I don't know if any of you caught my response on my post about the Ladder pull-up when my readers asked about how to progress up to doing one-arm push-ups (OAP, as it's known by on the Internet forums). As I wrote down my response, I realized that I had a pretty good topic for a blog entry.
In theory, anyway. I kind of felt like I wasn't qualified to answer that question since my progression wasn't really based on a set-program. Back in December, 2006, I decided to try them in my hotel room just to see if I could. Long story short: I could... about 7 on each arm. I didn't start using them regularly until this year. Now, I'm good for 15 on each arm for several sets.
Still, it's the Internet and I guess that allows above-average, sort-of (but not really) experts like me to say pretty much whatever I want (or any other no-mind, out-of-shape fool for that matter). I have a few ideas about how to get there and they go back to a series of posts I made a while back. When you're working with any push-up, including the OAP, increasing it's level of ease or difficulty stems from the placement of your hands and feet as well as what you're holding onto when you're doing the push-up.
The first approach that comes to mind is to place one of your hands on an object while keeping the other hand on the floor. The higher this object is, the more difficult it will become. If you extend that hand away from the body, it also gets harder. This is a good approach if you're lacking the upper body strength required to perform the OAP.
If you're having trouble with the OAP because your core, then you could elevate your upper body by placing your one hand on a chair, bench, or whatever you have available that can hold your body and allow you to place your shoulder over your hand. This is important because if you have your shoulder behind your hand, you risk pushing the object out from underneath you. The higher the bench/chair/whatever, the easier the OAP becomes.
Now, I said that I didn't have a set-program at the top of this blog entry but there is a tip in my approach to push-ups. I do so many different flavors of push-ups in one week. I work do different intensities, different angles, directions, etc. I've been confusing muscles before Horton invented it in P90X! So, you could say that constantly changing it up creates carry-over strength to other movements, including the OAP.