Harvard doctors say this overlooked move is the quickest way to get strong abs

If you think sit-ups are the quickest ticket to 6-pack abs, the physicians at Harvard Medical School have news for you: That classic exercise isn't as efficientas it seems.Instead of crunches, they suggest doing planks, the exercise that involves holding yourself on your hands and toes in a pre-push-up position. The findings are detailed in a Harvard Medical School health report called "Core Exercises."As opposed to sit-ups, which target only your abdominal muscles, planks recruit several groups of muscles along your sides, front, and back. If you want a strong core ' especially the kind that would give you 6-pack-like definition across your abs ' you need to challenge all of these muscles."Sit-ups or crunches strengthen just a few muscle groups," write the authors of the Harvard Healthbeat newsletter, which summarizes the report's key takeaways. "Through dynamic patterns of movement, a good core workout helps strengthen the entire set of core muscles you use every day."Conventional crunches may also be hard on different parts of your body, including your back, which gets pushed against the floor. Additionally, when you pull your body up into a sit-up position, you're working a group of muscles called the hip flexors which run from your thighs to the lumbar vertebrae in your lower back. When these muscles get too tight or become overly-strengthened, they can yank on your lower spine. This can cause pain or discomfort in your lower back.And unlike ab-crunch machines, planks don't require a single piece of equipment, soyou can do them anywhere.Ready to give them a try'The folks at Health.com recommend starting out by lying face-down with your legs extended and your elbows bent, directly under your shoulders, with your hands clasped. Your feet should be hip-width apart; your elbows should be shoulder-width apart. Next, tighten your abs and tuck your toes to elevate your body, keeping your forearms on the ground. Your body should be in a straight line from your head to your heels. To start, hold it for oneminute.As you get stronger, you can gradually build up to maintain the position for longer periods of time, and extend your arms tohold yourself up on your palms.SEE ALSO:11 fitness 'truths' that are doing more harm than goodDON'T MISS:We talked to an exercise scientist about whether diet or exercise is more important for weight loss, and his answer surprised usJoin the conversation about this storyNOW WATCH: 6 'healthy' eating habits you are better off giving up
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