The Push Up is a classic strength move; a standard in fitness testing programs for decades. The Push Up is so much more than that, however. First, the name says it all. It is having the ability to get the body up - from a chair, the ground, etc. It is an essential human movement.
Those same pushing muscles are also used to open doors, push lawnmowers, and press carry-on luggage into the overhead compartment.
Start with the hands and feet on the floor in a push up position. Take a moment to check the alignment of the body. The shoulders should be down and away from the ears; the shoulder, elbow, and wrist should be in a straight line; the tailbone tucked and the muscles around the bellybutton feel switched on; the kneecaps are zipped up to engage the muscles in the thigh; the heel is directly over the ball of the foot.
Slowly lower the chest down to the ground, maintaining a straight line from the shoulders to the rump. Envision a stick (or better yet, use a real stick!) resting on the back of the head, the shoulder blades, along the spine,and down to the tailbone.
Have the elbow-shoulder-torso form a 45 degree angle as the body descends. Pause just above the ground and try to have the nose, chest, and bellybutton hover as close to the ground as possible without touching.
Press the body back up in a smooth and controlled manner. Avoid pressing the shoulder up and leaving the hips down, causing the torso to sag. If this happens, regress to a less challenging version by elevating the hands. If plank push ups are not challenging enough, progress to elevating the feet. Either way, maintain strict form to get the most from the movement.