Around about the time I left high school (and exited my last PE class ever), it seems like everyone started doing crunches instead of sit-ups. Why the change? What’s the difference?
Is there a reason I shouldn’t do sit-ups or is it OK to keep using that exercise?
Sit ups can be dangerous for your back by unnaturally bending the lower portion of your spine. A crunch done correctly should keep the lower back straight.
Word started to get around that situps put a lot of force on the lower back. The psoas muscle can tug pretty hard on the lumbar during a situp. (In fact most of the lifting work in a situp is done by the psoas, not the rectus abdominus, as is commonly believed) The real problem with situps is that most people do them way too fast - especially kids. Done slowly (6+ seconds), a situp is no different than getting up out of bed in the morning. It’s a good strengthener of the hip flexors. But if done quickly - or by someone with a back problems or swayback - it could spell trouble.
I disagree with ShibbOleth that flexion of the lower spine is dangerous. The lumbar was meant to flex forward and back (wiggle like Elivis and you’ll see), it just wasn’t meant to flex with much power (= force x distance / time).
“Do the thing you fear most and the death of fear is certain.” – Mark Twain
I was talking with a friend of mine who works as a personal trainer about this very question.
He said that most folks do sit-ups worng, but if you’re doing them correctly, they’re much more effective than crunches.
I had started working out and tried switching from sit-ups to crunches. Another friend accompanying me on the workouts watched to make sure it looked like I was doing the sit-ups correctly. The results? I definitely felt a lot them a lot in my abs than I had felt the crunches.
Anyone have anything more specific on this, though?
Full sit-ups work the upper and lower abs, while crunches work mostly the upper abs; so if you’re only doing one kind of ab exercise, a full sit-up would be more effective at working the whole area. You should try several different types of ab exercises though, unless you’ve got the type of body that only seems to need one (which most people don’t). Since there is less movement with a crunch, you don’t have quite as much opportunity to put stress on the back. Done properly though, full sit-ups are OK. The reason they might be phasing them out of school PE classes is that most kids in gym class aren’t really focused on doing the exercises properly… more likely they just knock out as many as they have to using the slackest technique they can get away with in order just to muddle through the routine so the class can go out and play football sooner (at least that’s my recollection of high school gym class). Crunches are a safer ab exercise for untrained or less motivated school kids.