Why Yoga Works ( By Alisa Bauman, Yoga Journal)

Exactly how does yoga build fitness? The answer you get depends on whom you ask. Robert Holly, Ph.D., a senior lecturer in the Department of Exercise Biology at U. C. Davis and one of the researchers on the U. C. Davis study, says that muscles respond to stretching by becoming larger and capable of extracting and using more oxygen more quickly. In other words, side benefits of flexibility include increased muscle strength and endurance.

"My own belief is that the small but significant increase in maximal oxygen capacity was due to an increase in muscle endurance, which allowed the subjects to exercise longer, extract more oxygen, and reach an increased maximal oxygen uptake," says Holly.

Then there's the pranayama theory. Birkel suspects that yoga poses help increase lung capacity by improving the flexibility of the rib area, shoulders, and back, allowing the lungs to expand more fully. Breathwork further boosts lung capacity—and possibly also VO2max—by conditioning the diaphragm and helping to more fully oxygenate the blood.

Birkel, Dina Amsterdam, and others are also quick to point out that Suryanamaskar (Sun Salutations) and other continuously linked poses increase the heart rate, making yoga aerobically challenging. And many yoga poses—particularly standing poses, balancing poses, and inversions—build quite a bit of strength because they require sustained isometric contractions of many large and small muscles. Of course, holding the poses longer increases this training effect.

Finally, yoga tunes you into your body and helps you to better coordinate your actions. "When you bring your breath, your awareness, and your physical body into harmony, you allow your body to work at its maximum fitness capacity," says Dina Amsterdam. "Yoga class is merely a laboratory for how to be in harmony with the body in every activity outside of yoga. This improved physical wellness and fluidity enhance not just the physical well-being but also permeate all levels of our being."