These misconceptions are hard to battle sometimes, as they keep being reinforced through many channels - TV and cinema being just two of them. However, media can also be a powerful tool to show research results and helü deconstruct the misconceptions. This is just what the film here is trying to do:
A medieval knight's gear is, weight-wise, about the same as a modern soldier's full kit, or the gear of a modern fire-fighter. So in the film, you can see three men run an obstacle course in their respective kit. It's an impressive display of the agility still possible in a 15th century armour - and also really interesting to see how close the three people are in their results.
This is a really nifty thing!