An interesting study found words that specifically describe pain such as excruciating and gruelling made the part of the brain that processes these sensations become activated.
Read the article here (WebMD)
So if you're competing against someone in a race, would it be unfair to say over and over again, "I'm going to make you hurt"? Hmm, that does't really follow the research. Might be better off saying, "this is going to be gruelling, and I'm going to cause you excruciating pain".