More than 20 studies found that static stretching decreased muscle strength and power. It seems like a no-brainer to eliminate it from the pre-exercise warm-up. Researchers from the Nicholas Institute of Sports Medicine and Athletic Trauma at Lenox Hill Hospital in New York City, in a review of literature, were more conservative. While static stretching decreases strength by 3-18 percent, its effect on power is much less. It is not clear if stretching has negative effects when combined with an active warm-up.
Also, several studies found that pre-exercise stretching decreased the incidence of muscle strains by 50 percent. For the present, athletes should use an active warm-up prior to exercise and static stretch at the end of a workout when the muscles are warm. We need more research before we can ban stretching as part of the pre-exercise warm-up. (Scandinavian Journal Medicine Science Sports, 20: 169-181, 2010)