Background
Rheumatoid Arthritis (RA) is the most common, chronic autoimmune disease. It results in joint swelling, tenderness and destruction of the synovial joints, pain, severe disability, and decreased functional ability [
1]. RA occurs in 1% of people worldwide, with the prevalence being two times higher in women than in men [
2].
The health assessment questionnaire (HAQ)- a disease specific measure of functional ability in RA, is a widely used outcome measures for RA [
3]. A large qualitative study conducted in female patients with RA found that patients report pain and decreased functional ability as having the most widespread effect on their daily lives [
4]. Inability to perform normal daily activities not only decreases health related quality of life (HRQoL), but also further perpetuates a sedentary lifestyle. HAQ scores have been shown to be improved in patients with RA who have participated in exercise interventions aimed at increasing their regular levels of physical activity [
5].
Physical activity as a functional measure of HRQoL can be difficult to assess. Commonly used questionnaires and recall diaries are subjective [
6] and rely on fluency in the English language. Accelerometers are thus growing in popularity as an objective way to measure physical activity, especially in healthy populations [
7]. Accelerometers are small, unobtrusive and comfortable, and measure acceleration of the limb to which they are attached by detecting low frequency (0.5-3.2 Hz) gravitational forces (0.05-2.0 g) [
7]. Acceleration is directly proportional to muscle forces generated, which is proportional to energy expenditure [
8]. This theory along with an inbuilt algorithm allows for the conversion of acceleration into activity counts. These counts can be classified into thresholds, indicating light, moderate or heavy intensity levels [
8]. Accelerometers are able to track intensity, duration and frequency of an activity without relying on patient recall [
9]. Actical accelerometers in particular, can detect varying levels of activity, being able to detect lower level activities and movement in multiple planes [
7] and may therefore be an ideal tool for measuring physical activity and sedentary behaviour in patients with RA, where most movement is functional and of a low frequency and intensity, and therefore unlikely to be reported accurately using self report measures. Indeed accelerometry has already been used to this effect in other rheumatic diseases [
10]. Although there is a paucity of research which has objectively assessed physical activity levels in people with RA, our group, as well as Semanik et al. [
11] have recently demonstrated that sedentary behaviour as assessed using accelerometery is indeed more prevalent in patients with RA when compared to their healthy counterparts [
12].
Patients with RA have lower bone mineral density (BMD) at the hip, spine, and whole body than age matched controls [
13]. Lower BMD and higher incidence of osteoporosis in patients with RA may be as a result of the presence of circulating inflammatory cytokines inherent to the disease, the decreased mobility of these patients, or due to certain medications taken to treat the disease such as corticosteroids. Osteoporosis in RA can be generalised or peri-articular in nature. Studies have shown that the majority of bone density loss in RA occurs in the first six months of disease [
14]. Furthermore, patients with higher RA disease activity have been shown to exhibit a greater loss in BMD, as well as higher indices of bone metabolism compared to those with lower disease activity. Mobility and functional ability have been correlated with BMD; as have age, stature, and sex independently of RA disease [
15,
16].
The skeleton transforms it’s mass and morphology according to individual activity levels and forces placed upon the bone [
17]. Furthermore a minimum effective strain must be placed upon bone in order for remodeling to occur [
18]. A sedentary individual does not place sufficient strain on the skeleton, and bones are thus remodeled in a direction that promotes bone loss. Patients with RA are therefore at increased risk of osteoporosis due to inflammatory processes inherent to their disease; as well as their sedentary lifestyle [
19]. Bone mass in RA can be modified using treatments designed to increase bone mass; decrease RA disease activity; and by increasing physical activity or decreasing sedentary behavior sufficiently in order to increase bone loading and remodeling. Research has shown that exercises aimed at increasing or attenuating loss of BMD should be dynamic- comprised of short and vigorous bouts of high impact exercise incorporating rest periods [
20], yet this type of exercise is usually not feasible in patients with a chronic, disabling pain condition such as RA.
Exercise interventions making use of light aerobic activity, strength training, and stretching, have produced varied results in cohorts of RA patients. Most studies show exercise improves physical fitness and muscle strength with either no change or improved disease activity outcomes [
21], however these interventions have not specifically addressed the problem of low bone mass in these patients. Whole body vibration (WBV) is a potential novel exercise intervention for people with RA. WBV therapy is an exercise whereby a mechanical vibration platform produces energy via forced oscillation. The vibratory waves are then transferred to an individual via propagation through the feet, legs, trunk and finally, the head [
22]. Although the exact mechanisms whereby WBV therapy increases BMD are unclear, it is likely that there are multiple mechanisms at play. WBV has been shown to activate fluid flow in the caniliculi and lacunae of bone matrix in rats [
23], in a manner proportional to loading frequency. This fluid flow creates shear stress on the plasma membrane of osteocytes, bone lining cells, and osteoblasts, which therefore respond accordingly [
20]. WBV thus activates mechanotransduction in bone and stimulates osteogenesis [
23]. Furthermore, muscle forces have been shown to exert the greatest osteogenic stimulus on bone, and the generation of these forces through vibration stimulus is likely a contributor to the skeletal adaptations that occur [
24]. Vibratory stimuli must sufficiently load bones in order to increase bone deposition.
WBV has been used to treat osteoporosis in otherwise healthy populations with low BMD [
23], older individuals [
25], postmenopausal women [
26], athletes at risk of osteoporosis [
27], as well as in other diseased populations [
28] with mainly positive results including increased or attenuated loss of BMD, increases in muscle strength, improved proprioception and balance, and decreased pain and fatigue levels. Furthermore, WBV therapy has been shown to increase peripheral blood flow [
29] as well as cardiovascular performance [
30], and could therefore have an effect on cardiovascular health. Trans et al. [
31], used WBV in patients with knee osteoarthritis and found 8 weeks of twice weekly vibration training to significantly improve knee strength in these patients, but did not assess BMD. Alentorn-Geli et al. [
32] used a dynamic and static WBV protocol, twice weekly for 6 weeks in a group of female patients with fibromyalgia. Patients in this study were divided into a control group who underwent no therapy, an exercise group who underwent standard RA exercise therapy only, and a WBV group who underwent WBV training on top of the standard exercise therapy. The authors of this study found that the WBV protocol significantly improved fatigue scores, as well as pain scores in comparison to the exercise group and the control group, however no measures of BMD were taken. Other studies have shown WBV therapy to have no effect on BMD in healthy adults [
33], or on fatigue or pain levels, balance, or strength [
34].
WBV has not, to our knowledge, been used as an exercise intervention for RA, yet it may be a feasible means to increase functional ability in these patients. Since patients with RA are already at risk for developing osteoporosis, and are therefore at greater risk of fracture; WBV could also potentially be a means to attenuate the progressive loss of BMD observed in patients with RA, without the need for a vigorous exercise programme. Previous studies that have used WBV in other chronic inflammatory or pain conditions do not suggest that WBV would elicit any adverse effects in this population. With this background in mind, the aims of this study are primarily to determine the effects of a WBV programme on functional ability in patients with established RA in comparison to a control group of patients, as well as to determine any effects WBV therapy may have on BMD, disease activity, physical activity levels, HRQoL, or body composition in these patients.
Discussion
The present study will contribute to the current field of rheumatology by potentially providing a non-pharmacological means to improve functional ability and attenuate the loss of BMD associated with RA. This study may provide a safe, sustainable exercise intervention for these patients that could potentially improve certain aspects of disease activity, as well as HRQoL and habitual physical activity.
The advantages of the present study over previous exercise interventions in RA include, firstly, the use of a novel therapy in RA. WBV therapy has not previously been used in patients with RA (to the best of our knowledge), and could provide a safe and easy form of exercise for patients who are often unable to participate in strenuous activities. Furthermore, the application of an intermittent WBV programme could potentially exhibit the added benefit over the previous HRQoL and strength benefits seen following WBV therapy in other rheumatic diseases, of attenuating BMD loss in these patients. Very few studies have focused exercise interventions on improving or attenuating the loss in BMD in this population, despite the very high prevalence of osteoporosis that exists. Usually, interventions designed to increase BMD are dynamic and strenuous, which is not feasible in an RA population. WBV therapy could provide a solution to this problem.
Secondly, the use of an objective measurement of physical activity could further elucidate the benefits of the WBV intervention by providing an accurate, and detailed description of changes that may occur during and following the WBV intervention. Accelerometry allows for the novel examination of changes in patterns of habitual physical activity in this population following the intervention, which will help elucidate which thresholds of physical activity are affected by WBV therapy. Previous research conducted by the authors has shown by using accelerometry for the first time in this population as a means to compare physical activity levels to healthy control participants, that patients with RA are extremely sedentary, and that patients with higher levels of physical activity fare better on certain disease activity and HRQoL outcomes [
12]. The potential ability of WBV therapy to increase physical activity levels could therefore attribute to any changes seen in functional ability, BMD, disease activity and HRQoL in the present study.
Lastly, the inclusion of a post intervention assessment allows the sustainability of the present protocol to be examined. If any changes are observed in any of the primary or secondary outcomes of the present study, it is important to be able to report on whether these changes will be sustained after cessation of the intervention, thereby adding strength to the feasibility of the intervention.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
AP was involved in conceptualisation of the study and wrote the protocol. MT was involved in conceptualisation of the project. JAM was involved in conceptualisation of the project and editing of the protocol. All authors read and approved the final manuscript.