Explanation:

1. Place your feet shoulder-width apart;
2. Raise your left knee as high as possible diagonally to your right elbow;
3. Move back to the starting position;
4. Next, raise your right knee as high as possible diagonally to your left elbow;
5. During the knee lift, you also move the elbow diagonally to your knee;
6. Repeat this movement at a fast pace.