Popularity and growth Trail running has gained in popularity, particularly in the United States. 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 and Pacific Coast States. Because of the natural or serene setting, trail running is viewed as a more spiritual activity than roadside running or jogging. Another reason for its growth and popularity is the continual acknowledgment of environmentalism. There is emphasis from many trail-race organizers to keep these races "green" or environmentally friendly and minimize disturbance within the natural environment. Equipment 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 contains a lightweight, flexible nylon plastic layer to protect the feet from puncture wounds from sharp rocks or other objects. Since trail running takes 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. 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, hats, gaiters, insect repellent spray, headlamps, headphones, 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 to use a hydration bladder with a drinking tube carried in a backpack, waist pack, or hydration pack. Today, there are many racing vests that are lightweight alternatives that 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 or trekking poles, to increase speed and stability. Races Trail running races are organised globally. Due to the relatively short history of trail running as an organised sport, there are very few established organizing bodies. For example, in the United States, the