Notwithstanding the healthy influence of sporting activities on risk factors, in particular those of cardiovascular disease, it is becoming increasingly apparent that sports can present a danger to health in the form of sports injuries. The extent of the sports injury problem calls for preventative action based on the results of epidemiological research. For the interpretation of these facts uniform definitions are needed and limitations of research designs should be known. Measures to prevent sports injuries form part of what is called the 'sequence of prevention'. Firstly the extent of the sports injury problem must be identified and described. Secondly the factors and mechanisms which play a part in the occurrence of sports injuries have to be identified. The third step is to introduce measures that are likely to reduce the future fisk and/or severity of sports injuries. This measure should be based on the aetiological factors and the mechanism as identified in the second step. Finally the effect of the measures must be evaluated by repeating the first step. In this review some aspects of the first and second step of the sequence of prevention are discussed. The extent of the sports injury problem is often described by injury incidence and by indicators of the severity of sports injuries. Sports injury incidence should preferably be expressed as the number of sports injuries per exposure time (e.g. per 1000 hours of sports participation) in order to facilitate the comparability of research results. However, one should realise that the outcome of research applying this definition of sports injury incidence is highly dependent on the definitions of 'sports injury' and 'sports participation'. The outcome of such research also depends on the applied research design and research methodology. The incidence of sports injuries depends on: the method used to count injuries (e.g. prospective vs retrospective); the method used to establish the population at risk: and on the representativeness of the sample. Severity of sports injuries can be described on the basis of 6 criteria: the nature of the sports injury; the duration and nature of treatment; sporting time lost; working time lost; permanent damage; and cost. Here also uniform definitions are important and necessary in order to enhance the comparability of research data. In the second step of the 'sequence of prevention' the aetiological factors that play a role in the occurrence of a sports injury have to be identified by epidemiological studies. Epidemiological research on the aetiology of sports injuries requires a conceptual model. The most commonly applied model is a stress/capacity model in which internal (personal) and external (environmental) aetiological factors are identified. In this model stress and capacity must be in balance and preventative measures must be designed to achieve or maintain this balance. However, merely to establish the aetiological factors is not enough; the mechanism by which sports injuries occur must also be identified. Athletes are in constant interaction with their environment and aetiological factors must be approached from this point of view. In a second, more dynamic. conceptual model on the aetiology of sports injuries, the importance of the determinants of sports behaviour, as well as the interaction between the various aetiological factors. is discussed. Whether or not a sports injury results from sports behaviour largely depends on the extent to which 'prevention' is incorporated in the determinants of sports behaviour. The drawback of both conceptual models is the fact that neither of them incorporate a time perspective. They can therefore not be applied to research on the aetiology of overuse injuries. In this perspective the application of a stress/strain/capacity model can be useful. This is a more dynamic and time-based 3-phase sequential model in which behaviour, amongst other aetiological factors, plays an important role. In this model an athlete is seen as an active manipulator of stress by whom the amount of strain evoked by sports participation can be altered. thereby influencing the capacity to perform in a certain sports situation. but also influencing the risk to sustain a sports injury, either acute or long term. Finally, despite the importance of the model of choice in studying the aetiology of sports injuries one should realise that again the choice of research design influences the outcome of such research. Case series usually give no information on the underlying population at risk, so they are of no value in drawing valid conclusions on the risk factors of injuries. Only by relating the injuries to corresponding population denominators can one estimate injury rates and identify important risk factors and high risk sportspeople. As in research on sports injury incidence; research on risk factors should be undertaken on groups that are homogeneous with regard to age, sex, level of competition and type of sport.
