The only problem with this study is knights were professional soldiers and generally in extremely good physical shape. They were not what we would consider of civilian physique. In all likelihood the knights would be in similar shape as marines, as their constant martial training would have kept them in prime form what with war being a constant in those days.
Additionally, knights were primarily cavaliers, and rarely engaged in foot combat, a popular misconception made more common by Hollywood films like Excalibur.
The Battle of Agincourt was a tactical blunder on the part of the French. The Henry V forced the engagement on terrain he chose, established firing positions for his archers who were better armed than the French counterparts on better terrain for them to fire from (dense woods and hills), not to mention positioning his infantry in a location that would force the French to bottleneck. So after the French cavalry charge failed to flank the archers, as well as being poorly organized and not at full force, the French cavalry ended up being dismounted from their horses by the English longbows (dead horses). After the failed cavalry charge the French then advanced with about 8000 arms-men on foot. Forcing 8000 arms-men to walk through 300 yards of mud would naturally tire them out, especially when they were under a constant barrage from the English archers. Of course the knights and arms-men were not the total of the French forces, who had closer to forty thousand total, with 10k armored soldiers, and the other 30k made up of light infantry and archers vs the English's total of about 9k including all arms-men, infantry, and archers.
So Agincourt was not simply won because of the rain and the weight of plate armor, but of a more traditional sequence of circumstances and tactics which resulted in favorable conditions for the English.