Most studies discussing the effects of Yoga usually conclude with some variation of, “the studies were inconclusive and more evidence-based research needs to be done.” The inconclusive results of most Yoga research stems from study designs and unknown or unaccounted for variables.
Reviews that summarize Yoga research for the effects of Yoga on Mental and Physical Health indicate positive outcomes. There is a lack of clarity around the difference in Yoga as compared to other forms of “exercise.” Yoga research design needs to consider the best ways to evaluate the elements of psychophysiology.
Heart Rate Variability: the Evidence
Heart Rate Variability (HRV) can be used an evidence-based component in Yoga research. HRV is the quantitative measure of several features of the autonomic nervous system (ANS). It can provide the evidence of changes to the sympathetic and parasympathetic branches of the nervous system. All research works to reduce variables in order to best answer the question being posed. HRV has its own set of variables because of the far-reaching range of activity within the ANS. Everything that affects heart rate can also affect the variation between the beats. Activities such as eating, sleeping, moving, respiration, and the psychological state (i.e., virtually all body systems) have an effect on Heart Rate Variability.
There are several different and complex elements within the measurements of HRV. Similar to the debate on left and right brain activities being segregated, HRV is not simple or segregated. The scientific community used to consider LF (low frequency) the domain of the sympathetic nervous system, and HF (high frequency) as representing the parasympathetic branch. The effect of respiration and respiration sinus arrhythmia (RSA) is not limited to parasympathetic activity. That new understanding calls into question the RSA effect on the sympathetic system, and now brings a new debate in the scientific literature.
Yoga Research: the Participants
The confounds (independent and dependent variables) in Yoga research begin with the individual participants in the study. Selection consideration needs to be made with regard to the participant’s general health, lifestyle, eating habits, and their previous experience with Yoga and Meditation. Selecting participants who have practiced Yoga may introduce the confound of a “pre-existing” healthy lifestyle.
Yoga Research: the Protocol
Research requires a consistent, rigorous, repeatable protocol. The Yoga practice is the protocol. It must settle on choosing the appropriate tools from a wide range of multiple techniques. Research has the following “yoga protocols” to consider:
• Frequency and duration (90 minutes, 2x/6 weeks? More? Less?)
• Yoga style (Hatha, Iyengar, Ashtanga, specialized Therapeutic Yoga?)
• Frequency and duration of a particular breathing practice (Pranayama)
• Choice and sequence of poses (Asana)
• Inclusion of Mudras, Mantras, Affirmations, or Intention setting
• Meditation, spiritual and philosophical approaches, etc.
Yoga Research: the Quantitative Measure of HRV
Yoga research has elite athletes and psychologists who specialize in biofeedback to thank for blazing the measurable path. After all, the sciences and practices of athletic physiology and psychophysiology have been using HRV for quite some time, albeit for very different reasons. The elite athlete wants to push the body to extreme stress, the territory of a practiced sympathetic nervous system. Tracking HRV will indicate the approach to that edge, alerting the athlete before the risk of injury. The elite athlete wants to avoid injury and the resultant over reaction of the parasympathetic nervous system needed for recovery.
The psychologist, on the other hand may use HRV to help patients understand the relaxation response. It is one method of biofeedback, and is different than the HeartMath® technique for achieving immediate coherence. Learning to control breathing patterns and negative thought rumination can bring the body back into a more balanced state. Keeping that balance as an everyday, all day condition is an advanced, full body science. Tracking HRV levels is the physiological evidence as to the state of eustress and distress, the required “good and bad” forms of stress.
Yoga research starts with a careful design considering participant selection, a consistent, well-defined Yoga protocol (practice), and consistent, frequent and quantifiable psychophysiological measures such as HRV, along with the traditional subjective measures of self-reporting.