Sixty seconds goes by fast, right? Not when you’re doing the plank! But it is a great exercise for strengthening your core muscles. If you need inspiration, consider Supreme Court Justice Ruth Bader Ginsburg, 86, who has incorporated the move into her workouts. When planking, the goal is to keep your body in a straight line, from the top of your head to your heels, as you balance on your forearms and toes.1. Position your...