HOW TO DO IT: Start with your left leg forward and your right leg back. Place your left foot onto one end of a towel and grab the other end in your right hand. Pull the towel as hard as you can without holding your breath. Hold for 30 to 60 seconds, then switch sides and repeat. If you can’t maintain the hold continuously, break it up into shorter five- to 10-second bursts with brief one- or two-second rests in between.