Dynamic stabilizer: Biceps Brachii (short head only)
Get into a push-up position, supporting your body on your hands and knees instead of on your hands and forefeet. Your hands should be a little wider than shoulder width apart.
Put one hand behind your back so that you are now only supporting your body on one hand and both knees.
Keeping one hand behind your back and your body as straight as possible, inhale as you lower your chest to the floor. The elbow of your supporting arm should be tucked in slightly.
Exhale as you push your body back up to the starting position.
Repeat for the desired number of repetitions.
Repeat the exercise with your opposite arm.
Comments and tips
The one-arm knee push-up is a compound unilateral exercise that’s great for building your pectoralis major and triceps brachii. It will also challenge your core, making it a little more difficult than the knee push-up.
For the safety of your shoulder joints, keep your elbow tucked in slightly.
Place your knees wide apart and engage your core muscles for stability.
Be sure that you have mastered the standard push-up before performing the one-arm knee push-up.
Perform the one-arm knee push-up with your weaker arm first. Follow with your stronger arm, but do not perform more repetitions than you did with your weaker arm. This will allow your weaker arm to catch up in strength with your stronger arm.
To put your body out of balance even more and force the recruitment of even more stabilizer muscles in your core, you can raise your arm out to your side instead of putting it behind your back.
See also the diamond push-up on knees, though this exercise targets your triceps brachii, not your lower pectoralis major.