Push-ups are good, but if you want to know the all-time best ab workout try this. Lay flat on your back with your arms to your sides and lift your legs 6" off the ground for 2 mins. If thats too long start with 30 sec and work your way up every other day. Believe me, they taught us this in football camp my freshman year and i had abs instantly. Try it during commercials while your watching tv and concentrate on something else cuz it will BURN lol. good luck
