The trunk rotation exercises with a medicine ball target the internal and external abdominal oblique muscles. The external abdominal oblique muscle is the outermost muscle of the trunk which covers the abdomen on the front and on the sides. The fibers of this muscle run diagonally, forming a 'V' shape, similar to putting your hands in your coat pockets. The internal abdominal oblique lies under the external abdominal oblique, however, the muscle fibers run in an upward diagonal pattern opposite the external abdominal oblique fibers. Both of these muscles function to side-bend and rotate the trunk.

Anatomical drawing of the external abdominal oblique muscles

Anatomical drawing of the internal abdominal oblique muscles

Begin by sitting up straight in the chair with your feet flat on the floor and shoulder width apart. Contract your abdominals for trunk stability. Choose a ball of appropriate weight that allows you to hold it at chest level through the sets of this exercise. If you do not have a medicine ball, any weighted object will work. With the ball held at chest level, exhale and twist from the trunk to one side, keeping your arms in line with your chest. Inhale as you slowly move the ball back to starting position. Exhale again as you twist to the opposite side. Repeat this process 8-12 times for 3 sets.

A man is seated demonstrating a start position for a Trunk Rotation Exercises with a Medicine Ball

A man is seated demonstrating an end position for a Trunk Rotation Exercises with a Medicine Ball