Kate also discussed the fact that, for a long time, stretching before workouts was encouraged. "This was the power of our middle school PE teacher that basically needed to kill 20 minutes of time everyday in gym class," she recalled. (Boy, can I relate!) "You don't prepare to move by not moving, which is all static stretching is. You go to a position and freeze." Holding a static stretch before you start exercising can, as it turns out, negatively impact muscle strength and performance, she said, and you can actually harm muscles by overstretching.
If you're about to go on the treadmill or StairMaster, she said, the easiest active warmup is walking. Preparing for high-intensity cardio simply requires you to elevate your heart rate beforehand. If you're about to do some strength training, warm up the muscle groups you're going to target in that workout. For instance, on leg day, Kate will have her clients do some light lunges. She also might have them warm up their legs by doing a light jog. Dynamic stretches where you incorporate movement are OK.
Static stretches after workouts, Kate said, are great. "Improving muscle flexibility, improving mobility in general, that's something that should be done after your focussed work because you are warm and you reduce the risk of injury that could come from overstretching."