Patanjali's Yoga Sutra, a seminal second-century yoga text, defines yoga as the restraint of the fluctuations of consciousness—sound like concentration? When asanas (postures) are practiced , the mind is focused on minute sensations within the body, and this concentration enables a person to balance on one leg or encourage the muscles to move in precise ways. However, if you are distracted, there is often a disconnect between your body and mind—you catch yourself shredding a piece of paper without being aware of the action.
Yoga helps to integrate mind and body, so that your awareness is not fragmented but whole. Also, yoga ismeditation. According to the ancient yogis, asana practice is a preparation for the more esteemed (and difficult) practice of sitting, when there is no movement and thus the mind can really be still. Meditation (dhyana) is not a separate practice, but the seventh limb of the eight-fold path of ashtanga yoga (asana is the third).
Just as a variety of fruits and vegetables is good for the diet, having both a movement-oriented practice and a sitting meditation practice delivers two different, complementary approaches to the challenge of observing and quieting the mind. But some might find that it's easier first to concentrate on the efforts in the external form of the postures before turning attention to attention itself in meditation.