Maybe to add to what Legolas said, from more of a lay point of view, I came to bowhunting from many years of rockclimbing and mountaineering. I was quite slim in those days, and could easily do 20 pullups. Easily, because I was using my back muscles primarily to do the pullups, and not my biceps. I found it rather easy to learn to use a 65# bow, at the time, using the same muscles I used in rockclimbing and for doing pullups. The years have passed, and I don't shoot my 65# bow much anymore, and carrying a few more pounds myself, I'm happy to crank off five pullups, but I still feel quite comfortable hunting with a 60# bow.