Nurturing Young Distance Runners

Richard C. Blagrove, Philip E. Kearney and Karla L. Drew

Highlights

• • Young athletes (<16 years old) are frequently pressurised into specialising in distance running from an early age in the belief that this is the best long-term approach to achieve success as a senior athlete.
• • Success as a junior distance runner is a poor indicator of adult potential.
• • Early specialisation in distance running is strongly associated with a high prevalence of overuse injury, drop-out, poor bone health, psychological burnout, overtraining and delayed menarche.
• • The most common pathway to senior success as a runner involves participating in several sports during childhood and teenage years, and specialising in a single sport only during late adolescence (16 years+)
• • Effective long-term development of young athletes should encompass a well-rounded programme of physical activities and sports, including strength training.

Introduction

Recent data from Sport England’s active people survey indicate that childhood participation in athletics and distance running is increasing. Athletics is the sixth most popular sport amongst 11- to 14-year-olds in the UK, and 18% of this age group regularly participate in cross-country or road running (Statists, 2018). Junior parknw also sees approximately twenty thousand 4- to 14-year-olds participating in distance running events around the UK every Sunday morning. Some of these youngsters will enjoy their early experiences of the sport and decide to join their local Athletics Club. Many will subsequently choose to focus their training efforts on reaching the highest level as a senior runner. For junior runners that excel at a young age, research shows that very few transition into successful senior runners, and a high proportion drop out of the sport altogether (Bussmann and Alfermann, 1994; Enoksen, 2011; Shibli and Barrett, 2011).

Nurturing a talented young distance runner into a successful senior is a challenging task. Given the current popularity of the sport and the plethora of long-term health benefits associated with running, it is important that parents, coaches and teachers are aware of the factors and training practices that are likely to lessen the risk of drop-out and maximise the likelihood of young runners achieving their long-term potential. Clearly a genuine passion and involvement in the sport of distance running from a relatively young age is important if an athlete wishes to succeed at the highest level as a senior. However, the timing of specialisation in the sport and the volume of specific running training utilised at various stages of growth and maturation is more controversial.

Growth, Maturation and Development Considerations

The tempo (rate) and timing (chronological age) of biological growth and maturation varies considerably between physiological systems, sexes and individuals. Development is a more general qualitative concept that is behavioural as well as biological (Stratton and Oliver, 2014). Development of physiological systems affects a range of biomotor qualities that have important physical performance consequences; however, development of cognitive (knowledge, problem solving, understanding) and affective (social, relationships) domains are also important for performance, and these factors may mature at different times. During childhood (from age 2 to the start of adolescence), growth and maturation of biological systems are relatively steady and similar between sexes. Adolescence commences at the onset of puberty, which is problematic to define, but typically occurs around 10 years of age in girls and 11 years of age in boys. Changes in the hormonal system during adolescence stimulate the development of secondary sexual characteristics, as well as a rapid change in stature, known as ‘peak height velocity’, or more colloquially, the ‘growth spurt’. The timing of these changes is difficult to predict and assess, however, due to the large inter-individual variability that exists.

Radiographic skeletal age assessment perhaps represents the gold standard in measurement of maturity status, but it is costly, is time-consuming and requires specialist equipment. Sexual age can be assessed by a trained medical professional but is invasive; however, the onset of menstruation (menarche) in girls provides a useful marker of maturation in the reproductive system. Tracking of stature and body mass by taking measurements ever)' three months after childhood offers a cheap strategy to detect when the growth spurt is occurring with reasonable confidence. When this strategy is not practical, several equations that utilise anthropometric ratios have been developed using sitting height and leg length or stature (Mirwald et al., 2002; Moore et al., 2015). The most straightforward of these equations for practitioners to use is shown in Box 19.1 (Moore et al., 2015). This equation is most accurate for circa-pubertal young performers, i.e. boys age 12-14 years and girls age 11-13 years (Koziel and Malina, 2018). When error is accounted for in these somatic estimations of maturity, it is recommended that young athletes are at least 6 months post peak-height velocity before they are considered ‘post- pubertal’. Although these equations provide important insight into biological maturation status, cognitive and affective maturation may not occur in synchrony with physical development; therefore, judgements concerning readiness to engage in higher volumes of training should not be made purely on the basis of the values generated from these equations.

Determinants of Performance in Young Runners

In studies that have assessed the physiological factors that determine performance in young runners, participants have typically been similar for age but may differ markedly in their

BOX 19.1 CALCULATING MATURITY OFFSET (MOORE ET AL., 2015):

Boys = -7.999994 + [0.0036124 x (age x stature)]

Girls = -7.709133 + [0.0042232 x (age x stature)]

Age is measured in decimal years and stature is taken as standing height in centimetres.

Example

For a 13.5-year-old girl who is 168 cm tall.

Maturity offset (years) = -7.709133 + [0.0042232 x (13.5 x 168)] = 1.9 years post peak-height velocity.

maturation status and level of training. This is likely to influence the extent to which physiological parameters correlate with performance measures compared to groups of well-trained adult runners, who generally have similar characteristics with respect to these confounding variables. Moreover, the method used to partition groups of young participants for differences in body size for variables such as maximal oxygen uptake (ИЭ_2|ШХ) and running economy is also likely to influence findings (Eisenmann et al., 2001).

In general, the physiological determinants of performance for adolescents appears to be similar to those of adult runners. A number of investigations have confirmed that ЙЭ₂,_ШХ is a significant predictor (r = 0.5-0.9) of performance for 1500 m (Abe et al., 1998; Almarwaey et al., 2003; Blagrove et al., 2019c), 3 km (Abe et al., 1998; Blagrove et al., 2019c; Mahon et al., 1996; Unnithan et al., 1995), 5 km (Abe et al., 1998; Cunningham, 1990) and cross-country (Cole et al., 2006; Fernhall et al., 1996) in young (10—18 years) groups of runners. Running economy (or oxygen uptake at ventilatory threshold or lactate threshold) also appears to be related to middle- (Almarwaey et al., 2003; Blagrove et al., 2019c; Mayers and Gutin, 1979; Unnithan et al., 1995) and long-distance performance (Cole et al., 2006; Fernhall et al., 1996), although this is not always the case (Abe et al., 1998; Cunningham, 1990). The discrepancy in findings in these studies is likely due to the small inter-individual variability in running economy despite differences in running performance compared to other studies. Additionally, speed at K0_2max (Abe et al., 1998; Almarwaey et al., 2003; Blagrove et al., 2019c; Cole et al., 2006; Cunningham, 1990) and fractional utilisation (Mahon et al., 1996; Unnithan et al., 1995) have also been shown to significantly correlate with distance running performance in adolescents.

'Trainability' of Aerobic Capabilities

During running tasks, prepubertal children exhibit poor mechanical efficiency and a high oxygen cost, thus have a lower overall work capacity compared to post-pubertal adolescents and adults (Frost et al., 1997; Moritani et al., 1989). As a result of changes in anatomical, metabolic and thermoregulatory factors during the adolescent growth spurt, efficiency improves, and aerobic exercise performance is enhanced. Despite possessing a lower work capacity compared to adults, surprisingly, children have similar K0_2max values (when scaled for body mass) to young adults (Vinet et al., 2002). Prior to puberty, children have underdeveloped anaerobic metabolic pathways and therefore rely heavily upon energy contribution from oxidative metabolism during exercise. During puberty, when muscle mass increases and anaerobic energy pathways develop, the relative energy contribution from oxidative metabolism decreases (Fleis- chman et al., 2010). It has been speculated that endurance-based training may become more important during early adulthood to offset the reduction brought about during puberty (Ratel and Blazevich, 2017); however, this has not yet been scientifically verified.

The changes that occur in P0_2nux during adolescence are highly complex and are influenced by numerous factors. Appropriate scaling for body mass is one important ongoing area of controversy (Armstrong, 2017). In both sexes during childhood, ЙЭ_2шах increases linearly with age; however, there is a divergence in the rate of improvement after around 8 years of age. Post-puberty, females experience little change in absolute P0_2max values, whereas male scores continue to rise until adulthood. Expressed relative to body mass, differences between sexes are even more pronounced. Once puberty has commenced, P0_2max (mL-kg ' nun ') decreases gradually each year (8—18 years) for females into early adulthood but remains relatively unchanged in males (Armstrong and Barker, 2011).

The extent to which aerobic capabilities are trainable during childhood and adolescence is an area of ongoing debate (McNarry et al., 2014; Armstrong, 2017). Due to the naturally high aerobic capacities possessed by children, compared to adults, it has been suggested that prepubertal children are less adaptable to endurance training or that a ‘maturational threshold’ exists where endurance training starts to become more effective (Mercier et al., 1987; Payne and Morrow, 1993; Rowland, 1985). However, this does not appear to be the case, as a large number of studies have shown that aerobic capabilities and performance can be improved in children, and these improvements are similar in those <11 years and >11 years of age (Armstrong and Barker, 2011; McNarry and Jones, 2014). It is likely that previous speculations around a potential period of enhanced aerobic trainabilitv during adolescence are heavily influenced by methodological limitations, most notably a lack of consideration for baseline fitness in participants. Constraining young athletes to specific types of training during ‘windows of opportunity’ lacks evidence and has potential risks such as overtraining and burnout (McNarry et al., 2014).

A close relationship exists between many measures of physical performance and maturity; therefore, during early adolescence, the runners labelled as the most ‘talented’ are usually the most biologically mature, despite being of the same chronological age as the rest of their comparator group. This is almost certainly the case with young male distance runners who excel within their peer group between the ages of 11 and 15 years (under-13 and under-15 age groups; Kearney et al., 2018). The increase in androgenic hormones during early puberty provides natural increases in explosive power, sprint speed and anaerobic capacity, as well as the aforementioned changes to aerobic capabilities. A more physically mature adolescent competing against a field of largely less-developed boys, despite being of the same chronological age, will therefore possess a significant advantage during a race. Performance during early- adolescent years is typically a poor predictor of a young runner’s future potential (see the next section). Thus, maturation status should be considered, and the importance of psychosocial behaviours should not be overlooked.

It may also be the case that over longer distances (i.e. cross-country), the best female runners in younger age groups (under-15) are late-developers with less mature physical features. Distance runners are typically lighter and have lower body fat than swimmers and other track and field athletes (Housch et al., 1984). The physically under-developed appearance of many high-performing adolescent female distance runners suggests they may excel due to their physically immature musculoskeletal structure. A narrower pelvic girdle, lower body fat percentage and lighter mass are all likely to provide a benefit to physiological qualities such as maximal oxygen uptake and running economy (Anderson, 1996). Late maturation of the female reproductive system (i.e. delayed menarche) could be a natural occurrence (Malina, 1994) but could also be caused by insufficient energy' intake and/or excessive training.

Early Sport Specialisation

It is understandable how a coach or parent seeking to maximise a young athlete’s performance potential might encourage intensive training in a single sport on a year-round basis from an early age (i.e., early specialisation). For this reason, young athletes are sometimes pressured into focusing their training on a single sport at a young age from their club or school coaches, fervent parents or to obtain a collegiate athletic scholarship (Bell et ah, 2018; Brooks et ah, 2018; Gould et ah, 2009; Post et ah, 2018). For example, a survey of parents and coaches involved in track and field within the United Kingdom revealed that 29% of parents and 7% of coaches advocated that athletes should train year-round at 12 years of age (Kearney et ah, 2020). Furthermore, 31% of parents and 8% of coaches advocated athletes specialising in in track and field by 14 years of age, while 28% of parents and 13% of coaches advocated specialising in a single athletic discipline by 14 years of age (Kearney et ah, 2020). There are several well-publicised accounts of highly successful runners who report training very' hard during their early adolescent years and who competed exclusively in the sport (Denison, 2004; Miller, 1981; Tjelta, 2019), which naturally inspires youth runners and their parents/coaches to copy this approach. Extreme examples can be found at the opposite end of the spectrum too, such as Australian athlete Sinead Divers, who started running aged 33, and at the time of writing holds the IAAF over-40s 10,000 m world record and is ranked 19th in the world over the marathon. Flowever, these stories are the exceptions (Bahensky, 2019), and the most common pathway to senior success involves participating in several sports during the childhood and teenage years and specialising only during late adolescence (Bergeron et al., 2015; Gullich, 2018; Huxley et al., 2017).

Arguments for early specialisation are typically based on economic reasons; as organisations have limited resources (e.g., limited places on development squads), then athletes who are performing at a higher level relative to their peers will have an advantage in gaining access to those resources (Ericsson et al., 1993). However, middle-distance runners ty'pically peak during a 2.5- to 3-y'ear window centred around age 25 years for men and 27 years for women (Haugen et al., 2018; Hollings et al., 2014), with marathon runners peaking slightly later (~28-29 y'ears; Haugen et al., 2018). Thus, there is plenty of time for an individual to develop without engaging in intensive training during early adolescence. Furthermore, early engagement in intensive training brings considerable risks (Blagrove et al., 2017; Myer et al., 2011). For example, Huxley et al. (2014) tracked the training profiles and injuries of Australian track and field athletes who were members of a regional emerging talent squad. Athletes who suffered a serious injury (defined as time off training > 3 weeks) had trained at a higher

296 Richard C. Blagrove et al.

intensity and had a greater yearly training load at age 13-14 years, and reported more high- intensity training sessions at age 13-14 and 15-16 years than their uninjured peers. 17.3% of athletes in the sample had to retire due to injuries prior to turning 18 years. These results clearly highlight the dangers inherent in engaging in adult-like training practices too early in a young runner’s development.

The value in adopting a ‘slow and steady’ approach to athlete development is further supported by research examining the relationship between performances at differing age grades in youth track and field. Kearney and Hayes (2018) identified all athletes ranked in the top 20 of youth track and field in the United Kingdom between 2005 and 2015 and examined the extent to which athletes retained their top ranking in subsequent age grades. The results for middle-distance runners are given in Table 19.1. The table clearly shows that only a minority of top performing 12- and 14-year-olds retain their top-ranked status by Under 20 (male, 9.3%; female, 14.8%). Even between the two oldest age categories examined, only 40% of athletes who were top ranked at U17 retained their top 20 ranking at U20. The dropout from athletics amongst these high-performing individuals is also stark; for example, at most 50% of Under 15 middle distance runners who were ranked in the Top 20 were still competing as 19-year-olds (see also Shibli and Barrett, 2011).

While Kearney and Hayes (2018) primarily focused on the relationship between performances at different stages of youth development, other researchers have further examined the relationship between youth and senior success. For example, Bahensky (2019) investigated historical data on female distance runners from the Czech Republic. The majority of the best female distance runners in the U16 (85%) and U18 (65%) age grades ran their personal best before the age of 20. Athletes who were successful from U16 through to adulthood were rare exceptions. In an investigation of Spanish middle- and long-distance runners, Latorre-Roman et al. (2018) reported that of270 individuals ranked in the top 10 in long- or middle-distance events as a Cadet (U15), Youth (U17) and Junior (U20) in 2004, only 12 (10 male, 2 female) were also listed as top 10 seniors in 2014. Similarly, Weippert et al. (2020) analysed individual performance trajectories of German international-level middle-distance runners from the age of 14 until their top performance. Forty percent of male middle-distance runners who would progress to represent Germany internationally as seniors had not run fast enough at age 16 to meet the national association standard to earmark them as having potential for the future; this

TABLE 19.1 Tlie extent to which athletes ranked in the top 20 at an age grade (a) remain participating in athletics and (b) retain their top 20 ranking across age grades

Note: N = number of athletes ranked in the top 20 identified within the sample.

group included a future Olympic champion. In contrast to the male athletes, and to the results from both Bahensky (2019) and Latorre-Roman et al. (2018), only two runners out of the 32 cases examined from the female sample had not reach the standard set for 16-year-olds. Taken together, these results for distance runners are consistent with investigations of a broader range of track and field events (e.g., Foss et al., 2019; Kearney and Hayes, 2018) and clearly illustrate that youth success is a poor indicator of adult potential.

Rather than focusing on performances, other research has investigated the practice activities undertaken by successful track and field athletes using a variety of survey and interview-based approaches (Giillich, 2018; Huxley et al., 2017; Huxley et al., 2018). Giillich (2018) matched pairs of athletes from German national squads based on sex, discipline (including middle- distance events) and baseline performance in competitions when they were aged either 13 (junior sample) or 19 years (senior sample). Participants completed a detailed survey on the types of activities engaged in across all sports and all ages. Their unequal subsequent performance development during junior (13-17 years; n = 138) and senior (19-23+ years; n = 80) age ranges defined ‘strong responders’ and ‘weak responders’. Junior-age strong responders were found to have accumulated more organised practice in athletics than weak responders (e.g., age 14-15 years, weak responders had 636 hours organized athletics training versus 792 hours for strong responders; age 16-17 years, 946 for weak responders and 1194 for strong responders), while there were no differences between the groups in the amounts of all other types of activities or starting ages. That is, early investment in athletics training can facilitate junior success. However, the results were very different when senior performances were examined. In contrast to those who responded favourably to training up to age 17, senior-age strong responders did not accumulate a greater amount of organised or nonorganized practice in athletics. However, they had engaged in more organised practice and competitions in other sports over more years (9 vs. 2 years) and specialised in athletics at a later age than weak responders (16 vs. 11 years). Thus, rather than specialising in athletics, it appears that the interplay of childhood/adolescent practice in other sports alongside gradually increasing practice in athletics maximises an athlete’s potential for long-term performance improvement into adulthood.

These results from Giillich (2018) are consistent with research by Huxley and colleagues (Huxley et al., 2017, 2018) on Australian Olympic and World Championships track and field athletes. These studies reported that while many participants were involved in track and field from a young age, the majority were late specialisers. These high-performing athletes were not ready to fully invest in intense training in a single discipline until late adolescence (on average, 17.7 years old). Interviews with 14 elite Australian junior track and field athletes who had successfully transitioned into elite senior careers revealed that parents’ understanding that some athletes were not ready to specialise before 16 years of age, and in some cases even by age 18-19, was particularly important (Huxley et al., 2018). This delay enabled athletes to make a full commitment when they were physically, mentally and socially ready, rather than giving up because of pressure, expectations and unsupportive behaviours by parents and coaches (see also MacPhail and Kirk, 2006). In relation to middle-distance running in particular, Tjelta’s (2019) account of three brothers who all won European Championships over 1500 m illustrates the diverse and individual nature of pathways to expertise; while one brother (the youngest) specialised in distance running at 12 years of age, Tjelta (2019) reports that the others participated in football and cross-country skiing throughout their adolescence. Thus, in addition to an openness to engage with other sporting activities, it is important to recognise that there is considerable variability in the pathways to specialisation undertaken by high- performance athletes.

Relatively little research has focused on the specific training activities undertaken by successful distance runners during their development. In a comparison of elite standard long-distance runners from Kenya and Spain, and national standard Spanish athletes, Casado et al. (2019a) showed no evidence that starting systematic training at a younger age was advantageous. Furthermore, elite and national standard distance runners showed no differences in the accumulated distance in tempo runs, long interval training or short interval training. Indeed, the only variable that consistently differentiated elite and national standard Spanish runners was accumulated distance in easy runs. These findings are relatively consistent with those of Young and Salmela (2010), who found no differences between Canadian national, provincial and club level runners in terms of the average age at which they began running (National: 12.9 ± 2.4 years; Provincial: 11.5 ± 2.4 years; Club: 11.5 ± 2.9 years), or the average age at which they began year-round full-time training (National: 16.1 ±1.9 years; Provincial: 14.8 ±1.8 years; Club: 16.3 ± 2.4 years). Similarly, national, provincial and club athletes did not differ in terms of the total volume of training that they had accumulated, or the volume of distance-specific training (e.g., interval training). However, national runners could be distinguished from the other groups on the basis of the amount of weight training and technique-focused practice that they had accumulated at various points in their development. Thus it appears that coaches wishing to ensuring effective long-term development of their charges should emphasise training practices that supplement endurance development (e.g., technique, weight training, easy runs) rather than intensive race-specific training that produces short-term benefits at the cost of longterm risk (Giillich, 2018; Huxley et al., 2014).

Psychosocial Factors

Drew (2020) qualitatively explored the psychosocial factors associated with the junior-to- senior transition in the context of British track and field athletes. Figure 19.1 outlines the internal and external factors athletes perceived to impact their transition and compares the findings from those who experienced a successful transition outcome to those who did not.

The results from the study demonstrate that the process of transition from junior to senior level is unique to each athlete and involves various factors that have the potential to aid or hinder athletes’ progress. Athletes perceived that the transition is an ever-changing dynamic process and the factors associated with the transition are not fixed, with some factors becoming more salient than others at various points of the transition, and vice versa. Consistent with existing literature, the study highlights a number of psychosocial factors that can facilitate the junior-to-senior transition (e.g., patience, understanding of the transition process, sport- specific knowledge; Mills et al., 2012; Pummell and Lavallee, 2019), in addition to a number of debilitative factors (e.g., increase in pressure, injuries, over-trained as a junior/burnout; Jones et al., 2014; Pummell et al., 2008). For example, athletes believed it was important to view the transition as a long-term process and perceived patience to be a crucial psychological resource during the transition period. As one 1500 m Olympic finalist reflected, “I didn’t over-train as a young athlete. I didn’t try and do too much too soon, I was patient”. Furthermore, the study highlighted the complex nature of the transition as the factors perceived to influence the transition vary amongst individuals. For example, a factor that one athlete perceives as particularly challenging (e.g., increase in pressure to perform) may not be identified by another athlete or may even be perceived as a motivator to the transition.

FIGURE 19.1 Individual and external factors perceived to impact the junior-to-senior transition in British track-and-field athletes

Source: Drew (2020).

Early specialisation in a single sport is often characterised by high volumes of physical training that over a prolonged period can cause serious health consequences. These issues are also likely to contribute to the high drop-out rates observed during late-adolescence (Enoksen, 2011; Konittinen et al., 2013; Shibli and Barrett, 2011). It is probable that an optimal volume of sport-specific training exists for each individual performer at various stages of their development, which provides sufficient overload to adequately prepare musculoskeletal structures and physiological systems for higher volumes of specific training in the future, but does not expose the individual to high levels of risk. These risks can be summarised as follows (Blagrove et al., 2017; Myer et al., 2015; Cote et al., 2009).

Relative Energy Deficiency in Sport (RED-S)

The RED-S syndrome describes a range of negative physiological and psychological symptoms that affect metabolism, reproductive function, bone health, immunity, protein synthesis and cardiovascular health as a consequence of chronic low energy availability (Mountjoy et al., 2014). When intensive training regimens are combined with insufficient energy intake and recovery to support the exercise being undertaken, young athletes are at risk of developing RED-S (Hoch et al., 2009). Athletes who specialise in disciplines that demand high levels of leanness and endurance, such as distance running events, are particularly vulnerable (Nichols et al., 2006). Several important consequences associated with developing RED-S at a young age are summarised in the following and discussed in detail in Chapter 18.

Menstrual Cycle Dysfunction

The menstrual cycle is highly sensitive to physiological stress; therefore, female athletes engaged in intensive physical training programs are susceptible to developing menstrual cycle dysfunctions. High amounts of physical training and lifestyle stress can cause a negative energy' balance, which first affects the female reproductive system as it is non-vital for survival (Horn et al., 2014). Primary amenorrhea is the absence of menstrual cycles at age 15 despite normal growth and signs of secondary sexual characteristics. A lack of menarche 3 years after initial development of secondary' sexual characteristics, or no sign of these characteristics by the age of 14, is also a cause for concern (Weiss Kelly et al., 2016). Secondary amenorrhea is the absence of menses for more than 3 consecutive months or 6 months in females who have previously had regular menses. Oligomenorrhea is defined as menstrual cycles that occur >35 day's apart (Horn et al., 2014). For active girls, the timing of menarche relative to peak height velocity is generally similar to non-athletic girls (Geithner et al., 1998). However, there is a high prevalence of menstrual dysfunctions during adolescence, particularly in athletes involved in intensive sports training (Hoch et al., 2009).

Poor Bone Health

The female sex hormone oestrogen, which contributes to regulating the menstrual cycle, play's an important role in bone formation. It is therefore unsurprising that adolescent athletes who present with amenorrhea possess significantly lower bone mineral density compared to eumenorrheic (regular menses) young athletes and non-athletic controls (Barrack et al., 2008). A relationship between age at menarche and likelihood of stress fractures has also been reported (Bennell et al., 1996b). This is particularly worrying, as adolescence represents an important window of opportunity for formation of bone density. By adulthood, approximately 90% of bone mass has been accrued (Sabatier et al., 1996); therefore, young female athletes who experience primary amenorrhea and fail to maximise bone mass during their development years are unlikely to compensate at a later age, even following resumption of menses (Baxter-Jones et al., 2011). A low bone mineral density increases the risk of stress fracture injuries, but also osteoporosis and sustaining fractures from falls in later life.

Overuse Injury

Early specialisation and maturation status have both been identified as independent risk factors for overuse injury in young athletes (Myer et al., 2015). High volumes of training are generally associated with a higher risk of injury in adolescent athletes (Emery, 2003; Maffulli et al., 2005), particularly those who participate in a single sport, as opposed to a range of sports (Hall et al., 2015; Jayanthi et al., 2015). During adolescence, the connective tissues, muscles and bones develop in a non-linear manner and are not fully developed until late adolescence. Following the adolescent growth spurt, there is often a lag in the development of the neuromuscular system, which can affect strength and coordination (Quatman-Yates et al., 2012). Rapid changes in stature, strength and limb lengths can contribute to poor movement patterns, and inappropriate attenuation of forces may exacerbate risk of injury when combined with high-volume regimens of physical work (Hawkins and Metheny, 2001). Moreover, female athletes with menstrual cycle abnormalities are also three times more likely to sustain a musculoskeletal injury compared to eumenorrheic adolescents (Barrack et al., 2014; Rauh et al., 2010). Although the association between menstrual disturbances and injury is not causative, a low energy state alters the profile of thyroid and stress hormones, which directly affects bone metabolism and the health of muscle and connective tissue (Lindholm et al., 1995; Loucks et al., 1989).

Mental Health Issues

A decision to specialise and compete year-round in a single sport brings an inevitable pressure to achieve pre-determined goals and continually progress. This pressure is often further compounded by the pressures placed on young athletes by coaches and parents. Chronic exposures to highly stressful and professionalised sporting environments at a young age are unlikely to be effective at nurturing talented performers into future elite athletes (Moesch et al., 2011; Waldron et al., 2019). Intrinsic motivation factors, such as enjoyment of practice, are most important in retaining young athletes and achieving long-term ambitions (Le Bars et al., 2009). Appropriate psychological challenges during an athlete’s development stimulate a positive response to promote long-term attainment of goals (Collins et al., 2016). However, excessive psychological overload resulting from unrealistic expectations can be detrimental, causing depression, anxiety and ultimately burnout (Waldron et al., 2019). From a psychosocial perspective, concern has also been raised that placing high training demands on a young athlete limits their opportunity to develop a normal, multifaceted identity (Coakley, 1992). Young athletes who specialise in a single sport report they become consumed by their training and feel a sense of isolation (Coakley, 1992). When fitted around school timetables, intensive training programmes severely restrict the time young athletes can dedicate to other activities. Therefore, young athletes develop a unidimensional identity and feel defined by their sport, which can lead to stress and anxiety if they fail to reach their goals.

Overtraining

Overtraining is caused by an accumulation of training and non-training stress, which results in chronic under-performance, taking several weeks or months to recover from (Meeusen et al., 2013). Approximately one-third of competitive athletes (13-18 years) across a range of sports in various countries have suffered from overtraining-related symptoms or burnout at least once (Gustafsson et al., 2007; Matos et al., 2011; Raglin et al., 2000). Overtraining is characterised by a plethora of signs and symptoms, which are derived from several different physiological systems including: increased perception of effort during exercise, frequent upper respiratory tract infections, sleep disruption, excessive muscular fatigue and a loss of appetite. Many of these symptoms are also likely to impact other aspects of a young athlete’s lifestyle, including their academic work and social life.

Limited Skills and Experiences

Early sport-specialisation, particularly in activities involving repetitive actions like distance running, limits the acquisition of a wide range of motor skills. This may seem beneficial in the short term, for the child athlete aspiring to greatness in their chosen event; however, it drastically limits opportunities to participate in other sports, which the performer may enjoy or excel in (Stodden et al., 2013). Equally, a reduction in motor skills could adversely affect lifelong participation in physical activity as the athlete feels limited to the sport they have always competed in. Furthermore, participation in a single sport limits the opportunities for human interaction in other social spheres (Coakley, 1992). It has been hypothesised that these lost opportunities for development of a diverse range of sports skills may in part contribute to the current high levels of physical inactivity and obesity in adulthood (Mostafavifar et al., 2013).

Long-Term Development of Youth Athletes

Unlike many game sports in European and Western countries, high-performing young distance runners are rarely placed into highly structured talent development systems that are controlled by professional clubs or governing bodies. In many respects this is likely to provide several advantages, such as less pressure to travel and compete, and a greater flexibility to participate in other sports at a young age. However, a lack of specialist support in this scenario can also mean that guidance on training and competition schedules at various stages of a young athlete’s development is left to parents and inexperienced club coaches.

Contemporary approaches to long-term athlete development suggest children and adolescents should avoid training routines that focus on intensive training in a single sport (for >8 months per year), or a total weekly training volume which exceeds the athlete’s age in years, until late adolescence (Lloyd and Oliver, 2012; Myer et al., 2016). Figure 19.2 provides a visual representation of a long-term development model for a youth athlete. The pie charts on the right-hand side of Figure 19.2 represent a theoretical distribution of activities for a

FIGURE 19.2 Suggested performance pyramid and model for long-term development of a youth performer who displays talent and/or motivation to succeed as a distance runner. The width of the pyramid represents the number of sports/activities that the performer should aim to participate in. The pie charts represent a theoretical example from three different time points (~8, ~13, ~17 years old) of a young athletes development to illustrate how various physical activities and sports could be distributed

fictional young athlete who displays talent and/or a high level of motivation for distance running during their development. Whilst some degree of sport specialisation is necessary during adolescence to reach elite status, the timing of single-sport specialisation is more contentious. Evidence across a range of sports shows elite senior athletes tend to specialise at a later age and to participate in a diverse range of sports during their childhood (Cote et al., 2009; Moesch et al., 2011). Young athletes who adopt an early-diversification, late-specialisation approach to their development have fewer injuries, are at less risk of overtraining and play sports longer than those who specialise in one sport before puberty (Brenner and Council of Sports Medicine and Fitness, 2016; DiFiori et al., 2014). A recent reconceptualised approach to the idea of sampling before late adolescence, is a domain-specific approach termed ‘specialised diversification’ (Cote and Erickson, 2015). Using this method, it is recommended that a young performer who enjoys participating in endurance-based sports could specialise in this sport-specific domain, and sample through different experiences within this domain during adolescence. For example, a young athlete who enjoys and excels in distance running events could participate in cross-country, road and track running, swimming, cycling and orienteering. Emphasis should remain on free play and sampling of activities within these contexts, rather than high volumes of deliberate practice and structured training.

Strength Training for Young Athletes

The long-term health and fitness benefits of participating in a well-rounded programme of physical activities and sports during childhood and adolescence, which promotes physical literacy and develops a breadth of physical qualities, has been recognised by the International Olympic Commitee (Bergeron et al., 2015). A key component of a systematic approach to the development of young athletes is a progressive and well-managed programme of strength training, which enables aspiring young athletes to cope with the rigours of sports training and reach their potential (Faigenbaum et al., 2016; Lloyd et al., 2014). Strength training techniques develop a broad range of physical capacities such as agility, speed, muscular strength, balance, co-ordination, and motor control, which underpin performance across numerous sports and everyday living tasks (Lloyd and Oliver, 2012). Moreover, strength training activities which develop neuromuscular function are likely to offset the risk of injury in youth athletes (DiFiori et al., 2014; Mver et al., 2011), which may reduce drop-out rates and facilitate the transition of talented young performers to an elite level (Myer et al., 2016). Several leading professional organisations and authorities in the area of paediatric exercise science and sports medicine have published statements advocating the inclusion of age- and individual- appropriate strength training activities for young athletes (Behm et al., 2008; Bergeron et al., 2015; Faigenbaum et al., 2016; Granacher et al., 2016; Lloyd et al., 2014, 2016; McCam- bridge and Strieker, 2008; Smith et al., 2014).

A large body of literature exists that demonstrates strength training activities are a safe and effective way of enhancing proxy measures of athletic performance in children and adolescents of both sexes (Behringer et al., 2010, 2011; Blagrove et al., 2020; Harries et al., 2012; Lesinski et al., 2016). Specifically, in post-pubertal adolescents, compared to sport-only training, various forms of strength training augment improvements in muscular strength, explosive power, muscular endurance, sprint speed, agility test time and general motor skills.

The safety of resistance training (i.e. lifting weights) in young athletes has previously been questioned with concerns centred around epiphyseal plate injury and growth abnormalities the most commonly cited (Benton, 1982; Gumbs et al., 1982; Legwold and Kummant, 1982). However, any isolated observations associated with damage to growth cartilage appear to be related to poor lifting technique or inappropriate training volumes. Providing training is supervised and prescribed by a qualified practitioner, the current consensus in the field of pediatric sports medicine indicates that strength training is not inherently harmful and does not pose a risk to epiphyseal plates or normal growth (Lloyd et al., 2014; Milone et al., 2013; Myers et al., 2017). Indeed, prospective investigations that have included appropriate levels of supervision and coaching have demonstrated no increased incidence of physeal-related injury (Ramsay et al., 1990) and overall low injury rates (Lillegard et al., 1997).

Research investigating the impact of strength training techniques on performance-related measures in young athletes has tended to use participants from field-based sports, martial arts, court sports, aquatic sports, gymnastics and strength-based sports (Granacher et al., 2016; Lesinski et al., 2016). Two studies have used middle- or long-distance runners between the ages of 15 and 18 years old (Blagrove et al., 2018b; Mikkola et al., 2007). Mikkola et al. (2007) took a group of trained male and female distance runners (17.3 years, K0_2max: 62.5 ml kg ¹ min ') and, following 8 weeks of heavy- and explosive-strength training, observed improvements in anaerobic capabilities (speed during a maximal anaerobic running test and 30 m sprint time). Similarly, Blagrove and colleagues (2018b) also found significant improvements in sprint speed and a ‘possibly beneficial’ effect on RE following 10 weeks of strength training. Importantly, this study reduced the overall volume of running by around a third (29%) to accommodate the addition of two weekly strength training sessions (Blagrove et al., 2018b). This demonstrates that, at least for a period of several months in this age group, greater gains can be achieved in important determinants of performance when two running sessions per week are replaced with strength training.

Summary

Young athletes represent a vulnerable population, and participation in sport provides an important vehicle to facilitate their physical, social and psychological development. Distance running is becoming increasingly popular amongst adolescents; therefore, coaches, parents, teachers and practitioners have an obligation to ensure the long-term well-being and development of this group. The tempo and timing of growth, development and maturation varies considerably in a group of young athletes of the same chronological age, therefore the runners who excel at a young age tend to be the most physically mature relative to their peer group. Unfortunately, for those athletes who specialise in middle- or long-distance events at a young age (<15 years old), and rank highly in their age group, achieving the same level of success as a senior runner is rare. Specialisation in the sport of distance running at the exclusion of all other sports before the age of 16 years old tends to be associated with a range of negative health implications that result in drop-out during late adolescence. These include overuse injury, poor bone health, psychological burnout, overtraining and delayed menarche. The transition from junior- to senior-level competition should be viewed as a long-term process, and elite senior athletes perceive patience to be a crucial psychological resource. Although there is considerable variability in the routes that high-performing distance runners take to reach an elite status, the most common pathway to senior success involves participating in several sports during childhood and teenage years, and specialising in a single sport only during late adolescence. Adopting an early-diversification, late-specialisation approach to long-term athlete development tends to result in fewer injuries, reduces the risk of overtraining and lowers rates of drop-out compared to those who specialise in one sport before puberty. Strength training also represents a safe and effective form of exercise that young athletes should engage with from an early age to offset the risk of injury as training volume progressively increases.

20