There is increased interest in determining the psychological factors associated with athletic performance as evidenced by the growth in the number of sports psychologists and sports psychology academic programs. This is likely because of the increased awareness that psychological factors, and particularly stress, impact the physical health and functioning of both student athletes and nonstudent athletes. Psychological stress can be operationalized as a state of mental or emotional tension resulting from adverse or demanding circumstances. Although studies have indicated that academic-related psychological stress is associated with poor health for students (8) and psychological stress is related to increased physical injury for football players (6), the link between perceived academic stressors (e.g., examination periods) and increased illness and injury has not been clearly delineated in collegiate football players. Psychoneuroimmunology (PNI) is the study of interactions between behavioral, neural/endocrine function, and immune processes (1). This may be a key factor in understanding the linkage between the academic stressors and injuries.
Several PNI studies have supported the relationship between psychological factors such as stress and anxiety and aspects of physical health such as susceptibility to illness and recovery from wounds/surgery (8) and even the occurrence of accidents and subsequent severity of injury (3,7,10). The relationship between stress and physical health is especially relevant in collegiate athletes, who often face multiple life stressors (e.g., transitioning between campus and home life, academic performance, and athletic performance) and frequently place high demands on their bodies while engaging in activities that place them at risk of injury. The relationship between stress and injury in athletes has been described by Anderson and Williams (2) in a stress-injury model. This model proposes that when athletes engage in demanding practices or competition, their history of stressors, personality characteristics, and coping resources contribute to a stress response. It further suggests that those individuals with a history of many stressors, personality characteristics that exacerbate stress response, and a relatively few coping mechanisms will exhibit greater physiological and attentional changes (i.e., narrowing of the visual field to a smaller portion of the athlete's typical focus at the expense of vital visual information, increased distractibility of the athlete's attention by small or irrelevant stimuli, and increased muscle tension), which can increase the potential for injury.
Williams and Roepke (14) conducted a review of the PNI literature examining the relationship between life stress and sport injury. They found that 18 of 20 studies showed a positive relationship between stress and injury across many sports (e.g., skiing, gymnastics, soccer, field hockey, track and field, and wrestling), and that the strongest relationship was evident in football. The authors also indicated that injuries occurred 2–5 times more frequently in athletes with high compared with low life stress. Furthermore, the risk of injury was proportional to life stress. It has been noted that since Williams and Roepke's 1993 report, 9 out of 10 subsequent studies found a similar relationship between life stress and sports injury (13).
Football players are of particular interest in stress-injury models given the nature of the constant physical contact and frequency of injuries. Holmes (6) reported that 50% of the athletes who experienced high life stress during the year before the football season incurred injuries that required them to miss 3 days of practice or 1 game, which meant substantially missed more playing time than athletes with moderate stress (i.e., 25%) and low stress (i.e., 9%). Cryan and Alles (4) found similar results with an elite division 1 college football team. It has also been reported that injury frequency and severity in football players were significantly correlated with tension/anxiety (9).
In addition to physical stress, student athletes also face considerable academic stressors given the significant number of hours required for practice, training, and preparation with a reduced number of hours available to study (particularly given the fatigue associated with training/practice) (8). Kiecolt-Glaser et al. have conducted many studies that have examined the relationship among medical students, and their findings have generally indicated that students experience a higher level of perceived stress and decreased cellular immune responses during examination periods. These studies indicate that during examination periods, students are more susceptible to illness and their wounds heal more slowly. Although these studies examined a nonathlete population, it is likely that similar increases in stress and decreases in cellular immune response would occur in students in general including student athletes. Although it could be argued that medical students classes are more rigorous (and thus more stressful), medical students do not have to contend with training, practicing, and competing in athletics concurrent with their academic endeavors. Furthermore, according to the stress-injury model by Anderson and Williams (2), increases in academic stress during periods of examination could relate to increased injury risk.
Despite the relationship between life stress and injury among football players and the relationship between increased stress and decreased immune function during examination periods, no studies to our knowledge have explored the relationship between specific periods of increased academic stress and injury restrictions among collegiate football players. The purpose of this study was to examine the relationship between periods of heightened physical and academic stress and injury restriction by examining injury restriction rates in 101 division I collegiate football players during the fall 2011 athletic season/academic semester. We hypothesized that based on stress-injury models, periods of high academic stress (HAS) would increase injury rates among these collegiate athletes.
Experimental Approach to the Problem
The goal of this analysis was to compare the number of football-related injury restrictions during periods of high physical stress (HPS), HAS, and low academic stress (LAS) during a 20-week season for a college athlete. It should be noted that only injuries that would cause any restriction to any drill or other component in practice were recorded. Injuries that did not cause a restriction to practice, although may have caused pain and hampered performance, were not listed. Injury restrictions included when the injury occurred, what the injury was, how intense the injury was, and the length of time the injury caused restriction. The independent variable in the study was a 3-level categorical variable, which broadly reflected the type of stress in a given week: HPS (i.e., training camp weeks), HAS (i.e., university-wide examination weeks), and LAS (i.e., all other weeks of the semester). Training camp weeks included the first 3 weeks of the season (before the start of classes) and were classified as HPS weeks (including 2-a-day practices over the first week of camp). University-wide examination weeks included those weeks during the semester in which midterms, pre-Thanksgiving, or final examinations were offered, and these weeks were considered HAS weeks (corresponding to weeks 10, 14, 16, and 20). All other weeks (i.e., not involving training camp or university-wide scheduled examinations) were included as LAS weeks (i.e., weeks 4–9, 11–13, 15, 17–19). The dependent variable in the study was a binary variable indicating whether an injury restriction occurred during a given week for each subject.
Subjects in this study were student athletes older than 18 years (age range 18–23 years) on a division 1 college football team who had been injured during the course of the 2011 season in which the team achieved an 8–5 record and participated in a bowl game. Of the entire team (n = 101), 60 different athletes were restricted by injury for a total of 86 injury restrictions, which limited them in practices or games. Demographic characteristics of all athletes are given in Table 1. Retrospective analysis of these data was approved by the University of Missouri Institutional Review Board.
The total number of players who incurred injuries that restricted them from practice were listed on the weekly injury report, a report that details all possible limitations to the individual athlete (including illness) than impacts practice or game time (Table 2). The team injury report, which was used to construct the data set analyzed, revealed the initial date of injury restriction, the length of injury restriction, intensity of injury restriction, and area of injury restriction over the course of the 20-week season (i.e., weekly from preseason to the last scheduled game of the season).
Hierarchical logistic regression with repeated observations over time (i.e., each week) was used to assess differences in the likelihood of injury restrictions under HPS, HAS, and LAS. This approach is a special case of a generalized linear mixed model, which can be used to properly account for the dependency induced by the repeated observations within each subject (5). A benefit of this observational study design (note that a randomized design would be impossible) is that each subject is observed multiple times under each of the 3 stress types. Therefore, as with any within-subjects design (also known as split-plot design), there is a substantial increase in power to detect differences in the variable of interest. This study could also be consider a quasi crossover design because each subject moves back and forth between HAS and LAS although the sequence order is fixed. The model was fit using SAS PROC GLIMMIX (SAS for Windows, Version 9.3; SAS Inc., Cary, NC, USA) with an unstructured covariance matrix with player as the subject. Statistical significance for all tests was accepted at p ≤ 0.05 after Bonferroni correction (i.e., p < 0.0167). We also performed separate analyses on players who did (and did not) play (Table 1).
Figure 1 shows the proportion of injury restrictions within each of the 3 stress periods of interest with the denominator for each proportion being the number of subject-weeks (i.e., number of subjects × number of weeks in the period). Figure 2 shows the temporal progression of injuries throughout the season. Hierarchical logistic regression demonstrated that the odds of an injury restriction were different between the 3 stress periods of interest (F2,2017 = 23.33, p < 0.0001). Post hoc analyses showed that when considering all players on the team, the odds of an injury restriction during HPS were nearly 4 times higher than during LAS (OR = 3.65; p < 0.001) and twice as high as weeks of HAS (OR = 2.05; p < 0.003). In addition, the odds of an injury restriction during HAS were nearly twice as high as during LAS (OR = 1.78; p = 0.09). Finally, after excluding players who did not play, we focused our analysis on the key members of the team, our findings showed an intriguing difference. In those athletes who played, the odds of an injury restriction during HAS were more than 3 times higher than during LAS (OR = 3.19; p = 0.002); however, there was no significant difference between HPS and HAS (OR = 1.13; p = 0.75) (Table 3). These data suggest that for starting players, HAS may play an even greater role in injury than HPS. Additionally, when analyzing only those players who did not play (data not shown), the results were similar to the results from the full data set. All 3 comparisons were significant and in the same direction (Table 3).
The major finding of our study is that psychological stress, and not just physical stress, plays an important role in the occurrence of physical injuries for college football players. The data for all athletes in this study showed that the greatest number of injury restriction occurred during times of increased physical stress (i.e., preseason workouts involving frequent and longer duration workouts) as might be expected. However, results also show that academic stress (during regular examination periods) was associated with a significant increase in the numbers of physical injury restrictions, consistent with stress-injury models of health. What may be most compelling was that HAS was just as important as physical stress in the onset of injuries among athletes that play regularly. Thus, these players seemed to be more affected by periods of HAS than athletes who were not actively participating each week in games. We believe that coaches need to be aware of both the physical and psychological stressors experienced by their players during the season to prevent the incidence of injury in their athletes, especially starting athletes.
Previous studies have shown that increases in physical stress increased the number of physical injuries incurred by division I college football players (11). Specifically, performance predictors (vertical jump performance, agility, strength measures, sprint speed, and testosterone/cortisol ratio) were significantly compromised and a greater numbers of injuries occurred during high-volume phases of training compared with low volume phases of training. The findings of this study are novel in that they show that psychological stressors are significantly associated with the number of injuries in this similar population of college athletes. In the full team analysis, injuries during periods of HAS in this study more than doubled (from 6.2 injuries per week to 12.0 injuries per week; Figure 1) compared with periods of LAS. Selye (12) has reported that all stressors, physical or academic, will invoke the same stress response albeit not equally. The academic stress-injury relationship may be best explained by Andersen and Williams (2) who defined stress response as a “bi-directional relationship between cognitive appraisals of the demands, consequences, and resources of the person and situation and physiological and attentional responses associated with stress.” (page 302). Thus, the stress of athletic competition may actually result in an athlete's cognitive reassessment of a given situation and a narrowing of attention and focus to meet that perceived demand, which could increase risk of physical injury.
Our data supported previous research showing that life stress events can cause an increase to injury risk/incidence, and HAS is in fact a life stressor. It should be pointed out that although HPS in the full team analysis showed the greatest number of injuries per week (19.3 injuries per week; Figure 1) in the athletes who played regularly and contributed to weekly wins and losses. Injuries during the weeks of HAS were no different than weeks of HPS and were more than 3 times greater than during weeks of LAS. Athletes who do not play regularly seem to have greater incidence of injuries during weeks of HPS compared with HAS and LAS. These findings suggest that there are inherent difference between the players who play regularly and those who do not play regarding how they respond to different stressors and support previous work by Petrie (11) who found that being a starter was in and of itself an additional life stress. It could be that players who do not play regularly may put themselves at a greater risk of injury during training camp (HPS) because they are battling for a starting position and may be willing to take greater chances to earn that spot on the starting roster. This may account for the greater number of injuries in weeks of HPS in those athletes who do not play regularly. Athletes who do play regularly may have a greater number of injuries during weeks of HAS because there is increased pressure to maintain their grades and remain academically eligible to play compare with those who do not play regularly. Or, it may be that athletes who play regularly have to devote a greater amount of time during the academic semester learning plays and studying the team playbook at the expense of academics. Thus, examination periods may result in greater levels of stress in those who play regularly compared with those who do not play regularly because the latter can devote more time to schoolwork. In all athletes, whether they play regularly, there were greater numbers of injuries during periods of HAS compared with LAS. Therefore, it may be beneficial for the coach or practitioner to carefully consider controlling the physical stress (i.e., strength, power, agility, speed, or conditioning tests) during periods of HAS periods (e.g., examination weeks) during the season to mitigate the incidence of injuries. Other factors that could be driving these findings such as poor nutrition and sleep deficits were not examined in this study and could be the basis of future research.
Several programs, such as Oklahoma State University, have begun to address imbalances in the physical stressors during the season, reducing 2-a-day practices during training camp and practice times during the season (personal communication, Robert Glass, May 10, 2013). To decrease psychological stress associated with academic demands, a well-funded and fully staffed academic support center (typical at most major division I schools) may help reduce academic stress and thus protecting against injury while they are competing at the collegiate level. Interestingly, although there was a program in place that addressed academic assistance with the aid of tutors and mentors at the time of this study, academic stress was still found to be a critical factor in injury rates. Because such a program may not be available at smaller schools, the impact of academic stress on physical injury may be even greater and require increased attention. It is incumbent upon coaches to be aware that academic stressors exist, and that in some cases, these stressors are just as critical to the incidence of injuries as physical stressors. Academic stressors are a form of life stress but can be anticipated by a coach more readily than other life stresses that may arise in the lives of their athletes. Adjusting physical stress at times of HAS accordingly during the course of the season may be critical to reducing injury rates among collegiate football players.
Future research should include things such as sleep monitoring, wellness questionnaire, nutrition logs, among other things to be able to control for more variables. As this was a retrospective study, data such as this could not be imposed.
Whether an athlete is playing regularly or not, our findings suggest that periods of HAS are a significant factor contributing to injuries during a competitive football season. To the coach or practitioner, it may be advantageous to be cognizant of this and reduce the amount of physical stress during these stressful periods of the semester to avoid injury. Knowing the examination weeks in advance allows the coach to customize training and conditioning around these weeks, perhaps implementing strength, power, or agility training or increasing physical conditioning during periods of LAS while tapering these activities during weeks of HAS. This periodization may be even more critical to consider in the athletes who play regularly as HAS contributes to more injuries than in players who do not play regularly.
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