It was a shocken experience that I had today, I wasn't expecting it because I have been long down doing push ups for quite some time now, the experience I had was that while I was actually doing my morning routine of push ups a friend Walk up to me and introduce a more reliable way of doing push-ups that will be challenging enough to booster muscle enlargement, which is to sustain and become more slower in your pushups, I gave it a try and all my body system changed instantly and vibrating like it was my first time such that am even managing to type right now hence I see the need of prioritizing a more quality push ups than quantity if actually any one will want to experience muscles enlargement, the 100 pushups challenge can be done in different pacing, sessions and sets while striving to achieve it. Am very certain that if I could continue with this new method introduced to me by my friend trust me my muscles can never remain the same.
Of course you feel the impact of the push up more when you go slow with it. That is to say when you push up go with it as if you are following the seconds on the clock. Like using 2 seconds to achieve one push up. I don't know if it's the same thing your friend told you but mine is also very effective and it enlarges the muscles and your chest becomes broader. When you push up sustain it for a second or two and stretch up fully. I observed that many people don't stretch up fully when doing push-ups. If you don't stretch fully you might not actually get the impact that someone who does will get.