This plyometric exercise builds strength in your core.
Instructions
Start in a modified side-plank: right hand on the ground, inside of the left foot flat on the chair, right leg elevated off the floor, left hand behind the head.
Pull the right leg toward the chest while simultaneously twisting the body so the left elbow connects with the left knee.
Extend back to starting position. Repeat reps on one side, then repeat on the other.