Get in plank position with your hands wider than shoulder-width apart (A). Lower your chest as close to the floor as you can. Holding that position, lift your right knee to the outside of your right elbow (B). Return to plank position, then push back up to start; repeat on the other side. That's one rep. Do three sets of 12 to 15 reps, resting for 30 seconds between sets.
The skin also serves as a release point for heat. (See “Why Does My Face Turn Red When I Exercise?” for more on that.) When you exercise, your muscles generate a lot of heat, which you have to give up to the environment so your body temperature doesn’t get too high, Hackney says. The heat in the muscle transfers to the blood, which shuttles it to the skin; it can then escape into the atmosphere.