Forward Lunge / Forearm-To-Instep

1. Start from a standing position.
2. Take a big step forward with your right foot.
3. Place your left hand on the floor at shoulder width distance from your right foot, and balance your weight between your left hand and your right foot.
4. Bend your right arm and move your right elbow to the floor between your left hand and your right foot.
5. Put your right hand next to your right foot. Put your hand on the outside and not at the side where you just put your elbow.
6. Push your hips upwards, extend both legs, and point your right foot upwards.
7. Go back to the starting position and repeat these movements with your left foot and your right hand.
8. Repeat these movements a number of times.

The person in the video pulls his knee towards his torso before taking a step. You can find more variations of this exercise on YouTube. The version described here is the one presented in the book Core Performance by Mark Verstegen.