A complete suit of 15th-century plate armor weighed less than the gear worn by modern firefighters.

During the 15th century—the "Golden Age" of plate armor—a complete harness represented a masterpiece of engineering. Research by Dr. Tobias Capwell at the Wallace Collection in London confirms that a typical field suit weighed approximately 20 to 25 kilograms (44 to 55 pounds). This is significantly lighter than the 35 to 50 kilograms (77 to 110 pounds) of equipment often carried by modern U.S. infantry or structural firefighters in full turnout gear.The mobility of medieval armor came from its sophisticated weight distribution system. Unlike a heavy backpack that concentrates force on the shoulders, plate armor was custom-fitted to the wearer's body using leather straps and internal attachment points. This design spread the weight across the entire skeletal structure. Historical manuals and modern recreations demonstrate that trained knights could perform rolls, cartwheels, and even climb ladders with relative ease.A 2011 study published in the journal Proceedings of the Royal Society B by researchers from the University of Leeds used gas analysis to measure the energy cost of wearing armor. While the weight did increase the metabolic cost of movement by roughly 1.9 to 2.3 times, it did not render the wearer immobile. The widespread myth of "clumsy" knights largely stems from heavy 19th-century tournament armor, which was specifically designed for safety in jousting rather than the mobility required for actual battlefield combat.