So while I was doing some exercises I was wondering if ancient warriors did push-ups just like I was doing and if so how long have humans performed this movement. It seems to me like it is a fairly simple exercise and has probably been around for quite some time but I feel there is also the chance that it is a fairly modern thing. I am also vaguely curious about other similar exercises like sit-ups or pullups or just weight lifting in general and how physical exercise as progressed through the years.
I want to start by saying that some preliminary research into push ups and press ups as a term I found that the first recorded use of the phrases were recorded in the early 20th century (http://dictionary.reference.com/browse/push-up and http://dictionary.reference.com/browse/press-up)
The legend of Milo of Croton using a bull calf in his training. It was said that he would lift a calf and either put it on his shoulders or just lift it, and would do so everyday as the calf grew. Unfortunately, this may be just legends as the only sources that I can find report Milo lifting a calf on his shoulders through a stadium (Galen, Exhortation 13) and running with it.
Equally, as you mentioned weightlifting, on this page from the Perseus website (http://www.perseus.tufts.edu/Olympics/milo.html) you can see there is an inscribed stone weighing 316lbs that reads "Bybon son of Phola (?), has lifted me over [his] head with one hand."
I hope that my sources there aren't too shaky for you, I'm sure there are others who will be able to provide you with more in depth answers.