Rheumatoid arthritis (RA) is a chronic autoimmune disease that usually presents as symmetrical polyarthritis, particularly of the hands, feet, and other synovial joints [1
]. The prevalence of RA is approximately 1% in the general European population [3
]. It is associated with pain, stiffness, swelling, fatigue, and sleeping problems [5
], having a debilitating effect on functionality. RA is also associated with cachexia [6
], low quality of life (QoL) [7
], limitations in everyday life [9
], lower work ability [11
], and sexual problems [13
There is a wealth of evidence supporting the beneficial effects of physical activity (PA) in improving joint health, physical function, and mental well-being, as well as reducing cachexia and fatigue in patients with RA [14
]. Additionally, it was shown that physical activity is a protective factor in the etiology of RA. As such, there was a statistically 35% lower risk for developing RA among women in the highest category of leisure-time activity as compared to women in the lowest category (less than 20 min per day of walking/bicycling and less than 1 h per week of exercise) [16
]. Consequently, the European League Against Rheumatism (EULAR) recommends 150 min of moderate physical activity per week, or 75 min of vigorous physical activity or a combination of both, with a minimum duration of 10 min per session. In addition, it is recommended that resistance training should be performed twice a week [17
]. Even though RA patients commonly report that they are aware of the positive effects of physical activity [18
], systematic reviews have shown that physical activity is lower in RA patients than in healthy controls [14
]. In a cross-sectional study of 21 countries, only 13.8% of patients with RA reported regular physical activity [21
Associations between clinical factors and the total amount of physical activity have also been reported. A 2017 review reported that higher moderate to vigorous physical activity (MVPA), as measured by a questionnaire, correlated with lower disease activity, the number of comorbidities, the number of hospital admissions, low body mass index, low blood pressure, a lower risk for insulin resistance, and improved physical function [22
]. Furthermore, it was also reported that physical activity frequency did not differ significantly between patients with early- and long-term RA, whereas 37% of early and 43% of long-term RA patients did not achieve the MVPA recommended levels [23
]. In terms of the effects of physical activity levels on functional limitations, one study reported only a moderate association between physical activity and functional limitations, as measured by the Health Assessment Questionnaire Disability Index (HAQ-DI) [24
]. In addition, a study by McKenna et al. [25
] demonstrated a significant negative relationship between physical activity and functional limitations, as well as inflammatory parameters.
To sum up, although the literature suggests that physical activity is an essential part of RA therapy, very few people meet the recommendations. Factors affecting physical activity behavior in this population have rarely been studied, especially where physical activity levels are objectively measured, and it would be necessary to produce tailored physical activity recommendations. Hence, the aim of the present study was to assess the association between health-related factors such as body mass index and smoking status with physical activity in seropositive RA patients.
Initially, 83 people fulfilled the inclusion criteria, and valid measurements were obtained from 70 patients, of which 72.9% were female. Participants had a mean age of 57.9 (SD: 9.5) years. The youngest participant was 37 years of age, and the oldest was 76 years of age (Table 1
). According to the BMI, 22.9% were of normal weight, and 75% were obese or overweight. For the other categories, 40% were smokers, 38.6% were working at the time, and 50.0% were already of pension age. Among the sample, 62.9% had a handgrip strength score under the age- and sex-specific reference values for healthy European adults. The participants had lived with RA for 8 years on average (25–75% percentile: 5–12 years). The current median pain intensity was 30 (10–50) points. The majority of the participants were in “remission” or had “low disease activity,” and three out of four had “mild to moderate” functional disabilities. In addition, a quarter of the population had increased CRP values. Comparable results were found in the blood sedimentation results. The majority of the RA patients had moderate comorbidities. In detail, 14.3% had diabetes mellitus type 2, and 11.4% reported having chronic lung disease. Moreover, 5.7% reported having heart insufficiency, with the same frequency being reported for peripheral vascular diseases, liver disease, and a solid tumor, respectively. Two persons reported diabetes mellitus type 1 or hemiplegia. Additionally, one person had chronic leukemia, and another one an ulcer disease.
When looking at the accelerometer data (Table 2
), RA patients did 1222.9 (SD: 484.5) min per week of light physical activity. They had an average of 215.2 (SD: 136.6) min a week of moderate physical activity and 9.1 (SD: 26.3) min a week of vigorous physical activity. Adding up the moderate and vigorous physical activity, RA patients did 224.3 (SD: 146.5) min per week of MVPA, on average.
Patients of normal weight did significantly more MVPA than those classed as overweight and almost double the physical activity of those classed as obese (Table 3
). In addition, patients who did not smoke and patients who were working performed significantly more MVPA (p
< 0.05). Even though not statistically significant, younger patients, patients with a higher work ability score, patients with lower functional disabilities, patients with lower pain intensity, patients with lower disease activity, and patients with only moderate comorbidities spent markedly more minutes per week performing MVPA than their counterparts. For sex, education level, handgrip strength, laboratory findings for inflammation, and disease duration, the data were inconclusive in this regard.
The results of the univariate linear regression analyses (Model 1), treating variables continuously showed that HAQ-DI, BMI, smoking status, and the WAS score were significantly associated with MVPA (Table 4
). After adjusting for sex, age, and education (Model 2), only BMI was significantly associated with MVPA. After adjusting all the variables for each other (Model 3), only BMI showed a significant relationship with MVPA.
The findings of this study show that RA patients of normal weight, non-smokers, and patients with a high work ability do more MVPA than those with a higher BMI, smokers, and those not in employment. However, after adjusting all the variables for each other, only BMI shows a significant relationship with MVPA. Furthermore, the data demonstrate that vigorous physical activity is rarely undertaken by seropositive RA patients.
The finding that RA patients do little vigorous physical activity is in agreement with the results of a study of 50 RA patients by Hernández-Hernández et al. [45
], who came up with a median value of 0.6 (0.2–1.6) min/day. In our study, the corresponding values were 0.2 (25–75% percentile: 0.1–0.5) min/day. When looking at the levels of moderate physical activity, our data are with a median of 25.6 (25–75% percentile: 17.0–40.6) min/day, again comparable to those obtained by Hernandez-Hernandez et al. [45
], who reported 22.0 (SD: 15.0) min per day. The amount of MVPA with a media of 26.0 (25–75% percentile: 17.3–40.8) min/day was higher than that reported in a US-based study [46
], where it was reported that patients (disease duration: 14 years; aged 55 years) spent a median value of 14 min/day. The results were also higher than the results of an English study (disease duration: 7 years; aged 55 years), which reported a mean value of 18 min/day [47
]. However, the results of this study are comparable to the results of Hörnberg et al. [23
], who reported a median duration of 34 min/day in early RA and 26 min/day in long-standing RA, and are also comparable to the results of Khoja et al. (median disease duration of 14 years, aged 58 years), who reported a median value of 36 min/day [48
]. The variation between studies may partly be explained by the differences in disease severity. Furthermore, comparisons are hampered by the use of different activity monitors, with differences in device sensitivity, sampling, and data filtering, as well as the use of proprietary algorithms and cut-off values for the data handling. With the present data, the reasons for the low amount of vigorous physical activity can only be hypothesized. As proposed by Baslund et al. [49
], the fact that many RA patients have concerns about potentially increasing pain and exacerbated disease activity may lead to them avoiding high levels of vigorous physical activity. As vigorous physical activity is also recommended for RA patients [17
], and with regard to our results, healthcare professionals should point out that vigorous physical activity is also health-enhancing, and they should help patients to dispel some of the fear that vigorous physical activity can increase disease activity.
The amount of physical activity was similar to the measured physical activity in patients with type 2 diabetes (disease duration: 13 years; aged 65 years) [50
]. In this study Mathe and colleagues reported 22.2 (SD: 19.4) min/day of moderate and 0.2 (SD: 0.71) min/day of vigorous physical activity. Our results are also comparable to women with a low bone mineral content (mean age 64.5 years), who conducted 25.7 (SD: 22.6) min of MVPA/day [51
]. However, men included in this study did 41.3 (SD: 25.3) min of MVPA/day more physical activity. When putting our results in relation to people with knee osteoarthritis and overweight (n
= 160; aged 66 years), who came up to 10.6 (SD: 8.9) min of MVPA/day, we can see that our included RA patients did more PA [52
When looking at the factors associated with MVPA, BMI shows the only association when adjusted for other factors. This means, when adjusted for all other variables, one minute more of MVPA per week, was associated with a 0.35 lower BMI. As in another study by Albrecht and colleagues [53
], the percentage of obese patients in the RA population was higher than in the general population. In addition, the fact that overweight or obese RA patients do less physical activity than patients of normal weight has also been reported in a study by Hugo et al. [54
]. As disease activity has been shown to be higher and disabilities more severe in obese RA patients, increasing physical activity in these patients might be of particular importance [55
], especially when considering that physical activity can reduce the inflammatory process, metabolic syndromes, and other comorbidities (osteoarthritis, depression, diabetes) [54
We also found that non-smokers are more likely to do more physical activity. That smoking is an established risk factor for developing seropositive RA has already been shown [56
]. In this context, it has to be mentioned that the percentage of smokers in the present sample was high (40%), especially when compared to the general Austrian population (22% in women and 26% in men) [57
], and also to other RA patients [56
]. This could be attributed to the relatively high number of participants with only primary education.
It was also found that patients in employment do more physical activity. This might be due to the fact that retired people are older and have a higher disease activity, as shown by our data. However, the finding contradicts the study of Qvarfordt et al. [58
], who reported that RA patients who were working and those on sick leave failed to fulfill the recommendations, whereas retired patients were more likely to meet the recommendations. The authors hypothesized that retired RA patients had more free time for physical activity than those who were working.
Clinical parameters such as disease activity, pain intensity, more severe comorbidities, lower work ability, and more functional disabilities were not found to be significantly associated with MVPA; however, the estimates for MVPA are clearly (up to two times) higher in patients with a lower clinical disease burden. An association between functional disability, as measured with the HAQ-DI, and MVPA was found by Prioreschi et al. [59
], who reported that the HAQ-DI score was negatively correlated with physical activity (r = −0.343, p
= 0.026). Khoja et al. [48
] also found an association with very light (r = −0.277), light (r = −0.261), and moderate physical activity (r= −0.384).
A possible limitation of this study is the cross-sectional design, making a causal and temporal link impossible. Although the sample size in our study was high in comparison to other accelerometer studies in RA patients [33
], the sample size was not high enough to reach a satisfactory statistical power for many of the analyses. A more appropriate study design would be the multicenter design using the same methods that would allow for a more satisfactory sample size, which should be considered for future studies. Furthermore, stationary sports, such as the use of a cycle trainer and weight training, in addition to water sports, were not recorded, which could lead to an underestimation of the total physical activity. It has also been considered that the included participants wore the accelerometer for 7 days, whereas at least 4 days have to be valid. This method is based on previously published literature [33
]. However, the extrapolation of the data might influence the results.
The fact that we undertook the recruitment in a rheumatology outpatients’ clinic might also bias the results, as patients with lower disease activity and overall better health status were more likely to be included. A strength of this study is that the data were objectively measured, providing objectively measured data with high validity and reliability [60