Stand barefoot on one leg on an uneven surface, like half of a foam roller. Have a partner stand about 5 feet behind you, where you can't see him or her. Concentrate on maintaining your balance as your partner lightly tosses a physioball so that it strikes you in the back. Your partner should not warn you. The point is for you to stay upright when the unexpected happens.
Reps: 5-10 on each leg
Photo Credit: Getty Images // Thinkstock