I decided to spend my last summer before college at a job that wasn't just work, but a workout.

I applied for a position as a loader at UPS and got hired. They paid me $8.50 an hour to climb into the back of an 18-wheeler in 90 degree heat and stack boxes for four hours straight, five days a week, at a load rate of 650 boxes an hour. That's about ten boxes a minute, or one box every six seconds, with an average box weight of 35 pounds. No joke. And, oh yeah, you had to read the zip code on each box that passed through your hands to make sure it was going in the right truck.

I was all alone in the truck with boxes coming at me on conveyor belts. Every moment was like a constantly changing 3-D puzzle. I had to find the smartest, fastest way to add the next package to the wall of boxes.

There was a VERY specific way to "build walls" as it was called, and supervisors would regularly test your knowledge as you struggled to keep up with the flow of incoming packages. They would even send mis-sorted packages into your trucks to make sure you were reading the zip codes.

Working at UPS not only put me into the best shape of my life, but was also a constant mental and physical test. I liked it so much that I did it again the next summer. But this time I also got a gig moonlighting at the local ice cream shop. You know, to replace all those calories.