Ray Jardine is the famed and highly-opinionated US rock climber who, with his companion, was the first to free climb the West Face of El Capitan in Yosemite Valley and designed and produced a kind of spring-loaded camming device that revolutionised rock climbing in the late 1970s. He is against the use of trekking poles, considering them unnecessary given correct training and exercise and less important than an umbrella.
Many Inca Trail guides, however, disagree, as do innumerable books. You may start out regarding hiking poles as goofy, but once converted, you would probably take them with you to the supermarket if only your spouse would allow it. Purchasing poles can be injurious to your pocket if you opt for sophisticated, height-adjustable poles constructed from lightweight (= costly) composite substances.
Rather than being just another way to sell more gear, hiking poles have been used by travellers for centuries. They were “multi-tools” before the term was invented. They can be used to pitch a shelter, probe stream crossings or defend against wild animals and bandits (perhaps not an issue on the Inca Trail). No woodsman would ever be without one. They can be hired, although in such a case, they will not be in an immaculate state. Trekkers often concede that they will use poles when their back, knees, legs or whatever gets worse, but prevention in such a key respect is massively better than cure.
There are downsides to sticks. Firstly, they represent extra weight. Ski poles are on the US Transportation Security Agency’s list of items prohibited as carry-on luggage. Also, umbrellas are indispensable on the Inca Trail, but it would be awkward to combine the use of one and a stick and no umbrella will last long if used as a stick. Similarly, you may wish to keep your hands free to use a camera and you will certainly need to do so to use handholds on rockfaces or a map. At least you will have no need for an ice axe. You should devote some attention to walking technique when using poles, as detailed at Peter Clinch’s Hiking Poles Page. Failure to do so could reduce the poles’ effectiveness.
One factor concerning poles that is oft-neglected is they they require more kundlini, or energy, if you can’t speak Sanskrit. Yours arms were not designed to prop you up, so they perform this task inefficiently. But while more energy is used, by creating more contact points, the load is more evenly spread around your body and your legs are not doing all the work. It all depends on whether you have more concern for your knees or your whole body.
The upside of sticks is that they improve your balance and reduce the load on your knees by as much as 25 percent. They are indispensable for people with knee problems. The steeper a hill, the more welcome will be poles, as they will put you into 4×4 mode to work against gravity. They greatly assist in tackling vast sets of Incan stairs, and will be 1,500 of those along the way. They help you to balance on climbs and water crossings. They are like having a handrail all along the trail. They are a godsend when the terrain is wet, rocky or slippery and guides speak of “ankle-breakers” and “knee-destroyers.” The terrain of the Inca Trail is sufficiently rugged to make hiking poles or merely a stick close to a necessity.
On a final note, trekking poles with metal tips are not permitted on the Inca Trail because they damage it. They loosen the soil, and farmers have long known that loosened soil erodes faster than compacted soil, which is why farmers often prefer “no till” or at least a minimum of it. Rubber tips can be purchased from any camping shop. This is an important point: poles are the first thing inspected at checkpoints after your permit and passport.
For a complete packing list see: http://www.machupicchutrek.net/inca-trail-packing-list-machu-picchu/