Dr Zemper was director of research at the International Institute for Sport and Human Performance, University of Oregon, Eugene, when this paper was written; he is now president and director of research for Exercise Research Associates of Oregon, Eugene. He is a member of the American College of Sports Medicine.

*NOTE: The National Sports Injury Surveillance System was the forerunner of the Athletic Injury System currently being operated by Exercise Research Associates of Oregon.

The total number of football injuries incurred by high school and college athletes each year is high because there are many large teams across the country (an average of approximately 100 players per team at the college level). However, the number of injuries per 1,000 athlete-exposures (AEs) for football is actually lower than that of some other sports such as wrestling, men's and women's soccer, and women's gymnastics (1-4).

There have been short-term studies of football injuries (5,·6) and long-term studies of football fatalities and catastrophic injuries (7). But the only attempts at long-term, national studies of football injuries have been made by the National Athletic Injury/Illness Reporting System (NAIRS), which operated from 1975 to 1982 (8, 9), and the National Collegiate Athletic Association Injury Surveillance System (NCAA/ISS), which began collecting data in 1982(1). More recently the National High School Injury Registry began collecting football injury data during the 1986 season, under the sponsorship of the National Athletic Trainers Association (10), and the National Sports Injury Surveillance System (NSISS) began collecting data on college football injuries, also during the 1986 season.

The NSISS, housed at the International Institute for Sport and Human Performance at the University of Oregon, is a longitudinal data collection system for sports injuries that provides analyses of national injury rates and patterns. Its purpose is to provide data that will assist in developing ways to prevent or to reduce the severity of sports injuries through rule changes, equipment modifications, or changes in coaching techniques. It also provides a vehicle for investigating special issues. For example, ongoing studies are being conducted of injury rates on artificial vs natural surfaces, brands of helmets worn by players who incur a cerebral concussion (11) and the efficacy of prophylactic knee braces (12).

Initial reports on two special NSISS studies have been published (11, 12). One concerns the relationship between various brands of football helmets and the rate of cerebral concussions (11). Results from the first 2 years of operation of NCAA/ISS showed no difference in concussion rates (1). This pattern continued with the NSISS data during the 1986 season. However, during the 1987 season there was a significant difference between two brands. Further data are needed to determine whether this difference is real and a result of changes in helmets, or if it is a statistical anomaly in 1 year's data. Because of frequent changes in helmet design and material, these data need continual monitoring. The other special NSISS study (12) concerns the efficacy of prophylactic knee braces. Analysis of the first 2 years' data indicates that the incidence of knee injuries is slightly higher among players wearing braces. In addition, braces do not reduce the number of injuries to the medial collateral ligament (MCL), and there is no apparent difference in injury incidence among the various brands of braces. Nor was any difference found in the severity of knee injuries or MCL injuries in braced vs unbraced players when measured in days lost from play or degree of MCL injury. When injuries in games were isolated to control the "intensity" of exposure to the risk of injury, the results were the same as those for games and practices combined.

Until now the NSISS has been operating on a pilot basis, collecting data from a national sample of college football teams, but there are plans to expand its operation to include larger samples and a variety of sports at different levels (eg, collegiate, high school, and youth sports). The basic operational format for the NSISS was first developed and implemented by the author in 1982, while at the NCAA, as the NCAA Injury Surveillance System. The NSISS has since been used to collect injury rate data for a number of sports (1, 4, 13).

This article summarizes two years of football injury rate data collected by the NSISS from a national sample of college football teams.

Data were collected during the 1986 and 1987 college football seasons. The NSISS meets the major criteria for reliable studies of sports injury rates outlined by the American Orthopaedic Society for Sports Medicine (14). We used a stratified sample of NCAA and National Association of Intercollegiate Athletics (NAIA) members sponsoring intercollegiate football. Stratification was based on four geographic regions and three NCAA/NAIA divisions. The sample was designed to represent approximately 5% of all NCAA and NAIA intercollegiate football teams, including both varsity and subvarsity. Therefore the results can be generalized to the total population of intercollegiate football players. The sample included all football players at the participating institutions. During the 1986 season, data were collected for 32 teams (3,431 players); during the 1987 season, data were gathered for 27 teams (2,798 players). The average team size over the two seasons was 105.6 players.

Only time-loss injuries were recorded--ie, those that kept a player from full participation for one day or more beyond the day of the injury. The injury rate is the number of injuries per 1,000 AEs (an AE occurs each time a player takes part in a practice or a game, thus being exposed to the risk of injury). Therefore, if a football team had 100 players who took part in five practices during a given week, that team had 500 AEs in practices for the week. If 40 players played in the game on Saturday, there were 40 game exposures, for a total of 540 AEs for the week for that team.

Injuries per 1,000 AEs is considerably different from injuries per 100 players per season, which is most commonly used in research. However, the former is a much more precise measure of injury rates. The use of injuries per 100 players per season assumes that all players participate in every practice and game and that all teams have the same number of practices and games. Since this is obviously not the case, injuries per 100 players per season can be quite misleading, especially when trying to compare data from different teams or studies, or trying to compare injury rates across different sports. Use of injuries per 1,000 AEs compensates for the fluctuating number of players who attend practices each week and who play in games. In most cases the number of those who play in the game is much lower than the total number of team members. This method also takes into account the varying number of practices for each team.

Prior to the start of each season the head athletic trainer of each participating team was sent copies of brief, easy-to-use forms for reporting AE and injury data on a weekly basis, along with detailed instructions. From the first preseason practice until the final regular season or post-season game, the trainers returned forms that listed the number of practices and games played during the week and the number of players participating in each. They also returned separate forms that described each football injury.

Hard-shell helmets and shoulder pads are designed to protect the wearer from injury. However, because there is some concern about the role of hard-shell helmets and shoulder pads in causing injuries to other players, the trainers were asked to indicate whether each reported injury was directly caused by impact from another player's helmet or shoulder pad. If a medical staff person directly observed that this happened, or if an injured player recalled it, a positive response was recorded. Otherwise the response was recorded as negative or unknown.

In reporting the number of days lost because of an injury, the trainers were instructed to disregard the end of the season and indicate the number of days before an injured athlete returned to unrestricted activity, as if the season were continuing indefinitely. This provided a consistent and accurate record of time lost for injuries that occurred at the end of the season. An injury that kept a player out for more than 90 days was considered season-ending.

Each returned form was screened for completeness and consistency before the data were entered into a computer for later analysis. Trainers were contacted for clarification of any incomplete or inconsistent information on a form. During the two seasons, 98.8% of the forms were returned.

For the 1986 and 1987 football seasons there was a combined total of 6,229 players in the study, with 445,856 AEs. Of the AEs, 410,165 (92.0%) occurred in practices and 35,691 in games (8.0%). A total of 2,820 injuries were reported, for an overall injury rate of 6.32/1,000 AEs, or 45.27/100 players. The rate in practices was 3.93/1,000 AEs; in games, 33.68/1,000 AEs. Thus the injury rate was 8.6 times higher in games than in practices (in which 57.1% of total injuries occurred). This major difference in injury rate between competition and practice is consistent with most other sports that have been studied (1-3).

Taking into account recurring injuries from the same season and athletes who were injured more than once, 32.1% of the players were injured at least once. The median number of days lost per injury was 4 (1986) and 5 (1987). Over the 2 years, 8.3% of the injuries were season-ending. Surgery was required for 8.5% of the injuries. Approximately half of these were treated arthroscopically, which allowed many players to return to football before the end of the season.

Based on positive responses, the impact from another player's helmet was the direct cause of injury in at least 14.4% of injuries; from a shoulder pad, 7.0%. During the 1986 season, injuries caused by impact from another player's knee brace were also noted and were reported as the cause of only 0.3% of injuries. Thus wearing a knee brace appears to play a negligible role in causing injuries to other players.

The knee and the ankle were injured most frequently (table 1), followed by the shoulder, quadriceps, head, neck, and hamstrings. Sprains were by far the most common type of injury (table 2), followed by muscle strains, contusions, fractures, and cerebral concussions. Being tackled, blocking, tackling and being blocked were the most common mechanisms of injury (table 3), followed by noncontact categories ("sprinting/running" "no evidence of contact").

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Offensive players incurred 50.9% of the reported injuries, defensive players 45.2%, and special team players and kickers/punters 3.9% (table 4). Injury rates were adjusted for the number of players in each position on the field at any one time (eg, one quarterback, two offensive tackles). These adjusted rates indicate that the flankers/wide receivers and running backs apparently had the highest rates, followed by offensive ends. Defensive linebackers and halfbacks/cornerbacks had the highest rates among defensive players, which were similar to the injury rate of offensive ends. Defensive safeties and offensive slotbacks/wingbacks had the lowest rates. All other positions were roughly equal.

Injuries occurred most often during the third quarter and least often during the first quarter (table 5).

The overall injury rate was 60% higher on artificial turf than on natural grass (table 6). Of the 445,856 AEs over the two seasons, 386,957 (86.8%) were on grass and 58,899 (13.2%) on artificial turf. In games, 27,978 AEs (6.2%) were on grass and 7,713 (1.7%) on artificial turf; in practices, 358,979 AEs (80.5%) were on grass and 51,186 (11.5%) on artificial turf.

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