We come to our mats for different reasons, and hopefully we walk away from a practice with greater awareness, greater compassion, and more focus. If you practice a vigorous yoga flow, you'll also see obvious physical benefits like cardiac, respiratory and muscle conditioning.
But have you considered the effects a regular yoga practice has on the nervous system? Did you know that by training the nerve supply to the heart and arteries to be more responsive to your breath, the very function of your heart may improve? These changes happen during a variety of yoga practices and should be a good reason participate in yoga and be ambassadors for others to join us. One of the most important ways yoga can benefit your cardiovascular health is through heart rate variability (HRV).
The term HRV reflects the ability of the heart rate to change beat to beat. If you're healthy and you breathe in deep, your heart rate will speed up; if you exhale deeply, the opposite will occur. These rapid changes occur predominantly due to the influence of the parasympathetic nervous system (PNS). This healthy response is counterbalanced by the sympathetic nervous system (SNS), which releases adrenaline, the premier stress hormone. When the PNS predominates, HRV is high during deep breathing, stress is reduced, and health is promoted. The SNS predominates during stress, and in sufferers of diseases like diabetes mellitus, poor sleep, heart disease, alcoholism, kidney failure and other conditions.
Does a healthy HRV matter? There are nearly 900 research studies measuring HRV in humans, both in healthy and disease states. In survivors of heart attacks, diabetic patients, COPD patients, persons with congestive heart failure, in smokers, and even in the general population, these studies have shown that low HRV identifies loss of cardiac nervous system PNS/SNS balance and an increased risk of dying suddenly. Yikes, serious outcomes of a low HRV. As an example of what a low HRV looks like, I've seen patients with a resting heart rate of 100 that won’t vary at all during deep breathing. This is worrisome to me.
How does yoga fit in this story? HRV has been measured in people both before and after practicing various styles of yoga for a given period. For example, following eight weeks of Hatha yoga, nine of 12 subjects showed a significant increase in HRV. Fourteen practitioners of Isha yoga were compared to 14 matched controls. Yoga practitioners showed overall increased HRV and improved PNS function. In another study, 45 pregnant woman participating in yoga for an hour a day were compared to the same number who did not attend the classes. Stress was reduced only in the yoga group, and by the 36th week of practice HRV increased by 150%. Yoga Nidra relaxation was studied alone or in combination with Hatha yoga in 20 volunteers. All subjects who practiced the relaxation techniques showed improvements in HRV and PNS function on the heart.
Mind-body practices, mindfulness and yoga practice focusing on relaxation and the breath can have profound and lasting effects on the brain and nervous system. This has been called neuroplasticity, to reflect the fact that we can mold our nervous system towards long-term health by intermittent bouts of training. When you come to your mat next time and begin pranayama breathing, know that you're utilizing one of the most powerful tools known to improve cardiac function. Patanjali said that yoga “is the practice of quieting the mind.” Apparently it is also the practice of healing the heart.