This post is how to do a Plank with alternating knees exercise.
Plank with alternating knees

Begin in perfect plank position. Neutral Spine, naval pulled into the spine, hands directly under the shoulders and the shoulder blades pulled back. Feet should be shoulder width apart.

Staying in plank position (meaning don’t raise your butt or sink your hips), bring your right knee to your right elbow (front);

then bring left knee to left elbow;

Then bring right knee (cross) to left elbow,
Plank with alternating knees

then left knee (cross) to right elbow;

then lift right knee out to the side (like a dog peeing) keeping knee bent and leg parallel to the floor and bring the knee as close to the shoulder as possible, then back into plank;

Lift the left knee up and out to the left shoulder;

do a push up, making sure you keep your spine in neutral and your naval pulled in (end of one set).
This concludes this post on how to do the Plank with alternating knees exercise.