The medicine ball Russian twist is one of the best ways to work your obliques, the muscles that help rotate your torso. Without strong obliques, all the support of the core falls to the abdomen and lower back, which can cause problems.
Step 1. Lift feet off floor and lean upper body back slightly so you’re balancing on your bottom. Hold the medicine ball to one side of your body, twisting at the waist.
Step 2. Lift medicine ball off the floor and transfer it across to the other side of your body. Lower medicine ball down to the other side of your body, twisting through your waist. Continue to move ball from one side to the other.