Library books are arranged by the Dewey Decimal classification scheme whereby each subject is represented by a number. You will find books on the same subject will have the same number. The shelfmark is preceded by the letter D and will be followed by 3 letters, which are usually the first 3 letters of the author's name.
Useful Sport and Physical Activity and related subjects shelfmarks:
D 611 Anatomy
D 612.044 Physiology of sport and exercise
D 613.07 Health education and health promotion
D 613.71 Exercise psychology
D 796 Athletics and outdoor sports and games
D 797 Aquatic and air sports