As someone who has worked as a shipyard welder and a mechanic... Good lord, yes, working most trades are going to be much harder on your body than sitting around. It is not a close comparison.

It depends, as a technician I was active, mobile, exercised my muscles daily, and was in very good shape. After I got my CS degree, I spent the next year sitting in front of a desk staring at an editor and couldn't stand it. I moved back into the trades and it seemed like the healthier (and better paying) option.

Not to mention white collar workers have to the luxury of being able to request standing desks, mats, anything for ergonomics.

Ask for something like that at a job site and you'd probably get laughed off.