A character is trained to endure pain and injuries, how does that training look like?

Honestly, there’s no real way to tell. They look like people and the training affects each individual in unique ways. It will change their personality, but what that change is? That depends on the individual in question. You may know, but most of the other characters probably won’t unless the character in question has told them or they’ve seen him or her in action.

It’s a little cheesy but I’ll throw out an example from Stargate SG-1.

We have Jack, we have Sam, and we have Teal’c. They have all been trained to endure pain and work while injured. Eventually, Daniel gains this ability through his own experiences in the Stargate program. What do they have in common in their personalities? What specific tells do they share? They’ve all been through it, but if you knew nothing about them when you met would you know?

It gets more confusing if we throw Teyla, Ronon, and Sheppard on the pile from Stargate Atlantis. Ronon and Teal’c fulfill the same role in the narrative and have a baseline of similar experiences, however they are very different as individuals.

People are not simple and how they respond to adversity isn’t something that can be broken down to a simple statistic. It’s made worse by the fact that all training is not the same, not all experiences are the same, and people change based on what they’ve gone through. You can put two different people of similar personalities through the same meat grinder and end up with wildly different results in how they’ve changed and who they’ve become.