[titusjohnson]

> I truly have no idea where all that energy was going.

Growing your body. I was the same in my late teens and early 20's. Family called it the POW Aesthetic. 6'1" & 150lbs, couldn't put an lb more on. I was strong as shit though, in a practical sense. No issue throwing 100lb feed bags over a shoulder and walking it up some stairs into storage, things like that. I was both doing active things all the time, and finishing growing my body. The summer I got my last growth spurt was agony, my bones hurt every night and I was a bottomless void of hunger.

Also, do not underestimate this bit:

> All I did for activity was ride bikes some and lift weights a little, plus usual kid stuff, no serious sports or training.

Specifically I believe the "usual kid stuff" part was doing a lot for you, I know it was for me. Looking back I now realize that my "usual kid stuff" was me being very, very active. I was pounding out 20k+ steps a day just moving around the family farm, miles on a bike (often on grass too), and then maybe an hour of pick-up soccer in the evening. This was just normal activity for me back then, I would not have considered any of it Intentional Exercise. Today I'd have to intentionally train for an ironman to even start approaching that level of activity.

I gained 15lbs the _summer_ I got my first desk job, that was entirely because I replaced 8 hours of walking around and doing things with 8 hours of sitting in a chair, and about 30 minutes of walking for breaks and lunch.