Nobody loves a pushup, right? They're practically a hallmark of
every basic-training Army sceneusually performed by a bunch of
soldiers laboring under a brutal drill sergeant and in a torrential
downpour. Pushups don't have to be quite so punishing, though, and
they're an excellent indicator of your muscular strength.
Men and women will perform this test differently: Men will assume
the full-body pushup position, with hands shoulder-width apart,
back straight, toes on the ground. Women, meanwhile, will perform a
"knees pushup"identical to the men's in the upper body, but
abbreviated below so that their knees are on the ground.
Once the basic set-up is mastered, simply perform as many pushups
as possible in two minutes, keeping the back straight and, lowering
the body until the chin touches the ground. Dont let the stomach
touch, though. On the way up, be sure to completely straighten the
armsbending them so that only half a pushup is performed is not
allowed.
Once the two minutes are up, youll want to record your score and
see how youve done. Its a bit complex, as age and gender affect
the evaluation.

Source:U.S. Department of Health
and Human Services
http://health.msn.com/fitness/articlepage.aspx?cp-documentid=100167955