This might seem a little bit strange but there's actually a type of push-ups that works your abs and in a very effective way.
All you have to do is to put yourself in the regular push-up position but putting your hands side to side and letting them slide until they go as much far from your head you can, without putting your knees, elbows or stomach on the floor.
Once you're in this position you'll have to go up and down as in normal push-ups.
If you can't stand in that position very well, try putting your feet or hands next to a wall.
