Ye olde treadmill. Researchers measured the energy expenditure of armor-wearers while they exerted themselves.

Graham Askew/University of Leeds

Heavy Armor Gave Knights a Workout

Knights in shining armor paid a heavy price for the protection their suits provided them from swords, arrows, and Frenchmen catapulting cows. Researchers have found that the steel plate-mail armor worn during the 15th century, which weighed 30 to 50 kilograms, required its wearers to expend more than twice the usual amount of energy when they walked or ran.

"Everybody's got a certain fascination with medieval armor. It's so different from anything we see today," says physiologist Graham Askew of the University of Leeds in the United Kingdom. With the age of chivalry dead, physiologists curious about just how difficult armor was to move in have a hard time recruiting people who know how to wear armor, much less move efficiently in it.

But four historical interpreters at the Royal Armouries were thrilled to participate in his study, says Askew. He says he was impressed with how mobile they were in their replica suits, which were modeled after armor depicted in a marble effigy of William Martyn, a sheriff of London who lived in the late 15th century. The interpreters could even perform cartwheels in the heavy mail.

Wearing it for a long period, however, carried a very heavy energy cost. That's what Askew and colleagues found when they had the armor-clad interpreters run on a treadmill at different speeds and monitored their oxygen consumption, heart and respiration rates, and stride length. The interpreters expended about 2.3 times the amount of energy usually required to walk and 1.9 times the energy usually required to run while wearing armor than when they weren't, the team reports today in the Proceedings of the Royal Society B. This energy expenditure is much greater than the energy that a person wearing a backpack of an equivalent weight would use.

Knightly jog. Swinging limbs covered in armor is a heavy investment for historical interpreters.
Credit: Graham Askew

The problem is the legs. The pseudo-knights wore heavy leg protection: cuisses on their thighs, greaves on their calves, and pointed shoes called sabatons on their feet. Together, these weighed 7 or 8 kilograms, Askew says, and having to swing that weight with each step really weighed them down. The farther the weight was from the center of the body, the more energetically expensive it was.

The researchers also measured the interpreters' breathing patterns, which normally increase in both rate and volume when a person works out. But the volume of oxygen consumed by the armored runners stayed the same—presumably, Askew says, because the torso was compressed by a chest plate—so they were forced to take many rapid, shallow breaths.

So was leg armor worth it? Well, Askew says, soldiers probably wouldn't have protected the lower leg if it wasn't a site of attack. But as armor began to become obsolete in the 1600s with the invention of gunpowder, the greaves and sabatons were the first things to go.

The study might help answer some historical questions, such as why the French lost the 1415 Battle of Agincourt. They had to march long distances across muddy fields and must have been exhausted by the time they met the English archers.

"First you laugh, and then it makes you think," says Rodger Kram, a physiologist at the University of Colorado, Boulder, paraphrasing the motto of the Ig Nobel Prizes. One interesting aspect of the study, he says, is that the pattern of walking—parameters such as stride length, angle of stride, and the amount of time the foot is on the ground—doesn't change even when a person is carrying a heavy weight on his foot. "It says there's a way we prefer to walk," Kram says.

Thomas Roberts, a physiologist at Brown University, says that the authors' methods "are very reliable and well tested," and he praises the paper's "good argument." But we can't know if the knights of old made some sort of modification to their movement or weight distribution that would have made their load more bearable, he cautions. Sherpas, for instance, expend much less energy than would be expected when carrying a heavy load on their backs; Roberts says it's unclear why that is.

In the future, Askew says he's interested in looking at other types of armor from other time periods, such as chain mail, which preceded plate armor, and styles from Asia. Horses, too, wore armor, called barding, but running a similar study with equine subjects would be dangerous, he says. You wouldn't want to stand behind a horse in full armor on a treadmill.