The United States is experiencing a regrowth in grass roots tennis. Recent data from the Sporting Goods Manufacturer's Association show that tennis is the fastest growing sport in the country, with participation increasing 43% since 2000 and 9.6% last year (2008) alone (22).
With the success of the United States Tennis Association (USTA) QuickStart format (25) that uses age-appropriate equipment (smaller tennis racquets and lower bouncing balls) and smaller court sizes with lower nets, children are again playing and enjoying tennis by the thousands.
Tennis at a high level, however, is an open-skill sport that requires many physical and mental skills and superb physical conditioning. If the United States wishes to return to its previous dominance in the sport, there are physical, tactical, technical, and mental progressions that should be followed to allow the young player to develop into a capable and independent individual. This article will focus on the physical skill acquisition necessary to attain a high level of athleticism and tennis skill development.
The stages of growth and maturation to consider in the progressive development of an elite tennis player are prepuberty, puberty, and postpuberty. Puberty is the period during which skeletal, sexual, and somatic changes occur, and its timing can vary greatly from child to child (16,23). Typically, in the United States, the first signs of puberty in girls occur between the ages of 8 and 13 years with menstruation occurring approximately 12 to 15 months after peak height velocity (PHV) or approximately 12 years of age. The average age of menarche is 12.4 years. In males, peak height occurs on average at approximately 14.4 years (23) Although there can be extreme variability in rates and timing of growth and maturation among athletes, it is necessary for the strength and conditioning professional to be aware of the athlete's status with regard to puberty, so that care and consideration can be given to the progression and intensity of physical workouts. It is important to understand that once puberty begins, the biological age of each individual is more important than chronological age. As most parents and coaches can relate to chronological ages, the authors have used general age recommendations for the different developmental stages as a guide. It should be noted that occasionally certain individuals will have a chronological age that may not be consistent with the typical stages of development.
PREPUBERTY (AGES 8-11 FEMALES AND 9-12 MALES)
THE STAGE OF DEVELOPMENT AND SPECIFIC CONSIDERATIONS
To prepare a young athlete physically for year-round tennis participation, the type of training, training load, and goals must be age dependent, assessing where the child is in relation to onset of puberty (biological age). Prepuberty is typically the ages between 8 and 11 years for girls and 9 and 12 years for boys. Boys and girls in prepuberty can usually be grouped together for physical activity because they are all at the same stage of development. At the end of this stage, there will be some variation between children depending on earlier growth and development. The physical skills for this stage are the fundamental movement and physical skills that underpin future physical capacities and without which athletic development might be compromised later (19).
The skills are
- agility, balance, and simple to complex coordination;
- running, jumping (and landing), hopping, and skipping;
- throwing, catching, and kicking;
- speed (improved running economy and “speed play” over short distances and time frames);
- body awareness and control;
- core and shoulder stability;
- reaction speed.
The goal for the coach working with prepubescent athletes should be to provide training that improves and develops physical skills in order to develop athleticism, coordination, and “whole body” strengthening to support proper tennis mechanics and ultimately lower the risk of injury (10). Another important goal in this developmental stage is to teach proper exercise and movement technique through a full range of motion. Athletes who learn correct technique at a younger age will make faster improvements through puberty and especially during the postpuberty developmental stage. Movement and total body strengthening can also be achieved by multisport participation. Early specialization in a sport such as tennis can lead to 1-dimensional athletes and burn out at a young age (4,28).
Strength gains at this stage are similar in both males and females. However, these improvements are due to improved motor coordination, economy of movements performed, and neurological adaptation. They are reversible without consistency in training (18).
Experience suggests that the best time to learn new skills is between the ages of 8 and 12 years when the body is not growing rapidly (19). In addition, proper motor firing patterns are more easily obtained at this time, and proper mechanics helps to ensure future performance in these skills with decreased injury risk (10). By using the following skill acquisition table (Table 1, Figures 1 and 2) and encouraging alternate sport participation as a physical development tool, the prepubescent tennis player will develop physical skills and more balanced movement biomechanics. This type of balanced training should limit injury and lead to future sport success (6).
Because balance and postural control skills mature to adult levels by 7 to 8 years of age, it would seem logical that true strength programs do not start before the child demonstrates proficiency of these and other sport-specific skills (5).
Repetition and review of the fundamentals through games, speed play, and group drills encourage socialization and fun. Relay races also develop speed in an appropriate work to rest ratio of 1 to 5 (12). Circuit training is ideal for keeping concentration with children who typically have a short attention span.
Once a foundation of athletic or general fitness skills has been established, tennis-specific movement and strengthening can begin. As noted earlier, an important factor in muscular strength in prepubescent males and females is the development of the nervous system. If myelination of nerve fibers is incomplete, the skilled movements and quick reactions necessary for tennis are impossible (6). When designing a program for this stage of development, it is always wiser to err on the side of caution, underestimating rather than overestimating the athlete's neural development. High repetition low-intensity training performed twice a week for 30 minutes is appropriate to develop adaptations in strength, coordination, and muscle endurance. Focus on
- 1. Fundamental skills
- Agility, balance, and coordination-the changing center of gravity as children grow affects coordination and balance.
- Developing speed on the court with rapid changes of direction.
- Increasing movement economy and efficiency of neural pathways
- (examples: cone drills [Figure 3], hurdle step drills, on-court movement drills [both forwards/backwards and side to side], ladder drills, dot drill, and jump rope).
- 2. Whole body strengthening and injury prevention
- During this stage of development, most increases in strength are due to increased economy of movement, motor development, and neurological adaptations (6,9).
- Hormones are limited at this stage, so maintaining gains should involve at least 2 sessions per week. Maximum of 30 minutes due to short attention span.
- Scapular stabilization, hip and core strength, leg strength, and deceleration development.
- Examples: circuit training (Figure 4) rotating upper- and lower-body exercises with core exercises. Single-leg dynamic and static balance exercises and shoulder prevention should also be included.
Proper dynamic warm-up, cooldown, and nutrition and hydration information rounds out a proper strength and conditioning program for the prepubescent athlete. There is a distinct benefit in beginning the education process at this age. Parent involvement and education are also strongly suggested at this stage.
PUBERTY (AGES 10-13 FEMALES AND 11-15 MALES)
THE STAGE OF DEVELOPMENT AND SPECIFIC CONSIDERATIONS
The onset of puberty is denoted by rapid increases in height and changes in body composition, together with the development of secondary sex characteristics. Players will develop and mature at different times and at different rates. Girls mature earlier than boys and so the option of training them together need careful thought. It is therefore very important to realize that there can be a significant difference between a child's chronological age and biological age (2,20). Chronological age is a child's age in years and months since birth and is not an accurate gauge to use when assessing the stage of physical, neurological, or mental development during puberty. Biological age reflects the stage of growth based on skeletal, somatic, and sexual maturity.
Between the ages of 8 and 13 years for girls and 11 and 15 years for boys, players are at a pivotal stage of growth and maturation in which they can transition from prepuberty through puberty to postpuberty. Although they will enter puberty at different chronological ages and proceed through it at variable rates, it is an important time for them to train (14). During this stage, special consideration should be given to the differences in growth and development of boys and girls. The adolescent growth spurt begins around 10 to 11 years for girls and 12 to 13 years for boys. Because girls have an earlier onset of puberty, they undergo a large amount of growth earlier than boys including significant changes in height, weight, body composition, and development of sexual characteristics (14). Many pubescent girls reach their maximum rate of growth, also known as peak height velocity (PHV), by 13 to 14 years of age. PHV signifies the maximum velocity of growth in stature (14). Once PHV has been reached, the player will continue to grow but at a much slower rate. Boys reach PHV later than girls.
Training players moving through puberty must be undertaken with an awareness that growth and maturation are taking place. In addition, because growth is often “uneven,” it will be necessary to make adjustments throughout the training plan.
According to a review of gender and development by Keller, differences in the development of fitness attributable to intrinsic gender factors exert the greatest influence around puberty. For this reason, there should be different training goals for pubescent boys and girls. In the developing player, strength is related to linear growth, weight, and muscle size (9). Girls therefore have the ability to train and develop strength earlier. Boys develop later and therefore do not have the strength window at the same time as girls. Instead, boys should focus on building a basic strength foundation and training movement and endurance (8,9).
Bone development is critically important for long-term health, and early puberty is a critical period during which bone growth is most responsive to weight-bearing exercise. Collectively, the data on bone growth in youth suggest that the optimal time for physical activity, including progressions of weightbearing exercises, is during the premenarchal period for girls and the early puberty period for boys. Activities that include periodic brief moderate to high muscle force output, such as tennis, will stimulate bone remodeling to a greater extent. Therefore, tennis-related drills remain an important component of the high-performance tennis players' strength and conditioning program during puberty (1).
PROGRAM DESIGN AND EXERCISE SELECTION
To design a training program for a pubescent player, it is necessary to consider the stage of maturation and the phasing of the growth spurts. Because it is very difficult to have an accurate assessment of the stage of development based on chronological age, measurements of stature, body composition, shoe size, and sexual maturation could be used as a reference point to design an appropriate program for an individual (14). The most effective and useful markers of the stage of growth and maturation are the height at onset of PHV, PHV itself, and the onset of menarche for girls. The onset of menarche correlates to PHV (15). Sexual characteristics in boys are not an effective measure because they do not correlate either with each other or with PHV. The regularly scheduled measurement of stature, ideally weekly, will be helpful to the strength and conditioning coach to make necessary adjustments throughout the program as the athlete continues through various growth spurts. Figure 5 shows increases in height for athletes of the same chronological age. Athlete A is taller than athlete B at the age of 10, 11, and 12 years because athlete A reaches PHV earlier than athlete B. Figure 6 shows PHV for athlete A between age 9 and 10 (she grew 8 in) and also shows athlete B's potential yet to come PHV.
As stated previously, before puberty, the athlete should have a foundation of fundamental athletic skills and should have undergone tennis-specific movement drills and strengthening. As the athlete enters puberty, training should continue to reinforce complex coordination and focus on the development of footwork, tennis-specific movement, and dynamic balance. Growth spurts in the young tennis player can affect balance, footwork, and movement patterns as well as coordination. A temporary loss of coordination will occur with rapid increases in height (17). For this reason, athletes need to “relearn” movement patterns and include footwork drills and movement patterns as a part of the daily regimen. With the onset of PHV, proper resistance should be gradually applied on weightlifting (quick lift movements) and other primary lifting exercise techniques, such as squat, lunges, deadlift, bench press, bent-over row, etc. As a result, players should build a strong foundation of the basic lifting techniques during PHV. This will help to prevent injury and enhance optimal adaptation to strength training (1). A progression of tennis-specific strengthening is important. A largely overlooked component of a quality strength and conditioning program is flexibility training. Optimal individualized and sports-specific flexibility is a key training need and should be established at a very early training age (1). An emphasis on flexibility training is of great importance given the rapid growth of bones, tendons, ligaments, and muscles at this stage (1). As the demands of tennis apply repeated stress to the lower and upper body of a growing player, muscles and tendons can become very tight and overworked.
FREQUENCY AND VOLUME OF TRAINING
The onset of PHV and the progression to PHV will determine the extent and frequency of weight training during this stage. The critical periods of accelerated adaptation to strength training will occur toward the end and immediately after PHV for females and 6 to 12 months after PHV for males (9). Table 2 summarizes the recommended frequency and volume of training for high-performance tennis players.
VARIATION OF TRAINING
As young tennis players experience growth spurts throughout puberty, it is necessary to make adjustments to their training regimen. A player who experiences a rapid increase in height, for example, 7.1 to 9.1 cm/y in girls and 8.2 to 10.3 cm/y in boys (14), can have tight quadriceps and may also develop patellar tendon pain. In these cases, at the discretion of the strength and conditioning professional, adjustments should be made to the training program to allow for the knee injury to heal and to prevent further injury. Options may include eliminating lower-body exercises that cause pain and place stress on the knee, increasing lower-body flexibility, and adjusting aerobic training from ground contact drills to biking or swimming drills for a period. It may be necessary to modify training of various joints and movements during puberty, and excessive stress on growth plates, tendons, ligaments, or muscles may lead to a variety of developmental injuries (6).
Pubescent players, who have built a foundation of basic athletic skills such as running, jumping, and throwing, are now able to learn tennis-specific skills. During this stage of training, it is appropriate to begin tennis-specific drills that focus on upper- and lower-body strength as well as hip, knee, ankle, and shoulder stability. Examples of such exercises include rows, lat pull-downs, shoulder lateral raises, lunges, squats, single-leg balance, multidirectional band walks, and shoulder external rotation band pulls at neutral and 90/90 shoulder external rotation.
POSTPUBERTY (14+ FEMALES AND 15+ MALES)
THE STAGE OF DEVELOPMENT AND SPECIFIC CONSIDERATIONS
It has been explained that chronological age is not an accurate means of defining the stage of maturation. Many players, because of early or late maturation, can be 2 or 3 years ahead or behind their chronological age. The timing of puberty therefore can vary chronologically from 8 to 13 years in girls and from 9 to 15/16 years in boys. Girls typically begin puberty about 2 years before boys irrespective of early or late maturation (6).
SPECIFIC CONSIDERATIONS OF THE AGE GROUP
Girls in this age group will be able to start more intense and advanced strength and conditioning programs earlier than boys if the athlete has proper exercise techniques and a strong foundation.
The popularity of strength and conditioning programs among young athletes has increased, and safety of the programs, especially strength training (with qualified supervision), is well supported in the literature (2,7). One of the particular concerns for a young athlete is the possibility of damage to growth plate/cartilage, especially without qualified supervision. The most common time for epiphyseal (growth) plate fractures in children occurs about the time of PHV (6). However, well-designed and supervised strength and conditioning programs are safe to perform by the young athletes (2,7). Therefore, strength and conditioning professional must be aware of an athlete's growth stage and adjust programs accordingly. Because increased gains in peak strength occur about 6 to 12 months following peak weight and PHV in males (9), this is the window of opportunity for young male athletes to start high-intensity/volume and advanced strength training. It is also important to start professionally supervised strength and conditioning programs as early as possible so that the athlete will be ready to train, with great technique. If the athlete does not have strong foundation and exercise techniques, it is not feasible to start this volume training.
During the time athletes are growing rapidly, they may temporarily lose some of their motor skills (3). It is important to understand what athletes are going through and adjust programs accordingly or take some time off if necessary.
Concepts and assessments
It is very important to design strength and conditioning programs for this age group with considerations of the athlete's biological age and training age. Biological age can be measured in terms of skeletal age and somatic maturity or, in the case of girls, the onset of menarche (6).
Anthropometric measurements, such as heights and weights, can be used to identify an athlete's biological age. Competitive tennis athletes should be regularly measured for their height, seated height, arm span, and 3-site skinfold to identify athletes' growth stages and body types. Regularly scheduled anthropometric measurements, for example, once a week once the onset of PHV has been noted, will give a strength and conditioning professional very valuable information of an athlete's timing and rate of growth.
The length of time the child has been in resistance training and this will also influence actual training program design. It is extremely important to identify the child's training age to deliver correct program design. For example, an early maturing 15-year-old boy without any training experience may not adapt to complex technique strength training or heavy resistance exercises, whereas another early maturing 15-year-old boy with 2 years of resistance training experience will be ready for more complex technique heavy-intensity training.
It is always important for a strength and conditioning professional to select proper assessment tools to create sport-specific and individualized programs. For a high-performance tennis player, a strength and conditioning professional needs to assess the following areas:
Many high-performance tennis players have intense tennis training (practice) experience by this age. It is not rare for the tennis professionals and/or coaches to have regularly conducted some form of on- and/or off-court training. The strength and conditioning professional must understand the full training history of the athletes to prevent overstress to the athletes' body and to adjust training schedule.
Strength training is one of the popular training methods for high-performance tennis players in this age group. It is important to assess an athlete's exercise techniques not only to identify an athlete's ability to perform certain exercises correctly but also to observe muscular imbalance, functional flexibility, and balance.
Overhead squat (Figure 7), back squat, and single-leg squat (Figure 8) are great ways to observe the following areas of high-performance tennis players:
- Shoulder stability/muscular imbalance
- Core stability/muscular imbalance
- Hip and ankle flexibilities
- Hip region muscular imbalance/deficiency
- Knee stability
- Overall balance
Strength and power
Tennis requires explosive movements (12,21). Basic strength and speed are necessary to produce power. Therefore, assessing both strength and power is important for high-performance tennis players. However, a strength and conditioning professional must be extra careful when measuring the strength level for this age group. Strength assessments, such as repetition maximum (RM) testing, require appropriate testing guidelines, and athletes must practice and possess proper lifting techniques (7). Following are examples of strength and power assessment tools that are currently used by the USTA Player Development:
- Squat 5RM (lower-body strength)
- Deadlift 5RM (lower-body strength)
- Bench press 5RM (upper-body strength)
- Bent-over row 5RM (upper-body strength)
- Vertical jump (lower-body power)
- Medicine ball chest pass (upper-body power)
- Medicine ball forehand and backhand throw (rotational power)
Acceleration and agility
A high-performance tennis player makes an average of 4 directional changes per point over relatively short distances (average of 2.5-4 m) for each stroke (12,21). Therefore, acceleration and agility training should directly relate to athlete performance on court. Following are examples of acceleration and agility assessment tools that are currently used by the USTA Player Development for high-performance tennis players:
- 20-yd dash (linear acceleration)
- Spider test (agility) (Figure 9)
- Sideway shuffle (lateral agility)
- Hexagon test (agility/quick feet and body balance)
Although the relationship between flexibility and on-court performance or injury rates is unknown (17), it is important to assess athletes' flexibilities in different joints to understand athletes' lack of flexibilities and to predict athletes' limitation on their performance and potential injuries. The USTA High Performance Profile (24) is used as a tennis-specific movement and musculoskeletal screening tool.
High-performance tennis players require a high level of aerobic fitness. A typical tennis match usually lasts more than an hour (21) and it is common for long matches to last more than 3 hours. Similar to peak strength gain, the peak aerobic velocity coincides with the onset of PHV and contributes to accelerated adaptation in the aerobic system (1). Therefore, it is important to implement aerobic fitness training for this age group. For high-performance tennis players, aerobic fitness training should limit the amount of traditional long slow distance running. More emphasis should be placed on tennis-specific endurance drills. It is important to understand metabolic specificity and the energy systems for tennis in order to design tennis-specific endurance drills. It is recommended to use 1:2 to 1:5 work to rest ratio (exercise time 5-20 seconds) for tennis-specific endurance drills (11).
Training goals, exercise selections, and intensity of training
The basic training goal for players postpuberty is developing strength and power provided that the athlete has a strong foundation from previous training stages. As previously mentioned, if an athlete is mature and has done proper preparation, he or she should start high-intensity and advanced tennis-specific strength and conditioning programs with a certified professional.
The training goal has to be very specific to the stage of individual development and the sport. Table 2 summarizes the examples of specific training goals for each development stage.
Frequency and volume of training
Training frequency and volume are directly influenced by biological age and training age. Table 2 also suggests frequency and volume of training suggestions for high-performance tennis players.
Variation of training
Tennis is a sport without a true off-season. It is always a challenge for the strength and conditioning professional to create periodized strength and conditioning programs for a high-performance tennis player. Each tournament is important for the players. However, it is important to determine with an athlete and the tennis coach the priority of tournaments and schedule strength and conditioning programs based on tournament and practice schedules. The training status (age) will affect tremendously the variation (periodization) of training. If an athlete has just started a strength and conditioning program, he or she needs to focus on developing proper exercise technique and foundation throughout the year. In this case, a high-intensity training phase, such as strength/power phase (26), may need to be adjusted because the athlete may not yet be ready for the intensities. Also, the intensity and volume before each tournament may need to be lowered because of the athlete's training status.
After a couple of years of basic training and building a solid foundation, a high-performance tennis player should focus on tennis-specific training. Especially at this stage, athletes will have several years of tennis training and some may have specific muscle imbalance and flexibility deficiencies. Flexibility and strength in shoulder/scapular, the hip core areas, are common issues to work with high-performance tennis players. Also, tennis-specific movement exercises should be incorporated to the strength and conditioning programs. More than 70% of tennis movements are lateral movements, and less than 20% of movements are in the forward direction (27). Each movement distance averages 2.5 to 4 m (maximum of between 8 and 12 m) depending on court surface and competition level. Also, tennis players make more than 15 directional changes in a very long point (20) and may make more than 1,000 directional changes in a competitive mach. Therefore, in addition to linear speed and lateral movement, deceleration training is necessary for high-performance players because most points are a series of changes of direction (13).
SUMMARY AND CONCLUSION
There are sufficient studies and reviews available to confirm the safety and effectiveness of strength and conditioning programs in young athletes (5,7,9,18). However, injuries to young athletes every year usually arise as a result of unsupervised and nonprofessionally organized programs (7). It is extremely important to understand all the issues with young high-performance athletes to deliver safe and effective strength and conditioning programs.
Strength and conditioning professionals need therefore to understand tennis-specific movement requirements but also how to monitor the individual athlete's rate and timing of growth and maturation. They need to communicate with parents, coaches, and even the athlete's physician, to deliver developmentally appropriate strength and conditioning programs.
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Keywords:© 2009 by the National Strength & Conditioning Association
growth; development; tennis; maturation