Push-ups are the ideal exercise for building upper-body strength if you don't have access to a gym or training equipment, as all you need to perform them is your own body-weight. Even if you are a gym-based trainer, push-ups can still be a useful addition to your chest and triceps workout. It can be frustrating, however, to notice your push-up numbers going down, as this may make it seem that you're getting weaker.
As push-ups are a body-weight exercise, they are an excellent indicator of your strength-to-weight ratio. This means though that as you get heavier, push-ups get harder. Performing a push-up at 150 pounds is much easier than performing one at 200 pounds. Push-ups aren't an indicator of of overall strength at all. A powerlifter might be able to bench press over 400 pounds but struggle to do 30 push-ups, while an intermediate trainer can bench 165 but perform over 80 strict push-ups, according to Donnie Kiernan of Critical Bench.
Your push-ups may drop off as you get older. Standard push-up tests make allowances for age and predict that the older you are the fewer push-ups you'll be able to perform. An excellent score for a male between 20 and 29 years of age is more than 54 push-ups, while for a female it's 48. For a man of 60, however, more than 29 push-ups is considered excellent, and 19 ranks as excellent for a 60-year-old woman.
Just because push-ups don't involve weights or any equipment doesn't mean technique is any less important. Keep your whole body tensed when performing push-ups, descend until your chest touches the ground and completely extend your elbows in the top position, advises trainer Mark Sisson of Mark's Daily Apple. Ensure that your elbows don't flare out to the side and keep your head facing the ground.
Fatigue -- from what you've done in previous sessions as well as in the same session as your push-ups -- can have a huge effect on performance. As they involve a chest-, triceps- and shoulder-dominant movement, performing push-ups the day after working any of these muscles could very well make you weaker. Likewise, because you will have less strength at the end of an upper-body session than at the beginning, push-ups later in the session may be more challenging and less productive.