Creatine?

I've heard a lot about creatine being great for strength training, but that's the only good thing I've heard about it. Some folks I work with used it for a while and found that (according to them) it caused problems with endurance training, especially in the heat of the southwestern desert. Allegedly (I don't know first-hand) the guys who used creatine were having problems staying hydrated because a lot of the water they ingested went to their muscles and wasn't properly distributed throughout their entire bodies.

Again, I don't know first-hand.

When taken right (most people take it wrong) It is helps you recover between sets when using the atp/pc energy system (short bursts)  but not in the aerobic system.

I would not use it over 50 or even 30 for that matter.  too many unknowns.  Then there is the hydration issues and questions like, how does long term use effect the body's ability to naturally recover (body adjusting its levels out of dependence) etc..

Wish I had the problem of being too light. I'm no doctor but I don't think 140 pounds is underweight for a distance athlete and would go with it unless you are losing significant weight. I think the loss of some muscle mass is to be expected but you would obviously know your body better.

Years ago I took creatine for a little while as a supplement and had  my normal semi-annual blood test. My creatine levels were far outside of what were considered safe so I stopped it and will never do it again.

Please note that this is the main reason that creatine is not good for endurance athletes.  The water retention at the cellular level actually puts you at higher risk for dehydration and things like strokes. 

As another poster mentioned, you'd be a lot better off by upping your protien intake while increasing your strength training if you are looking to add muscle.  But remember, muscle weighs a lot and it's not much fun carrying extra weight up hills on the bike or run.