At least the injury probabilities appear to be proportional to the stamina loss involved (if you assume my lack of Cup injuries is a blip). Over 3.5 seasons I've had a 3% chance of an injury stretching, 6% cardio & 9% practice match, and 18-19% in an actual game.

Knee Cartilage Tear from low intensity stretching.-injury-cause-s8_2.png