What does the research on the impact of yoga tell us, and what remains unknown?
As a scientist it is my nature to be somewhat of a skeptic. Skepticism isn’t about negativity. It means having a certain degree of discriminative awareness, particular when reviewing research.
I am also a yoga teacher, educator and therapist. I have a lot of first-hand anecdotal experience with the benefits of yoga practice, both personally and professionally. And indeed, some of that experience could be on the magnitude of miracles.
As someone who travels in both the research and the yoga worlds I sometimes feel conflicted. I see that yoga benefits people in a number of ways, and I read the yoga research, which, for me, is often less than compelling. I cringe when I go to yoga classes during which well-intended yoga instructors extol the virtues of particular postures or practices, when there is no real evidence to support their claims.
While I understand their enthusiasm, it is factually inaccurate to make overarching claims about the effects of a particular posture or practice. While the research is growing in volume and quality, there are many things that we just don’t know. Exaggerated claims have the potential to do harm, which exactly the opposite of what yoga is about.
While the research on yoga is proliferating, it is still in its infancy. Many studies on the effectiveness of yoga have methodological limitations that are important to be aware of. Not everyone can be a trained scientist, and most people don’t have the time or the inclination to read a lot of dry material about research methods and statistics.
The scientific yoga literature can be misleading without that wisdom under your belt.
So what is a well-intended yoga educator or therapist to do?
What to look for in yoga research studies
A systematic scoping review of yoga intervention components and study quality examined the “size and nature of the evidence base for yoga interventions,” identified “gaps in the yoga intervention literature”, and offered recommendations for future research.
The authors reviewed all studies published in English in which yoga was an intervention for individuals over the age of 18 years and the full text of the article was available.
Four hundred sixty-five studies in 30 countries (predominantly India and the US) were identified.
The authors highlighted a number of factors essential to empirically rigorous research, and noted where the field had made progress as well as targets for improvement.
First and foremost, it should be noted that the primary goal of publishing a study is to describe the intervention in enough detail the therapeutic methods and research protocol can be replicated. Without that level of detail, it is difficult for the research and clinical communities to accurately evaluate the outcome of a study.
Setting
Yoga studies were conducted in a variety of settings including laboratories (20%), residential yoga retreats centers (15%), health facilities/clinics (13%), yoga studios (10%), and university campuses (8%). The location was not described in 103 of the 465 studies (23%).
Why does this matter? While there is yet to be research to assess this, it makes sense to assume that people’s experiences of yoga may differ depending on the setting where classes are held. When evaluating a study, it is important to see where the intervention was done, and to consider whether or not that may have enhanced or detracted from a participant’s experience.
Yoga tradition/style
As you can imagine, a wide variety of yoga traditions were represented in these studies. The most common were Hatha (28%), followed by Iyengar (9%), “yogic breathing” interventions (8%), Sudarshan Kriya Yoga (5%), Kapalabhati (2%), and Kundalini (2%). The style of yoga was not described in 15% of the studies.
Why does this matter? Yoga is not a one size fits all practice. There is tremendous variability in philosophy and approach to yoga classes and therapeutic approaches depending on the tradition. Consequently, comparing across these groups is like comparing apples to oranges. No definitive conclusions can be drawn.
Emphasis of yoga intervention
Asana was the most prominent component being used in 81% of interventions. The nature and form of asana was only described in 54% of studies and a mere 12% mentioned the amount of time that participants practiced asana or other forms of yoga.
A number of other yogic tools were also prominently featured in this research including pranayama (breathing exercises) 42%, meditation (dharana and dhyana) 23%, relaxation exercises (15%), and 37% with no additional emphasis reported.
Why does this matter? It is impossible to evaluate yoga research without knowing what was done, and how. Asana in one tradition (think Bikram) has very little resemblance to asana in another (Viniyoga). The use of these exercises varies dramatically between traditions as well, which may have a sizeable effect on participant outcomes.
Not only are the postures different, but the sequencing of the 8 limbs of yoga, and underlying philosophies and intentions vary considerably. As a rule of thumb, the tradition from which the practice emerges as well as every detail of the yoga intervention must be explicitly specified in every research paper so that the identical program can be employed and tested.
Dosage
Dosage refers to the frequency and duration of sessions, and the length of the intervention including criteria regarding home practice. In order to adequately evaluate and replicate a yoga study, other researchers must know explicitly what was done, to whom, by whom, and under what conditions.
It is encouraging that 75% of published studies considered in this review reported the frequency of yoga sessions (how often), and 83% described session duration (length of each yoga session). What is remarkable is the extreme variability for each of these factors. Frequency of classes spanned from one session total (14% of the time) to 6 sessions per week (4%).
Sessions were typically 60 minutes (24%), 75 minutes (5%) or 90 minutes (13%). Some of the laboratory sessions were less than 5 minutes in duration. The length of these interventions spanned from one session to two years.
Seventy-two percent of yoga interventions did not report a home practice component. This does not mean that it did not occur. In many of the interventions with home practice requirements no data was provided that examined adherence to these practices. As such, there is no way to determine the frequency or duration of yoga practice for participants in these studies.
Why does this matter? These data indicate a considerable lack of coordination and communication in the field of yoga research. It suggests that, in general, most research programs involving yoga interventions are unrelated, and that most studies pay little or no consideration of other yoga therapy research findings.
This is a serious problem for an emerging field. It is essential that yoga teachers, therapists and researchers learn from each other and build on each other’s experience. This cannot be accomplished when we continue to reinvent the wheel with each yoga study.
From a public health perspective, yoga therapy research must include a systematic evaluation what types and how much yoga practice is needed to create a sustainable positive effect for study participants and practitioners. At this point in time we know little to nothing about what works best, for whom and under what conditions.
Outcomes Assessment
Outcomes examined in the research included a very broad range of indicators such as physiologic (e.g. heart rate, blood pressure, hormonal levels – 26%), physical functioning (e.g. chronic pain and arthritis – 25%), mental and emotional health outcomes (8%), cognitive-perceptional outcomes (attention, concentration, and memory – 6%), and general wellbeing (3%).
Why does this matter? This suggests that yoga interventions are being used for a wide variety of physical, psychological, and physiological conditions suggesting that yoga has the potential to impact the human condition in myriad ways, which is exciting.
The heterogeneity of these studies also suggests the need for carefully crafted, condition-specific research that adheres to specific requirements regarding type of yoga, dosage, outcome assessment etc. in order for cross study comparisons to be made for a particular condition. In the absence of coordination, the field of yoga research will continue to generate fragmented research for which no clear, coherent story can be told regarding benefits and outcomes.
Yoga Instructor Qualifications
Instructor credentials were not reported in 60% of the studies reviewed in this systematic scoping review. For those studies that did make note of instructor qualifications, terms such as “certified in yoga” (11%), “trained in yoga” (8%), and “experienced” were used. In only 1% of studies were yoga instructors described as Registered Yoga Teachers.
Why does this matter? The field of yoga therapy and yoga intervention is entirely unregulated in the United States. There is yet to be a mechanism through which yoga professionals receive some form of certification that verifies their participation in a minimally acceptable yoga therapy training program. Consequently it is difficult to ascertain whether those delivering the yoga interventions in these studies received significant training to deliver the programs being researched.
"The most important thing that yoga teachers and therapists can do is to exercise caution, ask questions, stay informed, and
exercise humility when it comes to discussing yoga research."
Replication
Even well designed and executed studies are just that – one study. In order for a yoga program to be determined effective it needs to be identically replicated on different populations and by different groups of researchers. This is rarely ever done in the field of yoga research, which is a considerable problem for the field.
The most important thing that yoga teachers and therapists can do is to exercise caution, ask questions, stay informed, and exercise humility when it comes to discussing yoga research. While there are a number of promising studies and the field is continuing to grow, we still know very little about how yoga works and why.
More and more researchers are beginning to ask these questions, so it is only a matter of time until we understand the scientific basis for the miracles that we witness each and every day.