I took my first yoga class after a running injury left me unable to do much else. Imagine my surprise when what I thought would be an hour of light stretching left me sweaty and sore in muscles I didn’t even know I had. But I was hooked—it didn’t take long for me to fall in love and ditch running altogether. While I still do cardio regularly (it’s impossible to avoid it in a hilly city like San Francisco), I wonder if doing yoga alone is enough to keep me out of the gym. It’s a great method of strength training, since many of the asanas (poses) rely on arm and leg strength. But even though I sometimes sweat and breathe heavily through especially challenging sessions, does yoga actually qualify as cardiovascular exercise, too? Is it enough to keep us aerobically fit?

The Role of Oxygen Intake
Those unfamiliar with yoga might make the same mistake I first did: assuming that it calls for only a few gentle bends. Thanks in part to yoga’s increasing popularity, there are many different kinds. For example, Hatha yoga is slow-paced, calming, and perfect for beginners. Ashtanga involves flows (series of asanas) at a faster pace, elevating heart rate and increasing muscle endurance. Power yoga, a variation of Ashtanga, is equally rigorous but uses different flows. Obviously, Ashtanga and Power probably burn more calories than Hatha, but that doesn’t mean Hatha doesn’t have its own fitness benefits.

A 2005 study funded by the nonprofit American Council on Fitness (ACE) and conducted at the University of Wisconsin, La Crosse, divided thirty-four healthy, but inactive, women into two groups: one did fifty-five-minute Hatha yoga sessions three times a week for two months, and the other did nothing. Researchers tested the overall fitness levels of each woman before and after the two-month period. Those who did Hatha had significantly improved levels of flexibility, endurance, balance, and strength. On average, they could do six more push-ups and fourteen more curl-ups than before—and that was just after two months.

Unfortunately, researchers also found that there were barely any changes in their maximum oxygen intake, a measure of how efficiently oxygen moves through the body and is used by muscles (and one way of testing cardiovascular fitness). However, a study at the University of California, Davis, in 2001 did show that practicing yoga regularly increased maximum oxygen intake. Their results, which were published in the journal Preventative Cardiology, showed that when their ten volunteers—all aged eighteen to twenty-seven, and all yoga novices—attended eighty-five-minute Hatha yoga classes twice a week for two months, their maximum oxygen intake went up by as much as 7 percent, and researchers believed that number would have continued rising if the study had lasted longer.

Age might be a factor in the difference between these two studies’ findings, since the average age in the ACE study was thirty-three, and none of the UC Davis participants was over twenty-seven. Or perhaps it lies in the fitness levels of participants in each study: ACE used sedentary participants, whereas the participants at UC Davis were merely untrained in yoga. Either way, it’s clear that the participants in each study came away from their sessions stronger and healthier. But whether a 7 percent increase is enough to qualify Hatha as cardiovascular exercise is less clear.

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