I echo everyone above who had physically punishing jobs. I was a paratrooper for 5 years, and while I felt like a wimp for leaving the airborne life in my twenties, I wanted to go back to college, get my degree, and do something less brutal. I saw guys that were 30 looking like 40, and I didn't want to become them. Turned out to be a great decision, as here I am in my fifties with nothing but a bit of back problems from a tour in Iraq in my 40s--wearing all that body armor and carrying a basic load for long stretches will compress your spine. So, I count myself very fortunate to have a non-punishing second career where I can choose my exertion level, get enough sleep and so on. I salute all you folks with physical problems, especially who served society in whatever capacity, and am constantly amazed by the human capacity to overcome.