The number of trail runners is increasing annually. They have grown from 4.5 million to more than 6 million in the United States alone between 2006 and 2012. The amount of organized trail races has grown over the past few years throughout the world, now well into the hundreds in North America alone. Runners often cite less impact stress compared to road running, as well as the landscape and non-urban environment, as primary reasons for preferring trail running. This move to nature is also reflected in a large increase in competitors in non-traditional/off-road triathlons and adventure racing over the past five years.
A growing number of people are participating in solo backcountry trail running trips, carrying an ultralight form of backpacking to allow faster speeds than with a traditional, heavier backpacking, These trips are very difficult and more dangerous, but adherents find overcoming such challenges to be extremely rewarding.
Mountain or fell running, also known as hill running, is the sport of running and racing, off road, over upland country where the gradient climbed is a significant component of the difficulty. The name arises from the origins of the English sport on the fells of northern Britain, especially those in the Lake District. Fell races are organized on the premise that contenders possess mountain navigation skills and carry adequate survival equipment as prescribed by the organizer. As opposed to trail running, fell races are often unmarked and on the open fell, competitors often are able to choose their own course to the top of a mountain or checkpoint.
According to a 2010 special report on trail running published by the Outdoor Industry Foundation, "4.8 million Americans ages 6 and older participated in trail running in 2009." This research shows a particularly heavy following in the Mountain States, the Western US, and California.
Because of the natural or serene setting, trail running is viewed as a more spiritual activity than roadside running or jogging. Another reason for growth and popularity is the continual acknowledgment of environmentalism. There is a stress among many trail-race organizers to keep these races "green" or environmentally friendly and minimize disturbance within the natural environment.
Many trail runners use specially designed shoes that have aggressively knobby soles that are generally more rigid than road running shoes. The usually EVA compound midsole often contain a lightweight, flexible nylon plastic layer to protect the feet from puncture wounds from sharp rocks or other objects. Since trail running take place on softer surfaces (e.g., grass, dirt) than road races, cushioning is not as important so often the shoes are less 'cushioned' than their counterparts designed for tarmac, that's why you often get shoe brands like Vivobarefoot who specialise in thin soled trainers for trail runners. Additionally, trail running shoes are low to the ground which provides the best stability on uneven terrain. Recently, very thick sole running shoes are gaining popularity especially in Ultra-marathons. In events over 100 miles, they were the most common type of shoe used in 2013.
Other equipment includes wicking garments, water bottles, sunscreen, sunglasses, gaiters, insect repellant spray, headlamps and ivy block. Some trail runners attach lightweight crampons to the bottom of their shoes to aid with traction in the snow and on ice. An alternative way to carry water is use a hydration bladder with drinking tube carried in a backpack or waistpack. Today, there are many racing vests that are lightweight alternative which allow runners the choice of reservoir based bladder or water bottles while allowing for carrying other items such as nutrition, hydration supplements and cold weather gear. Carrying the Ten Essentials may reduce the hazards inherent in wilderness travel. Some trail runners use ultra light hiking poles (which are often not allowed during competition) to increase speed and stability.