From: "A right to BARE arms"

Read this portion of an article from the GAIAM LIFE blog written by Rodney Yee.....while I do not do yoga as a practice for building strong muscles, it is a nice side benefit!!! Read below about the positives of working against gravity with your own body weight as a way to build strength and tone muscles through yoga practice!

Unlike weight lifting, which tends to contract and shorten muscles, creating a bulkier look, yoga develops a long, defined and fluid physique through isometric poses that activate muscles while maintaining their length. This kind of resistance work encourages lean, “touchable” arms — the kind you want to show off all year long.
Graceful, defined muscles are simply a byproduct of any well-rounded yoga practice, says renowned yoga master Rodney Yee, who has studied the discipline for 30 years. “Moving your body in space is lifting weights. When you load the arms with your natural body weight, you are essentially lifting weights.”
He suggests that lifting free weights, for example, to sculpt the upper body may be too specific. Practicing yoga, on the other hand, helps the arms work in coordination — and therefore look more in proportion — with the rest of the body. “What you’re talking about is the whole look: the arms in relationship with the rest of the body.”
While a holistic yoga practice is integral to helping build proportional strength and definition, there are a number of ways that you can focus additional attention on yoga poses that strengthen and tone the arms, or modify certain movements to challenge and build strength in the upper body.