Running is a form of terrestrial locomotion characterised by alternating periods of support and flight, meaning that during normal running there is a phase in which neither foot is in contact with the ground. It differs biomechanically from walking because the gait cycle incorporates this flight phase and typically involves greater ground-reaction forces and higher speeds. Running requires coordinated action from the feet, ankles, knees, hips, pelvis and trunk, together with substantial cardiovascular and respiratory support. It can range from very easy jogging to maximal sprinting, and the physiological demands differ dramatically across that spectrum. Running can function as recreation, endurance exercise, competitive sport, transport and a training modality for many other activities.
Running mechanics involve the interaction of stride length, stride frequency, ground-contact time, vertical movement, joint angles, muscular forces and elastic energy storage. When the foot contacts the ground, forces are transmitted through the lower limb and trunk, while muscles and tendons absorb and subsequently return mechanical energy. The Achilles tendon and other elastic tissues contribute to running economy by storing and releasing energy during the gait cycle.
Running economy describes the oxygen cost of running at a given submaximal speed, and individuals with similar maximal oxygen uptake can therefore have different endurance performance because their movement efficiency differs. Technique is influenced by speed, anatomy, fatigue, footwear, terrain and individual adaptation rather than being reducible to one universally correct running form.
Running places substantial demands on the cardiovascular and respiratory systems. At moderate and higher speeds, oxygen consumption increases with workload, and trained endurance runners can sustain high fractions of their maximal aerobic capacity for prolonged periods. Faster running increasingly depends on anaerobic energy contribution, particularly during short intense efforts. Lactate production rises when glycolytic energy supply becomes substantial, although lactate itself is not simply a waste product and can be transported and oxidised as a fuel. Endurance training can produce adaptations involving stroke volume, peripheral oxygen utilisation, mitochondrial function, capillarisation and muscular endurance. Sprint training produces different adaptations involving neuromuscular power, acceleration and high-force force production.
Running has an extensive historical role in human societies and organised sport. Modern competitive running encompasses events ranging from short sprints through middle-distance races to road races, cross-country competition and ultradistance events. Training methods consequently vary according to event demands. Endurance programmes may manipulate easy mileage, longer runs, threshold efforts, intervals and recovery sessions, while sprint programmes emphasise acceleration, maximal velocity, technique, strength and recovery. The distinction between training intensity zones is useful for planning but should not be treated as a set of universally fixed physiological boundaries because methods for defining zones differ.
Running is commonly used to improve cardiorespiratory fitness, endurance and performance. It can also contribute to energy expenditure and maintenance of physical capacity. Training progression is important because cardiovascular fitness can sometimes improve faster than the musculoskeletal structures responsible for absorbing repetitive impact, creating a mismatch between perceived aerobic capability and tissue tolerance. Increasing running volume, speed, hills and frequency simultaneously can substantially increase training stress. Alternating demanding sessions with easier training and rest allows adaptation to occur. The appropriate workload depends on previous running exposure, current conditioning, training history and the demands of the chosen activity.
Running is frequently confused with jogging, although there is no universally accepted physiological boundary separating the two terms. In ordinary usage, jogging often describes slower recreational running, while running can encompass the entire activity spectrum. Running is also distinct from sprinting in that sprinting usually denotes very high-speed efforts where maximal or near-maximal velocity and neuromuscular power are central. Barefoot running, minimalist footwear and conventional footwear represent different approaches to managing the interaction between foot and ground, but footwear alone does not determine injury outcomes. Individual adaptation, workload management, technique and tissue capacity all influence how running stress is tolerated.
Potential disadvantages of running include repetitive mechanical loading, environmental exposure and the possibility of overuse problems when training exceeds current capacity. Running can also be difficult for people whose physical condition, mobility or musculoskeletal tolerance makes impact activity inappropriate at a particular time. Its advantages include minimal equipment requirements, strong scalability, ease of measurement and applicability across many fitness levels. Running can be performed outdoors or on a treadmill, with environmental and mechanical conditions differing between surfaces. Treadmill running generally provides a controlled environment, while outdoor running introduces terrain, wind and surface variation that can alter workload.
Understanding running requires distinguishing performance capacity from health-related exercise. Elite running involves specialised workloads that are unnecessary for obtaining general fitness benefits, and the training demands of competitive runners should not be treated as a universal model for recreational exercise. Important measurements can include pace, distance, duration, heart rate, perceived exertion, elevation and, where available, running power or biomechanical data. No single metric completely represents training stress. Running remains a highly adaptable activity whose benefits and demands depend on intensity, duration, frequency, terrain, individual conditioning and recovery.
