New Hampshire high school track and field coach refuses to make athletes wear masks outdoors, gets the sack. For reference, here's what the World Health Organization says:
Q: Can people wear masks while exercising?
A: People should NOT wear masks when exercising as masks may reduce the ability to breathe comfortably.
I don't know what the competition rules are, usually you want to train the way you'll compete, even if it kills you. New Hampshire does have a mask mandate for "public spaces, indoor and outdoor", although it has an exemption for "strenuous physical activity".