Heavy armour was more of a handicap to mediaeval knights than even the bloody outcome of the Battle of Agincourt has led historians to believe.
Wearing armour doubles the amount of energy needed to walk and move around, research has shown.
Body armour was a much greater burden than the equivalent weight in a modern soldier’s backpack and restricted breathing, according to a new study.
The findings reinforce the view of many experts that armour played a decisive role at Agincourt in 1415.
During the famous battle, heavily armoured French knights were forced to advance across a field of sticky, clinging mud.
They would have been far less mobile than the lightly armoured English archers and quickly exhausted.
British and Italian scientists carried out the study on skilled fight interpreters from the Royal Armouries, Leeds, who regularly wear replica armour in public performances.
The four men, aged around 36, wore suits of custom-made English, Italian and German 15th century armour as they undertook a range of walking and running exercises.
Face masks were used to measure the men’s oxygen consumption and energy expenditure.
Typically, mediaeval armour weighed between 30 and 50 kilograms, similar to the marching loads carried on the backs of post-World War II soldiers.
But unlike a backpack, armour consisting of interlocking steel plates distributed weight over the entire body, loading the limbs as well as the head, neck and trunk.
Lead researcher Graham Askew, from the University of Leeds, said: “We found that carrying this kind of load spread across the body requires a lot more energy than carrying the same weight in a backpack.
“This is because, in a suit of armour, the limbs are loaded with weight, which means it takes more effort to swing them with each stride. If you’re wearing a backpack, the weight is all in one place and swinging the limbs is easier.”
The findings, published in the journal Proceedings of the Royal Society B, showed that the net energy cost of walking was 2.1 to 2.3 times higher when wearing armour than when not wearing armour.
Running in armour incurred a 1.9 times higher energy cost.
The energy costs associated with wearing armour were higher than those predicted by experiments in which loads are added to different parts of the body.
The reason may be due to the impact of armour on breathing, the study suggests.
Rather than taking deeper breaths when they exerted themselves, the four volunteers took larger numbers of shallower breaths.
“Being wrapped in a tight shell of armour may have made soldiers feel safe, but you feel breathless as soon as you begin to move around in mediaeval armour and this would likely limit a soldier’s resistance to fight,” said co-author Federico Formenti, from Oxford University.
Heavy armour may not only have contributed to the French defeat at Agincourt, but also at the Battle of Crecy in 1346, experts believe. On this occasion the French knights fought the English and lost after an exhausting march lasting several days.