Gently lower your upper body onto your elbows, extend your feet backward, and straighten your body so that your body is being supported by your elbows and forefeet. Your feet should be close together, your neck should be neutral, and your elbows should be directly under your shoulders.
Raise one leg off the floor and keep it straight.
Hold this position for the desired period of time, breathing normally.
Repeat on your opposite leg.
Comments and tips
Raising one leg off the floor not only puts more stress on the supporting leg but also puts your body out of balance, thus forcing your core muscles (especially your obliques) to work harder to stabilize your body.
Keep your glutes and core tight, your shoulders down (away from your ears), and your neck neutral.
Keep your body straight and rigid. Do not allow your lower back to sag or your butt to rise.
All muscles are exercised isometrically (i.e. the muscles contract but do not change shape).
To make the one-leg front plank easier, perform it on your knee instead of on your forefoot.
Use the one-leg front plank to develop the strength and stability of your core. Master the front plank before you graduate to the one-leg front plank.