What does endurance improved means?Edit
Sometimes you see the following message when you level up:
In fact it's a message which tells you that you got a health bonus and your health point of your brute has been boosted up. In other word, Endurance improved is a health bonus.
Why is it called endurance? It's probably because more health points help you to stand and survive longer in arena fights and tournaments. You can endure more hits before falling down. That's why it's called endurance.