The Science of Yoga: The Risks and the Rewards

A surprising number of studies have documented benefits of yoga in reducing depression, fixing muscle and back problems, and possibly improving sex. In this well-documented book, science journalist William Broad discusses these benefits, as well as a number of mistaken beliefs about the benefits of yoga, possible sources of injury, and some history of the discipline. The kind of yoga Broad is referring to is basically postural yoga; the word yoga can have broader and more spiritual implications

A surprising number of studies have documented benefits of yoga in reducing depression, fixing muscle and back problems, and possibly improving sex. In this well-documented book, science journalist William Broad discusses these benefits, as well as a number of mistaken beliefs about the benefits of yoga, possible sources of injury, and some history of the discipline. The kind of yoga Broad is referring to is basically postural yoga; the word yoga can have broader and more spiritual implications. There are now so many forms of postural yoga that generalizations can be hard to make.

Texts on yoga go back to medieval times. However, the discipline as we know it in the west basically dates from the movement for Indian independence, when there was a need emphasize Indian cultural identity. Some of major gurus, such as Tirumali Krishnamacharya, were working in environments where western exercise techniques were also known, so assuming a purely Indian origin of postural yoga may be unwarranted. The medieval texts, such as the Hatha Yoga Pradipika were considerably more interested in sex than is perhaps typical of modern yoga.

The main misconceptions regarding yoga regard its benefits as aerobic exercise and th effects of associated breathing techniques on the oxygenation of the blood. In general, yoga reduces rather than increases ones heart rate. Even those forms that do raise your heart rate are not impressive forms of aerobic exercise, as compared with running or swimming. Therefore, yoga is not the most effective way to burn calories; however, if ones goal is to lose weight, yoga may well still be beneficial, because its effect on your mood may reduce your food consumption. Yoga is certainly good for ones flexibility. Yogic breathing does effect the chemistry of your blood, but the effects are on the carbon dioxide levels in the blood, not the oxygen levels. Carbon dioxide levels can vary considerably, while oxygen concentrations are surprisingly stable.

Yoga does have some risks of injury. Aside from the sorts of injuries to muscles, tendons and so forth that you might expect, a more drastic, if happily rare, possibility is the possibility of a stroke. The risk of stroke arises from postures that injure the vertebral arteries in such a fashion that can create a blood clot which can subsequently move into the brain, or other injuries to these arteries that reduce blood flow to the brain. Headstands seem to be a particular problem in this regard. The risks can be reduced by modifying a headstand so that less weight is placed on the next; other postures might be modified so as to avoid extreme bending of the neck. Broad notes that there is no official certification of yoga instructors, and that instructors of different forms of yoga vary considerably in how much experience they need to receive the certification associated with a particular form of yoga. Therefore many instructors may not be aware of the risks. Ironically, I noticed that some of the postures that Broad noted as having some risks turned up in later chapters as having benefits for such conditions as damage to the rotor cuff muscles in ones shoulders.

Yoga does appear to have some benefits in dealing with clinical depression. Yoga affects level of the neurotransmitter gamma-aminobutyric acid (GABA).
Certain poses (such as those headstands) can affect the autonomic nervous system, which affects ones moods. Broad sees the possibility of yoga being used to treat depression. As a cynic, I can't help but think that the inability to patent yoga is rather a disadvantage to encouraging its widespread use for this malady.

In the raciest chapter, "Divine Sex", Broad cites studies that show some yoga postures can increase the testostorone levels in both men and women; higher testostorone levels are associated with higher levels of sexual satisfaction. The effect seems to benefit women with problems with sexual satisfaction. Yoga also seems for a lucky minority to help bring about a prolonged orgasmic state without physical stimulation. Possibly the effect results from keeping the activity in more recently evolved portions of the brain to a minimum, allowing the sensations from the early evolved portions of the brain, which includes sexual responses, to be more apparent.

I found the chapter on yoga and creativity the least satisfactory, as the amount of scientific study in this area seems to be nearly nonexistent. Possibly yoga allows the right hemisphere of the brain, associated with creativity, to not be shouted down by the more analytical left hemisphere. The examples of the poetry written as a result of yoga did nothing to make me wish to encourage the wide-spread adoption of this practice.

Overall, I enjoyed the book. The book includes some illustrations of the poses, a chronology, a set of brief biographies of the persons mentioned in the book, a list of recommended reading, as well as detailed end-notes. I would caution that many of the scientific studies cited in the text have small sample sizes, so the possibility of significant effects due to sampling error cannot be excluded.