Among the advantages of barefoot running extolled by many of its devotees is that running unshod is more efficient than running with clunky shoes.

But a new study by researchers at the University of Colorado's Locomotion Lab -- which has studied the metabolic costs of running and walking for decades -- has found that running with shoes is actually more efficient, using a measure of how much oxygen people consume (and how much carbon dioxide they produce) while running.

"Running in lightweight shoes requires about 3 to 4 percent less energy than running barefoot," said Jason Franz, a CU doctoral student who led the study.

The inspiration for the research came from Corbyn Wierzbinski, a CU undergraduate who co-authored the study. Wierzbinski's boyfriend had recently taken up barefoot running, and she wondered if the advantages she kept hearing about could be scientifically proven. The lab decided to look into one of the more popular assertions.

"We started to see these claims that barefoot running -- because you remove the weight of the shoe -- is more efficient," Franz said.

Other scientific studies have shown that the weight of a shoe does impact a runner's metabolic efficiency. And the CU study confirmed earlier conclusions that the metabolic costs creeps up by about 1 percent for every 100 grams of weight added to a runner's feet.

Franz, Wierzbinski and Rodger Kram, director of the Locomotion Lab, confirmed the findings with the help of 12 male subjects, all of whom were experienced barefoot runners (logging an average of 19 miles a week sans substantial shoes) and all of whom landed on the mid-sole of their feet while running with or without shoes. (Many people who run exclusively in shoes tend to strike first on their heels.)

The researchers also devised a system for adding weights to the top of the runners' feet when they were barefoot as well as when they ran in shoes. For the study, the participants ran exclusively on a treadmill and they wore thin yoga socks when they ran without shoes. When they ran with shoes, they wore the lightweight Nike Mayfly -- the study was not funded or sponsored by Nike or any shoe company -- which tips the scales at just 150 grams and which has some cushioning but no other "motion control elements," such as arch support.

When researchers added weight to runners' feet, their efficiency slipped proportionally to that weight, whether they wore shoes or not.

All things being equal, that would mean that running without the weight of shoes should be more efficient -- but the researchers discovered that all things aren't equal.

When subjects ran barefoot with an additional 150 grams of weight added to their feet, about the same amount of weight as a Mayfly running shoe, they were 3 to 4 percent less efficient than when they wore the Mayfly, according to the study published in the journal Medicine & Science in Sports & Exercise.

The reason why is the subjects of another study at the Locomotion Lab. The research has yet to be completed, but Franz said that he thinks the drop in efficiency may have to do with the need for barefoot runners to compensate when the cushioning of the shoe is removed.

"The barefoot runner needs to cushion against the impact using their muscles," Franz said. "That requires a little bit of metabolic energy to cushion each stride."

Despite his study's findings, Franz notes that the research is not an endorsement for or against running barefoot.

"We recognize that people choose to run barefoot for a variety of reasons. Some want to connect to their inner caveman; some people think it protects against running-related injury," he said. "All we're trying to find out is if there is any scientific basis to those claims that it is more efficient."

Local barefoot running enthusiast -- and CEO of Invisible Shoes, a company that makes minimalist running sandals similar to those worn by the Tarahumara Indians in Mexico -- Steven Sashen said the kind of efficiency differences measured in the CU lab are so tiny that they may not matter to many barefoot runners.

"For most people, the kind of efficiency gain or loss that they're talking about is the kind of thing that most runners would never notice in a million years," he said.

He also is skeptical that having subjects pound out a workout on a treadmill wearing socks really approximates the barefoot running experience.

"Running on a treadmill is completely different from being barefoot," he said. "It's kind of like a medical study -- doing something in a test tube is not the same as doing it in the human body."

But Sashen agrees with Franz that there are many reasons to run that have nothing to do with efficiency.

"None of the research matters if you're having a good time," he said.

Contact Camera Staff Writer Laura Snider at 303-473-1327 or