>>6271705a renaissance soldier in full plate armor would be carrying less weight than a modern day US soldier with their kit would you know. in the plate armors case the weight would be spread across your body instead aswell.
the lung expansion limits are minimal since you should be wearing a gambeson in addition to padding sewn onto the armor which would allow comfortable movement.
in reality history has shown that in duels the armored opponent will win over the unarmored.
