Preferred walking speed

The preferred walking speed is the speed at which humans or animals choose to walk. For humans, it varies more by culture and available visual feedback than by body type, typically falling between 1.10 metres per second (4.0 km/h; 2.5 mph; 3.6 ft/s) and 1.65 metres per second (5.9 km/h; 3.7 mph; 5.4 ft/s). Individuals may find speeds slower or faster than their default uncomfortable.

Horses have also demonstrated normal, narrow distributions of preferred walking speed within a given gait, which suggests that the process of speed selection may follow similar patterns across species. Preferred walking speed has important clinical applications as an indicator of mobility and independence. For example, elderly people or people suffering from osteoarthritis must walk more slowly. Improving (increasing) people's preferred walking speed is a significant clinical goal in these populations.^{[citation needed]}

People have suggested mechanical, energetic, physiological and psychological factors as contributors to speed selection. Probably, individuals face a trade-off between the numerous costs associated with different walking speeds, and select a speed which minimizes these costs. For example, they may trade off time to destination, which is minimized at fast walking speeds, and metabolic rate, muscle force or joint stress. These are minimized at slower walking speeds. Broadly, increasing value of time, motivation, or metabolic efficiency may cause people to walk more quickly. Conversely, aging, joint pain, instability, incline, metabolic rate and visual decline cause people to walk more slowly.

Commonly, individuals place some value on their time. Economic theory therefore predicts that value-of-time is a key factor influencing preferred walking speed.

Levine and Norenzayan (1999) measured preferred walking speeds of urban pedestrians in 31 countries and found that walking speed is positively correlated with the country's per capita GDP and purchasing power parity, as well as with a measure of individualism in the country's society. It is plausible that affluence correlates with actual value considerations for time spent walking, and this may explain why people in affluent countries tend to walk more quickly.

This idea is broadly consistent with common intuition. Everyday situations often change the value of time. For example, when walking to catch a bus, the value of the one minute immediately before the bus has departed may be worth 30 minutes of time (the time saved not waiting for the next bus). Supporting this idea, Darley and Bateson show that individuals who are hurried under experimental conditions are less likely to stop in response to a distraction, and so they arrive at their destination sooner.

Energy minimization is widely considered a primary goal of the central nervous system. The rate at which an organism expends metabolic energy while walking (gross metabolic rate) increases nonlinearly with increasing speed. However, they also require a continuous basal metabolic rate to maintain normal function. The energetic cost of walking itself is therefore best understood by subtracting basal metabolic rate from total metabolic rate, yielding final metabolic rate. In human walking, net metabolic rate also increases nonlinearly with speed. These measures of walking energetics are based on how much oxygen people consume per unit time. Many locomotion tasks, however, require walking a fixed distance rather than for a set time. Dividing gross metabolic rate by walking speed results in gross cost of transport. For human walking, gross cost of transport is U-shaped. Similarly, dividing net metabolic rate by walking speed yields a U-shaped net cost of transport. These curves reflect the cost of moving a given distance at a given speed and may better reflect the energetic cost associated with walking.

Ralston (1958) showed that humans tend to walk at or near the speed that minimizes gross cost of transport. He showed that gross cost of transport is minimized at about 1.23 m/s (4.4 km/h; 2.8 mph), which corresponded to the preferred speed of his subjects. Supporting this, Wickler et al. (2000) showed that the preferred speed of horses both uphill and on the level corresponds closely to the speed that minimizes their gross cost of transport. Among other gait costs that human walkers choose to minimize, this observation has led many to suggest that people minimize cost and maximize efficiency during locomotion. Because gross cost of transport includes velocity, gross cost of transport includes an inherent value of time. Subsequent research suggests that individuals may walk marginally faster than the speed that minimizes gross cost of transport under some experimental setups, although this may be due to how preferred walking speed was measured.