Pushup Form Question

I used to think I could do a lot of pushups. However, I began to think of my form and thought it might be weak, I realized it was when I looked in a mirror while I was doing them. My pelvis sags and my back archs after awhile. I know if I keep a hard ab I can keep my back straight however I run into a significant problem when I try to do this - it is very hard to breath properly. Does anyone know what I should do?

Thanks in advance

Stop when your form breaks down. Rest. Repeat. Eventually you will be able to hold form the whole time.

-doug-

Some common mistakes...... 1 - looking straight down ( I find if you get tired, the head bobs up and down to try and give you more momentum, or...... the individual trys to get their chin to the floor ). I fond looking slightly ahead eliminates most of this.
2 - Not doing the full range of motion. Ensure you are coming up all the way each time. Not to the point of locking the elbows, but up enough so they are relatively straight.
3 - Keeping the lower body in the air, while the upper body arches up and down. Eliminate this, by keeping the butt tight, and ensuring your hips are touching / almost touching the floor, every so many counts.
4 - If you try to go strictly for quantity, instead of quality, you will usually end up compromising form. The body will try and find the easiest way. I thought i was doing 100 pushups in the past, till i saw myself on tape. Now, i do 2 sets of 50, in good form, and i feel it much more. Im working towards 100 again, but mostly working on proper form each time.
Good Luck !!

Thanks for the responses.

However, it is not that I find myself getting tired that's the problem. It is just hard to breath while keeping my abs tight. What's the best way to get around this?

Practice...when you are sitting around, tighten your abs and hold for as long as you can while concentration on your breathing.