I have a bit of a nuscance back.. (sp?) I wont say bad...
I use a hydration pack, it holds 2 liters of water, thats 2kilo's or 4.4 lbs
tools and a tube, and a cell phone, you never know....
nope, doesnt hurt my back at all!!
25k enduro with two water bottles on the frame and two clif shots...
Man was my back was sore, I agree with the standing for the rough sections!!