The assessment of yoga for arthritis is in its infancy. In general, the studies that are reported in the literature are very small in both size and scope. The use of recommended outcomes and validated measures was typical, but only a few outcomes were included in each study. Therefore, there is too little overlap in disease state and measured variables to pool data or draw preliminary conclusions.
HRQL is an important self-reported outcome that can inform about broad effects of interventions on several life domains. Few studies included HRQL, and none used it as a primary outcome. While instruments like the HAQ and WOMAC measure arthritis disability and its impact on daily activities, they do not assess eight domains of health, ranging from physical limitations to energy and mental health. Additionally, because they are primarily used in arthritis populations, this does not allow for comparison with health adults or other chronic conditions.
Study designs varied and each has drawbacks, including lack of masking, lack of control groups, group crossover, and biased group assignment. In these cases, limitations were often noted, but efforts made to reduce bias were not always explained. No study administered comparison treatment arms. This would strengthen findings, but requires a larger sample size and greater resources, which is a challenge in time-intensive, behavioral research trials 31
‘Yoga’ describes a range of practices. While most studies described a comprehensive intervention (poses, breathing, relaxation and/or meditation), the styles, doses and format varied. Researchers must be clear about the delivered intervention, and that it is population appropriate. Determining which aspects of the practice are safe and beneficial can only follow when it is known what has been tested. Especially with patients who have considerable musculoskeletal limitations and symptoms, what is taught and how it is modified should be detailed in future research and practice. Beyond this, researchers should provide protocol transparency so that larger, more rigorous trials can replicate the interventions utilizing the same methods to confirm or dispute findings. Furthermore, when design methods and statistical analyses are not well-described, research cannot be properly evaluated and readers are unable to determine whether methodological flaws may be responsible for error in findings.
For classroom-based interventions, it may be challenging to recruit participants willing to travel and dedicate several hours per week for months, especially with unpredictable, painful diseases. Understudied interventions are often limited to the safest and healthiest (by age and/or disease status) to first ensure no harm before expanding to vulnerable populations. This reduces qualifying participants, particularly for a rarer disease (such as RA). However, this can bias the sample and limit generalizability to all persons with the disease.
Arthritis encompasses many diagnoses. The two most common, OA and RA, have significant pathophysiologic differences, and effects of an intervention such as yoga may not be the same for each. Moreover, the effects of yoga on isolated hand versus knee OA may also have significantly different outcomes. Combining persons with different diseases in the same intervention and analyzing the data collectively could mask an effect that is strong for just a portion of participants, or could suggest a universal effect that only applies to a subgroup with one particular form of arthritis. The use of biomarkers as treatment outcomes will improve current understanding of how additional biochemical and pathophysiological parameters of diseases respond to interventions.
The research in this review was conducted in diverse populations across the globe, which suggests broad interest, as well as cross-cultural acceptance. However, perceptions of yoga, teaching methods and differences in arthritis treatment are likely to influence intervention effects and, possibly, results in different findings.
Overall, the most consistent findings were for tender orswollen joints in persons with RA, which improved for all three studies that used this outcome. Another common outcome was pain, which improved in six out of eight studies, measured by various instruments. Disability improved in three out of four studies. Self-efficacy improved in both studies for which it was measured. Mental health and energy improved for two out of three studies. For grip strength, improvements were seen in both studies of RA, but not the study of OA that included it. Results for global health and physical functioning were inconsistent. Measures of disease symptoms and physical functioning were more commonly used than markers of physical fitness or psychosocial functioning. Because different instruments were often used to assess the same outcome, interpretation of results across studies is compromised.
A goal of future studies should be to create standardized protocols that are optimized to enhance safety, enjoyment and long-term adherence (including specific poses and modifications). Studies have varied considerably with regard to the frequency and duration of yoga practice, as well as the style and specific class content. Authors need to thoroughly describing the practice studied, including specifying the yoga lineage (Iyengar, Kundalini, etc.) in the methods section or separately publishing intervention details.
Interdisciplinary collaboration in the design of yoga interventions is appropriate for this population. Yoga experts, rheumatology clinicians or clinical researchers alone are not equipped to create an authentic and appropriate yoga program without consultation with each other. Such a program requires careful attention to the stress on joints and connective tissue, as well as the consideration of joint range of motion and adaptation during potential disease flares. An arthritis-appropriate program that has been created in careful collaboration and well-tested through rigorous research methods is required as a next step in the evolution of this research.
It would be of significant interest to study the mechanisms by which yoga affects arthritis symptoms. The use of standardized outcome measures and appropriate statistical methods are essential for confirming findings. The field awaits large, comprehensive trials that may validate improvements indicated by this collection of small pilot studies.