Carrying furniture != riding bike. I believe the point was that weight doesn't influence efficiency if you're getting extra momentum for your extra effort. A big boy on a bike is harder to stop than a little one. For the furniture, that extra momentum ain't helping you since it's working in the wrong direction (i.e. down via gravity). Still, I agree muscles don't provide equal returns at certain loads.

PS: And you're not my hero now that it's not you in the photo. Sorry.