While humans have run on natural trails since the dawn of time, cross-country running began as a competitive sport in England in the early 1800s. With competition centered around both running clubs, known as "harriers," as well as universities, the sport was exported to the United States in the 1870s, where it quickly became a university competition. The National Collegiate Athletic Association (NCAA) has convened national cross-country running championships since 1938. The International Amateur Athletics Federation (IAAF) has organized the world cross-country championships since 1967. Cross-country running is not an Olympic event, although a 3-mi (5-km) cross-country run is the last of the five events in the Olympic modern pentathlon.
Unlike other forms of running, cross country lends itself to team as well as individual competition. In the team format, points are awarded for the position achieved by each team member in the overall race standings. In IAAF competition, there are no standardized world records or course lengths, given the variability of terrain and conditions from course to course. An IAAF championship race course for men must be a minimum of 7.5 mi (12 km) in length; the women's race course must be a minimum of 3.1 mi (5 km).
The significant difference between cross-country running and the running that takes place on the road or the track is the variability of both weather and footing. For this reason, the training for cross-country running events is quite specialized. Many runners will compete in cross-country, road racing, and track events, but it is a rare and exceedingly talented runner who can win on a national or international basis in all three disciplines.
To effectively deal with the combination of terrain and elements, cross-country runners tend to develop a shorter stride than they might employ in a road or track event. By having the heel of the lead foot strike the ground closer to the body, the runner sacrifices stride length for greater stability and balance. The physics of the cross-country running's surface, and the corresponding effect on stride, also differ from those of the road and the track. A harder running surface will produce greater elasticity in the return of energy from the ground into the runner's legs; the softer, off-road trails where cross-country running takes place are less elastic, requiring the athlete to use more energy to cover the same distances. In addition to being more inefficient, in terms of the relationship between the energy expended by the runner and the distance traveled, cross-country running requires greater thigh muscle action and a resulting greater overall effort from the abdominal muscles and the lumbar (lower back) to support the leg action.
Unlike the stride cadence into which a road or track runner will quickly settle to assist in the delivery of an efficient and uniform stride, the cross-country runner must continually adjust the stride length to the terrain and weather conditions. The precise planting of the foot of the cross-country runner is often variable throughout the race. For these reasons, cross-country running is the most difficult of the running sports. Cross-country runners tend to be more versatile and adaptive athletes as a result.
Cross-country running training reflects the diversity of the conditions that an athlete might encounter. As a sport that primarily requires endurance, training that tends to strengthen the cardiovascular system will form a large part of the weekly training volume, particularly those exercises that enhance the body's capacity to process oxygen, the indicator known as VO2max. To address the variability of the terrain, cross-country runners also devote significant time to hill training and interval repeat running. Cross-country running does not place significant emphasis on resistance training in the form of free weights, but some weight training is often relied on as a way of ensuring overall muscular balance and stability.
Stretching and flexibility exercises are an important component of all running training programs. Such exercises assist the cross-country runner in developing optimal range of motion, especially in the hip and leg joints, which assists the athlete in countering the effects of uneven terrain. Stretching also assists the cross-country runner in both warm up and cool down periods when the weather is cold and the muscles more prone to becoming tight. Runners often suffer injuries that are caused by weather and the running surface.
Cross-country running has tactical considerations that differ from other forms of racing. Most cross-country courses require a mass start for all competitors, which often lead directly into a narrow trail where passing a lead runner is difficult. To counter these circumstances, many successful cross-country competitors are front runners, athletes who can get to an early lead and hold their advantage for the entire race.