As aforementioned, stretching realigns muscle fibers. This speeds up the recovery process after a hard workout. When fibers are intertwined, scar tissue requires more time to heal. Serious bodybuilders know how important recovery can be. When a muscle takes too long to recuperate, an entire workout cycle can be interrupted, slowing down muscle gain.

Studies have shown that performing stretching excercises reduces the risk of injury and soreness. It also reduces soreness felt the next day by decreasing the build-up of lactic acid in muscles. Stretching can also prevent cramps; some muscles, like calves, have a tendency to cramp up more than usual.

Furthermore, stretching attenuates stretch reflex , the body's automatic defense mechanism to overextension. Holding a stretch for a prolonged period of time habituates the reflex so it reduces its signal. This helps muscles have a fuller range of motion -- quite useful in bodybuilding since a proper range of motion during reps increases a workout's effectiveness.

So make sure you stretch! :-)