I did a challenge once at a gym I used to train at: 10,000 pushups in a month. I started out dropping and doing 25 every hour, at least 10 times a day. I got really into it and ended up finishing the challenge in only 3 weeks. What I noticed was that my body responded really well and I gained muscle that's stayed with me. As I did them with my arms close to my body I was focusing mainly on tricep development, but I still got incredible development in my chest and deltoids.
How does this work? Well, the aim is not to train to failure. Imagine you're a soldier in the army, you have a crazy arm training session and the next day you have DOMS so bad you can't fight effectively. You're dead. Did you ever see 'Conan the Barbarian'? As a child he's chained to the 'wheel of pain' and made to push it all day. Our bodys live on Earth and we adapt to it's gravity. If we lived on Mars we'd be much taller and thinner. By exposing your body to a load constantly it will adapt and build, providing you give it the fuel (nutrition) to do so. Tom Hardy trained like this to pack on size for his role in 'Warrior'.
I've recently started doing 10 x 25 pushups every day to build my chest and triceps up. After 3 weeks I'll switch to doing 10 x 5 1-legged squats every day, as it's important not to get carried away and have little stick legs. If you want to try this method of training I would recommend not doing any other work on your triceps or shoulders and varying your hand positioning throughout the day. Also, STRETCH. Stretch your chest and triceps (or whatever you're working on) at least twice a day, preferably just after you've finished a set.