Annette Lang, a teacher of fitness professionals in New York City and at workshops all over the country, says it depends. Lang—who’s certified by the American Council on Exercise, the National Academy of Sports Medicine, and the National Strength and Conditioning Association—says that injuries are most likely to happen if you’re doing aggressive stretching or isolating a cold muscle.
 

Warming up before a workout draws blood to the muscles and tendons and helps them increase in length and elasticity in preparation for the stress of working out. Try a 5-minute warm-up of walking or jogging in place. To stretch safely when your muscles aren’t entirely warmed up, be sure either to move through full ranges of motion smoothly and slowly or to hold a static stretch just at the position of tension but no farther.