I'm not sure if having a strong core directly makes your endurance better. If you have a strong core, it is easier to exercise with better posture. In general, if you have good posture, you are able to take in more air with each breath because your ribcage can expand more, therefore allowing more oxygen into the bloodstream and into working muscle tissue. Maybe this was the connection being made? Not sure, but that would be my guess. Any other thoughts from anyone else out there?