<s>Testosterone</s>
I’ve worked cutting trees under a literal psychopath (just out of jail for murder), a guy had died of dehydration on that job the previous year. It was strenuous and I mourned/cried the loss of my girlfriend while sawing branches like a madman.
It was also the best time of my life.
See, using my body, requiring agility, quick varied microdecisions and physical strength, it makes use of the body I was given by mother nature. Compare that to working in front of a computer all day, using only the logical part of my brain, no emotions, gray screens everywhere: As much as I love being an entrepreneur and I love using my IQ 136, well, it uses 8% of the body’s capabilities - the brain and the fingers, period. It’s unnatural.
So I suspect hard physical work with actual people and emotions, triggers hormones (testosterone being the caricature of it) that regulates everything including motivation, a clean mind, and happiness. Of course I wouldn’t wish to work on a field all my life, but programming or Excel spreadsheeting may have a negative impact on the mind.