What happens to a character whose load exceeds maximum?

Rules give us 3 value ranges for load: Light, Medium and Heavy.

There are respective bonuses/penalties to those loads. I couldn’t find any mention of what happens after exceeding heavy load range (endpoint is named maximum load).

Can such character even move? Does such character get damaged by being smashed to the ground by his/her own equipment?

Also – what happens to creatures that are extremely heavy on their own (let’s say dragons) when their strength drops to very low levels? I can’t believe that such dragon would be able to move if it had strength of a regular human.