Let’s break the muscle down: at the highest level, the muscle is composed of many strands of tissue called fascicles. Each fascicle is composed of fasciculi which are bundles of muscle fibers. The muscle fibers are in turn composed of tens of thousands of thread-like myofybrils, which can contract, relax, and elongate. The myofybrils are made up of millions of bands laid end-to-end called sarcomeres. Each sarcomere is made of overlapping thick and thin filaments called myofilaments.
When we stretch a muscle fiber, it begins with the sarcomere. As the sarcomere contracts, the area of overlap between the thick and thin myofilaments increases. As it stretches, this area of overlap decreases, allowing the muscle fiber to elongate. Once the muscle fiber is at its maximum resting length (all the sarcomeres are fully stretched), additional stretching places force on the surrounding connective tissue. As the tension increases, the collagen fibers in the connective tissue align themselves along the same line of force as the tension. Hence when you stretch, the muscle fiber is pulled out to its full length sarcomere by sarcomere, and then the connective tissue takes up the remaining slack. When this occurs, it helps to realign any disorganized fibers in the direction of the tension.
So, what’s the best way to realign these fibers? Research suggests a combination of a well-designed aerobic warm-up and a series of dynamic stretches. Unlike static stretching, dynamic stretching uses speed of movement, momentum and active muscular effort to bring about a stretch. For more information, check out this recent article in the New York Times and talk to your physical therapist about incorporating dynamic stretching into your program.
http://www.nytimes.com/2008/11/02/sports/playmagazine/112pewarm.html