Begin in plank position with the arms and body straight, shoulders over the wrists. Keep the core engaged.
Bend the elbows behind you and lower your chest to the floor. Keep your upper arms tight to your body so your elbows are against your ribs on both sides.
Straighten the arms, coming back to plank position.
This counts as one rep. Do as many reps as you can with correct form in 40 seconds, resting the knees on the floor if you need to. Then rest for 10 seconds.