The plank is one of the best exercises you can do for your core because it builds isometric strength to help sculpt your waistline and improve your posture. What's more is that depending on the type of plank you try, you can engage your back, arms, shoulders, glutes, and hamstrings.
Start by lying facedown with your legs extended and elbows bent as shown in the picture. Feet should be hip-width apart, and elbows should be shoulder-width apart. Contract your abs, then tuck your toes to lift your body (forearms remain on the ground); you should be in a straight line from head to heels. Hold for 60 seconds or as long as you can.
Kneel on all fours with hands directly under shoulders. Come onto toes, contract abs, and straighten legs; keep body in line from head to heels.
From plank position, press your right hand into a mat and turn your body so your weight is on the outer edge of your right foot; stack your left foot on top. Imagine you have a big beach ball under your right side; press your torso up and away from the ball, extending your left arm with fingers pointed toward the sky. Tighten your lower-ab muscles and brace your entire core. Hold for 60 seconds, then return to plank position and repeat on the left side.
