Intrinsic factors

Age

Age is a non-modifiable risk factor for running injury. Several studies have attempted to determine injury rates in runners of different ages and ability levels. From 1994 to 2007, a total of 225 344 children (ages 6–18 years) presented to US emergency departments with running-related injuries. The highest injury rate (45.8 per 100 000 US population) was in runners aged 12–14 years old when compared with other child age groups.4 Interestingly, a study of youth marathon runners (ages 7–17 years old) reported an incidence injury rate of 12.9 per 1000 finishers; half the rate of adult runners in the same race.18

Despite these reported rates, information relating to age and running-related injuries in the youth runner is limited and conflicting. Two prospective studies of HS cross-country runners, ages 13–18 years, showed no difference in the average age between injured and non-injured runners based on overall injury rate (15.6±1.3 years vs 15.6±1.1 years, respectively (p=0.80))19 or the development of medial tibial stress syndrome (15.3±1.0 years vs 15.7±1.5 years, respectively (p>0.05)).20 In contrast, a study of 103 national elite youth runners comparing age groups suggest age and training intensity impacted injury. In this study, injured athletes, compared with non-injured athletes, completed more high-intensity training sessions (self-reported hard or very hard) at age 13–14 years (p<0.01) and 15–16 years (p<0.05), trained at a higher intensity at age 13–14 years (p<0.01), and had a higher yearly training volume (hours) at 13–14 years (p<0.01).21 Age alone does not appear to be a risk factor for injury in adolescent runner based on the equivocal findings of these studies. As previously noted, no studies address developmental stages as a risk factor for injury when comparing prepubescent, pubescent and postpubescent runners.

STATEMENT: To date, there are no consistent data addressing either age or developmental stage as a risk factor for injury among youth runners. (SORT B)

Sex

Sex has been examined as a risk factor for injury in HS cross country and track athletes based on self-report by runners, and/or reporting by coaches and sports medicine professionals. Since 1978, 8 of 14 studies showed a higher incidence of HS cross country running injuries in girls than boys.14 16 17 20 22–31Five prospective studies examining running injury per athletic exposures (AEs) during practice or competition found girls had higher injury rates than boys. A 15-year prospective study of 3,233 HS runners reported overall injury rates of 16.7/1000 AEs for girls and 10.9/1000 AEs for boys (rate ratio (RR) 1.5, 95% CI 1.4 to 1.7; p<0.05).25 Another prospective study of 421 HS runners found a similar RR of 1.3 (95% CI 1.0 to 1.6; p<0.045) for overall injuries in girls compared with boys (19.6 vs 15.0 per 1000 AEs).14 A more recent 8-year prospective study reported an RR of 1.96 for girls sustaining a stress fracture compared with boys based on AEs (10.62 vs 5.42 per 100 000 AEs).23

In HS track, most studies since 1981 (7 of 11, 63.6%) demonstrated girls had more injuries than boys.17 22 23 26–30 32–35 Of the four studies that controlled for AEs, girls had higher rates of running related injuries compared with boys.22 23 32 33 In a 6-year longitudinal study of HS track and field athletes, girls had higher overall injury rates (RR 1.37; 95% CI 1.27 to 1.48) and practice injury rates (RR 1.60; 95% CI 1.46 to 1.76) than boys, but injury rates during competition were similar (RR 0.93; 95% CI 0.80 to 1.07).32

Only one study has assessed injury rates by sex in cross country runners and track and field athletes at the middle school (MS) level, typically ages 11–13 years. This 20-year longitudinal study demonstrated higher rates of injury among girl cross-country runners (10.9/1000 AEs) than boys (8.0/1000 AEs) (RR 1.36, 95% CI 1.2 to 1.6; p<0.0001).36 Similarly, girl track and field athletes had greater rates of injury (12.2/1000 AEs) than boys (8.3 per 1000 AEs) (RR 1.46, 95% CI 1.3 to 1.6; p<0.0001).36

Four large prospective longitudinal studies found that girl HS cross-country runners and track and field athletes had greater time loss from participation due to injury than boys in the same sports. Girl cross country runners (RR 2.6; 95% CI 1.0 to 7.5) and track and field athletes (RR 2.6; 95% CI 1.7 to 4.0) were more likely to have a medical disqualifying injury than boys.22 Girl cross country runners had a higher rate of bone stress injuries compared with boys (10.62 vs 5.42 for 100 000 AEs).23 Two studies of HS cross-country runners found that the rate of injuries with ≥15 days of time loss were 1.5–3.2 times higher for girls than boys (p<0.0001).14 25 In summary, these studies strongly suggest that girls are at a greater risk for running related injuries and greater time-lost injuries compared with boys. Future research should explore specific factors that explain this difference and strategies that may help to reduce injury.

STATEMENT: Evidence strongly supports girls are at higher risk for running related injury and greater time loss from injury than boys. (SORT A)

Previous injury

Previous injury is a common risk factor for both reinjury and new injury in sports. Based on cohort studies of competitive HS runners, there is an increased risk for lower extremity injuries for runners with a previous injury versus those without, with a RR ranging from 1.2 to 9.14.14 16 17 24 25A prospective study of 748 competitive HS runners ages 14–18 years (442 girls, 326 boys) reported a history of a prior fracture is associated with a sixfold to sevenfold increased risk for stress fracture for both boys and girls.17 A single season prospective study of 421 runners (186 girls, 235 boys), ages 14–18 years, identified an injury during preseason summer training for girls and a history of any previous running injury for boys, when adjusted for mileage on terrain, as important factors associated with increased risk of in-season injury (RR 1.64, 95% CI 1.04 to 2.61, p<0.05).14 In this study, most injuries (77.6%) were minor with <1 week of time-loss from running. Further research is needed to assess the relationship between preventative interventions based on specific prior injuries and future injury risk in youth runners.

STATEMENT: Evidence strongly supports prior injury as risk factor for future injury in the lower extremity in adolescent runners. (SORT A)

Alignment and strength

Various studies have attempted to assess the impact of alignment, strength and balance on in-season injury in HS runners. Measures of static lower limb alignment including larger Q-angle and leg-length inequality have been identified as risk factors for injury. A study of 393 HS cross country runners ages 14–18 (171 girls, 222 boys) examined the association of an increased Q-angle and actual leg-length inequality with in-season injury. A runner with a Q-angle >20° of valgus alignment had an RR for injury of 1.7 (95% CI 1.2 to 2.4, p<0.05) compared with runners with a lesser Q-angle.37 In the same cohort, boys with an actual leg-length inequality >1.5 cm had over seven times greater risk (RR 7.47, 95% CI 1.5 to 36.9, p=0.05) for a running-related injury compared with boys with an actual leg-length inequality of <0.5 cm.38 These studies suggest that screening for Q-angle and leg-length inequality may identify runners at increased risk for injury. Other studies of cross country runners, ages 13–18 years, have shown that foot type (pronated, neutral or supinated) (right foot: Χ²=1.99, p=0.37; left foot: Χ²=1.13, p=0.57)24 and navicular drop >10 mm (OR 0.9, 95% CI 0.3 to 2.8, p>0.05)16 were not associated with an increased risk for in-season running injury. Additionally, a study of 230 cross country runners ages 15–18 (96 girls, 134 boys) identified increased hip internal rotation angle in girls as a risk factor for medial tibial stress syndrome over 3 years (adjusted OR 0.91; 95% CI 0.85 to 0.99).15

Hip and lower limb muscle weakness patterns have not been consistently shown to contribute to injury risk in youth runners. A prospective study of 68 HS cross country runners ages 13–18 years (47 girls, 20 boys) identified weak hip abductors (p=0.046), knee extensors (p=0.038) and knee flexors (p=0.046) as significant for higher incidence of anterior knee pain, but not shin pain, during the competitive season.39 Conversely, a prospective study of 98 HS runners (45 girls, 54 boys), ages 13–18 years, found greater baseline hip abduction normalised torque percent (OR 5.35; 95% CI 1.46 to 19.53, p<0.01) and abduction-to-adduction normalised torque percent (OR 14.1; 95% CI 0.90 to 221.06, p=0.05) were risk factors for future patellofemoral pain.40 Of note, strength was assessed in the above studies with a maximum volitional isometric effort using a handheld dynamometer.

Considering the uncertainty involving muscle weakness and imbalances as risk factors for injury in young runners,39 40 there are no interventional studies that demonstrate specific strengthening programmes modify injury risk. Exercise-based injury prevention programmes with elements of high intensity neuromuscular training, jumping, plyometrics and balance training can reduce injuries in youth athletes participating in ball sports (eg, basketball, soccer, football, volleyball, handball), but this has not been shown in runners.41–43 Despite the lack of evidence specific to youth running, neuromuscular training that incorporates running-specific functional movements progressing from double-leg to single-leg squats and hops to more demanding plyometrics and multidirection activities would be a reasonable approach to injury reduction in runners.

STATEMENT: Limited evidence supports quadriceps angle >20 degrees, and leg-length inequality (boys>1.5 cm) as risk factors for injury in youth runners. (SORT B)

STATEMENT: Exercise-based programs containing elements of high intensity neuromuscular training, jumping/plyometrics, and balance training may help reduce injury risk in youth runners, but prospective studies are needed. (SORT C)

Bone health and risk for bone stress injury

Youth runners, especially girls, are at risk for bone stress injury as evidenced by cross country runners experiencing the first (girls) and third (boys) highest rates of bone stress injury per AE among US HS athletes, respectively.23 In girls ages 9–15 years followed prospectively for 7 years, an increasing number of hours participating in cross country running was a risk factor for bone stress injury.44 For each year delay in onset of menarche, there was a 34% increase in risk for bone stress injury.44 As previously discussed, girls with a BMI <19 kg/m² have nearly three times greater risk for bone stress injury (HR 2.67, 95% CI 1.11 to 6.41, p=0.01) than those with a BMI >19 kg/m².17 Additional risk factors for bone stress injury include age of menarche >15 years of age, oligo/amenorrhea after menarche, prior fracture and prior participation in gymnastics or dance.17 44 45 While gymnasts often have better than average bone density, the association of gymnastics and bone stress injury in girls is unexpected. Increased risk of bone stress injury may be due to behaviours associated with participation in aesthetic sports or selection bias in prior gymnasts and dancers who choose to run competitively.17 Total impact loading in multisport athletes was suggested as an additional explanation for runners who also participate in dance and/or gymnastics, however, athlete participation in multiple sports at time of injury was not reported. In male adolescent runners, a history of fracture increased the risk for bone stress injury, while participation in basketball, which involves jumping and multidirectional movement, appeared protective for sustaining a stress fracture.17

Bone mineral density (BMD) has been assessed in limited populations of youth runners. For youth participating in weight-bearing sports, such as running, the term ‘low bone density for age’ is defined as a dual energy absorptiometry BMD Z-score ≤ -1.0 in female athletes46 and a similar threshold has been proposed in male athletes.47 Notably, the concept and definition for low BMD has not been evaluated specifically in preadolescent runners and limited studies have evaluated these measures in adolescent runners. Within adolescent runners, BMI (≤17.5 kg/m²) has been associated with increased risk of low bone density for age in both sexes, and estimated body weight below 85% of expected weight has been related to increased risk of low bone density in male runners.47 48 The belief that being thinner leads to faster running performances is associated with elevated risk for impaired bone health.48 In a population of 69 youth athletes (primarily composed of male adolescent runners), additional factors associated with impaired bone health included prior stress fracture, consuming fewer than one serving of dairy product per day and completing on average greater than 30 miles per week of training within the past year.47 Lower BMD in female adolescent runners is associated with menstrual dysfunction, prior bone stress injury, lower lean mass and more than five consecutive seasons of participation in endurance sports.45 48–50 These studies suggest female runners may be at increased risk for bone stress injury due to menstrual dysfunction and low BMI, while male runners are at increased risk of bone stress injury due to prior history of bone injury and low BMI.

STATEMENT: Limited evidence supports primary amenorrhea, BMI <19 kg/m², prior participation in gymnastics or dance, and prior fracture as risk factors for bone stress injury in female adolescent runners. (SORT B)

STATEMENT: Limited evidence supports menstrual dysfunction, low BMI, prior bone stress injury or fracture, and longer participation in endurance running as risk factors for low BMD in female adolescent runners. (SORT B)

STATEMENT: Limited evidence supports prior fracture as a risk factor for bone stress injury in male adolescent runners and participation in basketball may reduce risk for bone stress injury. (SORT B).

STATEMENT: Limited evidence supports low BMI, prior bone stress injury, low dairy intake, running >30 miles per week, and belief that being thinner leads to faster running performances are risk factors for low BMD in male adolescent runners. (Sort B).

Extrinsic factors

Footwear and Footstrike mechanics

Running footwear may influence running mechanics and potentially predispose an athlete to injury. Studies assessing the impact of footwear modifications on injuries in adults have not demonstrated any consistent preventative effects despite 50 years of running shoe development.54–56 One cross-sectional study has investigated the association between habitual footwear use with lower limb injury in 76 active children from the Kalenjin tribe of Kenya.57 Habitually barefoot adolescents were significantly more physically active and had a substantially lower injury prevalence compared with habitually shod adolescents (8% barefoot vs 61% in shod; p=0.01).57 The limited evidence in adolescents has led to speculation that barefoot or minimalist footwear might reduce injury risk, but prospective research assessing the risk of long-term injury is needed to appropriately evaluate this potential risk relationship.

Studies of footstrike mechanics in adolescent runners show conflicting information based on the population studied. Habitually barefoot runners from Kenya (37 males, 34 females, ages 11–17 years) had less dorsiflexion at footstrike and a lower rate of rearfoot striking (RFS) compared with their shod counterparts.58 59 Greater dorsiflexion at footstrike and more RFS patterns were noted when comparing cushioned footwear to minimal footwear or barefoot in preadolescent or adolescent South African and German children during running.60 61 In contrast, a study of 288 South African and 390 German children, age 6–18 years, noted that habitually barefoot children exhibited a higher rate of RFS than those who were habitually shod (p<0.001).62 Interestingly, this higher rate of RFS declined as the habitually barefoot children reached adolescence.60 Thus, inherent footstrike mechanics appear to be influenced by footwear and age; however, there are no reports based on a prospective design available that indicate if inherent footstrike mechanics or interventions to change footstrike mechanics alter the risk of injuries in youth runners.

STATEMENT: There are no prospective data available regarding the impact of footwear on injury risk in youth runners. (SORT C)

STATEMENT: There are no reports available to assess if inherent footstrike mechanics or specific interventions to change footstrike mechanics alter the risk of injury in youth runners. (SORT C)

Does youth running contribute negatively to long-term cardiac health and risk of sudden cardiac death?

Vigorous exercise, including running, results in a myriad of changes in the cardiovascular system that are generally thought to be healthy and adaptive. Though it has been debated as to whether the hearts of children are ‘trainable’ prior to puberty, cardiac enlargement that does not depend on age has been documented in youth athletes.63 More recently, longitudinal data have demonstrated the genesis of cardiac enlargement during endurance exercise training in youth athletes, supporting a temporal relationship between cardiac remodelling and training similar to adult endurance athletes.64–66 There are no reports available that have evaluated whether exercise-induced cardiac remodelling has any impact on the long-term health of youth runners.

Recognition of normal patterns of exercise-induced cardiac adaptation in youth runners is especially important in the context of interpreting the results of preparticipation or clinical cardiac evaluations. The primary goal of such evaluation is to exclude cardiac conditions such as cardiomyopathy, congenital disease or arrhythmia that would increase the risk of sudden cardiac arrest (SCA) and sudden cardiac death (SCD). Available reports suggest that SCD among youth runners is a very rare event. In the Minnesota State HS League, the rate of SCD was 0.24 per 100 000 athlete-years with SCD occurring in four athletes, of which two were male cross country runners.67 A separate investigation in organised youth sports reported 45 sudden deaths (34 of 45 cardiac related) at a rate of 1.83 per 10 million athlete-years.68 The largest number of deaths occurred in boys’ basketball, while only two occurred in cross country and one in track.68 Similarly, a larger multistate prospective registry of HS athletes identified 35 SCA events and 69 SCD events for a rate of SCD of 0.99 per 100 000 athlete-years, with over 88% of events in males and over half in football and basketball players.69 Overall, SCA/SCD events are rare in youth runners.

STATEMENT: Youth athletes may experience exercise-induced cardiac adaptations similar to that seen in adults; more data are needed about the long-term health implications of these findings. (SORT B)

STATEMENT: Rates of SCA/SCD are low in adolescent runners. (SORT B)

Are there evaluation tools to help identify athletes at risk for injury or illness?

The preparticipation physical evaluation (PPE) may help identify risk factors for MSK injury in the youth runner. The PPE fifth edition70 suggests using a functional assessment cascade, including a double leg squat, a single leg squat and a drop box test (to evaluate for neuromuscular control and strength deficits) may decrease the risk of patellofemoral pain syndrome in runners. However, there are currently no reports available that have assessed the effectiveness of this screening cascade for preventing injury in the youth runner.

Several screening tools may be used to assess issues related to energy availability (EA). The PPE fifth edition questionnaire queries for history of eating disorder and special diet strategies, but does not include formal screening for low EA. To improve the reliability of determining EA in youth runners, one should consider adding Female Athlete Triad (Triad) and/or Relative Energy Deficiency in Sports (RED-S) screening questionnaires and incorporate the Triad Return to Play criteria (Triad RTPC) and/or the RED-S clinical assessment tool (RED-S CAT),71 72 which address EA in greater detail in both boys and girls. EA plays an important role in the long-term health and the short-term performance and injury risk of youth runners.72 73 Low EA and associated consequences of Triad/RED-S increase risk for bone stress injury.71 73 Female youth runners with multiple triad risk factors (including BMI <19 kg/m², age of menarche ≥15 years, and prior fracture) are at risk for future bone stress injury.17 Identifying youth runners in higher risk categories can be used to modify training, begin individual sports nutrition education with a dietitian, and assess other medical concerns.

There are a variety of evaluation tools targeted at identifying risk in youth athletes of important medical conditions, such as cardiovascular disease. Though they differ, the cardiovascular section of the PPE fifth Edition, the American Heart Association 14-Point Preparticipation Screening Evaluation74 75 and the Youth Preparticipation Health Evaluation76 focus on medical history, family history and physical examination findings that may be suggestive of occult cardiac conditions for which further risk stratification prior to sports participation is indicated. Adding a 12-lead ECG to the standard cardiovascular history and physical exam may improve the sensitivity and specificity of the PPE74 77 to identify cardiovascular diseases associated with sudden cardiac death in youth runners, although SCA/SCD is very rare in youth runners. If an ECG is included in PPE screening, contemporary guidelines for ECG interpretation in youth athletes should be used.78 79

STATEMENT: The PPE may identify prior injuries in youth runners, but research is needed to assess its effectiveness as a screening tool and ability to affect future outcomes. [SORT C]

STATEMENT: Screening for low EA is important for both male and female youth runners. While additional prospective studies are needed to evaluate their use, screening tools such as the Triad RTPC and/or RED-S CAT are recommended to identify risk factors and address factors including low EA and menstrual dysfunction that may contribute to impaired BMD and risk for injury. [SORT C]

STATEMENT: Youth runners should undergo preparticipation cardiovascular evaluation using the focused history and physical exam based on the AHA-14 question survey or the PPE 5^th edition monograph. The use of additional testing (eg, ECG) should be based on available cardiology expertise and resources or local, national, or sport federation requirements. [SORT C]

Are there any nutritional guidelines for the youth runner?

Nutritional intake for a youth runner should aim to support growth and development, bone health, optimal performance, recovery from activity and enhance injury prevention. Sports nutrition recommendations for youth runners emphasise maintaining adequate carbohydrate, protein, and fat intake to maintain adequate EA for a growing and developing body. Meeting the minimum recommended dietary allowance for essential vitamins and minerals is important for runners’ health, including particular emphasis on iron, calcium, vitamin D, antioxidants and B vitamins. Current nutrition guidelines are based on research in young adult athletes,80 thus dietitians working with youth runners should consider each athlete’s stage of development and activity level when providing recommendations.

Studies investigating nutritional intake suggest that youth runners often do not meet their energy needs placing them at risk for low EA. Female HS runners report daily intakes ranging from 2000 to 2300 kcals compared with estimated daily requirements of approximately 2500–2800 kcal.81–85 Male youth runners’ calorie needs range from 3100 to 3600 kcal/day.85 86 Preliminary studies also indicate that runners may underconsume key vitamins and minerals.81 83 84

To promote adequate EA and intake of essential nutrients, youth runners should consume a variety of nutrient-rich whole foods during their regular daily meals and snacks (table 4). Youth runners without other medical conditions or gut malabsorption syndromes are likely to meet most primary nutrient needs through normal dietary intake. There is a potential role for vitamin D supplementation based on sun exposure, latitude, and time of year, and iron supplementation in runners who do not consume red meat, experience fatigue with associated low iron status, or have excessive blood loss, such as from heavy menstruation.80

STATEMENT: Youth runners of both sexes require adequate EA to promote optimal sports performance and support growth. As specific EA requirements for individual runners vary and that specific thresholds for adequate EA to support health and performance in this population are unknown, prospective studies are needed to determine appropriate and safe requirements for EA in youth runners. (SORT C)

STATEMENT: In youth runners, meeting recommended intake levels of micronutrients, including calcium and vitamin D, paired with adequate EA, may promote optimal bone health and reduce risk of bone stress injury. (SORT C)

What is the role of free play in running?

Free play promotes physical activity, movement and creativity, and cultivates friendships and socialisation.87 For preadolescent children, play improves energy balance and evolution suggests that the brain will naturally reinforce behaviours like regular vigorous activity that improve brain and body health.87 88 Vigorous-free play is better for developing motor skills in children and naturally develops endurance with the stop-start, often high intensity, activities that children pursue when given the opportunity.89

As part of free play, preadolescent children participate in many running-based games with added health benefits. A systematic review of fundamental movement skill competencies in preadolescent children and adolescents showed a positive association between locomotor (eg, running and hopping), manipulative or object control (eg, catching and throwing), stability (eg, balancing and twisting) skills and cardiorespiratory fitness and an inverse relationship with weight status.90 In a school-based physical activity programme (cluster randomised controlled trial of fifth grade students), adding two additional physical activity sessions a week for 9 months improved cardiorespiratory fitness and reduced adiposity.91 These findings support guidelines that suggest each child should accumulate 60 min or more of physical activity daily.92 93

STATEMENT: Free play outside of the sport of running should be encouraged for the overall growth and development of pre-adolescent runners. (SORT C)

What are specific recommendations for age-appropriate distances to compete in youth running?

Evidence-based guidelines for age to start participating in the sport of running on the track, on road, or off road, when to start running in competition, and distances for training and competition are lacking. Proposed recommendations for total distance and training volume for preadolescent runners are based on opinions of coaches and health professionals.94–96 A survey of 132 cross-country coaches suggested race organisers offer races of 1.5 km (1 mile) or less for early-elementary aged children, 1.5–3 km (1–2 miles) for upper-elementary aged participants, and restrict participation in the marathon distance to runners 18 years and older.94 Most coaches agreed the 5 km distance was appropriate for those 12 years and older.94 Other opinion recommendations suggest that children ages 5–6 years should be limited to 800 m ‘races’ and ages 7–11 years should be limited to 1600 m races, despite the lack of any supporting evidence.95 While these recommendations may be reasonable, there are no outcomes data to support specific distances or training recommendations for youth runners. Future research should attempt to address the issue of youth running distances and risk of injury to develop age appropriate evidence-based guidelines for distance and training recommendations.

There are child-specific running programmes associated with national running clubs, including the Boston Athletic Association, New York Road Runners, Twin Cities in Motion, and Students Run Los Angeles (SRLA) that have attempted to address the risk of injury in youth runners. A retrospective study of 310 runners, ages 7–17 years, who participated in the Twin Cities Marathon (1982–2007) during various temperatures (wet bulb globe temperature range from −4°C to 22°C), reported that only four of the youth runners required finish-area medical assistance for minor medical issues (representing half the rate of medical encounters for adult finishers).18 Of the 42 328 youth runners who finished the Twin Cities in Motion road races (2011–2018), only one 15-year-old boy experienced exertional heat stroke on a hot day when several adults also experienced exertional heat stroke (Roberts WO Unpublished data 2019).

SRLA (established in 1989) is a school-based 7-month marathon training programme that prepares ‘socioeconomically at risk’ children ages 12–18 years to run the LA Marathon. Through 2018, more than 66 000 MS and HS students have completed the marathon with no reports of serious injury or death.97 Prospective data on 2308 students (roughly 50% girls) over two separate seasons (2016–2017 and 2017–2018) indicated that 20% of runners reported pain at some point during the training programme, mostly involving the knee, foot and ankle regions. However, 99% of the participants who started on race day completed the marathon without serious injury.98 These findings suggest that with a supervised training programme, youth participating in distance running events such as marathons may be at low risk for significant injury or developmental delay during training and competition. Children participating in these running events should be prepared both physically (injury-free) and mentally (internally motivated and not pushed by parents or coaches), potentially lowering the risk of injury and burnout.

STATEMENT: There are no studies to support specific distances or training recommendations for youth runners to prevent injury or guide normal growth and development. (SORT C)

STATEMENT: Early evidence suggests that youth runners physically and mentally prepared through a supervised training program can participate in long distance events but may be at low risk of running-related injury. (SORT C)

Should children specialise in running and what is an appropriate age?

Overuse injury and burn-out related to early sport specialisation are current areas of interest in sports medicine.89 99 100 Several studies of youth athletes, not specific to runners, identify sport specialisation as an independent risk factor for injury.101–105 Youth athletes who played their primary sport more than 8 months per year had more overuse injuries in upper (OR 1.68; 95% CI 1.06 to 2.80, p=0.04) and lower extremities (OR 1.66; 95% CI 1.22 to 2.30, p=0.001).105 Youth athletes who participated in their primary sport more hours per week than their age in years had more injuries of any type (OR 1.34; 95% CI 1.12 to 1.61, p=0.001) and were more likely to have a history of overuse injuries if training volume exceeded recommendations for age.105 Based on these findings, many organisations advocate sport sampling and diversification for youth athletes.99 100

There are limited data to answer questions about safety and appropriateness of specialisation in running at young ages. A case–control survey of 989 girls and 1022 boys age 12–18 years (5.6% of the cohort participating in track and cross country) found high specialisation athletes compared with low specialisation athletes had more previous injuries of any kind (OR 1.59; 95% CI 1.26 to 2.02, p<0.001) and more overuse injuries (OR 1.45; 95% CI 1.07 to 1.99, p=0.011).105 A 1-year observational study of 126 female HS cross country and distance track (≥1600 m) athletes found an increased risk of injury in high specialisation runners (RR 1.75, 95% CI 1.1 to 2.7, p=0.02) compared with low specialisation runners. There was a disproportionate increase in lower leg injuries, severe injuries and recurrent injuries among highly specialised youth runners.106 In contrast, while a prospective study of 62 HS track and cross country runners observed an elevated risk of lower extremities injury in high specialisation compared with low specialisation athletes, the risk estimate was not statistically significant.103 Runners who participated only in SRLA over the course of the 2018–2019 season (N=1469, 49% male, 51% female) had similar injury rates (1.19 per 1000 person-miles) as those that participated in field and court sports (1.54 per 1000 person-miles) over the course of the 2018–2019 marathon training season (p=0.17, bivariate analysis).107

STATEMENT: There is limited evidence to support sport specialization as a risk factor for lower extremity overuse injury in HS cross country and distance track athletes. (SORT B)

STATEMENT: No evidence is available to define an appropriate age to start specialization in running or to suggest that specialization in running improves athletic performance. (SORT C)