Think biggest difference between other kabor intensive jobs and NFL lineman would be the eating habbits. General laborers arent trying to maintain a specific weight. Where lineman are usually consuming massive amounts of calories to maintain their playing weight. You see all the time a retired lineman a year or 2 after retirement and they have lost a significant amount of weight and its simply from they don't eat as much as they used to. I remember one story where a team wanted a tackle to gain 10 pounds. He said he would eat something over 7k calories. Late night snack would be a gallon of ice cream and he lost a half a pound over a week of training camp.