No, it has nothing to do with cardio fitness; it is a repetitive motion injury. The 'compartment' through which the tendons and and nerves pass from the forearm to the wrist/hand becomes irritated and swells, the swelling leads to more irritation, around and around in a downward spiral until you just can't stand the pain or use your grip properly. The surgery opens up the compartment size a touch to relieve the pressure. Of course, you have to lay off after surgery to recover for a while to insure that the inflammation completely subsides, etc. or you run the risk of recurrence.