Exercise testing in athletes and patients is an important and valuable diagnostic tool in the hand of the physician and sport scientist. A close collaboration between sport scientist and sport physician creates a win-win-win-situation for athletes and patients and professionals equally. According to the demands of the sport an incremental lactate threshold test (determination of the anaerobic threshold), testing of ­VO2max and performance at VO2max, and a testing of aerobic capacity (performance at competitional level) are the tests of choice. All tests need to be valid, reliable and sport specific. Sport specificity in testing is for practical purposes the most important.