One Leg Push Up
So changing the regular push up to a one leg push up increases activation of your core, lower back, and hamstrings and adds work to the muscles in your shoulders.
How to complete a one leg push up:
Start in a high plank position with your hands flat on the floor about shoulder-width apart, wrists under shoulders.
Lift one leg off the ground to hip height
Keeping your body in one long line (including your head), inhale as you bend your arms and lower yourself as close to the floor as you can.
Exhale as you push back up to start keeping the body strong and stable throughout the movement