Subjective and objective levels of physical activity and their association with cardiorespiratory fitness in rheumatoid arthritis patients

Yu et al. Arthritis Research & Therapy Subjective and objective levels of physical activity and their association with cardiorespiratory fitness in rheumatoid arthritis patients Chen-an Yu 0 Peter C Rouse 0 1 2 Jet JCS Veldhuijzen Van Zanten 0 1 Nikos Ntoumanis 3 George D Kitas 0 1 Joan L Duda 0 George S Metsios 1 4 0 School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham , Birmingham , UK 1 Department of Rheumatology, Dudley Group of Hospitals NHS Trust, Russells Hall Hospital , Dudley, West Midlands , UK 2 Department for Health, University of Bath , Bath , UK 3 Health Psychology & Behavioural Medicine Research Group, School of Psychology & Speech Pathology, Curtin University , Perth, Western Australia 4 Department of Physical Activity , Exercise and Health , University of Wolverhampton , Walsall, West Midlands , UK Introduction: The aims of the present study were: (a) to examine the agreement between subjective (assessed via the International Physical Activity Questionnaire; IPAQ) and objective (accelerometry; GT3X) physical activity (PA) levels in patients with rheumatoid arthritis (RA), and (b) to evaluate the associations of RA patients' subjective and objective PA to their scores on the maximal oxygen uptake test (VO2max). Methods: The participants wore the GT3X for seven days before completing the IPAQ and VO2max test. The Bland-Altman plot was used to illustrate the agreement between the objective and subjective PA data, and the Wilcoxon test was employed to examine the differences. The association between the PA measurement and VO2max test was examined via the correlations and the magnitude was presented by the Steiger's Z value. Results: Sixty-eight RA patients (age = 55 13 years, body mass index: 27.8 5.4 kg/m2, median of disease duration = 5 (2-8) yrs) were recruited. Smaller differences between the subjective and objective measures were found when PA was assessed at the moderate level. Wilcoxon tests revealed that patients reported less time spent engaged in sedentary behaviours (Z = 6.80, P < 0.01) and light PA (Z = 6.89, P < 0.01) and more moderate PA (Z = 6.26, P < 0.01) than was objectively indicated. Significant positive correlations were revealed between VO2max with all PA levels derived from accelerometry (light PA rho = .35, P < .01; moderate PA rho = .34, P = .01; moderate and vigorous PA, (MVPA) rho = .33, P = .01), and a negative association to sedentary time (ST) emerged (rho = .27, P = .04). IPAQ-reported moderate PA and MVPA positively correlated with maxV02 (rho = .25, P = .01, rho = .27, P = .01, respectively). Differences between the magnitude of correlations between the IPAQ-VO2 max and GT3X-VO2 max were only significant for ST (Z = 3.43, P < .01). Conclusions: Via responses to the IPAQ, RA patients reported that they were less sedentary and engaged in more higher intensity PA than what was objectively assessed. Accelerometry data correlated with VO2max at all PA levels. Only subjective moderate and MPVA correlated with VO2max. Findings suggest that self-reported PA and ST should be interpreted with caution in people with RA and complemented with accelerometry when possible. Trial registration: Trial registration: ClinicalTrials.gov ISRCTN04121489. Registered 5 September 2012. - Introduction Rheumatoid arthritis (RA), the most common inflammatory musculoskeletal disease, is characterized by joint swelling, pain and bone destruction but also a greater risk of cardiovascular disease (CVD) [1,2]. The latter has been partly attributed to an increased prevalence of classical CVD risk factors [3-5] and the effects of high-grade inflammation on the vasculature [6,7]. Another important factor that may lead to an increased CVD risk in RA is low levels of physical activity (PA) [8,9]. RA patients can and should engage in PA, as exercise may slow down disease progression and improve physical ability [10]. Nevertheless, it is repeatedly shown that PA levels are significantly lower in RA compared to the general population [11-14]. It seems, therefore, important that accurate methods should be available to both evaluate and monitor PA levels in RA patients. There are two ways of measuring PA, namely subjective and the objective methods, which are distinguished on how the data are collected. To date, subjective PA is predominantly measured via self-reported means, given that this method is easy to administer, low cost, and more efficient at gathering data from larger samples [15]. However, self-reported PA is subject to different types of bias [16] due to lack of understanding and/or differential perceptions of item content when employed in different populations. Due to increased physical disability there may be a risk of RA patients to over-report their PA. Further, it is not clear how self- reported PA corresponds to indicators of physical function in RA patients. On the other hand, accelerometry is one of the most frequent ways of measuring objective PA, (...truncated)