Let crunches be bygones. According to an editorial in Navy Times, the U.S. Navy is making moves to banish the traditional situp from their physical-readiness test, which sailors must pass twice each year. Crunches, the editorial says, are "an outdated exercise today viewed as a key cause of lower back injuries." The Canadian Armed Forces, too, cut the outdated core exercise from its fitness test, suggesting concern over the risk for injury and its lack of connection to actual military work, according to a report in The Wall Street Journal.

So we consulted with our top trainers to pull together the toughest ab moves to replace the crunch. They're not the craziest, most attention-getting tricks, but ones that will actually keep you building muscle after the initial gains have ended—and minimize injury and pain to your back. Mix them into your workout and take your routine to the next level. Because you can always be stronger.