According to a recently published study "runners who did these moves four times a week shaved a minute off their 5K times in six weeks."
Directions: Perform two sets of 12 reps of each exercise.
Begin by lying on your back on a exercise ball with your knees bent and your feet flat on the floor. To be safe you can anchor your feet under a stable object. Place your hands behind your head and extend your elbow out as you roll your upper body forward and up. Roll
For more of a challenge try: Weighted Ball Crunch
Lie on your back with your hands at your sides, palms down, and your legs bent on top of a exercise ball. Press your heels into the ball while raising your hips toward the ceiling. Your body should end at a 45 degree angle to the ball. Lower your hips to the floor and repeat.
For more of a challenge try: One Leg Hamstring Dips
Lie on an exercise ball with your belly button over the center of the ball and your arms and legs extended. Contract your abs and raise your upper body off the ball until your body forms a straight line from the top of your head to your ankles. Lower and repeat.
For more of a challenge try: Medicine Ball Hyperextension
Begin with your hands and knees on the floor, shoulder and hip width apart, facing downward with your back straight and parallel to the floor.