Can You Move in Medieval Armour? An Experiment in Mythbusting - Medievalists.net
Many believe the myth that medieval armour was hard to move in. However, with Boucicaut as an example, our video proves that late medieval armour allowed for surprising mobility.
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Not like that really. Problems will began around 10 minutes of wearing chainmail. At the beginning it is just heavy, but more than acceptable. Humans have relatively high limit of load. Problem is that this can't last long. Most people will have no problems lifting 50kg weight, but carrying that load for some time is completely another thing. I estimate average person will be unable to scratch a nose after an hour or two in chainmail.
You need months of training to adapt and be able to wear armor without exhausting. And still it will noticeably make you slower.
It is not surprising that you could shoot a video of how you can move in heavy armour for few minutes, but imagine you have to wear it all day long. :)