Not all forms of athletic endeavor involve the development of physical endurance qualities, but every successful athlete will be required to withstand or overcome a variety of both physical and mental hardships in the pursuit of their goals. As a noun, endurance is the state of being that requires perseverance; it is a word that conveys persistence, an ability to finish an event or a program in the face of challenges. It is also a descriptive term, such as in "endurance" exercise.

Endurance has a number of dimensions. The presence or the enhancement of athletic endurance will occur in concert with the development of six different aspects of sport training, each of which is a freestanding component of athletic performance. These aspects include speed (defined as distance ÷ time); power (defined as force × distance ÷ time); strength (represented as a weight moved over a distance, force × distance); muscular endurance (which is the development of the muscles or specific groups of muscles to provide muscular strength over time); cardiovascular endurance (which is the stamina to maintain heart rate, blood volume, and circulatory efficiency over time); and mental endurance (which is a subset of the broader study of sport psychology, the mental and emotional toughness or strength of will to complete a set athletic task).

The development of endurance in any of these areas is unlike other types of sport training, in that the typical tools of athletic skill development are not essential. Unlike the honing of techniques necessary to succeed in a sport, such as the building of an effective tennis serve or bending a soccer free kick around a defensive wall, agility, hand-eye coordination, reflexes, and peripheral vision are not required. Attitude and a desire to become stronger and more enduring as an athlete are the most important features of improved endurance, which will be developed using the larger body systems as opposed to fine motor skills.

Genetics and environment also play a role in the ability of particular athletes to excel in sports in which endurance is a particular feature. African runners from countries such as Kenya, which is located in the Rift Valley, have proven to be the most successful middle-distance racers and marathoners in the world. These athletes are raised at altitudes of approximately 6,500 ft (2,000 m) above sea level; they generally possess slim, relatively short, and lean bodies in an environment where the cardiovascular system will be stimulated to produce a greater number of red blood cells to compensate for the lesser amount of oxygen in the air. These factors, coupled with intense training programs, all contribute to Kenyan dominance as superior endurance athletes.

There is considerable evidence that when an athlete trains to a very high level in a particular discipline, the composition of the muscles may also change. Human muscles comprise two types of fibers: fast twitch fibers, so called for their utility in sprint and power functions, and slow twitch fibers, which are predominant in endurance events. Elite athletes such as cyclist Lance Armstrong have been tested over the span of their competitive career regarding the fiber composition in their legs. Examination revealed that Armstrong increased the slow twitch composition of his leg muscles, making him more efficient in long-distance cycling racing, a process that occurred after years of intense training.

The type of sport will dictate when each of the three energy systems of the body will be engaged and to what degree. In sports where energy is required in short intervals of less than approximately 90 seconds, the anaerobic alactic or the anaerobic lactic systems will be utilized. These systems are not themselves endurance sport systems. In sports such as long-distance cycling, running, or cross-country skiing, the aerobic system is used to produce energy. This energy system is the process typically associated with physical endurance abilities. All energy systems, no matter what the sport, require the development of endurance as a recovery mechanism; the ability to physically maintain a particular level of activity will assist the athlete who competes in short, intense intervals to return to the higher, more intense level more quickly.

As with all other physical attributes, endurance is a quality that can deteriorate just as readily as it was developed. Endurance is a type of fitness, and if the components necessary to support endurance are not brought into play, the endurance aspect of the athlete will decline. If a basketball player training for a sport in which the anaerobic lactic system provides the bulk of the necessary energy completes a program of 3-mi (5 km) runs four times per week in preseason, that athlete will have developed a measure of endurance capability he or she did not previously possess. Even though playing or practicing basketball every day once the season starts, if the athlete does not continue with his or her aerobic fitness program, that endurance aspect of his or her conditioning will decline. Just as readily, a return to aerobic activities will rebuild endurance.

No matter how vigorous the athletic effort to develop physical endurance, the mental ability to persevere is a more ephemeral quality. Mental toughness and doggedness of approach are not a constant in any athlete; all athletes will experience high points and depressions in their personal confidence and self-perception as to whether they can truly complete a training assignment or competition. The mental endurance component, while rooted in the concepts of stamina and determination, varies from sport to sport. A weightlifter, who must focus on each lift lasting only seconds as a discrete event in competition, will seek to develop a mental endurance to take him or her through competitions that may last for hours.

SEE ALSO Blood doping; Cardiovascular system; Endurance exercise; Hydration.