Get a whittle faster. In a study, runners who did these moves four times weekly shaved a minute off their 5K times in six weeks. Try two sets of 12 reps each.
Ball Crunch
Lie faceup on a stability ball, knees bent 90 degrees, feet on floor. Put hands behind head with elbows out to sides and crunch up, then lower.
Source: Study at Barry University in Miami Shores, Florida