Next time you scuffle past the aerobics room and peek an eye through the window, asking yourself, "What the hell are they doing in there," perhaps it's time to learn a thing or two about the fastest-growing phase in American fitness.

Yoga classes are becoming as common in American health clubs as sweat and testosterone, a timeless exercise regimen that is in the midst of a serious revamping phase.

While the common conception of yoga is that it is a meditation-type exercise, designed specifically for women, this couldn't be further from the truth. Yoga is a growing, widespread fad, an exercise aimed at increasing flexibility, toning and shaping the muscles, improving posture, and giving an overall better sense of self being for both men and women alike. In fact, take a peek into the aerobics room next time a yoga class is commencing. The proof is with all the men who are turning out for these intriguing sessions.

Check out these yoga forms and see which ones are offered at your health club:

Yoga Forms:

Hatha Yoga

This is the one that's offered at most places, the standard style that blends stretching and toning of the muscles with extensive breathing exercises. In other words, this is a perfect blend of various yoga concepts, focusing on both the mind and the body and helping you get the two in synch with one another.

Iyengar Yoga

This is the style of yoga that focuses on the body's alignment, helping you to achieve proper posture good overall balance in your body. This is a great yoga form for runners and serious athletes, a form that is more geared for the physical elements.

Ashtanga Yoga

This is also commonly referred to as "power yoga," a growing style of yoga that is considered far more rigorous than the other forms. In ashtanga yoga, you are quickly delving from one posture to another, and it can be so physically demanding at times, many people consider it an effective form of cardio. This style of yoga is becoming extremely popular among Hollywood celebrities.

Kundalini Yoga

Whereas ashtanga and iyengar styles of yoga are more geared for the physical challenges, this is the more "relaxing" form of yoga. In kundalini classes, participants are focusing on meditation, breathing exercises, and stress reduction.

Aside from providing all the great benefits (flexibility, balance, muscle tone, stress relief, etc.), yoga can also spree another grand treasure, one that can be strongly enhanced with the right instructor: Yes, yoga can be a blast.

But remember, many yoga classes offered at your gym may charge you a fee of around $10 for an hour-long session.

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