Careful With Your Pre-Workout Stretching

Old school pre-activity (exercise or sport) warmup involving the static stretching of muscles can be dangerous. Stretching cold muscles may create tiny tears that become big tears later, during strenuous activity. Though not new knowledge, we still see this improper warmup technique repeatedly at the gym and before races and other athletic events. Save the static stretching for after the physical activity.

http://www.webmd.com/fitness-exercise/new-ideas-on-proper-stretching-techniques?page=1