This variation, also one of the most common ways to perform a plank, is slightly easier than holding the body up with just the hands. Place the forearms on the ground with the elbows aligned below the shoulders, and arms parallel to the body at about shoulder-width distance. If flat palms bother your wrists, clasp your hands together. (Note: Any of the following plank variations can be performed with straight arms or in a forearm position.)

Work cited : https://greatist.com/fitness/perfect-plank