No matter what discipline you practice, from cycling to swimming, from running to walking, you need to have a strong core. Keeping your abs and back strong is key for life, and the plank teaches the front of your body and the back to work together. Plus, the plank will strengthen your arms. The plank offers a multitude of variations. Pictured here is the elbow plank, but you can also perform the plank in a push-up position. You can lift your legs (one at a time, of course) to increase the difficulty, and you can take your plank for a walk. Don't forget the side plank, which works your waist and lats.
Works: Core (abs and back), arms, and shoulders