I am a commercial/industrial electrician, so more often than not I get a work out on any given day. I am on my feet 8 hours everyday with a 5-50lb tool belt, sometimes more depending on what project I am working on. I put suspenders on my tool belt to help build up my shoulder neck and back muscles for backpacking.

Now combine this with walking up and down stairs, climbing ladders, lifting very heavy tools and electrical devices all wearing my gigantic tool belt it all keeps me in decent shape for backpacking.