Mental health status and leisure-time physical activity contribute to fatigue intensity in patients with spondylarthropathy




To examine the relationship between disease-related variables, leisure-time physical activity (LTPA), and mental health status with fatigue severity in patients with spondylarthropathy (SpA).


Sixty-six SpA patients completed questionnaires assessing disease activity (Bath Ankylosing Spondylitis Disease Activity Index [BASDAI]), functional ability (Bath Ankylosing Spondylitis Functional Index), and health-related quality of life (Short Form 36). LTPA patterns, demographics, and disease-related data were obtained by interview. A clinical examination determined tender point count. Fatigue was assessed with the BASDAI fatigue item.


The mean BASDAI fatigue score was 5.5 (SD = 2.7) with 59% of the sample obtaining a score ≥5. Disease activity, functional disability, and worse mental health contributed to greater fatigue (R2 = 0.56). The relationship between exercise duration and fatigue intensity was moderated by mental health status. For patients with poorer mental health scores, exercise did not influence fatigue severity. However, for patients reporting better mental health status, engaging in more LTPA decreased fatigue severity.


In addition to increased disease activity and functional disability, greater fatigue severity in SpA is associated with poorer mental health status. Integrating regular leisure physical activity into the comprehensive treatment of SpA may be useful for modulating fatigue.


The spondylarthropathies (SpA) encompass a group of chronic inflammatory rheumatic conditions. The primary pathologic sites include the entheses (the bony insertion of ligament and tendons), the axial skeleton, sacroiliac and limbic joints, and some nonarticular structures (1–3). Estimated prevalence rates range from 0.5% to 1.9% of the general population (3–5). Severity of symptoms varies widely among patients, and the clinical course of the disease is largely unpredictable.

Pain and stiffness have been widely recognized as important primary symptoms of SpA, whereas fatigue has only recently become featured as a core symptom significantly impacting patient quality of life (6). Although more than half of patients report fatigue as a major symptom, little is known about the possible correlates of fatigue in this patient population (5, 7). Fatigue has been conceptualized as a multidetermined phenomenon modulated by such factors as disease status, behavioral factors, and psychosocial variables (8, 9). Behavioral factors, such as leisure-time physical activity (LTPA), have been shown to have an impact on fatigue in patients with other chronic conditions (10, 11). In addition, psychological factors, such as depressed mood, have been consistently associated with greater fatigue in other arthritic diseases, such as systemic lupus erythematosus and rheumatoid arthritis (12–14).

Only 3 studies have been published examining determinants of fatigue in SpA, and all have focused on ankylosing spondylitis (AS). Jones et al (7), in their multivariate study, reported that pain, stiffness, and functional ability were all significant predictors of fatigue. Calin and colleagues (5) compared groups of AS patients by main symptom (i.e., pain, stiffness, and fatigue) and found that patients reporting primarily fatigue or pain scored significantly higher on depression and anxiety compared with the stiffness cohort. Recently, van Tubergen et al (15) reported that greater fatigue in AS was related to greater disease activity, functional disability, global wellbeing, mental health status, and age. No behavioral variables, such as physical activity, were assessed in that study.

The purpose of the present study was to determine the relative contribution of disease-related, behavioral, and psychosocial factors to fatigue in SpA patients. By systematically measuring disease activity, functional ability, health-related quality of life, and leisure-time physical activtiy, we hoped to gain a better understanding of fatigue in SpA and identify modifiable variables to target in treatment interventions. We hypothesized that mental health status and LTPA would be associated with fatigue, even after controlling for disease-related variables.



Sixty-six patients fulfilling the European Spondylarthropathy Study Group criteria for SpA (1) were recruited from a university-affiliated rheumatology department and a satellite community clinic. Thirty-two patients (48.5%) in our sample also fulfilled the modified New York criteria (16) for AS. All patients were at least 18 years of age, functionally fluent in French or English, and were not pregnant. The study was approved by the Montreal General Hospital, McGill University Health Centre research ethics committee. All consecutive patients fulfilling study criteria were informed about the study procedures and gave informed consent before entering the study.


The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) was used to assess disease activity (17). This widely used self-administered questionnaire is comprised of 6 visual analog scales (VAS) referring to symptoms experienced in the previous week. The symptoms assessed include fatigue, spinal pain, peripheral joint pain or swelling, tender areas, and morning stiffness (quantity and quality). The questions are answered on a 10-cm VAS anchored with labels “none” and “very severe” at either end of the first 5 items and “0 hours” and “2 or more hours” for the duration of morning stiffness. The mean score of the 2 items on morning stiffness is considered as 1 variable. The final score is determined by calculating the mean of the 5 items. For the present study, fatigue was assessed using the VAS score on the fatigue item of the BASDAI. For the main analysis, all items on the BASDAI were averaged, with the exception of fatigue, to assess the relationship between fatigue and other components of disease activity.

The Bath Ankylosing Spondylitis Functional Index (BASFI) is a disease-specific instrument assessing functional status (18). It is comprised of 10 VAS questions measuring functional ability in the previous week. Scores on each item range from 0 (easy) to 10 (impossible). A mean of the 10 items is calculated to obtain the final score with higher scores indicating greater disability (18). Both the BASDAI and the BASFI have been widely used in clinical trials with SpA patients and have been validated in various European countries for use in SpA (19–21).

The Medical Outcomes Study Short Form 36 (SF-36) was used to assess health-related quality of life (22). The SF-36 is psychometrically sound and widely used (23). It consists of 36 items measuring 8 different aspects of health and wellbeing: physical functioning, role limitation due to physical health, bodily pain, general health, vitality, social functioning, role limitation due to emotional problems, and mental health. Of the 36 items, 20 refer to the previous 4 weeks. Scores on each scale vary from 0 to 100, with higher scores indicating better health status. The SF-36 can also be summarized along 2 dimensions, the physical component score (PCS) and mental component score (MCS). Correlations between the 8 subscales and the summary scores support the physical and mental health distinction. The PCS and MCS are standardized to have a mean of 50 and an SD of 10 for the United States population (24). The 2 summary scores were used in the present study to assess the physical and mental health status of our sample.


All patients underwent a physician examination, a structured interview, and completed the questionnaires. All physician examinations were completed by 1 of the authors (MAF). Demographic and clinical variables were measured using a structured interview and included sex, age, disease duration, and a physician global assessment of disease status. The structured interview also inquired about current level of leisure physical activity. Participants who reported exercising were then asked to indicate the types of physical activities they performed. Only aerobic physical activities performed for exercise were coded (i.e., swimming, cycling, jogging). For each aerobic activity performed, participants provided a weekly estimate of duration in minutes.

Data analyses

Descriptive statistics including means, medians, and standard deviations were calculated for all variables as appropriate. Univariate outliers were identified for the variable pertaining to weekly duration (in minutes) of LTPA. Following the recommendations of Tabachnick and Fidell (25) for handling continuous variables with univariate outliers, the data were grouped on a scale of 0–4 (e.g., 0 = 0–29 minutes of weekly leisure physical activity; 1 = 31–90 minutes, and 4 > 361 minutes).

A Pearson correlation matrix was computed to examine bivariate correlations between fatigue severity and each potential predictor variable. The pattern of intercorrelations among possible predictor variables were also examined. Hierarchical multiple regression models were built to determine the relative importance of demographics, disease-related factors, LTPA, and mental health status on fatigue severity. Hierarchical multiple regression is the regression strategy of choice when the research goals are to determine the relative importance of predictor variables once other predictor variables have already been entered into the equation (26). Variable selection was based on theoretical relevance, pattern of correlation with the outcome variable, and other potential predictor variables. Efforts were taken to ensure that the ratio of number of subjects to predictor variables would not exceed the minimum requirement of 5:1 recommended by Tabachnick and Fidell (25). To investigate whether the relationship between LTPA and fatigue severity was conditional on level of mental health status, an interaction term between physical activity and mental health status was created. Following recommendations proposed by Aiken and West (27), this term was entered in the final step of the multiple regression model.


Sample characteristics

The characteristics of the sample are shown in Table 1. The mean age of the sample was 45.1 years (SD 13.7) and 60% (n = 40) were women. Disease duration varied widely with a median of 11.5 years. Overall, patients reported moderate functional impairment with a mean BASFI of 4.1. The mean BASDAI was 5.2 (SD 2.1), with 65% (n = 43) of the sample obtaining a score ≥4.

Table 1. Sample characteristics*
 Mean ± SD
  • *

    VAS = visual analog scale; BASFI = Bath Ankylosing Spondylitis Functional Index; BASDAI = Bath Ankylosing Spondylitis Disease Activity Index; PCS = short form 36 physical component score; MCS = short form 36 mental component score; Physical activity score = (scale 0–4 e.g., 0 = 0–29 minutes; 1 = 31–90 minutes, 2 = 91–210 minutes).

 Age, years45.1 ± 13.7
 Female n (%)40 (60.6)
Clinical variables 
 Disease duration, years16.5 ± 13.6
 Tender points (0–18)5.6 ± 6.0
 Physician global VAS (0–10)4.1 ± 2.4
 BASFI (0–10)4.1 ± 2.3
 BASDAI (0–10)5.2 ± 2.1
 PCS35.3 ± 9.5
 MCS46.6 ± 12.0
 Physical activity score1.3 ± 1.4

The PCS score was 35.3, indicating poor physical health status (24). The MCS was 46.6, indicating slightly worse mental health status compared with Canadian norms for the SF-36 for adults between the ages of 45–54 years (28).

The mean weekly physical activity score was 1.3, indicating that on average patients reported engaging in 31–90 minutes of exercise weekly.

Fatigue severity

The mean score on the BASDAI fatigue questions was 5.47 (SD 2.70). The median was 6.14 (range 0–10). Thirty-nine patients (59%) scored ≥5 on the BASDAI fatigue item.

Bivariate associations

Pearson correlations between demographic variables, disease-related factors, LTPA, health-related quality of life, and fatigue severity are shown in Table 2. Greater fatigue severity was significantly correlated with a higher tender point count, worse physician global assessment, more disease activity, poorer functional ability, less LTPA participation, and poorer physical and mental health status.

Table 2. Pearson correlations between fatigue and potential determinants*
  • *

    NS = not significant; w/o = without. For other abbreviation and acronym definitions, see Table 1.

Disease duration0.17NS
Tender points0.350.004
Physician global VAS0.430.001
BASDAI (w/o fatigue)0.600.001
Physical activity score−0.370.003

Factors influencing fatigue

To determine whether mental health status and LTPA remain significantly associated with fatigue severity, after controlling for the influence of disease-related variables, a hierarchical multiple regression analysis was computed. As shown in Table 3, functional ability, tender points, and disease activity were entered in the first step. Functional ability and disease activity contributed to the equation and explained 41% of the variance in fatigue scores. In the second step, only MCS contributed to the equation, resulting in a significant increment in R2. Leisure-time physical activity did not contribute to the equation. For the third step, an interaction term between LTPA and mental health status was created to test whether mental health status moderated the impact of LTPA on fatigue. The addition of the interaction term resulted in a significant increment in R2. To interpret the nature of the interaction, simple slope analyses were computed to determine the relationship between physical activity and fatigue severity at different levels of mental health status (1 SD above and below the mean on the MCS) (27). These analyses revealed that greater duration of weekly exercise participation was related to less fatigue only in patients who were in better mental health. For patients in poorer mental health, there was no significant relationship between exercise participation and fatigue severity. Together, the variables in the model accounted for 57% of the variance in fatigue.

Table 3. Results of the hierarchical multiple regression predicting fatigue in SpA patients*
  • *

    SpA = spondylarthropathy; BASFI = Bath Ankylosing Spondylitis Functional Index; TP = tender points; BASDAI = Bath Ankylosing Spondylitis Disease Activity Index; w/o = without; MCS = short Form 36 mental component score.

  • R2 = 0.44; adjusted R2 = 0.41; F(3, 62) = 16.34; P < 0.001.

  • R2 = 0.56; adjusted R2 = 0.53; F(5, 60) = 15.47; P < 0.001.

  • §

    R2 = 0.61; adjusted R2 = 0.57; F(6, 59) = 15.22; P < 0.001.

Step 1   
 BASDAI (w/o fatigue)0.600.280.05
Step 2   
 Physical activity score−0.37−0.120.192
Step 3§   
 Physical activity × MCS−0.46−1.00.01


Our findings confirm that fatigue is an important symptom in SpA. Fifty-nine percent of patients in this study reported moderate to high levels of fatigue. These results are consistent with those of van Tubergen and colleagues, who reported a BASDAI fatigue score of ≥5 in 53% of AS patients (15). We have also observed that fatigue was significantly associated with functional disability, disease activity, and mental health. These findings are consistent with those reported by other investigators in patients with AS (7, 15).

Mental health status has not typically been examined as a potential determinant of fatigue in SpA. Mental health status is emerging as an important factor linked to fatigue in other arthritic conditions, such as rheumatoid arthritis and systemic lupus erythematosus (14, 29). The association between fatigue and worse mental health may in part be explained by overlapping symptoms (e.g., overlapping symptoms of depression and fatigue). However, there is evidence to suggest that although fatigue and depression frequently occur together, fatigue is neither sensitive nor specific to the diagnosis of depression (30–32). Studies have also shown that fatigue can be measured independent of depression (33, 34). Prospective studies are needed to elucidate underlying mechanisms between fatigue and mental health in patients with SpA.

Exercise is considered an important treatment recommendation for patients with SpA and has been shown to be effective for improving mobility and pain (35, 36). We found that more LTPA was associated with decreased fatigue in patients reporting better mental health status. Exercise in other patient populations has also been shown to be effective for reducing psychological distress (37) and fatigue (10, 38). In contrast, leisure-time physical activity did not influence fatigue for patients reporting poorer mental health. A possible reason for this finding might be the cumulative impact of both symptoms. For this subgroup of patients, with more intense fatigue and poorer mental health status, a more multimodal intervention incorporating exercise and psychosocial (i.e., coping skills training) components may be more effective for managing fatigue.

The cross-sectional design of the present study did not allow us to determine the temporal sequence in the relationship between the variables found to be associated with fatigue severity. For instance, it is unknown whether exercise results in decreased fatigue or if the association reflects differences between exercisers and nonexercisers. That is, SpA patients who report more fatigue may be less inclined to engage in exercise. The sample size was also relatively small and patients were drawn from tertiary care rheumatology clinics, limiting generalizability to patients in comparable settings, who may be more likely to be in poorer physical and psychological health. Our quantification of LTPA requires refinement to determine the optimal exercise intensity required for alleviating fatigue. Future prospective studies, using a larger sample size and a more comprehensive assessment of behavioral (i.e., cardiovascular fitness, muscular endurance/flexibility, adherence) and psychosocial variables (self-efficacy, depression) are needed to better understand fatigue in SpA.

As in other chronic arthritic conditions, fatigue in SpA was found to be influenced by multiple factors. Importantly, worse mental health may place SpA patients at higher risk for greater fatigue, and these patients may present more of a treatment challenge. Integrating regular leisure physical activity into the comprehensive treatment of SpA may be useful for alleviating fatigue. Randomized clinical trials are needed to determine optimal exercise modalities for the accrual of significant benefits and to establish precise guidelines tailored to this patient population.