Athletic Training and Sports Health Care

Original Research 

Associations Between Sport Specialization, Running-Related Injury, and Menstrual Dysfunction Among High School Distance Runners

Mitchell J. Rauh, PhD, PT, MPH, FACSM; Adam S. Tenforde, MD; Michelle T. Barrack, PhD, RD; Michael D. Rosenthal, DSc, PT, ATC; Jeanne F. Nichols, PhD, FACSM

Abstract

Purpose:

To determine the associations between sport specialization, running-related injury, and menstrual dysfunction in high school distance runners.

Methods:

A total of 126 female runners competing in cross-country and distance track events in southern California during the 2003–2004 interscholastic sport seasons were prospectively followed. Baseline questionnaires assessed sport participation, menstrual history, demographic characteristics, and anthropometric measurements. Low back and lower extremity musculoskeletal running-related injuries were recorded using daily injury reports.

Results:

Fifty-seven (45.2%) runners incurred at least one musculoskeletal running-related injury. At baseline, 27 (21.4%) runners were highly specialized athletes, 38 (30.2%) were moderate specialization athletes, and 61 (48.4%) were low specialization athletes. Compared to low specialization athletes, the risk of musculoskeletal running-related injury was 75% greater (relative risk = 1.75; 95% confidence interval [CI]: 1.1 to 2.7) and menstrual dysfunction was four times more likely in highly specialized athletes (relative risk = 4.22; 95% CI: 1.7 to 10.8).

Conclusions:

High sport specialization was associated with increased running-related injury risk and menstrual dysfunction in female interscholastic runners.

[Athletic Training & Sports Health Care. 2018;10(6):260–269.]

Abstract

Purpose:

To determine the associations between sport specialization, running-related injury, and menstrual dysfunction in high school distance runners.

Methods:

A total of 126 female runners competing in cross-country and distance track events in southern California during the 2003–2004 interscholastic sport seasons were prospectively followed. Baseline questionnaires assessed sport participation, menstrual history, demographic characteristics, and anthropometric measurements. Low back and lower extremity musculoskeletal running-related injuries were recorded using daily injury reports.

Results:

Fifty-seven (45.2%) runners incurred at least one musculoskeletal running-related injury. At baseline, 27 (21.4%) runners were highly specialized athletes, 38 (30.2%) were moderate specialization athletes, and 61 (48.4%) were low specialization athletes. Compared to low specialization athletes, the risk of musculoskeletal running-related injury was 75% greater (relative risk = 1.75; 95% confidence interval [CI]: 1.1 to 2.7) and menstrual dysfunction was four times more likely in highly specialized athletes (relative risk = 4.22; 95% CI: 1.7 to 10.8).

Conclusions:

High sport specialization was associated with increased running-related injury risk and menstrual dysfunction in female interscholastic runners.

[Athletic Training & Sports Health Care. 2018;10(6):260–269.]

More than 720,000 female athletes participated in interscholastic outdoor track and field and cross-country events in the United States during the 2016–2017 school year.1 Track and field and cross-country are the first and sixth most popular girls' sports by number of participants, respectively.1 Despite the high participation in girls' track and field and cross-country, epidemiological research on injuries in these sports is limited. Prospective studies for girls' interscholastic track and field and cross-country runners reported varying cumulative seasonal injury incidences from 34% to 52%, with rates of 0.99 of 1,000 athletic exposures in track and field to 19.6 of 1,000 athletic exposures in cross-country.2–5 There have been limited reports of risk factors or determinants of injury, including training error,6,7 step/stride length,8 muscle strength,9 Q-angle,4,10 prior injury,3,4,11 and female athlete triad risk factors.11,12

There is concern for the increased risk of overuse injuries and adverse health outcomes related to sport specialization, especially because the prevalence of sport specialization may be increasing in young athletes.13,14 Sport specialization has been defined as “year-round” intensive training in a single sport at the exclusion of other sports13,14 that can result in psychological stress and overuse injuries.13,15,16 Jayanthi et al.13,17 developed a scale to classify athletes on a continuum of low, moderate, and high specialization based on the following three criteria: (1) year-round training (ie, training more than 8 months per year); (2) chooses a single main sport; and (3) quits all sports to focus on one sport. The literature for the high school age level is inconclusive regarding whether participating in an individual or team sport increases the likelihood of specializing in a single sport.15,18,19 High sport specialization may be more common for female athletes than for their male counterparts.15,18 Additionally, there is more evidence that high school athletes who are moderately or highly specialized are more likely to sustain a lower extremity injury than low specialization athletes.15,18–20

Both musculoskeletal injuries and menstrual dysfunction are health concerns for women with the female athlete triad.12,21–25 The female athlete triad is defined as an interrelationship between low energy availability, menstrual dysfunction, and low bone mineral density.26,27 The underlying cause for the female athlete triad is low energy availability.26,27 Female athletes who participate in endurance sports are at an elevated risk for low energy availability.28 Additionally, overtraining has been a risk factor for menstrual dysfunction, and it may be associated with a prolonged, low energy availability state.29

Female high school distance runners (ie, athletes whose main running event was 1,600 meters [1 mile] or longer) are an important population to study due to their high rate of injury, the concern for increased sport specialization, and their elevated risk for low energy availability and menstrual dysfunction. Although several studies examined sport specialization and injury in high school athletes or an overall population of track and field athletes,18,20 we are unaware of prior published research that focused on female high school distance runners. Thus, the purpose of this study was to examine the association between sport specialization (defined prior to Jayanthi et al.13), menstrual dysfunction, and prospective risks of running-related injury in competitive high school female distance track and field or cross-country runners. We hypothesized that distance runners with high sport specialization would have a greater risk of musculoskeletal running-related injury than distance runners with low sport specialization. Elevated sport specialization categories were expected to contribute to greater time lost to running-related injuries. We also hypothesized that the association between sport specialization and menstrual dysfunction would be greater for distance runners who are highly specialized than those who are low specialization.

Methods

The sample consisted of female distance track and field and cross-country runners from 6 high schools in southern California during the 2003–2004 interscholastic seasons in a population reported previously.12,21,30,31 All participants reported reaching menarche and were between 13 and 18 years old. One hundred twenty-six athletes who competed in distance events for their high school were included (track and field [1,600 meters/1 mile or longer] or cross-country [5,000 meters or 3.1 miles]).32 The participants were from a larger population of 589 athletes participating in 8 interscholastic sports (740 total possible athletes, 79.6% response rate).12,21,30,31 Each participant completed questionnaires regarding competitive sport participation and menstrual history and was measured without shoes for height and weight with a digital scale (Health-O-Meter; Sunbeam Products, Inc., Bridgeview, IL). One research assistant was available for every 6 to 8 athletes to provide clarification when the participants completed the questionnaires individually.12,21,30,31 The study was approved by the university's institutional review board. Written consent from parents and participants was collected prior to the runner's participation.

Data Collection

Musculoskeletal Running-Related Injury. The coaches and athletic trainers were trained to use the daily injury report prior to each season.3,4,12,21 Additionally, athletes were instructed to report any running-related injury symptoms to their coach or athletic trainer for daily injury report capture. We defined a musculoskeletal running-related injury as meeting the following criteria: (1) a reported bone, joint, or muscle condition localized to the low back or lower extremity (ie, hip, thigh, knee, shin, calf, ankle, or foot); (2) a running-related injury from a practice or competitive event; and (3) a running-related injury that required the athlete to be removed from or miss a practice or competitive event.3,4,12,21 The total time lost to running-related injury was defined as the number of days the runner was not able or permitted to participate in her sport in an unrestricted manner due to the running-related injury.3,4,12,21 The coaches and athletic trainers recorded details about each running-related injury including onset (eg, initial or new vs subsequent), body location (eg, knee, ankle), injury type (eg, tendinitis, sprain, or shin splint/stress reaction), and time lost due to running-related injury.3,4,12 Running-related injury data were also used to classify injuries as overuse (eg, tendinitis or stress fracture) or acute (eg, sprain or fracture).2 For analysis purposes, those who reported contusions or lacerations only were classified as uninjured because sport specialization and/or menstrual dysfunction were not expected to increase the risk of those types of running-related injuries.12

Resulting running-related injury data were used for the classification of the injury severity: (1) minor: 1 to 7 days missed; (2) moderate: 8 to 21 days missed; and (3) major: 22 days or more missed.2,12 Each athlete was also monitored for a subsequent running-related injury, defined as an injury occurring after the initial running-related injury.3,4,33 The two types of subsequent running-related injuries were identified as a reinjury to the same body location or an injury to a new body location.3,4,33

The study research team met with the coaches and athletic trainers twice a month and collected the injury reports each month. To assess the completeness of each team report, the daily injury report was reviewed and compared to the practice and competition schedules.

Sport Specialization. The sport participation data collected from the survey included current and prior participation and the total duration for each sport (years and months). If she competed in track and field, the athlete was asked to report the number of years and months she competed in sprint, distance, or field events. An athlete was classified as a distance runner if she competed in outdoor distance track and field or cross-country events.

For the purposes of our study, sport specialization classification was determined for each distance runner in three categories: (1) low specialization was defined as an athlete who participated in distance running sport(s) for 8 or fewer months/year and also participated in one or more other high school sport (excluding track and field or cross-country); (2) moderate specialization was defined as an athlete who participated in only distance running sport(s) for 8 or fewer months/year or participated in distance running sport(s) 9 or more months/year and one or more other sport (excluding track and field or cross-country); and (3) high specialization was defined as the athlete who participated in distance running sport(s) for 9 or more months per year and no other sports.

Menstrual Status. Data collected from the surveys included the participants' menstrual histories.34 The criteria for the classification of menstrual dysfunction were: primary amenorrhea (age of menarche: 15 years or older), secondary amenorrhea (more than 3 consecutive months of missed menstrual cycles over the past year), or oligomenorrhea (menstrual cycle intervals exceeding 35 days over the past year).26,27 Runners who met one or more criteria were combined into a single menstrual dysfunction classification group and compared to eumenorrheic athletes.30 To account for the influence of medications on menstrual function, each runner was asked to report her use of hormones, including oral contraceptive pills.

Statistical Methods

Only lower extremity running-related injuries that occurred during distance sport(s)/event(s) and were included in the daily injury reports were used in our study analysis. Analysis of variance and the chi-square test were used to compare demographic, physical, and menstrual history characteristics between the sport specialization groups. Running-related injury characteristics (ie, body location, time lost due to the running-related injury, onset of the running-related injury, and subsequent running-related injury) were presented for each sport specialization classification. Relative risks and 95% confidence intervals (CIs) were calculated for the association between sport specialization and running-related injury, comparing the proportion of runners in a high-risk group (ie, high or moderate specialization) versus the proportion of runners in a baseline or referent group (ie, low specialization).35

When determining the relationships between sport specialization and menstrual dysfunction, runners who reported using birth control (n = 21) were excluded from the study analyses. The remaining participants (n = 105) either reached menarche or were older than 15 years, so the presence of menstrual dysfunction could be accurately classified. Similarly, relative risks and 95% CIs were calculated, comparing the proportion of runners in the higher-risk sport specialization groups versus the proportion of runners in the low specialization group when assessing menstrual dysfunction.

Body mass index (BMI) was calculated by each runner's measured height (m) and weight (kg) as body mass/height2. BMI was categorized using the following groups: 17.5 kg/m2 or less, between 17.6 and 18.4 kg/m2, and greater than 18.5 kg/m2. The cut-off points were based on several reports suggesting that a mass of 17.5 kg/m2 or less or between 17.5 and 18.5 kg/m2 place female athletes at a greater risk for a bone stress injury or a lower bone mineral density (ie, ≤ −1.0 SD).22,25,27,36 The analyses were conducted using SPSS software (version 24.0; SPSS, Inc., Chicago, IL) with the alpha level set a priori at 0.05.

Results

Characteristics of Distance Runners

Of the 126 athletes who participated in a distance running sport, 27 (21.4%) were classified as highly specialized (Figure 1). The sample was primarily white (64.3%), followed by Hispanic (21.4%), African American (7.9%), Asian/Pacific Islander (5.6%), and other races (0.8%). No differences in racial distribution were detected by sport specialization status (P = .20) (Table 1). Highly specialized athletes had a lower BMI (P = .008) and a later age of menarche (P = .02) compared to low specialization athletes. When using the Female Triad Coalition classification for BMI,27 highly specialized athletes had a greater percentage of low BMI (BMI ≤ 17.5 kg/m2) than low specialization athletes (18.5% vs 1.6%, P = .001).

Percentages of female high school distance runners by sport specialization level. Low sport specialization = ≤ 8 months/year of distance running (track and field, cross-country, or both), competitve sport participation or training, and playing one or more additional sports. Moderate sport specialization = ≤ 8 months/year of distance running (track and field, cross-country, or both) or competitive sport participation, or ≥ 9 months/year of distance running (track and field, cross-country, or both), competitive sport participation, or training. High sport specialization = ≥ 9 months/year of distance running (track and field, cross-country, or both), competitive sport participation, or training.

Figure 1.

Percentages of female high school distance runners by sport specialization level. Low sport specialization = ≤ 8 months/year of distance running (track and field, cross-country, or both), competitve sport participation or training, and playing one or more additional sports. Moderate sport specialization = ≤ 8 months/year of distance running (track and field, cross-country, or both) or competitive sport participation, or ≥ 9 months/year of distance running (track and field, cross-country, or both), competitive sport participation, or training. High sport specialization = ≥ 9 months/year of distance running (track and field, cross-country, or both), competitive sport participation, or training.

Selected Demographic and Physical Characteristics by Sport Specialization Status

Table 1:

Selected Demographic and Physical Characteristics by Sport Specialization Status

Prospective Musculoskeletal Running-Related Injuries

Approximately half (n = 57, 45.2%) of the runners studied incurred injuries while participating in the distance running season(s) (102 running-related injuries). Compared to low specialization athletes, the risk of lower extremity running-related injury was 75% greater for highly specialized athletes (relative risk: 1.75; 95% CI: 1.1 to 2.7; P = .02) (Table 2). No statistically significant difference in running-related injury risk was identified for moderate compared to low specialization athletes (relative risk: 1.31; 95% CI: 0.8 to 2.1; P = .28).

Relative Risk for Musculoskeletal Lower Extremity RRI by Sport Specialization Status

Table 2:

Relative Risk for Musculoskeletal Lower Extremity RRI by Sport Specialization Status

Lower Extremity Running-Related Injuries

The most common location for running-related injury was the lower leg (shin/calf), followed by knee and hip (Table 3). The lower leg was the most frequently injured location across sport specialization categories. The knee was the second most common location for running-related injury in high and moderate sport specialization athletes, and the ankle was the second most frequent site of running-related injury in low sport specialization athletes.

Incidence and Characteristics of Lower Extremity Musculoskeletal Running-Related Injury (N = 102) by Sport Specialization Status in 57 Injured High School Distance Runners

Table 3:

Incidence and Characteristics of Lower Extremity Musculoskeletal Running-Related Injury (N = 102) by Sport Specialization Status in 57 Injured High School Distance Runners

Two-thirds of running-related injuries were minor (1 to 7 days lost) in severity, and major running-related injuries (≥ 22 days) were least common. Highly specialized athletes had a greater proportion of major running-related injuries (28.0%) than the moderate (8.6%) or low (11.9%) specialization athletes (P = .14).

Most running-related injuries were classified as overuse or chronic (n = 84, 82.4%). Overuse or chronic running-related injuries were more common than acute injuries across all specialization groups. The highest proportion of acute running-related injuries were observed among the low specialization athletes.

More than half of the injured runners (56.1%) sustained one or more subsequent running-related injuries. Of the subsequent running-related injuries, most (68.9%) were a reinjury to the same body part. In highly specialized athletes, all (8 of 8) subsequent running-related injuries were reinjuries to the same body part.

Menstrual Status and Sport Specialization

Of the 105 runners without hormonal medication, 26 (24.8%) met the criteria for menstrual dysfunction (oligomenorrhea/amenorrhea). Oligomenorrhea was most common (21.9%), followed by secondary amenorrhea (5.7%) and primary amenorrhea (1.9%) (Table 4). Compared to low specialization athletes, highly specialized athletes were four times more likely to report menstrual dysfunction (relative risk: 4.11; 95% CI: 1.8 to 9.6; P = .0005). Similarly, highly specialized athletes were four times more likely to report oligomenorrhea than low specialization athletes (relative risk: 4.22; 95% CI: 1.7 to 10.8; P = .002). No associations were observed between sport specialization groups for differences in history of primary amenorrhea or secondary amenorrhea.

Relative Risk of Menstrual Dysfunction by Sport Specialization Status

Table 4:

Relative Risk of Menstrual Dysfunction by Sport Specialization Status

Discussion

The purpose of this study was to determine if sport specialization was associated with menstrual dysfunction or increased risk for running-related injury in a population of high school female distance track and field and cross-country runners. Although our participant population data were collected prior to the currently recommended sport specialization definition,13,14 our results suggest that distance runners who reported high sport specialization were at the highest risk for running-related injury. Additionally, a greater proportion of running-related injuries in highly specialized athletes resulted in significant time lost to sport. Distance runners who reported high sport specialization were also more likely to report menstrual dysfunction. One prospective study reported the relationship between injury and sport specialization in high school cross-country runners and distance track and field athletes.20 To our knowledge, this is the first study to evaluate the association of sport specialization to injury and menstrual dysfunction in female high school distance runners.

Approximately half of the distance runners (57 of 126 [45.2%]) met the criteria for sustaining a running-related injury. Prior reports have also shown a high proportion of female high school distance runners incur an injury annually.2–4

Our findings support the hypothesis that sport specialization may increase the risk for running-related injury. Distance runners classified as highly specialized athletes were at a 75% increased risk for running-related injury compared to low specialization athletes. Moderate sport specialization athletes did not reach statistical significance for higher rate of running-related injury compared to low specialization athletes (relative risk: 1.31; 95% CI: 0.8 to 2.1; P = .28). The prospective study by McGuine et al.20 did not identify an increased risk for injury for primary sport of track and field or cross-country runners and lower extremity injury. Notably, differences may be due to different measures of sport specialization, injury reporting systems, and sample sizes (n = 62 boys and girls compared to our population of 126 female runners). Our larger population studied may have increased the power to detect differences in the risk of running-related injury between sport specialization status. We used an injury reporting system where coaches and athletic trainers were educated and trained to identify and record injuries in a systematic manner.3,4,12,21 This injury reporting system has been shown to be reliable and valid.3,4,12,21 In this study, we used a combination of coach and athletic trainer at schools who employed an athletic trainer. Because it was not likely that all runners would report to the athletic trainer, the reporting system was strengthened by the coaches who were present on a daily basis to observe the runners, record injuries, and notate the time lost until the runners were allowed to return with a non-injured status.

The higher risk association of running-related injury in high specialized distance runners has multiple indications. Participating in a variety of sports is thought to develop muscle groups in multiple planes, varying the stresses placed on the body and thus reducing the likelihood of overuse running-related injury. For example, older elite male and female distance runners who played ball sports during their youth had half the rate of stress fractures as a runner.37 The protective effects against stress fractures from youth participation ball sports such as soccer or basketball may result from optimizing bone strength and stiffness with multidirectional loading from the sport, similar to findings reported in the military.38 Thus, participation in sports outside running may provide a beneficial effect in reducing the risk for injury during running sport seasons. Second, the runners in the high sport specialization group also participated in their sport for 9 or more months during the year, whereas those in the low sport specialization group participated in running less than 8 months per year. Although this requires further study, consideration for a limit of 8 months per year of youth running or adding a non-primary running sport for those who participate in running for majority of the year might help reduce the risk for running-related injury. This supports Jayanthi et al.'s17 report that diversified activity from avoiding sports specialization may facilitate gains in neuromuscular skills for young athletes that are effective in injury prevention, and will reduce repetitive use of same body locations that contributes to overuse injuries.

For highly specialized athletes, the lower leg was injured over three times more than any other body location. Further, the highly specialized athletes had twice the number of lower leg running-related injuries than the moderate or low specialization athletes. This latter finding might be because moderate and low specialization athletes may have participated in other sport(s) that had different demands on the musculoskeletal system that may have modified their injury risk.

Most running-related injuries were classified as overuse, consistent with the repetitive kinetics and kinematics observed in typical running mechanics. Although most running-related injuries did not cause significant disability or time lost from sport participation, major injuries (ie, running-related injuries causing 22 or more days lost) were two times higher in the highly specialized group. With menstrual dysfunction more common in highly specialized runners, it is possible many of the major running-related injuries were bone stress injuries that were often recorded by coaches and/or athletic trainers in the daily injury reports. The reports in the daily injury report regarding the anatomical site of running-related injury were believed to be accurate based on our study's definition of injury and the education provided to both athletic trainers and coaches on the correct method to report running-related reinjuries.3,4,12,21 However, the accuracy of their reports on injury type was less certain without physician diagnosis or radiographic confirmation. Thus, because some injury types in the daily injury report can result in misclassification, we do not report injury types based on this methodology.35 Our findings suggest that highly specialized distance runners may experience a greater disability from sport (inability to participate due to injury) than moderate or low specialization runners. Future studies that classify other aspects of training (eg, terrain or running volume) and methods to confirm injury diagnosis may clarify this relationship.

More than half of the injured distance runners incurred a subsequent running-related injury, and most of the injuries were a reinjury to the same body part. Our findings are consistent with those reported by Rauh et al.3,4 Notably, all highly specialized athletes' subsequent running-related injuries were reinjuries to the same body part. Additional studies are needed to better understand the nature and effects of subsequent running-related reinjuries in high sport specialization.

To our knowledge, this is the first study to report the association between sport specialization and menstrual dysfunction in a high school sport population. Highly specialized athletes were four times more likely to report menstrual dysfunction than low specialization athletes; a non-statistically significant trend toward increased risk was observed in moderate over low sport specialized distance runners. Notably, a majority (13 of 25) of the female distance runners who were highly specialized athletes reported menstrual dysfunction.

Several studies in collegiate25,39 and high school31 sport populations have higher reports of menstrual dysfunction among those participating in sports emphasizing leanness (ie, the athlete having low body fat mass and high body muscle mass). These studies have suggested that a negative energy balance or energy drain associated with a high volume of distance running training in a sport that requires a lean build (eg, track and field, cross-country, and swimming) may explain why they are more susceptible to menstrual dysfunction than other classes of sports.31 Menstrual dysfunction, prolonged low energy availability state, and repetitive loading from running are all concerning for risk of not optimizing peak bone mass accrual in high school distance runners who are highly specialized.

In our study, the high and moderate specialization athletes by definition spent a significant amount of their training in distance running. Further, the highly specialized athletes had a significantly lower BMI than those in the low specialization group; the latter group where the athletes allotted some of their training time in sports that do not require a lean build (eg, basketball, soccer, softball, tennis, track [field events], and volleyball).25,31 Thus, we suggest that the high energy demands of distance running coupled with mild (or greater) energy restriction induced an energy imbalance, which in turn may have led to the larger percent of menstrual dysfunction reported by the runners in the high and moderate sport specialization groups than in the low specialization group. This may have been more apparent for the runners in the high specialization group who might have been in a higher chronic energy deficit due to 9 or more months per year of training. This is speculative because we did not measure dietary intake or energy expenditure, but others have reported lower circulating luteal hormone levels and a greater percentage of menstrual dysfunction among elite young adult female endurance athletes with low or reduced energy availability compared to athletes with optimal energy availablility.40,41

Limitations

Although distance runners reported yearly and monthly sport participation, data on more specific training volume (ie, training mileage hours/week) were not collected. It has been suggested that increased training volume might be a factor in the increased prevalence of menstrual dysfunction because increased training may contribute to the low energy deficit to menstrual dysfunction pathway.22 Second, menstrual status data relied on self report and did not have associated laboratory measures. Oligomenorrhea is common in the first few years after menarche and can contribute to difficulty determining age-appropriate changes in menstrual function following menarche.42 Two years after reaching menarche, approximately 90% of females attain regular cycles.43,44 Because the mean age of our population was 15.6 years and the onset of menarche occurs at 12.6 years on average, most runners in the study sample should have had regular menstrual cycles unless they truly had a menstrual disturbance. The study's data were deemed reliable30 and our method of reporting menstrual status is commonly used in clinical practice when evaluating exercising girls and women.

Our study used historical data to determine sport specialization status. Thus, we recommend that future studies in this area of study prospectively examine larger populations of high school distance runners using current criteria for sport specialization13,14 to better evaluate its associations to injury risk, menstrual dysfunction, and other important health outcomes. Evaluating other populations by geography may clarify other factors associated with sport specialization (eg, participation in indoor track and field and effects of weather on training variables). Our study included female runners; studies of male runners are needed to understand if similar relationship to injury risk exists and to identify sex-specific differences.

Implications for Clinical Practice

Results from our investigation suggest that highly specialized athletes (those who run more than 8 months a year and exclude other sports) are a population at an elevated risk for running-related injury and menstrual disturbances. Screening for risk factors of running-related injury in highly specialized athletes may be particularly important to reduce risk for running-related injury. Encouraging cross-training and other sports with high direction and multidirectional loading may promote bone health.45 Additionally, screening and managing menstrual dysfunction is important for highly specialized athletes. This includes nutrition evaluation and interventions when appropriate to ensure adequate energy availability.

Further research is required to address sport specialization for high school distance runners. Intervention studies should evaluate how to best mitigate risks for sport specialization in high school runners.45 Evidence-based consensus guidelines are needed for high school athletes, parents, coaches, and sports medicine health care professionals to ensure safe participation in high school running, especially because recent studies indicate sport specialization is growing in the United States.15

In this prospective study, highly specialized athletes were associated with menstrual dysfunction and a greater risk of lower extremity musculoskeletal running-related injuries than moderate or low specialization athletes. Coaches, school administrators, and sports medicine providers need to educate runners and their parents about the increased risk of running-related injury for highly specialized athletes and the importance of screening for menstrual dysfunction. All female high school runners should be screened regularly for menstrual dysfunction, particularly highly specialized athletes in distance running. High school distance runners with menstrual dysfunction should be referred to a physician for an evaluation of medical causes, and may require further evaluation by a registered dietician to ensure adequate energy availability.

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Selected Demographic and Physical Characteristics by Sport Specialization Status

CharacteristicTotal (N = 126)Low (n = 61)aModerate (n = 38)bHigh (n = 27)cP
Demographics (mean ± SD)
  Age (y)15.6 ± 1.315.5 ± 1.115.7 ± 1.315.4 ± 1.3.26d
  Height (cm)164.3 ± 6.2164.1 ± 6.2164.7 ± 6.2163.9 ± 6.1.84d
  Weight (kg)56.3 ± 8.058.3 ± 8.5e55.1 ± 7.853.4 ± 5.9e.02d
  BMI (kg/m2)21.0 ± 2.521.7 ± 2.5f20.7 ± 2.220.0 ± 2.5f.008d
BMI (n, %)
  ≤ 17.59 (7.1%)1(1.6%)3 (7.9%)5 (18.5%).001g
  17.6 to 18.414 (11.1%)2 (3.3%)6 (15.8%)6 (22.2%)
  ≥ 18.5103 (81.8%)58 (95.1%)29 (76.3%)16 (59.3%)
Race (n, %)
  White81 (64.3%)40 (65.6%)24 (63.1%)17 (63.0%).20g
  Hispanic27 (21.4%)14 (23.0%)5 (13.2%)8 (29.6%)
  African American10 (7.9%)4 (6.5%)5 (13.2%)1 (3.7%)
  Asian/Pacific Islander7 (5.6%)3 (4.9%)4 (10.5%)0 (0.0%)
  Other1 (0.8%)0 (0.0%)0 (4.2%)1 (3.7%)
Grade (n, %)
  9th34 (27.0%)19 (31.1%)11 (28.9%)4 (14.8%).52g
  10th36 (28.6%)15 (24.6%)9 (23.7%)12 (44.4%)
  11th29 (23.0%)14 (23.0%)9 (23.7%)6 (22.2%)
  12th27 (21.4%)13 (21.3%)9 (23.7%)5 (18.5%)
Age at menarche (y) (mean ± SD)12.6 ± 1.212.4 ± 1.0e12.6 ± 1.213.2 ± 1.4e.02d
Gynecological age (y) (mean ± SD)h3.0 ± 1.613.2 ± 1.4e3.0 ± 2.02.5 ± 1.5.21d

Relative Risk for Musculoskeletal Lower Extremity RRI by Sport Specialization Status

Sport Specialization StatusNRRI Incidence (%)RR95% CIP
Lowa6136.11.00reference
Moderateb3847.41.310.8 to 2.1.28
Highc2763.01.751.1 to 2.7.02

Incidence and Characteristics of Lower Extremity Musculoskeletal Running-Related Injury (N = 102) by Sport Specialization Status in 57 Injured High School Distance Runners

Running-Related InjuryTotalLowaModeratebHighc
Body location injured
  Lower back1 (1%)1 (2.4%)0 (0.0%)0 (0.0%)
  Hip/pelvis15 (14.7%)6 (14.3%)7 (20.0%)2 (8.0%)
  Thigh3 (2.9%)2 (4.7%)1 (2.9%)0 (0.0%)
  Knee21 (20.6%)7 (16.7%)10 (28.6%)4 (16.0%)
  Lower leg36 (35.2%)12 (28.6%)10 (28.6%)14 (56.0%)
  Ankle13 (12.8%)6 (14.3%)3 (8.6%)4 (16.0%)
  Foot13 (12.8%)8 (19.0%)4 (11.4%)1 (4.0%)
Severity of running-related injuryd
  Minor69 (67.7%)30 (71.4%)25 (71.4%)14 (56.0%)
  Moderate18 (17.6%)7 (16.7%)7 (20.0%)4 (16.0%)
  Major15 (14.7%)5 (11.9%)3 (8.6%)7 (28.0%)
Onset of running-related injury
  Overuse84 (82.4%)33 (78.6%)30 (85.7%)21 (84.0%)
  Acute18 (17.6%)9 (21.4%)5 (14.3%)4 (16.0%)
Subsequent running-related injury
  Reinjury to same body part31 (68.9%)11 (55.0%)12 (70.6%)8 (100.0%)
  Additional new body part14 (31.1%)9 (45.0%)5 (29.4%)0 (0.0%)

Relative Risk of Menstrual Dysfunction by Sport Specialization Status

StatusPrimary AmenorrheaaSecondary AmenorrheabOligomenorrheacMenstrual Dysfunctiond




N (%)RR95% CIN (%)RR95% CIN (%)RR95% CIN (%)RR95% CI
Low (n = 48)e0 (0%)1.00reference2 (4.2%)1.00reference5 (10.4%)1.00reference6 (12.5%)1.00reference
Moderate (n = 32)f0 (0%)0.00NA2 (6.3%)1.500.2 to 10.17 (21.9%)2.100.7 to 6.07 (21.9%)1.750.7 to 4.7
High (n = 25)g2 (8.0%)0.00NA2 (8.0%)1.920.3 to 12.811 (44.0%)4.221.7 to 10.813 (52.0%)4.111.8 to 9.6
Authors

From the Doctor of Physical Therapy Program, School of Exercise and Nutritional Sciences, San Diego State University, San Diego, California (MJR, MDR); the Spaulding Rehabilitation Hospital, Department of Physical Medicine and Rehabilitation, Harvard Medical School, Charlestown, Massachusetts (AST); the Department of Family and Consumer Sciences, California State University, Long Beach, California (MTB); and the Department of Family Medicine and Public Health, University of California–San Diego, La Jolla, California (JFN).

Supported in part by a grant from the National Athletic Trainers' Association Research & Education Foundation and the Graduate Division and Research Affairs, San Diego State University.

The authors have no financial or proprietary interest in the materials presented herein.

The authors thank the high school athletic directors, coaches, athletic trainers, and runners for their cooperation and participation in the study.

Correspondence: Mitchell J. Rauh, PhD, PT, MPH, FACSM, Doctor of Physical Therapy Program, School of Exercise and Nutritional Sciences, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182. E-mail: mrauh@sdsu.edu

Received: May 15, 2018
Accepted: August 22, 2018

10.3928/19425864-20180918-01

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