I notice that most of the 100 push ups a day people are NOT former military and there is a reason. The most common surgery for soldiers at about 5-15 years is rotator cuff surgery.

You want conditioning from push ups do one that takes you 1 full minute to complete. Of do as many as you can with your lungs empty and do those slow as though you are doing heavy lifting on the bench, slow up and down.

100 a day is a recipe for repetitive motion injuries. People get carpal tunnel from using a mouse or splicing telecom cables, think about it.