Bodyweight exercises such as pushups are a great way to build muscle. Doing more and more pushups, however, doesn't necessarily result in building more muscle.
The way a pushup or any other weight-lifting exercise builds muscle is by triggering protein synthesis. If you work out hard enough that you begin to break down muscle fibers, the muscle will need to rebuild. It takes in amino acids to rebuild proteins. These proteins become the fibers that give the muscle its strength. The muscle also takes in glucose (sugar) and water to restore its glycogen supply. This is what a muscle uses for most of its energy while you are working out. It also is what fills out or "pumps up" a muscle. You can't rebuilt muscle on protein alone, and you can't rebuild muscle when you are dehydrated.
If you are in "OK" condition, your muscles need about 48 hours to assimilate amino acids to make proteins and to turn glucose and water into glycogen. That means that you could benefit from working out about the same time every other day.
If you are in really good shape, your muscles rebuild themselves in about 24 hours. However, if you are in really good shape, the amount of improvement that comes from any single workout is a lot less. It's OK to work out, focusing on the same muscle groups, every single day once you are in athlete-level condition, but you won't see big improvements. You are just maintaining the conditioning you already have.
Other bodyweight exercises, such as dips, pullups, chinups ("chins" in the UK and Australia), and situps work the same way. The worse shape you are in, the longer you need to rest between workouts. It doesn't do any good to multiple kinds of exercises on the same muscle group, either. If you are doing pushups, then it doesn't do any good to work out on a machine for your lattisimus dorsi muscles.
However, you need to work out to the maximum of your abilities to improve.
Generally speaking, there are two ways to achieve the kind of workout that makes your muscles grow. One is to lift weights. If you lift weights, choose a weight that is heavy enough that you can't lift or press it more than six to ten times. When you have done this, quit.
When you are using bodyweight as your resistance, however, then you need to do the maximum number of repetitions of an exercise the muscle can stand. If that's one pushup and half of a pullup, that's where you stop, and let your muscles rebuild for three days. If that's 200 pushups and 200 pullups, that's where you stop, and let your muscles rebuild overnight.
Exercise is just one side of muscle building, however, Your muscles also need the raw materials for rebuilding. At least in the first couple of hours after a workout, muscles need amino acids (complete protein), sugar (not a lot, but some), and water. For about two hours, muscles will be approximately 50 times more sensitive to insulin so they can take the sugar and amino acids they need out of the bloodstream. If you happen to be diabetic, you need to take this into account when you are using insulin or taking medications. Intense, weight bearing exercise lowers blood sugar levels, sometimes drastically. However, if your muscles get the raw materials they need, they will rebuild and enlarge after intense exercise.
It's not necessary to keep on eating after that first two-hour period. In fact, there are even some benefits to short-term fasting, of just 18 to 24 hours. When you don't eat, your body, ironically, releases additional growth hormone to make sure your muscles don't get smaller. Eat your post-workout meal, and then relax. Don't worry about eating again until at least tomorrow as your muscles get a chance to grow.
- Heather Hitchcock. What Exercise Works the Same Muscles As Pullups? Demand Media. http://livewell.jillianmichaels.com/exercise-works-same-muscles-pullups-4385.html. Accessed 24 September 2015.
- Photo courtesy of SteadyHealth