Materials and Methods
Selection of Participants
In May 1981, all high school athletic trainers who were active members of the Pennsylvania Athletic Trainers’ Association were mailed a brief description of the proposed project. Trainers used the enclosed response card to indicate whether their school agreed to participate in the study and whether they were willing to provide the required reports of injury throughout the 1981 football season.
While most trainers expressed interest in the study, only 12 schools were willing to participate. This sample came from various locations across the state and provided 24 fields (12 game fields and 12 practice fields) for evaluation. Two of the schools did not provide a complete record of injuries, so injury results and correlations involving injuries are based on data from 10 schools. Field-condition and maintenance comparisons reflect evaluations at all 12 schools, however.
All injuries to football players in the sample schools were reported through the National Athletic Injury/Illness Reporting System (NAIRS), established by The Pennsylvania State University in 1974. NAIRS receives weekly reports, submitted by team trainers or physicians, of injuries and illnesses sustained by members of an athletic team during practice and during competition². In this study injuries and illnesses were classified by NAIRS into four categories, as follows
- Minor — any reportable injury/illness (other than dental or head injuries) that did not prevent an athlete from returning to practice or competition for longer than seven days following the injury or illness.
- Significant — all head and dental injuries (regardless of time lost from play or practice), and any injury/illness that kept an athlete from returning to play or practice for longer than seven days.
- Major — any significant injury/illness that prevented a player’s return to practice or competition for 21 days or longer.
- Severe — any permanently disabling injury, such as paraplegia.
Injuries/illnesses were reported on standard forms to NAIRS and coded into the system’ data bank. Trainers of the cooperating schools included in their reports the location of the activity at the time of injury (playing field, practice field, or elsewhere) and their opinions about the likelyhood of a casual relationship of playing surface to the injury (definitely related, perhaps/possibly related, or definitely not related).
At the end of the season, data collected during the football season of the 12 schools — nature and category of injuries, condition of the field (wet, frozen, etc.) when the injury occurred, and opinion of the trainer as to the relationship of playing-surface condition to occurrence or severity of the injury — were compiled for study and analysis by the authors of this study.
Injury reports from two of the schools were not complete, and these schools were not included in the comparisons of injuries to conditions of playing surfaces.
School representatives provided information about maintenance practices and uses over the previous year. Maintenance practices inlcuded fertilization, liming, aeration (core cultivation), mowing, irrigation, overseeding, and control of weeds, insects, and diseases. Uses included football games and practices, other varsity and intramural sports, physical education classes, band practices, community activities, and other activities. Estimated numbers of occurences for each use wer obtained.
Game and practice fields were evaluated twice — first in August, prior to or during preseason football practice, and again in November as the season was ending. Inspections and evaluations were made by two turfgrass specialists from the College of Agriculture. Data were collected on kinds and amounts of turfgrasses, kinds and amounts of weeds, total vegetative cover, turfgrass density, total weed coverage, smoothness of surface, vegetative clumps, and stones on the surface. the recorded ratings represented a concensus. Data for subjective evaluations were assigned code numbers for use in statistical analysis. Evaluators inspected game fields at nine areas (between inbound hashmarks and near each sideline at midfield and near each goal line). Areas inspected on the practice fields were selected to represent obvious differences in the playing surface.
As part of the initial field inspection, each field was also characterized according to undulations (free-draining swales), depressions (which could hold water), crown or slope, and internal drainage. In contrast to ratings for natural undulations or depressions, the field roughness rating was an indication of holes and other irregularities caused by play. Also during the initial visit, soil samples were taken for determinations of soil textural class, bulk density, pH, and available phophorus (P) and potassium (K). Samples for bulk density represented the more intensively used portions of the fields. The percentages of sand, silt, and clay and the textural class of the surface soil were obtained by particle-size analysis using a hydrometer method (Bouyoucos, 1962). Bulk density, the mass of dry soil per unit bulk volume, was determined from 10 soil cores, each an inch in diameter and 2.5 inches long. Samples from the surface 2.5 inches were used for pH determinations using a 1:1 soil-to-water paste, and for phosphorus (P) and potassium (K) determinations using Bray No. 1 and neutral, normal ammonium acetate extractants, respectively.
Upon completion of the second evaluation, Penn State specialists prepared a letter that described field conditions and suggested maintenance and/or renovation programs for fields at each school.
Characterization of Data
The number of injuries occurring during games, practices, and practice games (with the rate of injuries per 1000 exposures³) was compiled for the total sample of 10 schools and for each individual school. Data were summarized to indicate the number of reported injuries on each field, the relation of injuries to field conditions, and the number of injuries within various body-part categories.
Spearman rank-order correlations for non-parametric data were determined to ascertain the possible relationships among the incidences of injury, field characteristics, and maintenance practices. Variables used in correlations were as follows:
When field conditions varied across a field, ratings used for correlations were representative of the area between inbound hash marks.