The middle aged triathlete who just happens to be bald

Why are there a lot of 35 year-old triathletes who are bald?  


What is the mechanism at play here... is it the triathlete or the bald person? Here are two arguments...

Cause Bald Person: Their genes adapt their bodies to try to make them faster by making them bald.

Cause Triathlete: The repetitive chronic stress causing premature baldness.

Or is it simply the premature hair lost is creating an early mid life crisis and pursuit of iron-man status.