British scientists monitored volunteers wearing 15th-century replica armor weighing up to 110 pounds, or 50 kilograms, as they walked and ran on treadmills. The research published in the Proceedings of the Royal Society B proved that wearing a full suit of armor takes more than twice the energy of walking around unencumbered.
The armor weight could have influenced the outcome of medieval battles. For instance, heavily-armored French knights were defeated by lightly-armored English troops in the Battle of Agincourt in 1415, although the French outnumbered the English by up to six to one with a massive army of 36,000 soldiers.