Although Krogh received the Nobel Prize for his research on the function of capillary circulation, he had a major impact on numerous areas of investigation. Furthermore, like many productive investigator, his influence was due not only to his own work, but to that of his students and colleagues as well. Krogh’s collaboration with Johannes Lind hard resulted in classic studies dealing with carbohydrate and fat metabolism during exercise, and how the cardiovascular and respiratory system’ responses are controlled during exercise. Here of Krogh’s students, Erling Asmussen, Erik Hohwu-Christensen, and Marius Nielsen (called the three musketeers by Krogh), had a major impact on exercise physiology research throughout the middle of the twentieth century. These investigators, in turn, trained a number of outstanding physiologists, several of whom you will meet throughout this text. The August Krogh institute in Denmark contains some of the most prominent exercise physiology laboratories in the world Marie Krogh, his wife, was a noted scientist in her own right and was recognized for her innovative work on measuring the diffusing capacity of the lung. We recommend the biography of the Krogh’s written by their daughter, Bodily Schmidt- Nielsen (see Suggested Readings), for those interested I he history of exercise physiology.