Physio Ball Plank This exercise is intended to strengthen your core and the stability of both your lower abs and your pelvic girdle. For this exercise you only need a yoga mat and a medium sized physio ball. To begin this exercise lay on your stomach with the ball near your feet, rest your upper body’s weight on your elbows and forearms. Next, carefully place one foot at a time up onto the ball and cradle between the top of your foot and shin. Now that the only points of contact are your forearms and your feet on the ball hold this position with your hips level for 40-60 seconds while focusing on taking slow deep breaths. Repeat this 3 times or until failure.