This page is all about hiking poles (or trekking poles, as many know them): why you may want to use them, what to look for and how to use them once you've got them.
Many thanks to Frank Walter for taking the pictures, and Louise Copeland for getting my ugly mug off most of them.
Hiking poles are simply walking sticks, and though used to aid formal hiking rather than everyday walking the principle is just the same. They take many forms, ranging from single staves made from found wood to pairs of sophisticated height-adjustable poles made from lightweight (and expensive!) composite materials. This page is aimed at the user, or potential user, of purpose built trekking poles, which either are, or are similar to, ski touring poles which have been popular with walkers in the Alps for many years now. The information may be of use to other users who favour more traditional staves, but it's concentrated on the specifics of ski-type poles.
Hiking poles, like any hand-held walking support (sticks, crutches, zimmer frames etc.), are designed to provide extra stability and to spread the load on your legs onto your arms. Many people feel no need for this support when hiking, but there's a substantial minority who suffer for their pleasure in the backcountry, usually from knee pain, and they usually encounter it on hills and/or carrying heavy loads. If you end your days wishing your knees or whole legs were in better shape you may well benefit from using poles, as you can lower the amount of stress on them by taking the weight onto the poles through your arms.
The lists below summarises the main pros and cons of hiking poles...
Working through these in turn...
The typical knee has spent most of its life supporting body weight around on reasonably flat surfaces. Add additional pack weight, keep going for longer than usual and add in the additional stress on the joints and muscles caused by ascents and descents and it's not too surprising that quite a few hikers suffer from some discomfort in their knees. If you don't, you're not so likely to want or need poles, but if you do they'll probably make things better, especially coming down hill. However, also check out the Final notes on knee troubles section.
The steeper the hill, the greater the relative benefit of poles vs. no poles. You can use them to switch into 4x4 mode, and do some of the work against gravity with your arms so you get up quicker and spread the load more evenly around your muscles.
By spreading the load away from your legs, which are the bits that typically get tired on a hike, you can increase your total endurance. This isn't necessarily a "given" though, as poles do increase total energy expenditure. See the Cons section for more on this.
By enabling you to spread your weight onto two baskets as well as two feet, there's much less tendency to sink in snow and marshy ground. When traversing bogs, they also make aided jumps across particularly squishy bits possible, though if you don't have a basket at the bottom none of this will work. More on baskets lower down.
Three or four legs are better than two when trying to cross rivers towards the limits of fordability. As well as making the experience easier, they can make it a lot safer too. On scree they just lower the amount of time you spend sitting down, though they can increase the fun factor of a good running scree by letting you ski reasonably effectively, and certainly aid turning under control.
Many walking staves are made from found materials, but a dedicated ski-type pole will cost money. It isn't necessary to buy the most expensive models for a tangible benefit (in fact I prefer cheaper ones, finding them just as effective as the top-of-the-line models), but you are looking at money you may be better off spending on something else. Poles aren't a must-have like, say, warm clothing in cold conditions, so if the budget's tight, consider the need for a purchase carefully.
A fact not often proclaimed by marketing departments or pole advocates is that using them will increase your total energy budget. Using your arms to prop you up isn't something they were designed for, so they don't do it very efficiently. The flipside is that despite using more energy, you're spreading the load more evenly around your body, so the legs aren't doing all of the work. Thus, if you have tired legs and knees then poles can be a win, but if you have a tired body, with your cardiovascular system at its limits, then poles may be more of a hindrance than a help.
Or one of them, at least... with pole(s) in hand(s), it becomes more awkward to use handholds on rock faces in tricky sections or to consult with a map, take quick snapshots and the like. For fine navigation in difficult conditions, you'll generally have to stow poles to allow compass and map to be used most effectively.
As well as keeping hands full, there are places where poles just plain get in the way. Dense undergrowth, or climbing chimneys, poles can even get in the way when they're stowed. 3 part poles stow smallest, so suffer least here, but it's a hassle if you have to repeatedly collapse them to keep them out of the way.
Judging from the people I see in the UK using poles, the majority of folk get little or no benefit from them. There seems to be some strange perception that by carrying a pole and planting it softly on the ground every couple of paces then your knees will feel a lot better, but alas it isn't necessarily so. Getting a real benefit requires the user to do work and to adopt a useful technique. Without these two factors, poles do little good.
Most people take up pole usage to make their life more comfortable, specifically in the knees department. If you fall into this category it's important that you do more than just use poles, or you could just be putting off problems.
The best way to minimise knee trouble for many people is to have strong muscles supporting the knees, especially the quadraceps/thighs, as this allows muscles to take some of the load off the joints. To get these muscles well developed this usually means low impact exercises for them. I go cycling, XC skiing and roller skating for mine, and it's improved matters enormously. Exercising like this strengthens the muscles around the knee and lets the musculature support the knee better itself. Add poles to this and you're really helping. To let the thigh muscles help support your knees it's important to keep the knees bent, especially when coming down hill, and then rather than jarring the joint the load will be taken by muscular effort. Your muscles may well ache at the end of the day but tired muscles are generally nicer than painful joints and will naturally recover completely in a relatively short space of time.
Direct knee supports (i.e., a an athletic support or bandage around the knee itself) can be useful, but it's important to only use them when you need them, or the knee gets used to external support and may actually be weakened by over-emphasis on the support.
The poles work by removing weight, but a shock absorber in the boot/shoe will often help too: usually it's the combination of impact and weight that gives rise to the trouble, so sorbothane (or similar) footbeds in the boots will help. It's possible that you may benefit from a custom or off-the-peg orthotic footbed, as in many cases these correct the gait cycle and prevent some rotation of the knee and/or hip joint that's the root cause of the trouble in the first place. This is quite likely to apply to people who over-pronate or supinate, and the easy way to see if you do is check the heels of your shoes, especially soft soled athletic shoes. If they are wearing down unevenly, causing the footbed to slope in or out, then this applies to you: it's quite common. If you're unsure then see a foot specialist to check things out, especially if you're getting recurring trouble.
It's a very good idea to seek out expert advice if you are getting bad pain from your knees. A specialist will be able to advise on what is right for you, which you won't get reading a Web page.