
What most people really want is greater functionality (to be able to do more with their bodies while suffering less for it ) rather than greater muscular size. In this, a balanced and regular yoga practice has a firm place as being one of the best overall fitness regimens ever developed.
One develops strength in yoga by putting the body in a particular alignment and holding the alignment while making micro adjustments over a period of time. For upper body strength, one can study hand stand (arm balance), head stand, and forearm balance (all inversions as well). For lower body strength one can focus on the standing poses such as Triangle pose or Warrior I which emphasize leg and core strength.
For cardiovascular work one can practice the sun salute sequence that I often use as a warm up in class. Now try doing this sequence the way it was intended...108 times in a row...I guarantee a great cardio workout.
Balance comes from the practice of poses which require one to stand on one leg (Tree, Half Moon, Warrior III). These not only require core strength and flexibility, but build stamina as well as balance. Regular practice of these poses builds a stability that comes from a functional balance between the core and extrinsic musculature.
A regular practice of the different types of yoga postures (Standing, Forward Bending, Back Bending, and Restorative) builds poise in ones body, mind, and soul by burning away the impurities of the body, ego, and self understanding.