They were wrong when they said it would be tennis, and bowling just doesn't have the numbers. It might be yoga. While one part of the body is lengthening, another part is strengthening. The balance required by some poses causes the nervous system to work harder. The focus on breathing works the cardiovascular system.
Yoga strengthens the muscles, deepens breathing and makes the spine more flexible.
But its original purpose was to bring balance and self-knowledge to its practitioners. Most of us need a quiet mind as much as we need a good, toxin-shedding sweat. Each class begins and ends with a period of quiet and meditation. Yoga's new popularity may be a reflection of our need for stillness, for decompression and not our boredom with the treadmill. I'm not sure Americans can give up their need for results, however.