A scientific framework for yoga-based practices
The numbers of studies investigating yoga has increased in numbers. Especially the last two decades, going from around 200 to almost 1600. What's lacking is a theoretical framework and a clear operational definition. This is the starting point of a study I'm about to discuss.
Yoga-based Practices: the outset
Even though yoga research has boomed it's hard to get a grip around the results. Mostly due to uneven quality and the lack of framework. I've mentioned this earlier when I've discussed a study where meditation meets science. Schmalzl et al. (2015) has investigated the possibility for a comprehensive theoretical framework for yoga.
As always "yoga" has different meaning to different people. In this study the authors has aimed to define yoga-based practices (YBP). Also, in a secular and operationalized way. The set goal is to optimize health, promote stress reduction, and increase self-regulation. Both from a preventative and therapeutic perspective.
The authors has gone through the publications published on healthy populations. Some sort of posture and/or movement also had to be included. They then choose to include following in their study:
physiological parameters (5 studies)
body awareness (4 studies)
self-reported emotional states and stress (4 studies)
cognitive functions (9 studies)
The physiological parameters that's been included is cortisol, GABA-levels, cardiovascular factors, and blood pressure (BP) and heart-rate variability (HRV). A pilot study on BP and HRV held good quality, but would need a larger sample size. Only HRV showed significance which suggests an increased vagal tone and reduced sympathetic activity.
Body awareness includes proprioceptive and interoceptive awareness. Different studies measured it different. The findings suggested that experienced yoga practitioners had increased pain tolerance.
Self-reported emotional states and stress includes many factors. The findings suggests that attendees in studied yoga-programs showed lower levels of percieved stress. The were also documented reduced levels of self-reported depression, anxiety, and stress.
Cognitive functions includes attention, memory, and executive functioning. Where the findings suggested improvements in short-term and long-term memory. No significance was found for alertness and executive functioning. Although other studies suggests that yoga practice may promote neuroplastic changes in neural systems that support executive functioning.
The limitations reported was the small body of literature. Also, that yoga practitioners that was included may be driven by pre-existing characteristics. Many of the studies held low quality, did not include control groups, and had small sample sizes. Larger sample sizes and more description on individual characteristics is needed.
The use of self-reported data should also be noted. There is a need for more carefully developed and selected outcome measures. Also, poorly described interventions makes it problematic to make replications of studies.
Movement, breath, and attention
The suggested framework for YBP includes movement/or posture, breath and attention. As mentioned most already existing research doesn't describe their interventions and designs enough. This is a suggestion from Schmalzl et al. (2015).
This may be small subtle movements as well as larger motions. The range goes from both postures held for a longer time to movement sequences. Movement is an important aspect because of it's potential including:
interoceptive and proprioceptive awareness training
as a context for attention training
There are many techniques of training breathing patterns. The breath has potential both as an object of attention as well as an effect on the nervous system. It's for example said to promote parasympathetic dominance via vagal afferent stimulation. Breathing also has the above mentioned potentials.
This is an important aspect of many contemplative practices such as yoga. It's usually divided into different types of functional branches. Then these are linked to distinct neural networks. The study discuss this in detail.
The study has much more in depth descriptions then I've given away here. Especially if focuses on the neurophysiological and neuro-cognitive aspects of the YBP components. It also discuss YBP potential to regulate allostatic load and. I highly recommend reading it to get the full picture.
The important stuff (that I want to highlight) is that the design and descriptions in studies needs to be clarified. Why? Because otherwise we can't get a grip around the effects and mechanisms working. Also, there's a need for separating components of YBP from each other. In that way we could get a clearer view on what's effective and not.
We need this to better understand what possible potential yoga can have on a healthy population.
What does this mean?
We can't claim any certain benefits of YBP for a healthy population based on science. Not from what was included in the discussed study. The studies has too many limitations. So let's just stick with this; it's under investigation.
Although the increase in the amount of studies and the identification for higher quality makes the future look bright. We will probably say other things in a few years. This study is pinpointing something important for that to happen. We need a framework for when yoga and science meet.
Schmalzl L, Powers C and Henje Blom E. (2015). Neurophysiological and neurocognitive mechanisms underlying the effects of yoga-based practices: towards a comprehensive theoretical framework. Front. Hum. Neurosci. 9:235. doi: 10.3389/fnhum.2015.00235