It's because of mangos like this one, that I ended up thinking that princess carry / piggy-back is lax and easy.
It sure ain't. Heck, even carrying a light-weight grocery bag with your arms extended for a minute can start to hurt. It's tough to have that kind of endurance.
When I had to carry someone on my back a year ago, it was my arse of all things that ended up hurting.
Not enough squats. Not enough swoll.