Start in a plank position, with your shoulders over your wrists and your legs extended behind you. Engage your core to protect your lower back by pulling your belly button in toward your spine. Keep your back straight.
Bend your elbows and lower your shoulders so your torso is parallel with the floor. Straighten the arms back to plank position to complete the rep.
Do as many reps as you can with correct form for 30 seconds. If this is too difficult, elevate your hands onto the chair, bench, or box to make this exercise easier.