Crunches might receive most of the attention when it comes to sculpting a six-pack, but if you want a strong, chiseled middle, it also pays to stay still. Isometric exercises such as the plank are among the most effective ways to train your core, according to a recent study at the University of Waterloo. The reason: Not only does holding a rigid position extend your muscles’ time under tension (a key growth trigger), but it also reinforces your core’s primary job: Stabilizing your spine. So consider the plank a fitness twofer—a tool that will both strengthen every muscle between your hips and shoulders and help give you one less ache to worry about.
How to do it: Assume a push-up position, but with your weight on your forearms instead of your hands (your elbows should be directly beneath your shoulders). Squeeze your glutes and brace your core (imagine someone is about to punch you in the gut) to lock your body into a straight line from head to heels. Hold this position for up to 90 seconds. Rest for one minute. Repeat three to five times.
Make it easier: Perform the exercise in a push-up position with your arms straight and your weight on your hands instead of your forearms. The farther you are from the ground, the easier the exercise becomes.
Make it harder: Spread your legs to shoulder-width and raise an arm, or a leg, or an arm and the opposite leg. The less contact you have with the ground, the more unstable you will be, and the more difficult the exercise will become.
Bonus tips: To make sure you’re using correct form, have a friend place a yardstick along your back. It should touch your head, upper back, and butt. Squeezing your glutes and bracing your core will help you maintain that alignment. Also, press your elbows into the floor. Doing so will activate your serratus anterior muscles (located below your shoulder blades), completing the activation of nearly every muscle between your hips and shoulders.