why does he always look like he is in pain during races?

I have a teammate on my cross country team and when he runs he always looks like hes in pain... not during practices but only in races. He has never missed a cross country race in all 4 years, but our coach even thought of pulling him out once because he thought he may be hurt. (he is our 3rd varsity guy runner) Today he ran while he was sick and got a PR. (he had a cough, runny nose, and all), but it was the biggest race of the year. (largest meet in the state, almost more important than state.)