Medicine & Science in Sports & Exercise:
BASIC SCIENCES: Epidemiology
Prevalence of Preseason Conditioning among High School Athletes in Two Spring Sports
BROOKS, M. ALISON1; SCHIFF, MELISSA A.2,4; KOEPSELL, THOMAS D.2,4; RIVARA, FREDERICK P.3,4
1Robert Wood Johnson Clinical Scholars Program, 2Department of Epidemiology, and 3Department of Pediatrics, University of Washington, Seattle, WA; and 4Harborview Injury Prevention and Research Center, Seattle, WA
Address for correspondence: Alison Brooks, M.D., M.P.H., University of Wisconsin-Madison, 2870 University Ave, Suite 200, Madison, WI 53705; E-mail: email@example.com.
Submitted for publication April 2006.
Accepted for publication September 2006.
Purpose: To determine the prevalence and predictors of preseason conditioning among high school athletes.
Methods: Cross-sectional survey of 451 high school athletes participating on girls and boys track and boys soccer teams in five public high schools in Seattle, WA, spring 2005. Questions were modified from validated surveys of physical activity for adolescents. The main outcome measure was meeting criteria for adequate preseason conditioning, which specify a combination of aerobic conditioning (vigorous exercise for at least 300 min·wk−1) and stretching and strengthening exercises (at least three times a week for any duration). Log-binomial regression was performed to examine factors associated with preseason conditioning.
Results: The majority of athletes met the criteria for each of the components (59% for aerobic conditioning, 62% for stretching, 63% for strengthening). As defined by meeting the criteria for all three components, 33% of the athletes had adequate preseason conditioning. Of those athletes meeting criteria for all three components, the majority reported at least 1 month of conditioning to prepare for the season. Varsity athletes were more likely to meet the preseason conditioning criteria compared with junior varsity athletes (38 vs 25%, prevalence ratio 1.5, 95% CI 1.0-2.1). Athletes who reported help with conditioning from a coach were twice as likely to have adequate preseason conditioning compared with those who did not receive help from a coach (45 vs 23%, prevalence ratio 1.8, 95% CI 1.3-2.4).
Conclusion: The majority of athletes in this study did meet criteria for each individual conditioning component (aerobic, stretching, strengthening), but only a minority met all three criteria. These findings highlight the need for school- or coach-sponsored involvement to ensure that all athletes engage in comprehensive preseason conditioning programs.
Approximately 15-50% of all adolescent sports injuries have been attributed to overuse, which results in more time lost from sports than acute injuries (5,8,20,25,34). The American College of Sports Medicine (ACSM) estimates that many overuse injuries may be preventable with more fitness training, although currently there are limited prospective data to support this statement (29). Conditioning, or exercise, is defined as a structured and repetitive physical activity program that produces a higher level of physical fitness and athletic function, optimizing performance and minimizing risk of injury (3,7,27). Much of the preparatory conditioning for a sports season occurs in the preseason period. A preseason conditioning program is recommended to include three components: aerobic conditioning, muscular flexibility or stretching, and muscular strengthening (13,14,29). Aerobic conditioning increases the capacity and endurance of the cardiorespiratory system, and stretching increases the flexibility of major muscle groups and the range of motion around joints. Strengthening increases both muscle strength and endurance.
In its 1998 position stand, ACSM made recommendations on the amount and type of exercise required to develop and maintain adequate cardiovascular and muscular fitness in healthy adults (4). These recommendations were specifically developed to achieve fitness benefits beyond health benefits. Although there are numerous recommendations regarding the amount of physical activity needed to achieve health benefits and weight control in children and adolescents, no exercise prescription exists for competitive adolescent athletes. There are no studies describing general preseason conditioning in the U.S. high school athlete population. Our objectives were to determine the prevalence of adequate preseason conditioning among competitive high school athletes and to identify factors associated with participating in an adequate preseason conditioning program.
Study Population and Setting
We performed a cross-sectional survey of competitive high school athletes participating in the spring 2005 sports season. The survey was administered as close to the beginning of the sports season as possible; all were completed within 1 month of the season start. The average time of survey administration was during the third week of the season. Subjects were recruited from five urban public high schools within three school districts in the greater Seattle, WA area. The average enrollment of each school was 1000 students. Schools were enrolled for the study on the basis of willingness to participate. We included males and females between the ages of 13 and 19 who were playing on a spring sports team for their high school. The sports included were boys soccer and boys and girls track; girls soccer was not included because it is a fall sport. Five hundred fifteen athletes were eligible to participate, and 453 athletes completed the survey, for a response rate of 88%. Two completed surveys were excluded because one subject was the team manager and the other did not complete the survey, leaving 451 surveys for the analysis. This study was approved by the human subjects division of the University of Washington and by individual research review committees of the participating school districts. Informed consent was obtained from the parents and the athletes.
The survey instrument was a brief self-administered questionnaire that included data on gender, age, grade level, self-reported height and weight, self-reported race/ethnicity, type of spring sport (soccer or track), level of sport (varsity, junior varsity, or other), and whether it was their first time playing a sport for their high school. Body mass index (BMI) was calculated, and BMI categories were defined according to 2000 CDC growth charts (23). The physical activity questions were adapted from two validated surveys for adolescents, the Youth Risk Behavior Survey and the Modifiable Activity Questionnaire for Adolescents (1,2,17,22). To assess the three recommended components of a preseason conditioning program, athletes were asked about the vigorous exercise and the stretching and strengthening exercises in which they participated during a usual week in the 1 month before the start of the sports season. Athletes were asked to report all the physical conditioning activities they did to get in shape in the month before the start of the season. The duration of preseason conditioning was determined by asking athletes how many weeks before the start of the spring sports season they started doing physical activities to get in shape. To assess help with conditioning, athletes were asked to report all the sources that helped them with conditioning for the sports season. Athletes were also asked to list the other organized sports in which they participated, either for their school or for a nonschool club or organization, since the beginning of the 2004-2005 school year. Athletes from a single high school track team were asked to complete the survey at a 2-wk retest to assess the reliability of the athletes' responses. Fifty-eight athletes completed the retest; the average intraclass correlation coefficient across five items was 0.60, which corresponds to moderate agreement.
The primary objective was to determine whether the athlete met criteria for adequate preseason conditioning, adapted from the ACSM 1998 position stand on the amount of physical activity required to develop and maintain cardiovascular and muscular fitness in healthy adults (4). These criteria are intended to represent physical activity levels that produce a conditioning effect and achieve levels of fitness that are beyond the physical activity guidelines for adolescents designed to achieve basic health benefits and weight control (30,33). Adequate preseason conditioning required that athletes meet the adapted ACSM criteria for all three components: aerobic conditioning, stretching, and strengthening. Aerobic conditioning was evaluated by asking subjects to report the frequency in days and the duration in minutes of vigorous physical activity. Adequate aerobic conditioning was defined as vigorous exercise for at least 300 min or for 5 h·wk−1. To calculate total minutes of exercise per week, total minutes per day of vigorous exercise were multiplied by the number of days per week of vigorous exercise. Adequate stretching consisted of engaging in stretching exercises at least 3 d·wk−1. Adequate strengthening was defined as having engaged in strengthening exercises at least 3 d·wk−1. The latter two components did not have any duration in minutes associated with them. These variables (aerobic conditioning, stretching, strengthening) were combined to serve as the study's main outcome variable, the prevalence of preseason conditioning. We calculated the proportion of athletes who met each of the components, and then we calculated the proportion who met criteria for all three components.
To identify factors associated with adequate preseason conditioning, we compared the proportions who met the criteria between athletes with and without certain characteristics of interest. Bivariate chi-square analyses and multiple log-binomial regression analyses were performed to evaluate the association between the independent variables and aerobic conditioning, stretching, strengthening, and the summary adequate preseason conditioning. Because the outcomes of preseason conditioning were not rare, log-binomial regression was used to determine the prevalence ratio (PR) and corresponding 95% confidence intervals (CI). A backward elimination algorithm was used to reduce the number of independent variables to a smaller subset of the most important predictors. All of the following variables were included in the original model and were considered to be both predictors in their own right and possible confounders for other factors: gender, grade level, BMI category, level of sport, type of spring sport, first time playing, help with training, and winter school sports participation. Variables were dropped from the model if there was not a statistically significant association with preseason conditioning, using a P value cutoff of 0.20. A final multiple variable regression was performed to calculate adjusted prevalence ratios and confidence limits. All statistical analyses were performed using STATA, version 9.1.
Approximately two thirds of the subjects were male, and two thirds identified themselves as varsity-level athletes (Table 1). Seventy-two percent of the athletes participated in track. The majority of the subjects had a BMI in the normal category. The predominant racial/ethnic group was non-Hispanic white. Of the 15% of the athletes reporting that this was their first time playing a sport for their high school, the majority were less than 16 yr old and in the 9th or 10th grade.
Duration and Types of Preseason Conditioning Activities
Among all athletes who were surveyed, 52% reported more than 6 wk of any preseason conditioning in preparation for the spring sports season. Twenty-six percent did between 1 and 3 wk of conditioning, and 13% did between 4 and 5 wk. Nine percent of the athletes did no preseason conditioning of any type. Jogging and/or running were reported as the most common physical activity used to get in shape for the sports season for both males and females (Table 2). Female athletes also were more likely to participate in fast walking and exercise machines than in organized sports. Approximately one third of both male and female athletes reported physical education class as an activity used to help them get in shape for the sports season. Prior school sport participation was a source of physical activity for some athletes. Almost half of the athletes reported playing a fall sport for their school, with the largest number of athletes participating in cross-country (Fig. 1a). Fewer athletes (26%) reported participating in a winter sport for their school, with the largest number of athletes playing basketball (Fig. 1b). Thirteen percent played both a fall and winter school sport. One fifth of the athletes participated in prior organized sports activities for a nonschool organization or league, and 22% of the athletes reported no prior school sports or nonschool organized sports activities during the 2004-2005 school year. Of those male athletes playing spring soccer for their high school, approximately half reported also playing soccer on a nonschool team for six or more months per year.
Adequate Preseason Conditioning
Although the majority of athletes met the criteria for each component of preseason conditioning (59% for aerobic conditioning, 62% for stretching, and 63% for strengthening), only 33% had adequate preseason conditioning, as defined by meeting the criteria on all three required components. Seventy percent of the athletes meeting the summary criteria reported more than 6 wk of preseason conditioning in preparation for the spring sports season. Of the remaining athletes, 15% did between 1 and 3 wk of conditioning, and 15% did between 4 and 5 wk. There was no significant association between adequate preseason conditioning and BMI category, grade level in school, type of spring sport, gender, first time playing, and winter sport participation. Adequate preseason conditioning was associated with being a varsity athlete (PR = 1.5, 95% CI 1.0-2.1) and receiving help with conditioning (PR = 1.7, 95% CI 1.1-2.7) (Table 3). Athletes most frequently reported a coach or friend as a source of help with conditioning, followed by a teammate, parent, or physical education (PE) teacher, respectively. Athletes who received help from a coach or PE teacher were most likely to have adequate preseason conditioning compared with those athletes who received help from other sources. Receiving help from a parent or teammate was also significantly associated with adequate preseason conditioning.
Aerobic Conditioning, Stretching, Strengthening Components
The pattern of factors associated with each component of conditioning differed from that for the summary preseason conditioning in three characteristics of interest: gender, winter sports participation, and first time playing a high school sport. BMI category, grade level, and type of spring sport were not associated with meeting criteria for each component. As in the summary preseason conditioning analysis, varsity athletes and athletes who received help with conditioning were more likely to meet criteria for the individual components. Of particular interest, winter sport athletes were more likely to meet the aerobic conditioning criteria than non-winter sport athletes (70 vs 55%, PR 1.1, 95% CI 1.0-1.3). Females were less likely to meet aerobic conditioning criteria than males (48 vs 65%, PR 0.7, 95% CI 0.6-0.8), and first-time high school athletes were less likely to meet aerobic conditioning criteria than experienced high school athletes (35 vs 63%, PR 0.6, 95% CI 0.4-0.9). Compared with males, females were more likely to meet the criteria for stretching days (71 vs 58%, PR 1.1, 95% CI 1.0-1.3) and were less likely to meet the criteria for strengthening days (58 vs 66%, PR 0.8, 95% CI 0.7-1.0).
On average, athletes participated in aerobic conditioning approximately 90 min·d−1 for 4 d·wk−1, totaling 6 h·wk−1 of aerobic physical activity (Table 4). Athletes typically did 3 d·wk−1 each of stretching and strengthening exercises.
This study demonstrates that the majority of high school athletes in this study population and setting do not participate in all of the recommended components of a preseason conditioning program before starting a competitive sports season. Varsity athletes and those who received help with conditioning, especially if it was from a coach or PE teacher, had a higher probability of participating in increased levels of preseason conditioning. Female athletes and first-time high school athletes participated in less aerobic conditioning than males and experienced athletes. Females were less likely to meet criteria for adequate strengthening but were more likely to meet criteria for adequate stretching. The majority of athletes did not participate in a winter school sport as a source preseason physical activity. The results may be useful for athletes, coaches, certified athletic trainers, certified strength and conditioning specialists, and school sports administrators.
Much of the prior research on physical conditioning has focused on general physical activity in all adolescents, without specifically focusing on high school athletes. Past findings from the Youth Risk Behavior Survey (YRBS) have shown that 65% of high school students participate in vigorous physical activity for at least 20 min on three or more days per week, as defined by the Healthy People 2010 goals for adolescent physical activity (16,18,33). If those national results apply to this study setting, the results of this study suggest that the majority of competitive high school athletes had at least as much vigorous aerobic exercise as that of the U.S. high school student population. We found that female athletes were less likely to participate in the aerobic conditioning component of preseason conditioning. This may be explained by the findings of several studies noting that adolescent females engage in less aerobic physical activity in general (3,16,17). We also found that junior varsity and inexperienced first-time high school athletes were less likely to participate in preseason conditioning. We hypothesize that these athletes may not understand the importance of engaging in adequate preseason conditioning before a competitive sports season.
The important question remains as to whether preseason conditioning is effective in reducing the risk of athletic injury. There is consistent expert opinion that children and adolescents should engage in gradual, progressive, age- and developmentally appropriate general fitness conditioning in addition to sport-specific skill training to prevent injury, particularly chronic overuse or repetitive strain injuries (9,15,21,26,29). There have been few epidemiologic studies and no randomized controlled injury-prevention trials in youth to support this position. On the basis of a review of past studies, Emery (12) concluded that deficits in endurance or strength attributable to limited preseason training may be associated with higher rates of injury in adolescents and adults. The majority of this past research involved an intervention designed to prevent injury in a specific sport. Additionally, these prior studies have significant limitations including inadequate control for confounders, nonrandom assignment of the intervention, lack of a control group, and broad intervention programs that do not allow preventive components to be addressed individually (11,12). Research in military populations provides the best evidence that level of physical fitness is a predictor of injury. Low levels of aerobic fitness and muscular endurance among military recruits (especially women) entering basic training have been shown to be strongly associated with training-related injuries (6,19). Conditioning programs instituted for unfit recruits before entering basic training have decreased the rate of attrition from basic training attributable to musculoskeletal injury (24). Although stretching is recommended as a component of preseason conditioning programs, there currently is little evidence that stretching prevents injury (32).
Several limitations of our study exist. The participating schools were not a random sample from a defined population of schools and were all large urban, public schools. Selection bias is possible, and results may not be generalizable to other settings, sports, or years. An important limitation is the retrospective rather than prospective self-report of activity. There are possible recall errors because athletes were asked to recall information about activities in which they had participated 1 month before the start of the sports season. However, it was not possible to directly measure or to observe the preseason physical activities for all participating athletes. Several studies have demonstrated self-report to be a valid measure of vigorous physical activity, and in addition, subjects tend to overreport rather than underreport their amount of physical activity (10,22,28). Although a portion of this survey used validated physical activity questions, the survey in its entirety was not revalidated. Spring school sport athletes may have achieved preseason conditioning by playing a school sport the previous season. We considered winter sport participation, not fall sport participation, to be the functional equivalent of preseason conditioning for a spring sport. We believe that potential misclassification of this prior sport participation could lead to either overestimation or underestimation of the true prevalence of preseason conditioning in this study. The physical activity that the athletes reported did not provide details on increases in volume and intensity over the course of the month or on sport-specific training, such as mileage per week for track athletes. The criteria for "adequate" preseason conditioning were adapted from the ACSM position statement on fitness for healthy adults; these criteria represent expert opinion and not an evidence-based standard. We acknowledge that aerobic conditioning, muscular stretching, and strengthening represent the minimum in terms of preseason conditioning. The results, which show that relatively few athletes fit even this minimum standard, are therefore conservative. A preseason program of sport-specific functional training is likely more beneficial and warrants further investigation. Lastly, because this is a cross-sectional study, there may be residual unmeasured confounding.
Although it is not possible from this study to determine the effectiveness of specific interventions to improve preseason conditioning or the amount of preseason conditioning needed to reduce injury risk, the results suggest that school- and coach-sponsored preseason conditioning programs may be more effective in achieving higher levels of preseason conditioning among high school athletes. Whereas most state high school athletic associations have rules governing when coaches can officially start practice for a sports season, schools can likely find other means to offer preseason conditioning to help their competitive athletes. All of the study schools employed a part-time certified athletic trainer, but none were available daily to student athletes. There may be a need for schools to provide better access to certified athletic trainers to improve participation in organized preseason conditioning programs and as part of a comprehensive injury-prevention program. It may be useful to educate coaches, parents, and athletes about the need for and importance of preseason conditioning and age-appropriate training as part of participation in competitive athletics. More specifically, it may be possible for coaches to promote athletics as a means for adolescents to learn about and engage in general fitness training that will lead to increased lifelong physical activity (31). Specific interventions might be targeted at those groups that are most at risk of not participating in adequate preseason conditioning-namely, female, junior varsity, and first-time high school athletes. An ideal time to start these interventions may be at the middle school level before entering the demands of competitive high school athletics. Future research should include injury-surveillance studies that examine the association between preseason conditioning and injury rates throughout the course of a season.
This work was presented in part as a poster at the American Medical Society for Sports Medicine Annual Meeting, May 1, 2006 and the American College of Sports Medicine Annual Meeting, June 1, 2006.
This work was supported by the Robert Wood Johnson Foundation and its Clinical Scholars Program (Dr. Brooks). The opinions are those of the authors and not the Robert Wood Johnson Foundation. We would especially like to thank Allen Cheadle, PhD for his thoughtful discourse and statistical support, and the Seattle-area high school administrators, coaches, parents, and athletes whose cooperation made this study possible.
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TRAINING; AEROBIC; STRETCHING; STRENGTHENING; ADOLESCENTS; ATHLETICS
©2007The American College of Sports Medicine
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