Using trekking poles splits the load between your legs and arms, its not an even split, your knees still take the lion's share of the stress of walking and carrying a load, but by transferring at least some of this to the arms your legs get some relief and at the end of a long day they aren't as tired as they would have been.
Trekking poles are particularly useful for ascending slopes where the extra push from your arms can be a real help. They are also good for balance on uneven ground or river crossings, and they can even provide the structural support for your shelter.
It can be useful to adjust the length of trekking poles for ascents and descents, by lengthening a pole for descending and shortening the pole for ascending the action of using trekking poles becomes more natural. However manufacturers can make the poles lighter with a shorter pack-size if they are fixed length, and some people will not be bothered stopping to adjust the length of a pole if the terrain is changing quite a lot - so its down to personal preference as to whether you want the fine tuning offered by adjustable poles or the lightness and convenience of fixed length.
Some newly introduced poles have combined both technologies to provide a fixed length pole with a short adjustable section at the top - this is a good compromise as it delvers, lightness, short pack-size and adjustability.
Adjustable poles: There are basically two different methods used by manufacturers to lock the sections at the desired length, these are Twist Locks and Lever Locks.
Twist Locks have an internal locking mechanism activated by twisting the pole section one way to lock and the other way to unlock. These are very tidy leaving a clean outer joint on the pole but they can seize up if they are not kept clean after use - the best practice is to store them in pieces so that seizing cannot occur.
Lever locks come in various types but basically the mechanism for locking the pole is on the outside and involves a lever to reduce the diameter of one pole over another. These are more reliable than the twist mechanism and easier to use, but they are generally heavier and they add bulk to the pole joints.
Fixed length poles: Fixed length poles are generally locked for use using a spring and button mechanism. These seem to work well without any reported problems. When collapsed the sections are folded together.
The ends of the trekking pole is called the Tip and can usually be replaced when it gets worn out, we stock replacement Tips for most models we stock. The basket is the round plate that sits just above the tip and stops the pole sinking into soft ground. Most poles come with a standard basket which is about 8cm diameter, this can be changed for larger or smaller baskets depending on which the manufacturer supplies. The largest baskets are for use on snow. If you are going over rocky terrain then a small basket is usually the best - its just enough to stop the pole jamming in crevices. Some poles have a range of baskets included with the purchase price, but others have them as optional extras.
Rubber feet are used to deaden the sound made by trekking poles on rocks or tarmac and are a press fit. Again these are sometimes included with the poles, but often are optional extras.
Grips and straps - Grips are usually stiff foam, but quality can vary. There will also be a strap to keep the pole in position when you are using it, these straps should be easily adjusted and not slip once set - not all manufacturers get this right.
Anti-Shock Poles - Anti-Shock poles generally have a spring loaded mechanism which absorbs the impact of the pole as it strikes hard ground, providing added cushioning for greater levels of comfort. Some argue that it's not worth the extra weight but we would say that it depends on the trip and the person using them.