CLINICS 2011;66(10):1707-1712 the importance of athletes who do not pursue activities resulting from their injuries. Other definitions of injury have been used, such as the need for medical treatment due to injury (‘‘medical assistance’’) or the registration of all injuries regardless of whether or not the injury prevented the player from continuing to training or playing in the game (‘‘tissue injury’’). The definition of injury varies widely in the literature. However, we will use the classical definition presented by J. Dvorak and A. Junge: injuries are defined as events that occur during training or a game that cause an athlete’s absence from the next training session or game and are followed by the necessity for an anatomic diagnosis and treatment of the injured tissue.23 It is appropriate to include injuries that cause the interruption of training or playing in a game, regardless of whether the player is absent from the next game or training session. This is especially important for less competitive teams where games and training sessions occur less frequently. These injuries can be separately recorded as zero day injuries. In the time loss system, injury severity is classified according to the number of days that the player is absent. This number varies widely in the literature. Our model uses the following classification for injuries: mild (1-3 days), minor (4-7 days), moderate (8-28 days), major (.28 days and ,8 weeks absence), and severe ($8 weeks off). This classification system was divided into five types so that we can group together the various soccer injuries into more homogeneous groups that exhibit similarities in severity and prognosis. We disagree with the classification that divides the severity of injury into three types,3 because grade III (.28 days absence) covers a wide range of injuries that greatly differ in terms of their severity and recovery time. This three-step classification system groups together relatively benign cases such as muscle injury, where the recovery time varies from 4-6 weeks, and other more serious injuries, where the recovery time can average 6-8 months for an anterior cruciate ligament injury.8 The precise definition of various injury types is required to compare between studies conducted worldwide. Usually the injuries are divided into two major groups: trauma and overuse. Van Mechelen24 suggested that an injury be defined as acute if it is caused by a single traumatic incident and as overuse if it is the consequence of repetitive microtraumas. The national model divides injuries into eight categories, which are provided in Table 5. We defined injury recurrence as instances in which an injury of the same type and in the same location as the initial injury occurs within two months of the final day of the initial injury. This relates to rehabilitation for injuries prior Table 5 - Classification of injury types. Traumatic Model for epidemiological studies on professional soccer player Arliani GG et al. to the start of the study and within 12 months for injuries occurring during the study period. The choice of the two- month period for injuries prior to the start of the study was an attempt to reduce the bias of injuries that have occurred well before the current athlete monitoring. We believe that defining recurrent injuries as any injury sustained pre- viously would contribute bias to the study. Nevertheless, for injuries occurring during the study period during which we have detailed information, we stipulate the maximum time period to be 12 months for recurrence. We divide the recurrence of injuries into two groups: early recurrence (,2 months) and late recurrence (between 2 and 12 months).25 Another parameter to consider in the classification of re- injury is the number of games and/or training sessions performed between the initial injury and the re-injury. This is important because the frequency of training sessions and games are different among soccer clubs. Therefore, we classify early re-injuries as those occurring within 15 games and/or 60 training sessions and late re-injury as those that occur after$15 games and/or 60 training sessions. We performed this classification using the average frequency of games and training of Brazilian clubs (two games and eight training sessions per week). Therefore, 15 games or 60 training sessions are conducted over a period of approximately two months.4 A training session is considered to be any physical activity performed by the team that is directed by the coach. Therefore, a pool recovery session or a gymnastics session held after a game should be considered training. A video review or a lecture with the team should not be considered training. Individual training sessions should not be registered.26 An athlete presenting with an injury in the final game of the season who is still injured at the end of the study should, if possible, be accompanied by the researcher on the final day of their rehabilitation. If this is not possible, the researcher should estimate and record the probable time required for a complete recovery. If a player transfers or retires, the researchers must include the exposure time and injury until the date of transfer or retirement. If the athlete is injured at the time of transfer, the recovery of that athlete should be monitored, if possible, until a full recovery has occurred. Athletes who join a club during the season should not be included in this study. However, new players that are added to the roster during the pre-season should be included. CONCLUSION This study establishes a methodological model that can be applied to epidemiological studies of injuries to professional Sprain Acute wrenching or laceration of the ligaments or capsule of a joint Strain Acute distraction injury of muscles and tendons Contusion Injury that does not disrupt the integrity of the skin caused by a blow to the body Fracture Traumatic break or rupture of bone Wound Injury that breaks the skin, including cuts, scratches and puncture wounds Dislocation Forced separation and misalignment of bones in a joint cavity Other Injuries not classified elsewhere Overuse A pain syndrome of the musculoskeletal system with insidious onset and without any known trauma or disease which may have yielded previous symptoms 1711