INJURIES IN ELITE YOUTH ATHLETICS
GROWTH AND MATURATION AS POTENTIAL RISK FACTORS
– Written by Eirik Halvorsen Wik & Daniel Martínez Silván, Qatar
Athletics is a global sport with a unique ability to attract athletes from all corners of the world. This is also true at the elite adolescent level where the latest edition of the Youth Olympic Games in Buenos Aires (2018) saw athletes from more than 170 nations competing in the 36 track and field events1. Gold medals were collected by competitors representing 26 different countries covering all geographical regions, from New Zealand in the east (men’s discus throw) to the United States in the west (women’s 100m hurdles) and Argentina in the south (men’s shot put) to Iceland in the north (women’s 200m)2, affirming the wide reach of the sport.
Injuries represent a threat to a young athlete’s performance development, health status and enjoyment of the sport3,4. To ensure maximum availability for training and competition it is therefore important that the athletes themselves, coaches, parents and other support staff are aware of the most relevant injuries and risk factors. In this article we will address two potential risk factors that are unique to adolescents; growth and maturation, explaining the concepts and how they can relate to injuries in athletics.
INJURIES IN YOUTH ATHLETICS
Data from Jacobsson et al5. in Swedish track and field suggest that approximately six out of ten elite youth athletes sustain an injury leading to training modifications over a season, where half of them result in an absence of more than three weeks from normal training and competition. Injuries therefore appear to be a significant problem in youth elite athletics, although the available research is limited. The lack of studies on high level athletes is at least partly due to the difficulties associated with collecting enough injury data in an individual sport where athletes and coaches are geographically spread out with limited access to medical staff.
Boys and girls seem equally prone to sustaining an injury, with slightly lower percentages of injured athletes compared to seniors5(Figure 1a). Detailed injury characteristics are difficult to compare between studies since different classifications are used, yet, data from both Swedish youth5and American high-school6track and field suggest that overuse and chronic injuries represent a high proportion. Inflammatory conditions, strains and sprains are consistently listed among the most common injury types, and the majority are reported in the lower extremities.
In studies of younger age groups, the event-specific element is often neglected even though this reduces the practical relevance for a coach or athlete. Specialized throwers, jumpers and runners are exposed to different movement patterns, training demands and competition formats, which is manifested in the injuries sustained. For example, greater proportions of injuries to the vertebral column and upper extremities have been observed in throwers compared to sprinters, jumpers and distance runners5 (Figure 1b).
GROWTH AND INJURIES
Growth rate and the growth spurt
Most people have witnessed the rapid transformations that can occur “overnight” when a child hits puberty and enters adolescence. For an athlete, that could mean dealing with a body that is suddenly 10 cm taller and 10 kg heavier, with a new set of body proportions, coming off as slower and clumsier. The performance development may be impaired, and progression is slower than expected.
A coach, athlete or parent unaware of these natural changes can be tempted to push even harder to keep up with the improvements of team mates and competitors or make a rash decision to focus on a new event that now seems more appropriate. Sudden changes in training could, however, lead to overuse injuries causing further disruption to the athletic development. Worse again, the lack of progression may lead to the athlete being written off completely and dropping out of the sport.
A phase of rapid growth is a natural part of human development, although individuals experience it at different times and with different rates7. Growth refers to an increase in a physical dimension, either of the whole body or a body part, and is usually quantified using anthropometric measures such as stature (height), body mass (weight) or segment lengths (leg length, trunk height, arm span etc)7. Growth rate is used to describe a change in any of these variables over a given time-period, for example the increase in stature per month7,8.
A steady rate of growth during childhood is typically followed by a period of rapid growth, known as the adolescent growth spurt, starting on average at the age of 8 to 10 years in girls and 10 to 12 years in boys (Figure 2)7,9. The point of maximum growth in stature, referred to as the peak height velocity (PHV), is reached around age 11 to 12 years in girls and 13 to 14 years in boys where mean growth rates are in the area of 7 to 9 cm and 8 to 10 cm per year in girls and boys, respectively7.
It is worth noting that the growth spurt of different body parts and dimensions varies, with maximum growth rates in the lower extremities normally preceding the upper extremities and the spine7. The peak weight velocity (PWV) also lags behind PHV with approximately 0.2 to 0.4 years in boys and 0.3 to 0.9 years in girls7. Although reference samples are not athlete-specific, average population rates are reported around 6 to 9 kg per year for girls and 8 to 10 kg per year in boys7.
Growth rate and risk of injury
Several mechanisms have been suggested to cause an increased risk of injury during rapid growth (Table 1). Rapid skeletal lengthening during PHV has been associated with a transient period of decreased bone mineral density10, which could influence the risk of sustaining fractures11,12. Increased tensile forces on the vulnerable muscle attachments (apophyses) caused by mismatched skeletal and muscular development has also been proposed as a potential mechanism by several researchers11,13,14. This has been explained by muscles being stretched by a lengthening skeleton in combination with longer lever arms, stronger muscles and increased body mass.
Furthermore, rapid and mismatched growth of body segments and tissues has been suggested to affect neuromuscular control, causing a phase of “adolescent awkwardness” where the athlete struggles to adjust to new limb lengths and weight distributions7,13-15. Flexibility is also mentioned as a potential risk factor, although it is unclear whether this is actually related to rapid growth11.
There is some available evidence to support the association between rapid growth and injuries in elite youth football players, with a suggested increased risk during and after PHV14,16-18and when monthly growth exceeds 0.6 cm in stature or 0.3 kg/m2in body mass index19. There are no studies examining this relationship specifically in elite athletics, and it is not certain that findings from other sports transfer to this context, but it does suggest that the growth spurt is something that should be taken into consideration. It should also be mentioned that existing studies on this topic are considered at high risk of bias due to the limited number of athletes followed over time, differences in data collection methods, and a common lack of accounting for confounding factors such as chronological age8.
MATURATION AND INJURIES
Maturity status, timing and tempo
Where growth represents a relatively straight forward and obvious construct, maturation is more ambiguous and complex. Maturation is used to describe a process with a definite endpoint and represents the transition into an adult mature state7. A single assessment of maturation indicates where along the process an athlete is at the given time-point; the athlete’s maturity status8.
The two most common indicators of maturity status are secondary sex characteristics and skeletal (bone) age7,20,21. Secondary sex characteristics, such as stages of pubic hair, breast development and testicular volume are commonly used but are considered invasive in terms of privacy and the accuracy is questioned, especially if using athlete self-assessment20,21. Whether or not an athlete has reached PHV or the first menstruation (menarche) can also be used to group athletes based on maturity status20. Skeletal age in relation to chronological age is, however, considered the gold standard and single-best indicator of maturity status20, where the level of bony maturation in the hand and wrist complex is assessed using x-ray images21.
Maturation progresses at different times (maturity timing) and at different rates (maturity tempo) between individuals7,22(Figure 3), which is why chronological (calendar) age is not a very useful indicator of biological maturity20. Two age-group matched sprinters can be at very different stages in their maturation process, where the athlete in lane 4 can have the resemblance of a fully-grown high-school teenager while the competitor in lane 5 could be closer to the average elementary-school child.
Maturity timing can be assessed using the age at reaching landmark maturational events, such as a specific pubertal stage, PHV or menarche, while maturity tempo is traditionally assessed by regular assessments and the rate at which the individual passes through different maturity stages7,21,22. Typically, the onset of puberty is observed between the age of 8 to 13 years in girls and 9 to 14 years in boys11, highlighting the wide variation in maturity timing between individuals.
The timing and tempo of maturation varies within the same person as well, between tissues and organ systems7,20. The progression of dental maturation can, for example, take a different course than skeletal or sexual maturation20. Within the skeletal system one can also see differences in timing, and as mentioned earlier, the growth spurts of different bones are not matched and generally follow a bottom-to-top sequence7.
Maturation and injury risk
How maturation relates to injury risk is still an open question with many theories, but few answers firmly anchored in the scientific literature. In terms of maturity status, immature structures have been the main concern for musculoskeletal injuries, where the bone, cartilage and apophyses are considered especially vulnerable11,15. These structures are not fully developed and are therefore likely to be the points of failure or irritation when the system is exposed to excessive loads.
The developing brain has been suggested to be more susceptible to concussions15, although this is not a common injury in athletics and is perhaps a larger concern in contact sports. Underdeveloped neuromuscular control is yet another variable that has been considered as a potential risk factor15,23. Cognitive development and behavioral factors such as risk taking and impulsivity are likely implicated15, although these variables are beyond the scope of this article.
The sequential maturation of the skeleton means that an athlete will be susceptible to injuries to certain locations at different ages. In the same athlete, a bone in the foot could be at a different stage of maturation than the bones in the lower leg, pelvis or spine. This again can explain why Sever’s disease, related to irritations of the growth plate in the heel, is a more common complaint in younger athletes than Osgood-Schlatter’s disease, which is related to the growth areas in the upper tibia and the muscles crossing the knee24,25.
Differences between athletes maturing at earlier or later ages raises some questions around performance development and fair play, but is also interesting in terms of injury risk. It may be a more obvious risk factor in contact sports and it is uncertain how it translates into athletics events, although a plausible mechanism would be through the prescription of training. As a coach, you would probably not ask two athletes at 12 and 16 years to follow the same training program or enter them to the same competitions, however, this is in some way what happens when training groups and competitions are mostly based on chronological age and not biological age.
One study on maturation and injuries in athletics was performed in a sports academy in Qatar, comparing late, on-time and early maturing athletes based on their estimated age of PHV26. In this sample, later maturing athletes were more likely to sustain injuries to the foot, ankle and lower leg compared to the on-time and early maturing athletes. Similarly, a study on high-school distance runners in the USA observed that girls reporting a stress fracture had a later menarche than the uninjured athletes27.
The findings in other sports are very inconsistent8, and it is probably too simplistic looking just at overall incidence and single indicators of maturity. In French academy football, maturity associated differences were only apparent when looking at specific injury types, where osteochondral disorders were more common for late and normal maturing players while tendinopathies were more frequent with the early and normal maturing players28. In English academy football, no differences in injury incidence were seen in terms of maturity timing when maturity status was accounted for18, and in an earlier study, the apparently greater injury incidence in early maturing players was not significant when adjusting for training and match exposure, playing position and stature29.
ACCOMMODATING FOR GROWTH AND MATURATION IN ATHLETICS
Growth and maturation are non-modifiable factors and there is little anyone can do to control or affect their progression in healthy well-nourished individuals. Accordingly, increasing awareness and accommodating for the changes the athlete is experiencing is important in order to minimize the effects on performance and injury risk. Insufficient knowledge among coaches and parents on youth-specific training and confusion about how training should be implemented in growing children have been expressed as important contributing factors to overuse injuries in youth track and field30. We have therefore highlighted a few points that the athlete, coach and clinician can keep in mind in the context of youth athletics.
Recommendations for the athlete
As an athlete, patience is important. In individual CGS (centimeters, grams, seconds) sports, performance and progression is very objective and visible during training sessions and competitions. In speed and power events, early maturing athletes have a natural advantage while distance running has been suggested to favor later maturing individuals21. It can be difficult to see your training buddies and competitors outperform you, and it can be tempting to compensate by increasing training loads or changing training focus. Sudden changes can, however, lead to more injuries if not done in a systematic and progressive manner31. If you are unlucky and end up struggling with a growth-related condition, recognizing and addressing the symptoms early is important to minimize the time away from the track.
Recommendations for the coach
As a coach, knowing your athlete and training group is always a key factor for success, and the same is true when it comes to growth and maturation. If you know which athletes are going through the growth spurt and which are maturing early and late you have the opportunity to keep an extra eye out and adjust the training if necessary. Monitoring height on a regular basis (e.g. every three months) doesn’t require much time or equipment and is an easy way to keep track of growth rates.
To counteract negative effects of mismatched size and maturity status, one option is to group athletes based on their biological age (bio-banding) for at least some training sessions or competitions. This can be done based on maturity status (e.g. pre-, circa- and post-PHV) although the actual effect on injuries is unknown and you may want to consider social and psychological implications before trying it out with your athletes32.
Either way, a long-term mindset without placing too much focus on results and comparisons to age-matched athletes can be useful. Be ready to adjust your training plans and short-term goals and remind yourself and the athlete that adolescence may not be the most important time to top the podium. In fact, studies looking at Italian track and field athletes have shown that being a top-level athlete at a young age is not required in order to excel at the senior stage. Only 10-26% of top-level senior sprinters, jumpers and throwers were also top-level when they were 14 to 17 years old33,34.
Recommendation for the clinician
As a clinician, educating the athlete and coach on the normal progression and variations of growth and maturation is important to improve their awareness. Make yourself familiar with the most common injuries you can expect to allow you to recognize and manage them at an early stage. Although growth-related conditions such as Osgood-Schlatter’s disease are considered self-limiting and transient, many adolescents with knee pain display symptoms lasting more than a year and adjusting the training load seems to be the most useful tool to manage the pain35,36.
Depending on the resources and time available, monitoring not only growth rates, but also maturation can be useful. Anthropometric equations estimating the current percentage of predicted mature height or the age of PHV are cost-efficient methods if skeletal age assessments are not available and the use of secondary sex characteristics is not considered appropriate21.
The high proportion of injured athletes in elite adolescent athletics highlights a substantial problem, and even though the scientific evidence is not strong enough to claim direct associations between growth, maturation and injuries, there is reason to believe that these factors play a part in the development of at least certain injury types. The timing and tempo of growth and maturation varies between individuals and monitoring relevant indicators can therefore be useful both for interpreting performance development and for preventing and managing injuries.
Awareness, patience and willingness to adjust training plans and goals can be potential means of accommodating for these phases of an athlete’s life. In the end, reducing the injury problems associated with growth and maturation should be of interest to all involved parties to reduce time off the track and field and maximize the time for unrestricted performance development.
Eirik Halvorsen Wik Ph.D. Candidate
Aspetar Sports Injury and Illness Prevention Programme
Aspetar Orthopaedic and Sports Medicine Hospital
Oslo Sports Trauma Research Center, Department of Sports Medicine
Norwegian School of Sport Sciences
Daniel Martínez Silván P.T.
Aspire Academy Sports Medicine Center
National Sports Medicine Program
Aspetar – Orthopaedic and Sports Medicine Hospital
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