Let’s face it. It’s pretty easy to get in the habit of working your abs, say, three times a week with a regular routine of crunches and leg raises and a consistent rep range. But a Youngstown State University study published in the Journal of Strength and Conditioning Research reveals something that seems surprising, then painfully obvious. Failing to vary your weight and rep range will leave your abs on a permanent plateau. Researchers had male and female subjects hit their abs zero, three or six times per week with a variety of bodyweight-only crunch moves, three sets of 20 reps for all exercises with 30 seconds of rest between sets. After 11 weeks, they found that no matter the frequency, none of the subjects significantly improved on his or her starting ab strength. The lesson? To boost your abs, you’ve got to push them with weighted exercises (think cable crunches and machine crunches) and alternate between heavy weight and low reps, moderate weight and moderate reps, and light or no extra weight and high reps. In other words, treat ’em like any other muscle group.