Citation needed, big time. Everything I've ever heard (from high school and college level athletic trainers and strength coaches) has said that a strong core helps your back. I can back this up anecdotally, as years of heavy squats made it painful to drive far in my car's crappy driver's seat, but some ab work (and other exercise) made the problem go away.
When I googled I got http://well.blogs.nytimes.com/2009/06/17/core-myths/ which basically said "A couple of experts question the (what has so far been considered) the authoritative study.
Ab work and lower back work (hyper extensions) just seem like the way to strengthen ones back. Is there another solution that I'm not aware of?
I didn't do a study myself, I just heard it multiple times and assumed that it was true. I have also experienced lower back pain in school when we did sit ups, but of course that doesn't mean that it will do long-term damage.
> Situps can be dangerous due to high compressive lumbar load[1] and may be replaced with the crunch in exercise programs[2].
Doing them improperly can destroy your back. Doing them properly can really improve core strength and make you a much safer athlete, as core strength is needed for most activities you do in life.
Unfortunately most people are never truly taught how to exercise their core properly. (I'm certainly no expert, but have had a couple of sessions with trainers who actually know what they're doing.)
Why exactly do situps destroy your back? I am rather fond of doing hanging situps (hanging by knees) with weights. I wonder if they are just as bad...?
The sit ups: http://en.wikipedia.org/wiki/Sit-up_(exercise) I don't know if the same applies to hanging sit ups, but this Wikipedia article says:
> Situps can be dangerous due to high compressive lumbar load[1] and may be replaced with the crunch in exercise programs[2].
No citations on life extension.
Recommends situps, which destroy your back. Leg lifts have the potential to do the same.
Doesn't mention how many kcal/g fat is (it's 9 kcal/g), which is a useful figure if you're trying to lose weight.