Dr. Richard Stephens has spent a lot of time researching profanity. In past research he has found that swearing increases pain tolerance since it apparently triggers the body's "fight or flight" response which can then lead to a type of "stress-induced analgesia."
"Fight or flight" response also releases adrenaline which got Dr. Stephens thinking about the connection between swearing and athletic performance. Along with a colleage, Dr. Stephens had volunteers participate in a study in which they performed the Wingate endurance test twice.