Originally Posted by
Chris Pringle
You are better off not carrying anything heavy on your body, including a hydration pack. In the long run, it may cause you to hunch your back and this could then lead to Shermer's neck - a condition quite common on these very long randonnées. Find a way to carry an extra bottle (3 total) on your bike frame.
I have read about Shermer's neck and from what I've read the exact causes (besides long distance) are unclear. The majority of mountain bike ultra marathon racers ride with Camelbacks, so I don't see why it couldn't cross over to events much shorter such as PBP. The Tour Divide race is over 2700 miles, with top riders riding 175-200 miles a day on average, and that's mostly off-road.