A bit of theatrical license in the movie.

A couple of years ago, I saw a television program on several centuries of arms and armor, and it covered various kinds of battle armor, from chain mail (circa Crusades) through armor a few centuries later.One fellow on the show, kitted out in a full suit of plate armor, said that the weight seemed well-distributed and although it was considerably more cumbersome that a sweat-suit, it didn't really feel all that heavy to wear. In fact, he demonstrated by running, doing a couple of somersaults and other acrobatics, and vaulting a waist-high fence.

Excerpt from an article on historical armor:

While it looks heavy, a full plate armor set could be as light as only 20 kg (45 pounds) if well made of tempered steel. This is less than the weight of modern combat gear of an infantry soldier (usually 25 to 35 kg), and the weight is more evenly distributed. The weight was so well spread over the body that a fit man could run, or jump into his saddle. Modern re-enactment activity has proven it is even possible to swim in armor, though it is difficult. It is possible for a fit and trained man in armor to run after and catch an unarmored archer, as witnessed in re-enactment combat.

The notion that it was necessary to lift a fully armed knight onto his horse with the help of pulleys is a myth originating in Mark Twain's A Connecticut Yankee in King Arthur's Court. (And, in fact, the mere existence of plate armor during King Arthur's era is a myth as well: 6th century knights would have worn mail instead. [So the armor worn in the movie Excalber was bogus.—DF)   Even knights in enormously heavy jousting armor were not winched onto their horses. This type of "sporting" armor was meant only for ceremonial jousting matches and its design was deliberately made extremely thick to protect the wearer from severe accidents, such as the one which caused the death of King Henry II of France/

Tournament armor is always heavier, clumsier and more protective than combat armor. The rationale is that nobody wants to get killed in a game, but on battlefield the question is about life and death, and mobility and endurance is a more important aspect of combat survival than direct protection. Therefore combat armor is a compromise between protection and mobility, while tournament armor merely stresses protection on cost of mobility.

And as far as arrows were concerned, armor protected from glancing arrows, a fairly direct hit would penetrate the armor. A bolt from a crossbow definitely would.

Pierre Terrail LeVieux, seigneur de Bayard (1473 – 1524)—The Chevalier Bayard—("Without fear and without reproach"), considered to be the perfect embodiment of chivalry and the last of the "Knights in Shining Armor," was was wearing full battle armor when he was killed on April 30th, 1524 by a ball from an arquebus (the immediate predecessor of the musket) fired by a foot soldier.

That pretty well ended the wearing of full suits of battle armor.

Don Firth