On Calories

So the other weekend I moved around 8,000 lbs. (about 3 and a half tonnes for you metric types) of broken concrete and building materials, by hand, onto (and subsequently off of) a flatbed truck. Figuring that the truck bed was about a meter off the ground, I wanted to figure out how many calories I'd burned simply lifting the stuff up there. So we're talking mgh, or around 34,300 Joules. How many food (kilo) calories is that? Yup. A hair over eight. Eight?! That's only a couple more calories than are involved in giving a someone blow job. I draw several conclusions from this:

1. The human body is enormously inefficient
2. The marginal rate at which you burn calories working your ass off isn't that high. In other words, you're better off sitting on your ass and eating less from a calorie-balance standpoint.
3. Heat energy is pretty concentrated, if only you could harness it at greater than Carnot efficiencies (note to C-minus physics students: you can't). We're talking enough energy to imperceptibly heat about ten pounds of water.
4. Maybe that's why heating our homes takes so much damn energy
5. Insulation is a good idea

Discuss.