The plank is one of the most underrated exercises out there!  It may not look like much, but it is a killer for both the anterior (front) and posterior (back) muscle chains.  Plus, is the foundation for a lot of other exercises like in and outs (plank jacks), shoulder taps, mountain climbers, and many more 🙂
A few key points:  1) elbows should be directly under the shoulders and you should be pushing away from the ground 2) eye gaze should be slightly out in front of your hands so that your spine remains neutral 3) hips are level with shoulders- not way up in the air, nor sagging to the ground and finally if you want to make it harder squeeze the abs, quads, glutes, and biceps!!
Movement is life – Coach Mary D.