how to do sit up

yes i know it's a stupid question, but there is a reason i ask it.

last night me and my friends were at the gym and we were doin an excersise with a declined bench tossing a medicine ball while one leans back. it works your abs and such. well one of my friends said the bench needed a steeper decline and i said he just needed to go back farther. he then said, "you are supposed to curl your back when you do a sit up." I in returne said, "no, you should try and keep your back straight." he said, "how come in pilates they are always telling you to curl your back." I said, "i don't know i've never taken pilates."

basically i am wondering if you are supposed to curl your back or try and keep it straight when doing a sit up?

Well keeping your back straight is definitely more of a workout. So I would assume that's the way to go. Thats how I've always done it

edit: maybe its your choice, like the option of crossing your arms across your chest or putting them behind your head. Behind head is more of a workout, but across the chest seems to be more popular. In gym class they always made us do behind the head though

Across the chest is becoming more popular, especially in gym classes and such, because it keeps you from pulling on your neck. It really doesn't matter how you do situps/crunches as there are tons of variations. What matters is not to stress your neck and back. You want your abs to be doing the work, not the rest of your body...and you should be able to feel the difference between doing it right and doing it wrong.

I personally prefer less "travel" If you figure on a normal situp posture I don't raise to a full situp posture. I try to keep my lower back stuck to the floor more or less, and just crunch, bringing the upper half of my torso up 6 or so inches...that isolates my abs, and doesn't allow for much cheating, or for extra stress on my back/neck

I'd say if you're doing a situp you should keep your back straight and do it slowly. if you go faster you might have a tendency to do it faster and you might be hurting yourself by throwing your body upwards. a situp should be a controled thing, not a jerk. keeping your back straight can help prevent you from going to quickly.

All well said the better way is back straight while keeping head back not tilting forward, hands across your chest so you don't pull on your neck or tip your head forward.

You can intensify your ab work by doing crunches and holding them for a few seconds rather than just doing more. JMO but crunches are better because there is less chance you do it wrong and hurt yourself, when I was in school situps were timed for the fitness requirement thing and you were supposed to do them fast that was it.