The Flat-Belly Workout
Kneel on a mat on all fours with your hands directly under your shoulders. Stretch your legs back one at a time to come into plank position (the “up” part of a push-up); engage your ab muscles. Your body should be long and straight; don’t let your hips sag or lift your butt too high. Imagine there’s a seat belt tightening around your waist, drawing your lower-ab muscles inward.
Press your hands firmly into the mat, and press strongly back through your heels. Hold for 1–2 minutes (or as long as you can), then drop back to all fours. Do 3 reps.
Watch the video: How to Do a Straight-Arm Plank