Begin in an elbow plank with elbows directly under the shoulders and your abs engaged toward the spine. Don't let the pelvis sag down or pop up.
Lift your left leg off the ground, bending your knee so the sole of your foot is facing the ceiling. Keep your pelvis square to the floor — don't let your pelvis twist.
Pulse the left heel toward the ceiling for 10 seconds, then switch legs and repeat for another 10 seconds. This counts as one set.