I'm 47 and have sat in airconditioned offices the last 26 years and have the extra weight that comes from sitting for a living. Last summer I hired two different highschool seniors to help handle hay. The first kid was state wrestler and I hoped I could work hard enough to get a decent days work out of him (he threw them on I stacked). About the third wagon load he headed for the house saying he needed to cool off. About half an hour later he headed for home never to return and I finished off the last couple of wagons by myself.
Next week I had about 400 bales on the ground and another kid that is a physical trainer that wanted to "get a work out". He lasted two wagons and said he couldn't take it anymore and left me to finish by myself.
Granted both days were extremely hot and heat indexes were around/over 100 but I truly thought I would be the weak link working with these young men.