I was never a formal athlete like your son, but when I was young we had to do physical fitness tests periodically. I played sports
for fun a lot, but again, I wasn't a serious athlete -- no real talent. But I could run all day and play sports all day without any problem despite living in a place that was really hot, dry, and severely polluted. But when we had to run the 600, and that's a short race, I always got sick to my stomach afterwards.