Walking

Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined as an "inverted pendulum" gait in which the body vaults over the stiff limb or limbs with each step. This applies regardless of the usable number of limbs—even arthropods, with six, eight, or more limbs, walk. In humans, walking has health benefits including improved mental health and reduced risk of cardiovascular disease and death.

The word walk is descended from the Old English wealcan 'to roll'. In humans and other bipeds, walking is generally distinguished from running in that only one foot at a time leaves contact with the ground and there is a period of double-support. In contrast, running begins when both feet leave the ground during each step. This distinction has the status of a formal requirement in competitive walking events. For quadrupedal species, there are numerous gaits which may be termed walking or running, and distinctions based upon the presence or absence of a suspended phase or the number of feet in contact any time do not yield mechanically correct classification. The most effective method to distinguish walking from running is to measure the height of a person's centre of mass using motion capture or a force plate at mid-stance. During walking, the centre of mass reaches a maximum height at mid-stance, while running, it is then at a minimum. This distinction, however, only holds true for locomotion over level or approximately level ground. For walking up grades above 10%, this distinction no longer holds for some individuals. Definitions based on the percentage of the stride during which a foot is in contact with the ground (averaged across all feet) of greater than 50% contact corresponds well with identification of 'inverted pendulum' mechanics and are indicative of walking for animals with any number of limbs, however this definition is incomplete. Running humans and animals may have contact periods greater than 50% of a gait cycle when rounding corners, running uphill or carrying loads.

Speed is another factor that distinguishes walking from running. Although walking speeds can vary greatly depending on many factors such as height, weight, age, terrain, surface, load, culture, effort, and fitness, the average human walking speed at crosswalks is about 5.0 kilometres per hour (km/h), or about 1.4 meters per second (m/s), or about 3.1 miles per hour (mph). Specific studies have found pedestrian walking speeds at crosswalks ranging from 4.51 to 4.75 km/h (2.80 to 2.95 mph) for older individuals and from 5.32 to 5.43 km/h (3.31 to 3.37 mph) for younger individuals; a brisk walking speed can be around 6.5 km/h (4.0 mph). In Japan, the standard measure for walking speed is 80 m/min (4.8 km/h). Champion racewalkers can average more than 14 km/h (8.7 mph) over a distance of 20 km (12 mi).

An average human child achieves independent walking ability at around 11 months old.

Regular, brisk exercise can improve confidence, stamina, energy, weight control and may reduce stress. Scientific studies have also shown that walking may be beneficial for the mind, improving memory skills, learning ability, concentration, mood, creativity, and abstract reasoning. Sustained walking sessions for a minimum period of thirty to sixty minutes a day, five days a week, with the correct walking posture may improve health.

The Centers for Disease Control and Prevention's fact sheet on the "Relationship of Walking to Mortality Among U.S. Adults with Diabetes" states that those with diabetes who walked for two or more hours a week lowered their mortality rate from all causes by 39 percent. Women who took 4,500 steps to 7,500 steps a day seemed to have fewer premature deaths compared to those who only took 2,700 steps a day. "Walking lengthened the life of people with diabetes regardless of age, sex, race, body mass index, length of time since diagnosis and presence of complications or functional limitations." One limited study found preliminary evidence of a relationship between the speed of walking and health, and that the best results are obtained with a speed of more than 2.5 mph (4.0 km/h). Even a light walk after a meal offers benefits in reducing postprandial glucose spikes in people with or at risk for type 2 diabetes.

A 2023 study by the European Journal of Preventive Cardiology, the largest study to date, found that walking at least 2,337 steps a day reduced the risk of dying from cardiovascular diseases, and that 3,967 steps a day reduced the risk of dying from any cause. Benefits continued to increase with more steps. James Leiper, associate medical director at the British Heart Foundation, said that if the benefits of walking could be sold as a medicine "we would be hailing it as a wonder drug".

It is theorized that "walking" among tetrapods originated underwater with air-breathing fish that could "walk" underwater, giving rise (potentially with vertebrates like Tiktaalik) to the plethora of land-dwelling life that walk on four or two limbs. While terrestrial tetrapods are theorised to have a single origin, arthropods and their relatives are thought to have independently evolved walking several times, specifically in hexapods, myriapods, chelicerates, tardigrades, onychophorans, and crustaceans. Little skates, members of the demersal fish community, can propel themselves by pushing off the ocean floor with their pelvic fins, using neural mechanisms which evolved as early as 420 million years ago, before vertebrates set foot on land.