Whoa... How many bladders are you thinking of carrying? If you're typically running in a flat area, it certainly wouldn't matter at all. If you're running in a very hilly area, maybe, just maybe, it would be a noticeable strain on steep downhills. That is unlikely though. You're really only carrying an extra 5 lbs (guess) with a camelback filled up. I have the Cloud Walker w/70oz bladder and I fill it up and add weight. I'm only 165lbs and it's not noticeable on my knees. If you're heavy it'd be less so. I'm light and have knee problems and I always try to run with a pack for that extra "umph".

Remember to use those compression straps to really cinch it down and you MUST wear a shirt or risk losing skin from the rubbing.

Burns

I concur. And wear a crappy shirt that you don't like, because it really wears down your shirts with all that friction.

I have found that my camelback bounces to much when I run with it. Instead I use a small water bottle carrier that goes around my waist. One of my long runs has about five miles between water stops and in the summer thats to far without water. A small water bottle helps. For those really long runs I carry a small packet of Accelerade to mix with the water. It really helps out. I dont think that the weight of a camelback or a water bottle will matter either way.

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Once, I was fast. But I got over it.

I'm a big advocate of running with a pack on, and one of very few people who do it. I think it works. I used to have a girlfriend named Amber who I ran with and had to carry all her "crap" in a little backpack when we ran: Gum, mints, water, gu, chapstick, tapes and batteries for her walkman, Kleenex, a wind jacket if she got chilly. Yeah, she was high maintenance and totally psycho, but a babe. Actually inretrospect, it wasn't worth it. She was a pain. But I still run with a camelback and/or a pack on to get to the gym and the pool.

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Tom Demerly
The Tri Shop.com

I agree with Tom, I don't think it is so much the weight, but the distribution that is important. I used to run with a backpack as well, and as long as the weight was appropriately distributed, there was no jostling and this was fine at easier paces. Of course, it is nicer to run without a pack, but if you need to carry your water source, then you should get used to it.

I remember reading of a study, maybe on Danish runners?, where they had them wear 25lb wight vests while running for some weeks. As I recall, results were mixed with some runners actually slowing down from their times before the training. After some recovery time and normal running, though, they did see some improvement. That study made a tentative conclusion that the decrease in performance was due to decreasing cadence with the weight on.

So, I guess if you do train with some extra weight, the moral is to make sure your don't slow down your turnover.

My $.02.

If you decide to run with a pack with the purpose of carrying extra weight, start off very light and gradually add weight to it. I was trying to ramp my mileage up by running to and from work. So I wore a good backpack with waist straps to carry my clothes. Well adding clothes, a pair of shoes, toiletry bag and a towel put the weight close to 15 lbs. Got home that night and my hip was sore. I've been injured ever since (going on 6 weeks) with a trocanteric bursitis (hip).

My $0.02

Don't do it. One of the main reason that people get injured running is poor form. As soon as you add weight that is not part of your body I think that is messes up your natural stride. As a runner for 25 years, I've seen all sorts of theories on building strength, and doing things like running with hand weights, ankle weights and packs is not the way to do it. If you want to build strength and power on your run, forget about the camelback and find some hills to do interval training on. For your base work, choose a course that is hilly. Even if I know that I'm going to need fluids on a run, I drive out and place some bottles at key locations rather than carry a camelback or one of those water bottle belts.