Hey, I'm a 17 year old girl, and I'm going to this Naval Academy Summer Seminar thing that lasts for 5 days in June. I'm a 3-sport athlete, but I've been trying lately to get myself stronger, particularly with push-ups, because I've never been too good at them.

My question is this:

Would I get better results by doing sets (as in, do 20, take five minutes, do another 20, etc) each day

or

by 'maxing out' each time (I can do about 33 at the moment, I think. I've just been stuck at that plateau for a few days, so I don't know if I'm doing something wrong).

If you have any information yourself, or a link, I'd be very grateful. :)

Oh, and also, I've found that doing sit-ups puts a lot of strain on my lower back, are crunches just as good for getting my abs into shape, as long as I make sure to do enough that I can 'feel the burn'?

Definately by doing sets. Do like 3-4 sets of 15-20...if you can't do that many work your way up. Like start 15 reps, take a 30 second rest, and then go again, and do 3 sets, or 4 if you can do 4 but they get harder as you go & if that gets TOO EASY just add reps to each set. Good luck!

Doing sets of push-ups using a controlled movement and good form would be more effective than trying to max out. When you try to max out, you're working on muscle endurance more than strength. Of course, you can always mix it up by maxing out on some days. Or you can do 3 sets and max out on your last set. Either way, the more you just do push-ups, the easier they get. Generally, they're difficult to do when you first begin because you need to strengthen all the stablizer muscles involved in doing push-ups first.

You should avoid doing full sit-ups because, like you said, they put a lot of strain on your lower back. Crunches are just as effective, if not more, at training your abs.