People choose to run at their optimal speed.

OBJECTIVES: The purpose of this article is to test whether people choose to behave in a manner that reduces the amount of energy they use to travel a given distance. While this has been shown consistently for walking, it has never been tested with human running.

MATERIALS AND METHODS: We collected energetic data and lower limb anthropometrics on nine men running at six different running speeds. We collected on all six speeds on 3 different days and took the average of the energetic values for each speed. On each day we also asked the participants to choose the speed at which they could comfortably run for an hour, and we took the average of these preferred speeds. We then fit a 2nd order polynomial to the energetic data and compared the speed at which the minimum cost of transport (SpMinCoT) occurred with their preferred running speed.

RESULTS: All participants showed a curvilinear relationship between speed and their cost of transport (CoT). Additionally, the preferred speed was not significantly different than the speed at the minCoT (p = 0.215), and the best fit line between the minCoT and the CoT at the preferred speed was y = x (R2  = 0.994).

DISCUSSION: Humans are able to preferentially identify the speed which minimizes energy expenditure during running, as well as in walking. Over long distances, energy conservation during running would be particularly crucial so further investigations should focus on the mechanisms by which people are able to detect their 'optimal' running speeds.