When I was 14 I worked as a busboy at a BBQ place. For like 2 weeks, before they found out I was underaged and fired me. I was never so exhausted in my entire life, before or after. And I was a strong swimmer when I started that job, and was quite fit.

I worked at gas stations after that, before college, and while it was tiring, nothing at the same level.

I can totally imagine a pizza job would be draining.