Adding extra weight to your ab exercises can help you build up the midsection muscles for a better six-pack, and a 2012 study out of Copenhagen, Denmark, identified one of the better ways to do this. Researchers found that when individuals did crunches on an exercise ball combined with elastic-band resistance, they experienced higher rectus abdominis muscle activity than when using a seated ab-crunch machine like those commonly found in gyms. Results also showed that hip-flexor activity was lower on the ball/elastic-band exercise, which is exactly what you want when trying to isolate the abs.
How-To: Perform an exercise-ball crunch with banded resistance by placing the ball a few feet in front of a stable structure with an elastic band attached to it. Hold both ends of the band in your hands and lie back on the ball in the start position of a crunch. With your hands just outside your ears and the band extended behind you, crunch up slowly and lower back down for reps. Make sure there’s constant tension on the band throughout; if there’s not, move the ball farther away from the structure (the band’s anchor point).