A half marathon is a road running race covering 21.0975 kilometres, or 13.1094 miles, which is exactly half the distance of a standard marathon. It is one of the most widely contested long distance running events because it provides a substantial endurance challenge while requiring less total racing time and recovery than a marathon. The standard distance is precisely defined rather than being an approximate description of a race lasting half as long as a marathon. Competitors normally run on roads or paved urban courses, although some events use mixed surfaces. The objective is to complete the measured distance in the shortest possible time, with runners managing pace, effort, hydration, nutrition and fatigue over the entire course.
Half marathon racing sits between shorter road races such as 5 kilometre and 10 kilometre events and longer endurance races such as the marathon and ultramarathon. The distance is long enough that aerobic endurance is the dominant physiological requirement, but runners also need considerable speed because elite competitors sustain a very high fraction of their maximal aerobic capacity. Recreational runners may complete the distance in well over two hours, whereas elite performances are substantially faster. Unlike a marathon, the half marathon generally places less cumulative mechanical and metabolic stress on the body, although preparation is still important. Training commonly combines easy aerobic running, longer runs, threshold or tempo sessions, intervals, recovery running and rest.
The defining physical characteristic of a half marathon is its sustained aerobic demand. During the race, muscles require continuous energy production, with oxygen dependent metabolism providing most of the energy for the majority of competitors. Runners must balance speed against the limited ability to maintain very high intensity for more than an hour. Starting too quickly can cause premature accumulation of fatigue, depletion of readily available carbohydrate stores and loss of running economy later in the race. Effective pacing therefore involves controlling effort early, maintaining a sustainable rhythm through the middle kilometres and increasing effort when possible during the final stages. Terrain, temperature, wind, elevation changes, crowding and course design can all affect the relationship between pace and physiological effort.
Half marathon training normally develops several interacting abilities rather than simply accumulating as many kilometres as possible. Easy running develops aerobic capacity and allows training volume to increase without excessive fatigue. Long runs teach the body and mind to sustain movement for extended periods. Threshold running improves the ability to maintain a demanding but controlled intensity, while interval sessions can improve speed, oxygen utilisation and running economy. Strength training may support force production, stability and resilience. Training plans vary according to experience, age, previous injury history, available time and target performance. A beginner may concentrate primarily on consistent running and gradual distance progression, whereas an experienced racer may use carefully structured workouts involving race pace, threshold pace and faster repetitions.
Race strategy is particularly important because a half marathon is long enough for pacing errors to become costly. A common principle is even or controlled pacing, in which the runner avoids spending excessive energy during the opening kilometres. Uphill sections generally require attention to effort rather than blindly maintaining an identical pace, while downhill sections can provide opportunities for efficient acceleration without excessive braking. Runners may use kilometre or mile splits to monitor progress. Aid stations provide opportunities for drinking, and some competitors use carbohydrate drinks, gels or other easily digestible sources of carbohydrate. Nutrition requirements are individual and should normally be practised during training rather than introduced experimentally on race day.
Half marathons are organised in many different settings, including city races, charity events, club competitions and mass participation road races. Courses may be point to point, out and back, or circuits involving several laps. Official races are normally accurately measured so that performances can be compared meaningfully. Timing can be recorded using manual systems, electronic timing mats and transponders.
Participants may receive both gross time, measured from the official start signal, and chip or net time, measured from when an individual crosses the starting timing point. Age group categories, team competitions, wheelchair divisions and other classifications may also exist depending on the event. The surrounding event structure can therefore vary even though the fundamental distance remains 21.0975 kilometres.
The half marathon has significance as both a competitive event and a training objective. For beginners, completing one can represent a major endurance milestone. For experienced runners, it provides a distance at which pacing, threshold fitness and racing discipline can be tested without the full demands of a marathon.
A strong half marathon can also serve as an indicator of endurance development, although performance over one distance cannot perfectly predict performance over another because runners have different strengths and physiological profiles. The event is also popular because preparation can often be fitted around ordinary work and family commitments more easily than marathon preparation. Nevertheless, substantial increases in training volume or intensity can create injury risk, making gradual progression and recovery important.
The term half marathon should not be confused with any race that happens to be approximately half the length of another event. It specifically denotes the standard distance of 21.0975 kilometres. It also differs from a marathon in its distance, physiological demands, pacing requirements and typical preparation, although the two events share road racing traditions and training methods. The distance has become an important part of modern road running culture because it combines accessibility with genuine endurance competition.
Understanding the event therefore requires more than knowing its numerical distance. It involves recognising its standardised course length, aerobic emphasis, pacing demands, training structure, racing tactics, equipment considerations, event organisation and place within the broader progression from shorter road races to marathon and ultramarathon competition.
