A British study that measured the effort it took to wear a suit of armor on a treadmill has determined that the suits were so exhausting to wear that it may have affected battle outcomes during the 15th century.
The study used plate armor weighing 30~50 kg per suit. Among other battles studied, the famous Battle of Agincourt in 1415 CE may have been influenced by the fatigue factor. French knights outnumbered their English foes but were defeated after an extended charge across a muddy field while heavily armored.
The BBC story includes a video of one of the treadmill tests.