This past winter I showed up at the dive shop prior to a dive and analyzed the gas in my Worthington steel LP 108 doubles (incredibly heavy) and deco bottles. The planned dive was very popular, and the tank area of the shop was a madhouse of activity. I like to pick out my spot on the boat early and get setup as soon as I can. I saw it would be a darned long time before the staff brought the tanks down to the boat on their cart, so I picked up the doubles and carried them all the way to the boat, down the ramp, and to my seat rather than wait for the staff to do the job. It took nearly two weeks for my back to recover. I never did that again. At some point you have to start using your head, and hopefully that is starting to happen at my advanced age.