The fundamentals of exercise physiology (the study of the physiological effects of bodily exertion) form the basis for this booklet designed for teachers of physical education. The scientific principles underlying the building of muscular strength and flexibility are described and illustrated. Topics covered include: (1) muscular strength, measurement, and improvement; (2) anaerobic performance; (3) aerobic performance; (4) flexibility; (5) diet and performance; (6) temperature and performance; (7) aids to performance; (8) physical appearance; (9) exercise and disease prevention; and (10) the aesthetic, social, and psychological benefits of exercise. (JD)