continuous cardiorespiratory monitoring. Levels of thiobarbituric acid–reactive substances (TBARSs) were used as a measure of oxidative stress, and heart rate variability was used to assess vagal activity. Before and after the exercise, subjects were asked to rate their pain using a visual analogic scale. FindingsSignificant between-group differences in pain at both baseline and following exercise were found (both, P < 0.007). In healthy controls, pain was significantly improved following exercise (P = 0.002). No change in oxidative stress level after exercise was found. Significant correlation between TBARS levels and pain was found at baseline (r = 0.540; P = 0.021) and after exercise (r = 0.524; P = 0.024) in patients only. No significant correlation between TBARS and heart rate variability at baseline or following exercise was found in either group. However, a significant correlation was found between exercise-induced changes in HRV and TBARS in healthy controls (r = −0.720; P = 0.001). ImplicationsOxidative stress showed an association with pain symptoms in people with ME/CFS, but no exercise-induced changes in oxidative stress were found. In addition, the change in parasympathetic activity following exercise partially accounted for the change in oxidative stress in healthy controls. More research is required to further explore this link.

Low NK Cell Activity in Chronic Fatigue Syndrome (CFS) and Relationship to Symptom Severity

Background: Natural killer (NK) cells act as an immune surveillance against invading pathogens and tumors. NK cell cytotoxicity (NKCC) has been reported to be decreased in patients with CFS.Methods: The objective of this review was to conduct an analysis of available publications that reported NKCC data in CFS in order to evaluate any relationships to case definitions used to define CFS and symptom severity.Results: Of 17 studies that evaluated NKCC in patients with CFS, defined using the CDC 1988 and/or 1994 case definition (CD), 88% (15/17) concluded that NKCC was decreased in CFS patients compared to normal controls. The NKCC decrease was seen using two established methods, 51Cr release (11/13) and flow cytometry (4/4). The mean percent decrease in NKCC using the CDC 1988 CD (66.3%) was significantly greater than that using the CDC 1994 CD (49.7%) (p 0.5). Finally, seven studies investigating the ability of various agents to augment NKCC in patients with CFS showed increases of NKCC with both in vitro exposure (4/5) and in vivo exposure using randomized trials (2/2).Conclusions: Low NKCC is commonly seen in CFS and is associated with increase symptom severity.

Avoidance behavior towards physical activity in chronic fatigue syndrome and fibromyalgia: the fear for post-exertional malaise

Avoidance behavior towards physical activity in chronic fatigue syndrome and fibromyalgia: the fear for post-exertional malaise

Fear of movement and avoidance behaviour toward physical activity in chronic-fatigue syndrome and fibromyalgia: state of the art and implications for clinical practice

The paper “Fear of movement and avoidance behaviour toward physical activity in chronic-fatigue syndrome and fibromyalgia: state of the art and implications for clinical practice” [1] is interesting but problematic. We agree that mild exercise is good but over exercise can cause relapse. Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and fibromyalgia patients suffer from relapse when is subjected to over exercise. We at the ME/CFS Center at Mount Sinai School of Medicine, New York are investigating the postexertional malaise seen in (ME/CFS). This is one of the criteria in the Canadian Consensus of diagnosis of ME/CFS. [2] The notion that ME/CFS is caused by poor conditioning is no longer widely accepted. It is thought that it is an immune system dysfunction, which after onset can be provoked by stress, over exercise or overwork [3]. Indeed, there can be depression, but this depression is secondary to the disease much like any other chronic disease. Cognitive behavioral therapy may be helpful to reverse the secondary depression but one must understand that this depression is indeed secondary and the initial disease entity is in the immune system and must be identified and treated.

Fear of movement and avoidance behaviour toward physical activity in chronic-fatigue syndrome and fibromyalgia: state of the art and implications for clinical practice

Severe exacerbation of symptoms following physical activity is characteristic for chronic-fatigue syndrome (CFS) and fibromyalgia (FM). These exacerbations make it understandable for people with CFS and FM to develop fear of performing body movement or physical activity and consequently avoidance behaviour toward physical activity. The aims of this article were to review what measures are available for measuring fear of movement and avoidance behaviour, the prevalence fear of movement and avoidance behaviour toward physical activity and the therapeutic options with fear of movement and avoidance behaviour toward physical activity in patients with CFS and FM. The review revealed that fear of movement and avoidance behaviour toward physical activity is highly prevalent in both the CFS and FM population, and it is related to various clinical characteristics of CFS and FM, including symptom severity and self-reported quality of life and disability. It appears to be crucial for treatment (success) to identify CFS and FM patients displaying fear of movement and avoidance behaviour toward physical activity. Individually tailored cognitive behavioural therapy plus exercise training, depending on the patient's classification as avoiding or persisting, appears to be the most promising strategy for treating fear of movement and avoidance behaviour toward physical activity in patients with CFS and FM.

Severity of symptom flare after moderate exercise is linked to cytokine activity in chronic fatigue syndrome

Chronic fatigue syndrome (CFS) patients often report symptom flare (SF) for >24 h after moderate exercise (post-ex). We hypothesized that SF is linked to increases in circulating cytokines and CD40 Ligand (CD40L). In 19 CFS patients and 17 controls, mental and physical fatigue and pain symptom ratings were obtained together with serum for 11 cytokines and CD40L before and at 0.5, 8, 24, and 48 h post-ex. Before exercise, CFS had lower CD40L (p<.05) but similar cytokines versus controls. In subgroups based on SF at 48 h, high SF patients (n=11) increased in IL-1beta, IL-12, IL-6, IL-8, IL-10, and IL-13 (p<.05) 8 h post-ex. Low SF patients (n=8) showed post-ex decreases in IL-10, IL-13, and CD40L, and controls decreased in IL-10, CD40L, and TNFalpha (p<.05). Thus, in CFS, cytokine activity may vary directly with SF, which may explain prior inconsistent findings.

Diurnal excretion of urinary cortisol, cortisone, and cortisol metabolites in chronic fatigue syndrome

Objective The aim of this study was to obtain comprehensive information on basal hypothalamic–pituitary–adrenal (HPA) axis activity in chronic fatigue syndrome (CFS) patients who were not affected by medication or comorbid psychiatric disorder likely to influence the HPA axis. Method Steroid analysis of urine collections from 0600 to 2100 h at 3-h intervals in CFS patients and in controls. Results Urinary free cortisol and cortisone concentrations showed a significant normal diurnal rhythm, but levels were lower across the cycle in CFS. In contrast, while urinary cortisol metabolites also showed a normal diurnal rhythm, levels were not significantly different between the CFS and controls at any time. Derived metabolite ratios were similar in both groups. Conclusion This study provides further evidence for reduced basal HPA axis function in patients with CFS, based on lower free cortisol and cortisone levels, but this is not corroborated by cortisol metabolite data. The difference between these measures cannot be explained by an altered timing of the diurnal rhythm.

Employment status in chronic fatigue syndrome. A cross-sectional study examining the value of exercise testing and self-reported measures for the assessment of employment status

To examine the value of exercise testing and self-reported disability for the assessment of employment status in patients with chronic fatigue syndrome. Cross-sectional observational study. A university-based chronic fatigue clinic. Fifty-four consecutive, Flemish, employed (not self-employed) chronic fatigue syndrome patients (49/54 female). Not applicable. Participants were questioned about their current and premorbid employment status, filled in the Chronic Fatigue Syndrome Activities and Participation Questionnaire (CFS-APQ), the Medical Outcomes Short Form 36 Health Status Survey (SF-36), and performed a maximal exercise test on a bicycle ergometer with continuous monitoring of cardiorespiratory variables. A significant association was observed between the current employment rate and two SF-36 subscales (i.e., role limitations due to physical functioning and social functioning; rho = 0.39 and 0.35 respectively) (n = 54). Analysing only the female chronic fatigue syndrome patients (n = 49), the current employment rate correlated significantly with the peak workload (rho = 0.38). The associations between either exercise testing or self-reported disability and employment status are too weak to predict employment status.

Time course of exercise induced alterations in daily activity in chronic fatigue syndrome

In a previous study we demonstrated that while people with CFS had lower daily activity levels than control subjects, they were able to increase daily activity via a daily walking program. We reanalyzed our data to determine the time course of activity changes during the walking program. Daily activity assessed via an accelometer worn at the hip was divided into sleep, active, and walking periods. Over the first 4–10 days of walking the subjects with CFS were able to reach the prescribed activity goals each day. After this time, walking and total activity counts decreased. Sedentary controls subjects were able to maintain their daily walking and total activity goals throughout the 4 weeks. Unlike our previous interpretation of the data, we feel this new analysis suggests that CFS patients may develop exercise intolerance as demonstrated by reduced total activity after 4–10 days. The inability to sustain target activity levels, associated with pronounced worsening of symptomology, suggests the subjects with CFS had reached their activity limit.

Impact of a maximal exercise test on symptoms and activity in chronic fatigue syndrome

Objective This study examined the effects of exercise on symptoms and activity in chronic fatigue syndrome (CFS). Methods Twenty CFS patients and 20 neighborhood controls performed an incremental exercise test until exhaustion. Fatigue, muscle pain, minutes spent resting, and the level of physical activity were assessed with a self-observation list. Physical activity was assessed with an actometer as well. Data were obtained 3 days before the maximal exercise test (MET) up to 5 days thereafter. Results For CFS patients, daily observed fatigue was increased up to 2 days after the exercise test. For controls, self-observed fatigue returned to baseline after 2 h. Both CFS patients and controls spent more minutes resting on the day before and on the day after the MET. For CFS patients, self-observed minutes resting increased on the day of the exercise test. For neither group, a decrease of actometer recorded or self-observed physical activity after exercise was found. Conclusion Fatigue in CFS patients increased after exercise, but the level of actual physical activity remained unchanged.

Kinesiophobia in chronic fatigue syndrome: Assessment and associations with disability

Nijs J, De Meirleir K, Duquet W. Kinesiophobia in chronic fatigue syndrome: assessment and association with disability. Arch Phys Med Rehabil 2004;85:1586–92. Objectives To investigate aspects of the validity of the total scores of the Tampa Scale for Kinesiophobia (TSK), Dutch Version, which was modified to make it an appropriate questionnaire for the assessment of kinesiophobia (fear of movement) in chronic fatigue syndrome (CFS) patients (the Dutch TSK-CFS), and, using this assessment tool, to examine the associations between kinesiophobia, exercise capacity, and activity limitations and participation restrictions in patients with CFS. Design Prospective observational studies. Setting An outpatient fatigue clinic. Participants In the first study, 40 patients fulfilling the 1994 US Centers for Disease Control and Prevention (CDC) criteria for CFS were enrolled. The sample of the second study consisted of 51 CDC-defined patients with CSF. Interventions Not applicable. Main outcome measures Study 1: Subjects completed a set of questionnaires; the Utrechtse Coping List (UCL), the Dutch TSK-CFS, and the Dutch Baecke Questionnaire of Habitual Physical Activity. Study 2: All patients completed 2 questionnaires (Chronic Fatigue Syndrome Activities and Participation Questionnaire [CFS-APQ], Dutch TSK-CFS) and performed a maximal exercise stress test on a bicycle ergometer. The heart rate was monitored continuously by use of an electrocardiograph. Metabolic and ventilatory parameters were measured through spirometry. Results Study 1: The Cronbach α coefficient for the individual item scores on the TSK-CFS was .80. The total scores on the Dutch TSK-CFS showed a statistically significant correlation with both the avoidance/abide subscale of the UCL (Spearman ρ=.35, P=.029) and the total score of the Baecke Questionnaire (ρ=−.45, P=.004). Study 2: The total scores on the Dutch TSK-CFS showed a statistically significant correlation with the total scores on the CFS-APQ (ρ=.39, P=.004). No statistically significant associations were observed between the exercise capacity parameters and the total scores on the Dutch TSK-CFS. Conclusions These results provide evidence for the internal consistency and the convergent and congruent validity of the scores obtained by use of the Dutch TSK-CFS. Kinesiophobia appears to be associated with activity limitations/participation restrictions but not with exercise capacity in patients with CFS.

Chronic Fatigue Syndrome: Lack of Association Between Pain-Related Fear of Movement and Exercise Capacity and Disability

Patients who experience pain, a symptom of chronic fatigue syndrome (CFS), often exhibit kinesiophobia (irrational fear of movement). The purpose of this study was to examine whether pain-related fear of movement is associated with exercise capacity, activity limitations, or participation restrictions in patients with CFS who experience widespread pain. Sixty-four subjects met the inclusion criteria. All subjects fulfilled the 1994 Centers for Disease Control and Prevention case definition for CFS and experienced widespread myalgias or arthralgias. The subjects completed the Tampa Scale for Kinesiophobia-Dutch Version (TSK-DV) and the Dutch Chronic Fatigue Syndrome-Activities and Participation Questionnaire (CFS-APQ). They then performed a maximal exercise test on a bicycle ergometer. Heart rate was monitored continuously by use of an electrocardiograph. Ventilatory factors were measured through spirometry. Correlations between the TSK-DV scores and both the exercise capacity data and the CFS-APQ scores were assessed using the Spearman rank correlation coefficient. Using the Mann-Whitney U test, the TSK-DV scores were compared between subjects who performed a maximal exercise stress test and those who did not perform the test. Forty-seven subjects (73.4%) attained a total score of greater than 37 on the TSK-DV, indicating high fear of movement. Neither the exercise capacity data nor the CFS-APQ scores indicated a correlation with the TSK-DV scores (n=64). Subjects who did not perform a maximal exercise capacity test had more fear of movement (median TSK-DV score=43.0, interquartile range=10.3) compared with those who did perform a maximal exercise capacity test (median TSK-DV score=38.0, interquartile range=13.2; Mann-Whitney U-test score=322.5, z=-1.974, P=.048), but the correlation analysis was unable to reveal an association between exercise capacity and kinesiophobia in either subgroup. These results indicate a lack of correlation between kinesiophobia and exercise capacity, activity limitations, or participation restrictions, at least in patients with CFS who are experiencing widespread muscle or joint pain.

Disability evaluation in chronic fatigue syndrome: associations between exercise capacity and activity limitations/participation restrictions.

In an attempt to examine whether impairments in cardiorespiratory fitness are associated with daily functioning in patients with chronic fatigue syndrome (CFS), this study addresses the correlations between exercise capacity and activity limitations/participation restrictions. Prospective observational study. An outpatient tertiary care, chronic fatigue clinic at the Vrije Universiteit Brussel (VUB), Belgium. Seventy-seven patients fulfilling the 1994 Centers for Disease Control and Prevention (CDC) case definition for CFS. All patients filled in the Chronic Fatigue Syndrome Activities and Participation Questionnaire (CFS-APQ) and performed a maximal exercise stress test on a bicycle ergometer. Heart rate was monitored continuously by use of an electrocardiograph. Metabolic and ventilatory parameters were measured through spirometry. A statistically significant correlation between the score obtained with the CFS-APQ and the body weight-adjusted peak oxygen uptake (Spearman rho = -0.32; p = 0.005), functional aerobic impairment (rho = 0.33; p = 0.004), workload/body weight (rho = -0.30; p = 0.009), exercise duration (rho = -0.30; p = 0.008), and the percentage of target heart rate achieved (rho = -0.33; p = 0.004) was observed. The correlations between the remaining exercise capacity parameters and the scores obtained with the CFS-APQ all indicated a trend towards association (0.01 <p<0.05). These results suggest a moderate association between exercise capacity and activity limitations/participation restrictions in patients with CFS. The observed correlations lack strength to predict activity limitations/ participation restriction based on exercise capacity parameters. Disability evaluation in CFS should therefore encompass both exercise capacity testing and measurements at the activity/participation dimension.

Immunological Changes After Both Exercise and Activity in Chronic Fatigue Syndrome

AbstractBackground: The chronic fatigue syndrome (CFS) is characterized by post-exertional malaise and fatigue. We designed this pilot study to explore whether the illness was associated with alterations in immunological markers following exercise.Methods: We measured immunological markers before and up to three days after either a sub-maximal or maximal bicycle exercise test. We studied nine patients with CFS and nine age-and sex-matched healthy but sedentary controls. We also studied the same patients with CFS at home after a night's sleep and then after traveling to the study center.Results: There were no significant differences in any of the cell markers after a sub-maximal exercise test compared to a maximal test. However, we found elevated concentrations of plasma transforming growth factor beta (TGF-s), even before exercise, in subjects with CFS (median (IQR) of 904 (182-1072) pg/ml) versus controls (median (IQR) of 50 (45-68) pg/ml) (P < .001). Traveling from home to the hospital significantly ele...

Decreased Fractal Correlation in Diurnal Physical Activity in Chronic Fatigue Syndrome

Our objectives were to study the temporal correlation of physical activity time series in patients with chronic fatigue syndrome (CFS) during normal daily life and to examine if it could identify the altered physical activity in these patients. Fractal scaling exponents of diurnal and nocturnal physical activity time series in 10 CFS patients and 6 healthy control subjects (CON) were calculated by the detrended fluctuation analysis (DFA) and the wavelet transform modulus maxima (WTMM) method. We hypothesized that, due to their illness- and/or fatigue-induced resting episodes, altered physical activity patterns in CFS patients might be observed at the interruption of activity bursts. Thus, we further developed a new method, the wavelet transform negative modulus maxima (WTNMM) method, which could evaluate the temporal correlation at the interruption of activities. We compared the fractal scaling exponents for CFS and CON by each method. Both for CFS and CON, we found the fractal time structures in their diurnal physical activity records for at least up to 35 minutes. No group difference was found in nocturnal activities. The WTNMM method revealed that, in diurnal activities, CFS patients had significantly (p < 0.01) smaller fractal scaling exponent (0.87 +/- 0.03) compared to controls (1.01 +/- 0.03). Such a difference was identified neither by the DFA nor WTMM method. CFS patients had more abrupt interruptions of voluntary physical activity during diurnal periods in normal daily life, probed by the decreased correlation in the negative modulus maxima of the wavelet-transformed activity data, possibly due to their exaggerated fatigue.

Hypermobility in Patients with Chronic Fatigue Syndrome: Preliminary Observations

Objective: The present report aims at examining 1. the prevalence of generalized hypermobility in patients with chronic fatigue syndrome [CFS]; 2. whether hypermobile CFS patients experience more pain and have more severe activity limitations/participation restrictions compared to nonhypermobile CFS patients; and 3. whether the history of widespread pain is indicative of generalized hypermobility in patients with CFS.Methods: Forty-four consecutive patients with CFS filled in the Chronic Fatigue Syndrome Activities and Participation Questionnaire [CFS-APQ] for the assessment of activity limitations/ participation restrictions, rated three visual analog scales [for pain, myalgia, and arthralgia], were screened for generalized hypermobility according to the Beighton et al. (1973) criteria, and were questioned about muscle and joint aches.Results: Eleven of the 44 [25 percent] subjects met the criteria for generalized hypermobility. The Spearman Rank correlation analysis did not reveal statistically significant correlations between the Beighton et al. scores and any of the self-reported measures [P > 0.01]. Using the Mann-Whitney U test, no statistically significant differences in pain severity and activity limitations/participation restrictions were observed between hypermobile [N = 11] and nonhypermobile [N = 33] patients with CFS [P > 0.01]. The positive likelihood ratio for widespread pain in shifting the odds favoring the presence of generalized hypermobility was 1.24; the negative likelihood ratio was 0.749.Conclusions: The present report suggests that a subgroup of patients with CFS present with generalized hypermobility, but questions the clinical importance of hypermobility in patients with CFS. A history of widespread pain was not predictive of generalized hypermobility in this sample of CFS patients.

Construct validity and internal consistency of the chronic fatigue syndrome activities and participation questionnaire (CFS-APQ)

Identifying patients' activity limitations is crucial for teaching Chronic Fatigue Syndrome (CFS) patients to effectively manage their activity level. Therefore, a questionnaire to assess activity limitations/participation restrictions in CFS patients was recently constructed. In this study, the internal consistency, the discriminant validity, and the convergent validity of this measure, named the CFS-Activities and Participation Questionnaire (CFS-APQ), were investigated. Convergent and discriminant validity are considered two fundamental aspects of construct validity. An envelope containing the CFS-APQ and the Medical Outcomes Short Form 36 Health Status Survey (SF-36) was sent to 149 CFS patients. Eighty-eight out of 149 CFS patients (59.1%) filled in and returned the questionnaires. Cronbach's Alpha reliability coefficients were >0.87. The CFS-APQ total scores correlated statistically significant with six out eight SF-36 subscales (bodily functioning, physical role functioning, bodily pain, general health perception, vitality and social functioning), with Spearman Rank correlation coefficients ranging from −0.34 to −0.78. The highest correlation coefficients were obtained between the CFS-APQ total scores and the subscales ‘physical functioning’ and ‘social functioning’, no significant correlations were observed with the SF-36 subscales emotional role functioning and mental health. In conclusion, the items of the Dutch version of the CFS-APQ have been found to have good internal consistency, and these results substantiate both the convergent and the discriminant validity of the scores obtained with this questionnaire.

Psychometric Properties of the Dutch Chronic Fatigue Syndrome–Activities and Participation Questionnaire (CFS-APQ)

The Chronic Fatigue Syndrome-Activities and Participation Questionnaire (CFS-APQ) is a recently developed disease-specific assessment tool for monitoring activity limitations and participation restrictions in patients with chronic fatigue syndrome (CFS). In this study, the convergent validity, content validity, and test-retest reliability of data obtained with the Dutch-language version of the questionnaire were examined. One hundred eleven consecutive patients with CFS were enrolled, of whom 47 fulfilled all inclusion criteria. The subjects were first asked to rate their pain, fatigue, and ability to concentrate using 3 visual analog scales, to list at least 5 activities that had become difficult to perform due to their complaints, and to complete the CFS-APQ. Furthermore, subjects were asked to complete a modified version of the CFS-APQ at home and return it to the investigators. The content of the questionnaire was reviewed using the World Health Organization's International Classification of Impairments, Disability and Health (ICIDH) beta II draft. Spearman rank correlation coefficients (R) were used for the convergent validity analysis, and intraclass correlation coefficients were computed for the assessment of the test-retest data. Overall scores on the CFS-APQ correlated with the scores from the visual analog scales for pain (R=.51, P<.001) and fatigue (R=.50, P<.001). The majority of the responses (157 out of 183 answers [85.8%]) to the request to "list difficult activities" matched the content of the CFS-APQ. Using the ICIDH beta II draft, 21 out of 26 questions were found to address activities, and the remaining 5 questions measured the participation level. The Cronbach alpha coefficient was.94, and intraclass correlation coefficients for test-retest reliability of the overall scores were >or= .95 (P<.001). The results substantiate the convergent validity, content validity, and reliability of the CFS-APQ scores for patients with CFS.

Comparison of Activity Limitations/Participation Restrictions Among Fibromyalgia and Chronic Fatigue Syndrome Patients

AbstractFibromyalgia (FM) and Chronic Fatigue Syndrome (CFS) are related yet overlapping disorders; the current case definitions prohibit a clear-cut differential diagnosis. These diagnostic criteria mainly address the impairment level of the World Health Organization's International Classification of Functioning, Disability and Health. This study aimed at comparing activity limitations and participation restrictions in patients with FM (n = 90) and CFS (n = 47). The Chronic Fatigue Syndrome Activities and Participation Questionnaire (CFS-APQ) was used for assessing functionality in both groups. The convergent validity of the scores obtained with the questionnaire with visual analogue scales for pain, fatigue and concentration was investigated in FM patients, as well as the content validity. No differences in total scores and 25 out of 26 individual items on the CFS-APQ were observed between the 2 groups (independent samples Mann-Whitney U test). This sample of FM patients reported to be more disabled in ...

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; α=.68]. Subscales of Illness Beliefs ( α=.78) and Beliefs about Activity ( α=.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.