you can increase muscle tone and definition — and even muscle size — with yoga. But because you're limited to “lifting” your own body weight, it may take a lot more skill, time and determination than it would with lifting weights. - from gaiam life article
A regular yoga practice can reduce your risk of injury and condition your body to perform better at things you have to do every day: walk, sit, twist, bend, lift groceries .... A form of functional fitness, yoga moves your body in the ways it was designed to move to help ensure that it keeps functioning properly. For example, in yoga you use both large and small muscles and move in many directions (twisting, arcing, etc.), not just back and forth on a one-dimensional plane, as in the forward-back motion of a bicep curl.
Yoga tones muscles all over your body, in balance with each other. Weight training exercises typically isolate and flex one muscle or muscle group at a time.
- Yoga relies on eccentric contraction, where the muscle stretches as it contracts, giving the muscles that sleek, elongated look while increasing flexibility in the muscles and joints. Weight training relies on the opposite physical principle of concentric muscle contraction, which means the muscle gets smaller as it contracts. Without proper stretching, the muscle fibers heal close together, giving the muscle that compact, bulging look.
- Yoga increases muscle endurance because you typically hold any given pose for a period of time and repeat it several times during a yoga workout.