In reply to thespecialone:
> i can see the theory if you are caring a load in excess of 25 lbs and you are over 65yrs old, otherwise you will be knackered when you get to the crag with all that arm work, use them on descent or when caring more than 35 lbs winter sack. As a fitness instructor i suggest you get the quads and hamstrings up to scratch and that will take you to 65 then you can reconsider.
Ha! I fit the bill. I started using poles at 68 after surgery to replace a ruptured ACL. At first, I used them because my leg was both atrophied and proprioceptively challenged, but as I got better, I never gave them up, and now four years later I use them for trail-running as well. (My version of trail running is more like uphill shuffling, but pitiful as it is, it still feels like running to me.) I do load my poles going both up and down hill, but have never experienced any kind of arm fatigue; in fact I find they provide a pleasant and useful warmup for climbing.
Poles help me with everything, uphill is slightly easier, downhill is slightly less stressful, stability on rough ground when running is improved, I can plant them to vault over logs and other obstacles. I don't necessarily use them all the time; on level even terrain I just carry them in my hands (or perhaps put them away if such terrain is in the offing for a while) and I put them away for scrambling.
Balance is an issue as you age. My solution is to do some purposeful balance exercises. Nothing too fancy; standing on one foot of course, sometimes standing on one foot and bending down to touch the floor and then standing up again, and always standing on one foot or the other while brushing my teeth and doing other stationary chores. I'm ok with my eyes open, but at 72 have lost most of my ability to balance with my eyes closed.
I do feel that poles sometimes encourage an "unbalanced" approach to walking and running, as you careen from one pole plant to the next when you could instead be in equilibrium the entire time, but I've never felt the result of that is an actual loss of balancing ability. Perhaps this is partially because I compensate with other exercises, but I suspect that many of those who think poles decreased their balance were in fact going to lose some of it anyway just through the aging process. Most of my losses were before I started using poles and, with the addition of balancing exercises, I'm better than I was before "in spite" of pole use.