Running in bare feet — a trend that has been gaining popularity — requires more energy than running in lightweight shoes, a study has found.

"Running in a shoe used between three to four per cent less energy, which is pretty substantial," said Rodger Kram, a researcher at the University of Colorado in Boulder who co-authored the study, published in the current issue of Medicine & Science in Sports & Exercise.

Prior to the study, many people had assumed that running without shoes would be more efficient because shoes add extra weight that the runner has to move during each stride.

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Advocates of barefoot running say it will make a runner faster and prevent injuries. (Stefan Wermuth/Reuters)

Advocates of barefoot running, such as Montreal runner and trainer Gilbert Ayoub, say it will make a runner faster and prevent injuries.

"It's a more natural way to run because you're using your tendons, ligaments and muscles to absorb the impact of the ground instead of using your skeletal structure," said Ayoub. He added that the findings of the new study don't sway his beliefs about the technique he has been using for years.

Kram and his colleagues measured the amount of oxygen used by 12 runners with "substantial" barefoot running experience as they ran on a treadmill. The researchers compared the results when the runners were barefoot and when they wore lightweight racing shoes weighing roughly 150 grams.

They also attached small lead strips to the runners' feet or shoes, weighing between 150 and 450 grams, to look at the effect of extra weight alone.

They found that runners used three to four per cent less energy while shod than barefoot if the mass attached to their feet was equal. They suggest that during barefoot running, the body uses extra energy to absorb the shock that would otherwise be absorbed by the shoes.

Runners also used an extra one per cent more energy for each additional extra 100 grams of mass attached to their feet.

However, when no extra weight was attached, they used less energy while wearing shoes because the shoes weighed only 150 grams.

That means such shoes would increase energy use only 1.5 per cent — far less than the three to four per cent increase caused by running barefoot.