Commonly gets the most pleasure from doing slightly more, like an extra mile on a run, and claiming to "win".
Workout stalkers often friend you in online fitness social apps like Nike+, FitBit, or Strava so that they can easily observe their victims.
Closely related to the one upper.
James: "I'm not competing."
Kris: "You are. You're doing real good with the running and the biking lately. Your Nike Fuel is being earned really good."
James: "Dont be such a workout stalker."