Lift with your legs, get assistance from others, wear back support - it's all crap. If you have something gigantic, say, this extra large bale of cotton, that needs to be loaded in the back of a truck, just do what these guys did. Seems to work and you don't get your hands dirty.

It may not work for everything, but still, it makes it look easy.

And, actually, yes, you should left with your legs.