Early Sport Specialization and Intense Training in Junior Tennis Players: A Sport-Specific Review

Abstract

Context:

Early sports participation can provide significant physical, psychosocial, and mental benefits for young athletes. Sports engagement can be via sport sampling or sport specialization. Sport specialization is often encouraged by parents and coaches as it is perceived as a mechanism for achieving elite level play, particularly in tennis.

Evidence Acquisition:

A search on PubMed, Google Scholar, and Science Direct was conducted for pertinent peer-reviewed studies on sport specialization and overuse injuries in youth athletics and junior tennis using key terms including “junior tennis,” “youth sports,” “sport specialization,” and “overuse injury.”

Study Design:

Clinical review.

Level of Evidence:

Level 5.

Results:

Early sport specialization leads to increased injury risk, decreased athletic career longevity, and higher incidence of burnout without demonstrating significant benefits in terms of improving peak sports performance or the likelihood of reaching elite play.

Conclusion:

Youth athletes should avoid specializing in a single sport before age 12, avoid training more hours per week than their age in years, and limit training to 16 hours per week maximum. Specific to tennis, junior players should be at least 12 years old for tournament play, compete in no more than 2 tournaments per month or 12 per year, engage in a maximum of 12 hours per week of organized tennis, a minimum of 2 hours per week of injury prevention training, and consider another off-season sport. Injury may be more likely with early sport specialization, early intense training (before middle or late adolescence) and annual match volume (>40 matches annually). Finally, we provide novel recommendations for safe volumes of training, matches, and tournaments for junior tennis players based on their age and level of play.

Strength-of-Recommendation Taxonomy (SORT):

B - recommendations based on inconsistent or limited-quality patient-oriented evidence.

Youth engagement in sports and physical activity has long been promoted as a method to help develop confidence, social skills, and healthy habits from an early age. However, over the past 2 decades, there has been a shift in the patterns of youth sport participation. Traditionally, youth-driven recreational sports activity promoted sports sampling, or participating in >1 sport. This encouraged the development of physical literacy, engagement in long-term physical activity, and the improvement of motor coordination and athleticism.^9,12,37 Youth-directed sport sampling also fosters the development of intrinsic interest in specific sports, which is an important basis of continued skills development and potential elite performance.^{10,14,31 -33} In contrast to sport sampling, sports specialization is defined as intense, year-round (≥8 months per year) training in a single sport with the exclusion of other sports; this specialization is considered “early” when it begins before the age of 12 years.^29,40

Specialized sports programs are often parent or coach-driven with an emphasis on competition, comparison, and sport-specific skills development.^3,21,33 However, this model has been shown to increase the risk of injury and potentially decrease peak performance and career longevity.^{6,14,30,34,39} The most at-risk athletes for overuse injuries related to sport specialization are those engaged in individual sports that require large volumes of training and competition before adolescence, such as tennis.^15,35 There are some recommendations regarding sport specialization in junior tennis players ⁴² ; however, there has been no specific published review of the evaluation and management of sport specialization in junior tennis players. In this manuscript, we will evaluate the data available on the effects of sport specialization and intense training on injury risk, player wellbeing, and performance across sports, and then apply this to develop evidence-based sport-specific guidelines for the junior tennis player.

Sports Specialization, Training Hours, and Injury Risk

Specialized and highly structured sports participation often culminates in intense periods of organized training and competition without compensatory recovery. A recent meta-analysis demonstrated a >30% increased risk of injury in youth sport specializers versus multi-sport samplers. ⁹ These trends have been noted throughout organized youth sports.^20,24,35 In one of the first studies evaluating the risk of sport specialization and overuse injury, 1208 athletes were evaluated and it was found that highly specialized athletes were more likely to develop overuse injuries even when controlling for training load and age. ⁴ In another investigation, young athletes between the ages of 7 years and 18 years participated in a survey-based evaluation of injuries and sports participation. ²⁴ More specialized athletes demonstrated a higher risk of injury compared with less specialized athletes even after accounting for potential confounders such as age, sex, body mass index, and sports participation volume.

In a recent investigation, 1544 high school athletes with an average age of 16.1 years had their sport specialization determined on the AOSSM 3-point scale. ³⁰ After controlling for sex, grade in school, competition volume, primary sport, and previous injury history, the incidence of injury was found to be 50% greater in moderately and 85% greater in highly specialized athletes compared with athletes with low specialization. One proposed mechanism for the increased injury rate is that early specialization leads to a lack of variety in movement patterns resulting in muscle strength imbalances and deficiencies in neuromuscular control, which predispose developing athletes to injury. ³³

Tennis Specialization, Training Hours, and Injury Risk

For tennis players, it has been shown that early specialization and high tennis specific training hours can increase risk for injury. A 2011 cohort study of nearly 500 ranked United States Tennis Association (USTA) junior tennis players aged 13.5 years on average showed that 70% were already single-sport specializers in tennis and had done so at an average of 10.4 years old. ²² Those who specialized only in tennis had higher instances of injury throughout their career and were more likely to have medically withdrawn from tournament play than their multisport peers. A recent review article highlighted the benefits of multi-sport participation for youth tennis players. They found that participation in multiple sports can help reduce injuries, increase activity enjoyment, and improve fundamental motor skills necessary for success. ⁴²

In regard to training hours, increases in workload from tennis-specific training and/or match frequency are associated with increased rates of shoulder complaints, shoulder injuries, back pain, and lumbar spine arthropathy in competitive adolescent tennis players.^26,27 Rapid changes in training hours week to week has also been associated with increased instances of shoulder pain and injury in adolescent tennis players, favoring a more consistent training hour schedule for young athletes. ²⁰ In addition, medical withdrawals have been found to increase significantly for the fifth match and beyond in junior national tennis tournaments. ²⁵ Tournament scheduling should consider this factor and ensure adequate rest times between matches beyond the fourth match to decrease injury burden on young athletes. Although the exact age of specialization for injury prevention and peak performance in the junior tennis player can be variable, delaying specialization to closer to middle adolescence rather than pre-adolescence may be advised.

Sports Specialization and Quality of Life

As youth sport participation has become increasingly prevalent (nearly 60 million participants between the ages of 6 and 18 years), ¹¹ there has been a tendency of athletes, parents, and coaches to push for early specialization due to the perceived benefits of gaining a competitive edge in the sport, increasing the likelihood of earning collegiate scholarships, and ultimately becoming a professional athlete. ¹³ However, early sport specialization can lead to maladaptive social isolation, poor academic performance, increased anxiety, greater stress, and decreased family time. ⁷ The wide range of negative psycho-social effects of early specialization is broadly identified as “burnout.” Raedeke and Smith ⁴¹ developed a psychometrically validated metric by which to measure athlete burnout, originally based on competitive swimmers, called the Athlete Burnout Questionnaire (ABQ). They defined burnout as being composed of 3 parts: emotional and physical exhaustion, reduced sense of accomplishment, and devaluation of sport. ⁴¹ A recent 2020 meta-analysis on athlete burnout systematically reviewed over 3500 published articles, including final data on 1422 athletes between the ages of 12 and 17 years old who completed the ABQ. The results of the meta-analysis demonstrated that single sport specializers had higher rates of burnout than did multi-sport samplers. All 3 components of burnout were statistically significantly greater (P < 0.01) among the specializers. ¹⁶

In tennis specifically, 1 study demonstrated that tennis specializers had higher rates of burnout, lower motivation, and felt more withdrawn compared with multi-sport tennis samplers. ¹⁷ However, it is not clear that junior tennis players that are specialized have a lower health related quality of life (HRQOL). In a study by Schneider and Jayanthi, ⁴⁴ junior tennis players and their parent (dyads) did not have lower HRQOL when compared with multi-sport athletes. A further study of parent-child dyads of specialized athletes (including tennis players) also found that these players did not have lower HRQOL and in fact could have positive experiences with a supportive family and coaching environment. ³⁶

Sports Specialization, Training Hours, and Peak Performance

Bell et al ⁵ have suggested that the frequency of sport specialization in youth athletes has reached the level of public health interest, with little data to support this training model for improving long term athlete development. In a systematic review of 19 studies, there was no study that suggested improved task or career performance with early sport specialization. ²⁸ In fact, myriad international studies investigating elite versus near-elite athletes showed that elite athletes participated in fewer practice hours at an early age, specialized in their sport later in early adulthood, and surpassed the near-elite athletes in hours trained later in their careers.^1,18,31,32 In a recent 2022 meta-analysis of nearly 10,000 athletes across multiple sports and all levels of competition, the authors found that world-class adult athletes had more multi-sport exposure in childhood and adolescence, less main-sport practice, later single-sport specialization, and a slower progression into their chosen sport (Table 1).^2,21 Similarly, a study of 314 Division I collegiate athletes across 9 sports including tennis, found that a majority of those athletes did not specialize in one sport in high school. ³⁸

Table 1.

Predictors of senior-level sports performance

	World class vs national class			Lower-level comparisons			Comparison
Predictor variables	d–	95% CI	P value	d–	95% CI	P value	F	P value
Age
Milestones	0.420	0.22 to 0.62	<0.001	0.035	−0.52 to 0.59	0.90	2.17	0.16
Start	0.409	0.19 to 0.63	<0.001	0.174	−0.00 to 0.35	0.06	2.67	0.11
Main sport
Practice	−0.232	−0.38 to −0.08	0.002	0.474	0.27 to 0.68	<0.001	24.00	<0.001
Play	−0.033	−0.30 to 0.23	0.81	0.143	−0.25 to 0.54	0.48	0.17	0.68
Other sports
Practice/play	0.269	0.15 to 0.39	<0.001	0.140	−0.02 to 0.30	0.08	1.67	0.21
Practice	0.497	0.37 to 0.63	<0.001	0.208	−0.06 to 0.48	0.130	3.58	0.07
Play	0.114	−0.02 to 0.25	0.10	—	—	—	—

Adapted from Barth et al. ² Note the sign of effects for age- and activity-related predictors: a positive effect indicates that higher performance was associated with later (higher) ages and with greater activity amounts. d-, meta-analytic mean Cohen’s d- (– indicates not enough effect sizes [k < 5]).

Early specialization also hampers the career longevity of athletes who initiate intense training and high-level participation from a young age. Early specialization increases the risk for early retirement and sustaining career-shortening injuries. ²¹ In elite Russian swimmers, those who specialized earlier (<11 years of age) retired earlier and spent less time competing at the national level. ⁴ Minor league hockey players who dropped out earlier began “off ice” training at an earlier age and spent significantly more time practicing between the ages of 12 and 13. ⁴⁶ Finally, in a large retrospective survey of nearly 1400 tenth grade student athletes, 20% cited injury as the reason for quitting their sport. ⁸

In tennis, early specialization and intense training were scrutinized when young tennis professional “phenoms” had early career retirements. In 1994, the Women’s Tennis Association (WTA) mandated a new age eligibility rule (AER), as well as a player development program (PDP), which implemented a phased-in-approach to competitive tennis participation for players aged 14 to 17. A 25-year study compared the career lengths among >800 adolescent female tennis players who either began their careers before or after the new legislation. Compared with the pre-AER/PDP group, female tennis players who played in the WTA after the AER/PDP was enacted had careers 2 years longer on average (P < 0.001), higher probabilities of 15-year careers, and lower risks of premature retirement. ³⁴ A further study showed that elite adult tennis players specialized later in their athletic careers (age 13-15 years) compared with near-elite tennis players (age 11 years). ¹⁰ Evidence suggests that early specialization, intense hours of professional-level training, and high pressure for success do not necessarily lead to the emergence of elite athletes, yet pressure still exists on junior athletes to achieve early success in their sport. As such, there remains a need for recommendations to achieve this level of accomplishment while minimizing injury and overload risk.

Sports Specialization in the Resilient Youth Tennis Player

It is important to recognize that an accumulation of a significant number of activity hours is likely necessary to obtain elite skill level, although this may be done in other ways than early single sport specialization. A specialized sampling model in European youth football (soccer) athletes demonstrated that those youth athletes who accumulated the most hours of football training and other domain-specific (but not organized) activities were more likely to be elite than those that accumulated fewer total hours of activity. ⁴⁵

While there are known risks of injury with early sport specialization and intense training and competition loads, it does not necessarily predict injury in all junior tennis players. It is possible that some junior athletes are more “load tolerant” even through vulnerable developmental phases. ²² Theories exist as to why some youth athletes and junior tennis players may be tolerant to single sport specialization and high workloads, while others are not. Training programs such as INT (Integrated Neuromuscular Training) have been proposed to build strength and correct biomechanical deficits to better tolerate loads. ⁴³ In a study of junior tennis players, those who performed injury prevention training had lower rates of injury even with higher training loads. ²³ Despite warnings of potential injury risks with early sport specialization, it is estimated that approximately one-quarter of youth athletes may be highly specialized. ³⁵ Therefore, a model should exist to help train these athletes while mitigating injury risk.

In 2021, a training model for the sport-specialized youth athlete was developed to provide guidance to limit overuse injury and burnout. ²³ There are 4 main elements to evaluate each youth athlete (sport specialization, developmental stage, workload, biomechanics). This algorithm stratifies athletes into 3 categories based on their biological maturity, injury history, training habits, strength, and fitness: low-risk or “load tolerant”, moderate-risk, or “load naïve,” and high-risk or “load sensitive” athletes. ²³ To keep young tennis players safe, Jayanthi et al ¹⁹ recommend in most cases a minimum age of 12 years old for regular tournament play, no more than 12 tournaments per year or 2 tournaments per month, a maximum of 12 hours of organized tennis per week, a minimum of 2 hours per week of injury prevention training, and a consideration of another off-season sport. In addition, the authors recommend later specialization with more intense training occurring after 15 years old and reducing annual match volume to <40 matches to avoid medical withdrawal. However, adhering to these recommendations would make it difficult for an athlete to be ranked highly in the current juniors ranking system, where points are earned per match won, putting an emphasis on total volume of matches played. Table 2 outlines the authors’ recommendations for ratios of competitive play, number of matches and tournaments per year, and hours per week that junior tennis players should be participating in based on their age and division.

Table 2.

Recommendations for junior tennis player training, match, and tournament volume based on their age and level of play

Age division/type	JTT vs tournament, %	Matches per year, n	Tournaments per year, n	Hours per week and months per year (training)	Athlete development
U10	80/20	0-30	0-6	1-3 sessions/week (60-90 minute sessions); 6-10 months/year	Multi-sport ± nontennis physical activity
U12	75/25 a 50/50 b	20-40	0-6 a 4-8 b	2-4 sessions/week (60-120 minute sessions); 6-10 months/year	Multi-sport ± nontennis physical activity
U14	30-50/50-70	40-60	12-16	2-4 sessions/week (90-180 minute sessions) 8-10 months/year	Consider tennis specialization vs multi-sport + nontennis physical activity
U14-18/rec	75/25	20-50	0-6	1-3 sessions/week (60-120 minute sessions) 6-10 month/year	Consider tennis specialization vs Multi-sport + nontennis physical activity
U16-18/HPP	25/75	40-100	12-24	3-6 sessions/week (120-180 minute sessions) 9-11 months/year	Tennis specialization + nontennis physical activity

HPP, high performance profile; JTT, junior team tennis; rec, recreational; U10, under 10 years.

^aSafest option.

^bIncreased risk.

Limitations

This review is based on a comprehensive analysis of the current literature on overuse injuries in youth sports, with a specific focus on youth tennis. However, the majority of the studies included are retrospective, cohort, or case series designs, which may limit the strength of the evidence. There are limited prospective studies specifically examining overuse injuries in youth tennis. Future research employing prospective study designs, particularly investigating injury incidence in relation to adherence to restricted practice guidelines, would be a valuable extension of this review.

Conclusion

Although early sports participation can provide significant physical, psychosocial, and mental benefits for young athletes, early specialization, often a coach- or parent-directed phenomenon, can lead to increased injury risk, decreased athletic career longevity, and higher incidence of burnout without demonstrating significant benefits in terms of peak sports performance or the likelihood of reaching elite play. A number of simple guidelines for general youth sports participation have been proposed: avoid specializing in sports before age 12, avoid training more hours per week than a young athlete’s age in years, and limit training to 16 hours per week maximum. Specific to tennis, there have been recommendations of a minimum age of 12 years old for tournament play, no more than 2 tournaments per month or 12 per year, a maximum of 12 hours per week of organized tennis, a minimum of 2 hours per week of injury prevention training, and consideration of another off-season sport. ¹⁹ Later sport specialization, delayed intense training (starting >15 years old) and reduced annual match volume (<40 matches annually) are also recommended. ¹⁹ Finally, we provide novel recommendations for safe volumes of training, matches, and tournaments for junior tennis players based on their age and level of play. While these recommendations may diminish early performance (at the youth or junior level) they are supported by the currently available data regarding peak performance, playing career longevity, injury reduction, and burnout risk.