Footprints can tell how fast you walk or run

Researchers have developed a new formula that can accurately calculate a person's walking speed by just looking at his footprints.
Two Spanish scientists have designed an equation that provides a highly accurate estimate of an individual's speed based on stride length.
They used data from professional athletes and walking and running experiments on a beach in order to come up with the equation. The result has applications in the study of fossil trackways of human footprints.
In the spring of 2008, 14 palaeontology students from the Complutense University of Madrid ran along a beach in Asturias (Spain) at the request of a planetary geologist who was a friend of their fieldwork director.

Javier Ruiz, from the Complutense University of Madrid (Spain), and his colleague Angelica Torices, from the University of Alberta (Canada) wanted to check how accurately an individual's speed could be calculated based on their tracks.
The results, published in the journal 'Ichnos', show that, without needing any other data such as leg length, they were able to achieve quite a high degree of accuracy, with a margin of error of 10 to 15 per cent.

"For humans, we are able to calculate speed based on stride length alone with a very good degree of accuracy," Javier Ruiz told the Scientific Information and News Service (SINC).

Researchers applied their formula to estimate the speed at which the humans were travelling who left the Pleistocene era fossil trackways found in the Willandra Lakes Region of Australia.
In order to come up with their equation, Ruiz and Torices compared the data obtained in the experiments with the students with data from professional athletes who compete in 100 and 400-metre races.
Up to now, the individual's leg length or at least an estimate of the length was required to calculate speed based on tracks. An equation formulated by the British zoologist Robert McNeil Alexander in 1976 was used which he based solely on data obtained from his children running.

Ruiz and Torices measured the speed and stride length of the students as they ran along the beach and applied Alexander's equation.
The calculation works perfectly well both whether the individuals are running or walking and this was very surprising according to Ruiz.
"There is a little more variability in running but even so it works very well," Ruiz said.
Despite that fact that the speed calculation is very accurate, Ruiz admits that it cannot be applied in an absolute and unequivocal manner but rather statistically.
"Strangely, sometimes 400 and 100-metre athletes have the same stride length but run at different speeds. What the body does is try to optimise how energy is used at a given speed," Ruiz said.