Although exercise results in a number of well documented physical fitness and health benefits, accruing such benefits entails a risk of exercise-related injuries. Musculoskeletal injuries occur frequently among fitness programme participants, runners, athletes, military recruits and others who engage in routine vigorous exercise. The same parameters of exercise (intensity, duration and frequency) that determine the positive fitness and health effects of physical training also appear to influence the risk of injuries. Studies of runners and other physically active groups have consistently demonstrated that greater duration and frequency of exercise are associated with higher risks of injury. However, the sports medicine literature shows little association between exercise intensity and injuries, a finding which may be misleading. The strongest and most consistent association reported exists between greater total amounts of exercise and higher risks of injury. This is not surprising, since the total amount of exercise is the product of the intensity, duration and frequency of exercise. Recent military research confirms the finding that higher volumes of running are associated with higher rates of injury. Furthermore, the study of army recruits suggests that greater amounts of exercise not only result in greater risks of injury, but in some instances may also impart no additional increase in fitness, a finding consistent with an earlier study of civilian runners. Several military studies also demonstrate that those recruits who have been more physically active in the past are less likely to be injured during basic training. These military studies also document a number of other factors, such as older age, smoking, sedentary jobs and lifestyle, high or low flexibility and high arches of the feet, which may contribute to or modify the risks for exercise-related injuries. In conclusion, the present review suggest that, for activities such as running, specific parameters of exercise may contribute to the overall risk of injuries in rough proportion to their contribution to the total amount of activity performed. Also, better knowledge of the effects of the parameters of training and other factors on the risks of exercise-related injuries is necessary to make more judicious choices about how to best achieve the benefits of exercise and to prevent injuries.