Strength training and flexibility training should go hand in hand. It is a common fallacy that there must always be a trade-off between flexibility and strength. Obviously, if you neglect flexibility training altogether in order to train for strength you are needlessly sacrificing flexibility, and vice versa. Exercising for both strength and flexibility is as important for weightlifters as gymnasts; as a matter of fact, flexibility training and strength training enhance one another.
One of the best times to stretch is right after a strength workout such as weightlifting. Static stretching of fatigued muscles performed immediately following the workout helps not only to increase flexibility, but also enhances the promotion of muscular development (muscle growth), and will actually help decrease the level of post-exercise soreness.
After you have used weights or other means to overload and fatigue your muscles, your muscles retain a “pump,” and are shortened somewhat. This “shortening” is due mostly to the repetition of intense muscle activity that often only takes the muscle through part of its full range of motion. This pump makes the muscle appear bigger. The pumped muscle is also full of lactic acid and other by-products from exhaustive exercise.
If the muscle is not stretched afterward, it will retain this decreased range of motion (it sort of “forgets” how to make itself as long as it could) and the buildup of lactic acid will cause post-exercise soreness. Static stretching of the pumped muscle helps it to become looser, and to “remember” its full range of movement. It also helps to remove lactic acid and other waste-products from the muscle.
While it is true that stretching the pumped muscle will make it appear visibly smaller, it does not decrease the muscle’s size or inhibit muscle growth. It merely reduces the tightness (contraction) of the muscles so that they do not bulge as much.
Strenuous workouts will often cause damage to the muscle’s connective tissue. The tissue heals in 1 to 2 days but it is believed that the tissues heal at a shorter length (decreasing muscular development as well as flexibility). To prevent the tissues from healing at a shorter length, physiologists recommend static stretching after strength workouts.