The sport of gymnastics possesses a range of subdisciplines, including rhythmic, trampolining, tumbling and acrobatic, with an estimated 50 million participating worldwide (4); however, artistic gymnastics is one of the most popular in terms of participation rates among children and adolescents (4,5). Despite certain similarities, the demands of artistic gymnastics differ for males and females. Women's artistic gymnastics consists of 4 events (vault, uneven bars, balance beam, and the floor exercise), whereas men's artistic gymnastics comprises 6 apparatus (floor, pommel horse, rings, vault, parallel bars, and high bar). The physical abilities necessary to perform successfully on each apparatus vary considerably in the required neuromuscular power, strength, flexibility, speed, coordination, balance, and energy system demands (46) and are summarized in Figure 1. The development of these physical qualities in children and adolescents is nonlinear because of interactions of growth, maturation, and training (112). Consequently, the development of physical components in young gymnasts can be complex (61) because the timing, tempo, and magnitude of development will differ markedly between individuals of the same age (61). In addition to understanding the science behind the training process, practitioners working with young artistic gymnasts should also consider the key principles surrounding pediatric development to better understand the potential trainability and adaptability of gymnasts at different stages of development.
PHYSICAL FITNESS REQUIREMENTS FOR ARTISTIC GYMNASTICS
STRENGTH, POWER, AND SPEED
The sport of artistic gymnastics requires high levels of strength and power in the upper and lower limbs to successfully and safely perform a dynamic and diverse set of movement skills in sequence (5). Although these movements will invariably involve a combination of eccentric and concentric actions, the importance of isometric strength and body tonus should not be underestimated (21) because artistic gymnasts are judged by, and conditioned to, hold a sequence of technical shapes in both dynamic and static conditions (6). Thus, the ability to effectively recruit motor units in order to exert force at variable movement velocities appears to be an important determinant of performance for gymnasts from an early age. For example, during a routine on the floor, gymnasts are required to execute movement patterns that use various segments of the force–velocity curve and involve all types of muscular actions (74,78).
Takeoff characteristics for a double back somersault on the floor have reported vertical velocity of the center of mass of 4.2 ± 0.46 m·s−1 for males and 3.54 ± 0.85 m·s−1 for females at takeoff (35), whereas a planche requires high levels of isometric muscular force (50). Furthermore, kinetic analysis of takeoff forces during a straight back somersault tumbling series revealed that mean maximal vertical forces and maximal rate of force development were 6,874 ± 1,204 N and 6,829 ± 2,651 N·s, respectively (78). Specifically for boys, moving in and out of different positions with control is particularly important on apparatus that is upper-body dominant (e.g., the rings, pommel horse) (21). Gymnasts also rely heavily on lower-limb eccentric strength because they are frequently exposed to landing forces from varying heights, velocities, and rotations (35). Researchers have shown that when simulating the impact velocities female gymnasts experience during dismounts from the balance beam and uneven bars (drop landings from 0.69, 1.25 and 1.82 m), the gymnasts were required to tolerate vertical peak forces that exceeded 9 times their body weight (75). Those able to absorb such forces in an aesthetic manner obtain less deductions, which results in a higher overall score. Therefore, it is evident that gymnasts must manipulate the impulse–momentum relationship to maximize force production for skill execution and to safely tolerate landing forces to avoid injury.
Similarly, peak power is considered to be an essential component of successful gymnastics performance (46). Gymnasts with higher concentric and eccentric strength and power are able to produce more forceful muscle actions at higher velocities (34), enabling the execution of more challenging acrobatic skills. Researchers have shown that resistance training programs can improve relative power-to-mass ratios in gymnasts through increasing peak power outputs during both countermovement and squat jumps (46 and 43% improvement respectively), and reducing fat mass while increasing lean muscle mass. The authors stated that as a result of these adaptations, the gymnasts were able to jump higher, providing increased flight time in which to perform more advanced technical skills, thereby increasing their score potential (34).
The ability to produce high levels of muscular power is salient upon the type of muscular action involved and researchers have shown that when a muscle performs an eccentric action before a concentric action, greater power outputs are produced compared to a concentric action in isolation (54). This sequencing of an eccentric contraction followed immediately by a concentric contraction is referred to as the stretch-shortening cycle (SSC) (54). Research has shown that SSC utilization of both upper and lower limbs are key performance indicators for young gymnasts aged 8–15 years old (14,15). For example, research has shown that young gymnasts with an explosive takeoff from the board (short repulsive board contact time and high takeoff velocity) had increased postflight times, which resulted in fewer deductions and higher scores in vaulting performance (14). Evidence suggests that during the floor exercise, explosive tumbling involves takeoffs with contact times between 115 ± 10 and 125 ± 11 ms (73), underlining the importance of fast-SSC actions (ground contact times < 250 ms) for performance (15). However, recently researchers have found that young elite male gymnasts had unexpectedly poor fast-SSC actions when tested during a 30-cm drop-jump protocol (107). The authors suggested that the gymnasts were not effective in their execution of the drop jump because of an overreliance of sprung surfaces and longer takeoff foot contacts during training of tumbling and vaulting performance (107). The findings could also indicate that gymnasts are very proficient at gymnastics skills which require SSC actions, but have not experienced the use of drop jumps in their training on nonsprung surfaces (57).
The phase of running before the point at which an individual reaches their maximum velocity is referred to as the acceleration phase. The ability to accelerate effectively requires the application of high resultant ground reaction forces in a horizontal direction, relative to body weight (80). Maximal velocity usually occurs between 15 and 30 m in young athletes (76) and refers to the point at which external forces are no longer changing the velocity. The approach to the vault in gymnastics requires rapid acceleration up to 25 m to facilitate an explosive takeoff from the springboard (13). Achieving a high speed during the approach and subsequent power output for the aerial phase is directly associated with improved scores on the vault (15). Elite male gymnasts demonstrate speeds of up to 10.9 m·s−1 during competition (3). In young national standard female gymnasts, average speeds over 18 m were 6.07 m·s−1 (8–10 years old), 6.31 m·s−1 (11–12 years old) and 6.20 m·s−1 (13–14 years old), respectively (15). Interestingly, the results indicate a reduction in sprint speed together with an increase in body mass and height of gymnasts aged from 11–12 to 13–14 years old. Because the natural development of speed throughout childhood and adolescence is thought to follow a nonlinear process (65), the results could reflect a period of “adolescent awkwardness” whereby a temporary disruption in motor coordination occurs because of growth (11). Furthermore, a fast vault run-up speed and resultant takeoff velocity from the spring board were found to be strong predictors (r2 > 0.64) of floor tumbling ability (15), demonstrating the importance of developing high running speeds for artistic gymnastics.
BALANCE AND STABILIZATION
The aptitude to balance and stabilize the body is a complex process involving sensory information from the vestibular, visual, and proprioceptive systems (33) to maintain the body's center of gravity over the base of support (43,87). Gymnasts require the ability to balance and maintain postural control via the upper and lower extremity, during both static and dynamic movements. Factors that affect young gymnasts' ability to stabilize their bodies during such tasks include: the size of the base of support, center of gravity height, and number of limbs in contact with the apparatus (39). Unique to the sport of artistic gymnastics, the equipment's mechanical properties affect the stability of the apparatus which also influences the difficulty of the tasks (19). For example, the handstand is a fundamental skill for male and female gymnasts, which has considerably different demands to maintain stability when performed on different apparatus such as the floor, beam, parallel bars, and rings (19,39). A recent review concluded that when aiming to retain stability during a handstand, the “wrist strategy” can be adopted to maintain the position, providing the gymnast's body remains in a vertical position (39). The “wrist strategy” involves increasing the center of pressure in the fingers or wrists depending on the movement direction of the center of gravity (105). However, if the area of support is smaller for example on the uneven bars, the “shoulder strategy” may be required to maintain balance (39).
Expectedly, researchers have shown that gymnasts have superior balance ability when compared with controls (2,18) and various other sports (22,43). Recent findings from a large data set of children aged 5–14 found that scores from the balance error scoring system significantly improved with increasing age (38). Given the effects of gymnastics-specific training on balance (2,18,22,43), and the natural improvements in balance that manifest during childhood (38), devoting large amounts of time to balance training during young gymnasts' strength and conditioning provision may not be warranted. Instead, warm-ups and injury prevention sessions would serve as the opportune time to incorporate exercises that enhance postural/trunk control, stability, and that emphasize high quality (force absorption) landing tasks.
ENERGY DEMANDS OF GYMNASTICS
The duration of performance within artistic gymnastics varies among activities; the vault exercise can last approximately 5 seconds, whereas the beam and floor exercises can last up to 90 seconds (46). Both the explosive nature of the sport and short duration of the disciplines dictate that the main supply of adenosine triphosphate (ATP) in gymnastics is via the ATP-phosphocreatine and anaerobic glycolytic energy systems. Researchers have shown peak blood lactate concentrations (Lmax) above 4 mmol/L for elite males and females on all apparatus, with the exception of the vault (2.4–2.6 mmol/L) (68). Owing to the variety in duration, intensity and tempo of artistic gymnastics activities and the variability of muscle contraction types during competitive routines, gymnasts never reach a “steady state” in performance (46). Therefore, estimating energy costs from the relationship between V̇o2 and heart rate (HR) is likely to be invalid when drawn from laboratory testing of the athletes (46).
According to longitudinal data regarding the aerobic capacity of gymnasts, typical maximal oxygen uptake (V̇o2max) values have remained around 50 mL/kg/min over the last 5 decades (48). It would appear that aerobic capacity is not a key determinant of performance for artistic gymnasts. This is perhaps unsurprising considering gymnasts are conditioned to perform short, explosive routines, relying predominantly on anaerobic metabolism. However, this is not to say that possessing some level of aerobic capacity is unnecessary (46) because it has been shown that adolescent female gymnasts attain V̇o2max profiles as high as 85% (relative to body mass) after competitive routines, such as the floor exercise (68). Additionally, heart rate data of elite gymnasts have been investigated during each apparatus for both males and females (48,68). Maximal HRs were found to be approximately >180 ± 11.33 beats per minute, with the exception of the vault (and the rings because HR data were not included in the study) (48,68), demonstrating the high-intensity nature of the sport. It would appear from the aforementioned data that during competitive routines, elite gymnasts work close to their metabolic thresholds (45), indicating the need for high-intensity-based conditioning programs. Crucially, gymnasts that are able to recover more efficiently between a series of skills or different events are more likely to sustain a higher level of performance and reduce their relative risk of injury through fatigue. Therefore, although it may not be a primary training emphasis during the developmental years (61), strength and conditioning programs for youth gymnasts should not eliminate aerobic conditioning as a training stimuli, especially when trying to optimize recovery during repeated bouts of exercise.
CHILDHOOD PHYSIOLOGY: AN INCREASED ABILITY TO RECOVER FROM HIGH-INTENSITY EXERCISE
Balancing fatigue during intense training sessions and technical competency of difficult skills is essential to optimize the safety of young gymnasts (46). Performing highly skillful routines in a fatigued state may increase the risk of injury (97). Thus, it is important that young gymnasts are able to facilitate a fast recovery from high-intensity exercise. Researchers have shown that children recover more quickly from high-intensity exercise than adults (31). From a mechanical perspective, children are unable to generate relative power outputs to the same magnitude as adults (95), which is likely to result in less relative fatigue (31). Similarly, researchers have shown that children's type II muscle fibers are similar or smaller in cross-sectional area than their type I fibers (113), which suggests an extensive underuse of type II motor units during the prepubertal years (24). Thus, children's neuromuscular immaturity may impact on their ability to maximally recruit higher-order, type II motor units. This indicates a greater reliance on lower-order type I motor units that facilitates a faster resynthesis of energy substrates, resulting in a faster recovery (31). Additionally, faster phosphocreatine resynthesis has been attributed to children's greater reliance on oxidative metabolism and lower dependence on glycolytic metabolism (24). Children also produce lactate at a lower rate than adults during maximal exercise, resulting in reduced lactate accumulation, though their rate of lactate removal appears to be the same (24). Thus, when aiming to develop anaerobic capacity in young gymnasts, practitioners should consider the influence of growth and maturation on the trainability of this system. Furthermore, young gymnasts will require a certain degree of aerobic conditioning to recover from the high-intensity exercise that the sport demands. It is therefore important for coaches to encompass both anaerobic and aerobic conditioning stimuli in artistic gymnasts' programming.
FLEXIBILITY AND MOBILITY
Unlike other sports that require optimal ranges of motion for skill acquisition and mechanical advantage (61), artistic gymnastics is an aesthetic sport which demands large ranges of motion to achieve certain positions and techniques for the purpose of scoring (6). For example, after appropriate preparation, male gymnasts perform dislocation elements on the high bar and rings (47), underlining the extreme ranges of motion required by the sport. Furthermore, in women's gymnastics, the Code of Points penalizes gymnasts that do not attain 180° of splits during leaps, jumps, and acrobatic skills (6). It is essential to note that although the ability to achieve these limb positions relies heavily on extreme ranges of motion, these movements must be supplemented with appropriate levels of muscle strength throughout the range of motion (21,47).
TRAINING CONSIDERATIONS FOR YOUNG ARTISTIC GYMNASTS
GROWTH, MATURATION, AND TRAINING
Intuitively, gymnastics coaches may favor the selection of late maturing individuals and those that are genetically predetermined to have shorter and slighter statures (particularly in women's gymnastics). However, children develop biologically at different rates, particularly around puberty whereby they experience rapid fluctuations in growth (106). Chronological age is not a valid or reliable indication of maturational status (7). Although technical competency will always be a key determinant of training prescription, it is imperative that consideration is given to biological maturation when training young gymnasts within the same competitive age group. Predicting somatic maturity may be a useful and practically viable marker for coaches to monitor gymnasts' growth and maturation (62). For example, owing to the influence of stature on performance and the high representation of later maturing youth (108), practitioners could determine the percentage of predicted adult stature (52), which offers a practical and reasonably accurate measure of estimated maturity for youth populations (52).
With a clear understanding of biological maturation, practitioners working with young gymnasts should be better placed to prescribe and coach developmentally appropriate training strategies that meet the specific needs and goals of the individual (10,57,59). For example, by collecting basic anthropometric data on a quarterly basis, practitioners can identify with reasonable accuracy when a gymnast is experiencing a growth spurt and can tailor training accordingly. From a physical perspective, when working with youth who are undergoing rapid periods of growth, coaches should spend time addressing any decrements in range of movement (foam rolling soft tissue, unloaded stretches) and balance because of the changes in the height of center of gravity (static and dynamic balancing/stabilizing activities). Furthermore, coaches must individualize programs to target deficits in strength resulting in muscle imbalances (89). There are numerous training strategies available to practitioners to develop the physical performance characteristics of young artistic gymnasts, which can be seen in Figure 2. The challenge of working with youth who are experiencing a growth spurt is exacerbated when sport-specific training loads are high, which are common in youth gymnastics (90). This scenario can lead to high amounts of accumulated fatigue at a time when young gymnasts are experiencing significant biomechanical alterations (e.g., increased limb length, reduced relative strength) as a result of growth. Data suggest that the growth spurt poses an increased risk of injury in young athletes as a result of musculoskeletal vulnerability (70), especially with respect to overuse (17), and acute traumatic (111) injuries. Due to the heightened injury risk during this stage of development, routine screening of basic anthropometric data, and some form of movement screening (e.g., the tuck jump assessment or drop jump testing for knee valgus during landings) is recommended. Similarly, practitioners are also advised to make use of some form of health and well-being questionnaires to monitor sleep, fatigue, muscle soreness, mood, levels of social interaction, and any onset of pain that could be associated with musculoskeletal injuries (57). Furthermore, coaches must carefully monitor training loads (both volume and intensity) and closely monitor the total loads experienced by young gymnasts. This requires a quantification of training load during strength and conditioning training, sport-specific training, and competitions to reduce the risk of overuse-type injuries, nonfunctional overreaching, overtraining syndrome, and burnout (23). Practitioners should adopt an integrated approach to quantify training loads using a combination of both internal and external load metrics to provide insight into the total stress placed on the athletes (12).
A HOLISTIC APPROACH TO TRAINING
Research from numerous reports in various sports has suggested that children specializing in a single sport before puberty may be disadvantaged at a later stage (44,81,83). Historically, gymnastics coaches prioritize the implementation of traditional gymnastics-specific conditioning programs from a very early age (9,92), which often involves circuits of body weight exercises and repetitions of skills. However, although such training programs typically only involve the development of specific physical qualities and movement patterns for gymnastics, it is recognized that well-rounded athleticism should be developed in all youth (57). It is proposed that integrative neuromuscular training (INT), which uses a combination of general and specific strength and conditioning activities to enhance health and skill-related components of fitness (40) could be an advantageous addition to gymnasts' programs to enhance performance and reduce the relative risk of sport-related injury. Crucially, training provision for youth should be programmed in a holistic and integrated manner in order to provide a variety of training stimuli to develop multiple fitness components and overall athleticism (43).
Conventionally, gymnastics coaches' conditioning programs are largely skill driven owing to the specific demands of the sport (49). Training specificity cannot be underestimated in this sport and can be used to prepare gymnasts effectively, providing training is progressively loaded. However, the broader field of strength and conditioning may offer additional benefits to the physical preparation of gymnasts (34,37,67,91). Indeed, the challenge for the strength and conditioning coach working with young gymnasts is to safely provide an effective training stimulus that is different to that which they experience during their sport-specific training, yet is still relevant to their athletic development. Young artistic gymnasts will likely be accustomed to experiencing high ground reaction forces during activities such as tumbling or vaulting (53,103). For example, prepubescent female gymnasts have been shown to endure vertical ground reaction forces of 2–4 times body weight at the wrist and 3–8 times body weight at the ankle on the floor apparatus (16). A major role of the strength and conditioning coach is to increase the robustness of the child to repeatedly tolerate these ground reaction forces safely and effectively, in both a fatigued and nonfatigued state. Frequent exposure to specific movement patterns whereby the application of force is not varied may result in chronically overstressing the musculoskeletal system (8,23). Strength and conditioning coaches working within early specialization sports should be particularly aware of the benefits that movement variability provide for motor skill development and reducing the risk of overuse injuries (8,57). The strength and conditioning coach has a role to play in developing general levels of athleticism in the young child that will facilitate their lifelong participation in sports and activities outside of gymnastics. In the event that a young gymnast decides to disengage from the sport, it is important that they are physically prepared for the demands of other sports or physical activities (57), not just attempting to maximize specific abilities for gymnastics. Finally, coaches should be mindful that strength and conditioning provision with young gymnasts should be fun, challenging, and enjoyable to optimize athlete buy-in and long-term adherence to programs.
STRENGTH AND POWER TRAINING
Traditional fears that resistance training induces excessive muscle hypertrophy resulting in increased body mass have anecdotally discouraged some gymnastics coaches from using this training modality, particularly with young females (34). However, the adaptations from resistance training in youth before the onset of puberty are likely to be neuromuscular in nature (36), meaning that large increases in muscle cross-sectional area are unlikely (61). Consequently, increases in strength during this stage of development—especially in the early stages of the training intervention—will be as a result of improved neuromuscular qualities (motor unit recruitment, synchronization and firing frequency) as opposed to hypertrophic adaptations (59). After the adolescent growth spurt, both neurological and morphological adaptations may also occur as a result of training (61). However, because the goal for most gymnasts would be to develop relative strength, appropriate training prescription (lower repetition ranges, higher intensities, and longer rest periods) should result in myofibrillar hypertrophy and increased functional mass, as opposed to sarcoplasmic hypertrophy and increased nonfunctional mass (102). Sex differences in the rate of muscular growth are apparent after the onset of puberty, with males displaying accelerated gains in strength (65) and females a reduction in strength and power production (88). Decrements in neuromuscular strength during this stage of development may increase females' risk of certain injuries, especially those involving the anterior cruciate ligament (32,93), an injury which is highly prevalent during landings in gymnastics (42). Gymnasts are required to “stick” landings following certain skills and dismounts to avoid large deductions and to optimize performance (6); therefore, the need to develop eccentric strength to assist in force dissipation strategies is necessary. Programs that specifically focus on the development of eccentric strength in highly trained athletes improve power, velocity, and jump height characteristics, compared with controls that trained without an accentuated eccentric load (104). However, there remains a lack of literature that has specifically examined the effects of eccentric strength development in young athletes. Short-term neuromuscular training interventions that focus on “soft” landings with an emphasis on knee and hip flexion significantly improved adolescent female athletes' biomechanics during landings (82), which could be a beneficial strategy for gymnasts to adopt for dismounts and “sticking” landings. Given that gymnasts may develop greater activation in their knee extensor muscles because of a gymnastics-training-induced adaptation before puberty (77), and females are predisposed to deficits in hamstring strength after the onset of puberty (41), integrated neuromuscular training programs (84,86) targeting hamstring strengthening should be incorporated into prepubertal and adolescent young gymnasts training programs.
Irrespective of the stage of development, resistance training for gymnasts with a low training age and low levels of technical competency should begin with exercises that are low to moderate in intensity (e.g., body weight) and technically simple (85). The primary focus should center on building a base level of muscular strength and developing a broad range of robust movement patterns (57). Over time, gymnasts will become proficient at body weight exercises and will ultimately require a new stimulus to overload the body for further adaptation (99). Intensity (or load) can be increased with minimal or no equipment, by altering the body's position against gravity. Additional external load in the form of free weights, elastic resistance bands and medicine balls has been shown to be a safe and effective means of enhancing young athletes' strength within resistance training programs (57). Unfortunately, very few studies have investigated the effects of resistance training programs with artistic gymnasts. Recently, one study in elite prepubertal female gymnasts found that a 16-week training intervention, combing high-impact plyometrics with heavy resistance training, was more effective in improving various parameters of drop jumps (e.g., flight time, contact time, flight-contact ratio, and estimated mechanical power) than habitual skill training (67). As a result, the authors suggested a reduction in time spent on technical routines and repeatedly performing gymnastics movements and the inclusion of 2–3 intense strength and power workouts per week (67), using exercise prescriptions that are in line with existing youth resistance training guidelines (26,59). Furthermore, a recent meta-analysis in well-trained young athletes has concluded that on the premise that technical competency has been suitably developed, the most effective dose–response relationship occurs with conventional resistance training programs of periods >23 weeks, 5 sets per exercise, 6–8 repetitions per set, and a training intensity of 80–89% of 1RM (55). This underlines the need for progressive overload even in youth to ensure ongoing neuromuscular adaptation.
It should also be stressed that when technical proficiency is evident, young gymnasts will likely require exposure to larger external loads, typically elicited through barbell-related activities such as squatting, deadlifting, lunging, and weightlifting exercises (including their derivatives) to promote further adaptations. Resistance training should be implemented as an alternative training session to gymnastics training and not merely as an addition. Regular resistance training should form part of young gymnasts' training programs to develop/maintain levels of muscular strength, avoid detraining of neuromuscular qualities, and to prevent overuse injuries associated with high volumes/intensities of sports-specific training (23,26,28,29,59,110). One to 3 resistance training sessions per week are recommended for young athletes, providing that adequate time for rest and recovery is integrated into the gymnasts' periodized plan (59).
Gymnastic performance is characterized by powerful muscle actions and training must acknowledge the principle of specificity for optimal adaptations. Therefore high contractile velocities are appropriate for training modalities (34). Because training age and technical competency increases over time, resistance training exercises and weightlifting movements can be performed more explosively to promote appropriate neuromuscular adaptations (51). French et al. (34) used a power-specific resistance training program in elite female gymnasts, which significantly enhanced whole body muscular power capacities. The training included exercises that focused on applying as much force as possible in the shortest period of time which is an important factor for performance in gymnastics (34). This resulted in an increased level of performance, as demonstrated in their competition scores (especially on the floor), because of improvements in leaping and tumbling (34). Furthermore, a recent study investigated the effects of a 6-week resistance training program on jumping performance in prepubertal rhythmic gymnasts using sport-specific (3 repetitions of 10 dynamic exercises wearing a weighted belt that was 6% of body mass) and nonspecific (a moderate load/high repetition resistance training program with dumbbells) interventions (91). Although both strength training programs increased lower limb explosive strength by 6–7%, only the nonspecific training intervention significantly improved flight time in the hopping test that assessed leg stiffness (91). Drop jumps are a highly complex task for young athletes to develop proficiency in (9); however, importantly, they are primarily used as a training tool to target fast or slow SSC function through progressive overload. Cueing shorter contact times during drop jumps typically encourages faster SSC activity, whereas cueing athletes to prioritize maximum jump height may result in slower SSC actions (64). An increase in leg stiffness may result in reduced ground contact times, leading to a more efficient utilization of the SSC (1,55). Shorter contact times with rapid amortization periods have been shown to result in greater reutilization of elastic energy (115). Although gymnasts need increased leg stiffness for fast SSC actions, the optimal amount of leg stiffness is task specific (71). Certain skills in gymnasts will require a more compliant system involving longer contact times and slower SSC actions, resulting in greater jump heights (1). Plyometrics have been shown to enhance leg stiffness in young boys (58) and promote improvements in rebound jump height, vertical jump performance, running velocity, and rate of force development (60), all of which are highly relevant to gymnastics.
However, because a large proportion of gymnastics training already involves plyometric exercise, prescribing an alternative training stimulus that focuses on different regions of the force–velocity curve may be more beneficial, such as strength training (high force) or weightlifting derivatives (high force-moderate velocities). Cumulatively, existing research would suggest that integrating resistance training with gymnastic-specific strength programs may indeed provide an additional training stimulus to enhance performance and reduce injury risk in young gymnasts. Although studies have demonstrated the benefits of resistance training for adult gymnasts (34), the effects of a long-term resistance training intervention in prepubertal and adolescent gymnasts is yet to be explored.
The natural development of speed throughout childhood and adolescence is thought to follow a nonlinear process (65), with fluctuating improvements in sprint performance occurring in preadolescent and adolescent periods (112). Researchers have indicated that the trainability of sprint speed is optimal when the prescription matches the natural adaptive processes that occur during maturation, a phenomenon referred to as “synergistic adaptation” (63). For example, when aiming to increase sprint speed in prepubertal populations, using plyometrics to elicit neurally mediated adaptations during this stage of maturation is a favorable form of training (27,63). For postpubertal males experiencing other maturity-related changes, such as natural increases in muscle mass and changes in circulating androgens, (65,109) combined resistance training and plyometrics may be the most optimal training stimulus to improve sprinting velocity (63). It is important to note that coaches should prescreen athletes individually before implementing plyometrics to ensure good technical competency is present during landing tasks (56). This is particularly important for gymnasts if the exercises chosen are not performed on sprung surfaces that the gymnasts are accustomed to. However, as previously stated, gymnasts experience a large amount of plyometric-based training within their sport and therefore strength and conditioning coaches must carefully consider the prescription of such training. Controlling the volume (number of foot contacts) and intensity (via exercise choice) is critical for appropriate periodization of gymnasts' training.
Although integrated neuromuscular programs inclusive of resistance training and plyometrics increase speed (albeit indirectly at times) in young athletes (5,25,40,60,63,94), specific speed training may provide additional adaptations in running speed for young gymnasts. The vault run-up approach in gymnastics is up to 25 m; thus, technical coaching should focus primarily on developing relevant acceleration mechanics and horizontal force production, as opposed to those associated with maximal running velocity. A recent meta-analysis concluded that prescription of speed training for youth should occur twice a week and comprise up to 16 sprints of approximately 20 m, with a work-to-rest ratio of 1:25 (79). Furthermore, the underlying ability to run fast toward the takeoff board and vaulting table relies on both the gymnast's accelerative capacity and the ability to visually control and regulate the approach (13,15). Gymnasts that achieve high speeds when running but slow down as they approach the vault will limit their performance (13,15). Therefore, coaches should aim to develop running speed throughout the vaulting or tumbling sequence in young gymnasts to optimize the transfer of this ability to vaulting performance. To facilitate this transfer, researchers have recommended that coaches implement targeting activities early on with young gymnasts, such as practicing simple vaults from different approach distances (13).
FLEXIBILITY AND MOBILITY TRAINING STRATEGIES
It is common practice for gymnastics coaches to use the proposed sensitive period before puberty (98) for developing optimal levels of flexibility in gymnasts. After the onset of the pubescent growth spurt, researchers have shown that range of motion plateaus or declines, particularly in males (30). Thus, because of the scoring criteria involved in gymnastics which rewards extreme ranges of motion, coaches should emphasize flexibility training throughout childhood and adolescence to maximize whole body range of motion. However, as a caveat to this, it must be recognized that appropriate levels of muscular strength are required to safeguard the young gymnast when using potentially extreme ranges of motion. Thus, strength and conditioning provision of gymnasts should be directed toward balancing the development of large ranges of motion around joints with appropriate strength and neuromuscular stability to reduce injury risk and enhance skill acquisition potential.
Coaches should be aware that there are a number of training modalities available to develop optimal levels of flexibility and mobility in young artistic gymnasts. For static stretches, durations of 10–30 seconds, 3 times per exercise, seem optimal, because longer durations may result in greater gains but a potential weakening of connective tissue (68,98). Gymnasts often stretch on a daily basis because frequency is an important principle of training for maintaining and improving flexibility, and of importance, there are no studies in children that have shown adverse effects to this approach (98). For gymnasts with a greater training age, ballistic stretching can be an effective method to increase ranges of motion, providing they are performed under control (98). Proprioceptive neuromuscular facilitation (PNF) stretching can result in large improvements in range of motion in youth populations (96,114). Although many gymnastics coaches use this technique, caution is necessary so that stretching does not exceed the gymnasts' limits and cause injury (98). This highlights the need for appropriate prescription and supervision when choosing methods to develop range of motion in young gymnasts.
Recently, vibration training has been shown to be very effective in enhancing flexibility and range of motion in young gymnasts (72,100,101), with acute improvements of up to 400% and chronic adaptations of up to 100% reported (101). Greater benefits from vibration training may occur in the gymnast's less flexible leg because of the greater potential for improvement in range of motion available (72). Although the mechanisms underpinning these large improvements in flexibly from vibration training are currently unknown, proposed theories include reduced pain (72,100), inhibited activation of antagonist muscles (20), and increased blood flow resulting in increased tissue temperature (98).
Strength and conditioning coaches working with young gymnasts must provide an effective training stimulus that is different from what they experience during their sport-specific gymnastics training. Because of the demands of the sport, strength, speed, power, flexibility/mobility, and anaerobic power seem to be the key determinants of artistic gymnastics performance; all of which strength and conditioning can improve with appropriate training prescription. When looking to develop these physical capacities in young gymnasts, a number of training strategies can be adopted; however, technical competency must be prioritized at all times. Importantly, when designing training programs, coaches should be aware of the influence growth and maturation can have on the trainability of physical abilities.
One of the authors (G.D.M.) would like to acknowledge funding support from the National Institutes of Health/NIAMS Grant U01AR067997.
1. Arampatzis A, Bruggemann GP, Klapsing GM. Leg stiffness and mechanical energetic processes during jumping on a sprung surface. Med Sci Sports Exerc 33: 923–931, 2001.
2. Asseman FB, Caron O, Crémieux J. Are there specific conditions for which expertise in gymnastics could have an effect on postural control and performance? Gait Posture 27: 76–81, 2008.
3. Atiković A, Smajlović N. The relationship between vault difficulty and biomechanical parameters. Sc GYM 3: 91–105, 2011.
7. Balyi I, Hamilton A. Long-Term Athlete Development: Trainability in Children and Adolescents. Windows of Opportunity, Optimal Trainability. Victoria, Canada: National Coaching Institute British Colombia and Advanced Training and Performance Ltd, 2004.
8. Bartlett R, Wheat J, Robins M. Is movement variability important for sports biomechanists? Sports Biomech 6: 224–243, 2007.
9. Bencke J, Damsgaar R, Saekmose A, Jergensen P, Jorgensen K, Klausen K. Anaerobic power and muscle strength characteristics of 11 years old elite and non-elite boys and girls from gymnastics, team handball, tennis and swimming. Scand J Med Sci Sports 12: 171–178, 2002.
10. Bergeron MF, Mountjoy M, Armstrong N, Chia M, Cote J, Emery CA, Faigenbaum A, Hall G Jr, Kriemler S, Leglise M, Malina RM, Pensgaard AM, Sanchez A, Soligard T, Sundgot-Borgen J, van Mechelen W, Weissensteiner JR, Engebretsen L. International Olympic Committee consensus statement on youth
athletic development. Br J Sports Med 49: 843–851, 2015.
11. Beunen G, Malina RM. “Growth and physical performance relative to the timing of the adolescent spurt”. Exerc Sport Sci Rev 16: 503–540, 1988.
12. Bourdon P, Cardinale M, Murray A, Gastin P, Kellmann M, Varley M, Gabbett T, Coutts A, Burgess D, Gregson W, Cable N. Monitoring athlete training loads: Consensus statement. Int J Sports Physiol Perform 12: S2161–S2170, 2017.
13. Bradshaw E. Target-directed running in gymnastics: A preliminary exploration of vaulting. Sports Biomech 3: 125–144, 2004.
14. Bradshaw E, Sparrow W. The approach, vaulting performance, and judge's score in women's artistic gymnastics. Biomech Symposia: 311–314, 2001.
15. Bradshaw EJ, Le Rossignol P. Anthropometric and biomechanical field measures of floor and vault ability in 8 to 14 year old talent-selected gymnasts. Sports Biomech 3: 249–262, 2004.
16. Burt LA, Naughton GA, Higham DG, Landeo R. Training load in pre-pubertal female artistic gymnastics. Sc GYM 2: 5–14, 2010.
17. Caine D, Maffulli N, Caine C. Epidemiology of injury in child and adolescent sports: Injury rates, risk factors, and prevention. Clin Sports Med 27: 19–50, 2008, vii.
18. Carrick FR, Oggero E, Pagnacco G, Brock JB, Arikan T. Posturographic testing and motor learning predictability in gymnasts. Disabil Rehabil 29: 1881–1889, 2007.
19. Croft JL, Zernicke RF, Von Tscharner V. Control strategies during unipedal stance on solid and compliant surfaces. Motor Control 4: 283–295, 2008.
20. Dallas G, Kirialanis P. The effect of two different conditions of whole-body vibration on flexibility and jumping performance on artistic gymnasts. Sc GYM 5: 67–77, 2013.
21. Dallas G, Zacharogiannis E, Paradisis G. Physiological profile of elite Greek gymnasts. J Phys Ed Sport 13: 27–32, 2013.
22. Davlin CD. Dynamic balance in high level athletes. Percept Mot Skills 98: 1171–1176, 2004.
23. DiFiori J, Benjamin H, Brenner J, Gregory A, Jayanthi N, Landry G, Luke A. Overuse injuries and burnout in youth
sports: A position statement from the American Medical Society for Sports Medicine. Br J Sports Med 48: 287–288, 2014.
24. Dotan R, Mitchell C, Cohen R, Klentrou P, Gabriel D, Falk B. Child-adult differences in muscle activation—A review. Pediatr Exerc Sci 24: 2–21, 2012.
25. Faigenbaum A, Farrell A, Fabiano M, Radler T, Naclerio F, Ratamess N, Kang J, Myer G. Effects of integrative neuromuscular training on fitness performance in children. Pediatr Exerc Sci 23: 573–584, 2011.
26. Faigenbaum AD, Kraemer WJ, Blimkie CJR, Jeffreys I, Micheli LJ, Nitka M, Rowland TW. Youth
resistance training: Updated position statement paper from the national strength and conditioning association. J Strength Cond Res 23: S60–S79, 2009.
27. Faigenbaum AD, McFarland JE, Keiper F, Tevlin W, Ratamess NA, Kang J, Hoffman JR. Effects of a short-term plyometric and resistance training program on fitness performance in boys age 12 to 15 years. J Sports Sci Med 6: 519–525, 2007.
28. Faigenbaum AD, Myer GD. Pediatric resistance training benefits, concerns, and program design considerations. Curr Sports Med Re 9: 161–168, 2010.
29. Faigenbaum AD, Myer GD, Naclerio F, Casas AA. Injury trends and prevention in youth
resistance training. J Strength Cond Res 33: 36–41, 2011.
30. Falciglia F, Guzzanti V, Di Ciommo V, Poggiaroni A. Physiological knee laxity during pubertal growth. Bull NYU Hosp Jt Dis 67: 325–329, 2009.
31. Falk B, Dotan R. Child-adult differences in the recovery from high-intensity exercise. Exerc Sport Sci Rev 34: 107–112, 2006.
32. Ford KR, Shapiro R, Myer GD, Van Den Bogert AJ, Hewett TE. Longitudinal sex differences during landing in knee abduction in young athletes. Med Sci Sports Exerc 42: 1923–1931, 2010.
33. Fransson PA, Kristinsdottir EK, Hafström A. Balance control and adaptation during vibratory perturbations in middle-aged and elderly humans. Eur J Appl Physiol 91: 595–603, 2004.
34. French DN, Gomez AL, Volek JS, Rubin MR, Ratamess NA, Sharman MJ, Gotshalk LA, Sebastianelli WJ, Putukian M, Newton RU, Hakkinen K, Fleck SJ, Kraemer WJ. Longitudinal tracking of muscular power changes of NCAA Division I collegiate women gymnasts. J Strength Cond Res 18: 101–107, 2004.
35. Gittoes M, Irwin G. Biomechanical approaches to understanding the potentially injurious demands of gymnastic-style impact landings. Sports Med Arthrosc Rehabil Ther Technol 4: 4, 2012.
36. Granacher U, Goesele A, Roggo K, Wischer T, Fischer S, Zuerny C, Gollhofer A, Kriemler S. Effects and mechanisms of strength training in children. Int J Sports Med 32: 357–364, 2011.
37. Hall E, Bishop DC, Gee TI. Effect of plyometric training on handspring vault performance and functional power in youth
female gymnasts. PLoS One 11: e0148790, 2016.
38. Hansen C, Cushman D, Anderson N, Chen W, Cheng C, Hon S, Hung M. A normative dataset of the balance error scoring system in children aged between 5 and 14. Clin J Sports Med 26: 497–501, 2016.
39. Hedbávný P, Sklenaříková J, Hupka D, Kalichová M. Balancing in handstand on the floor. Sc GYM 5: 69–80, 2013.
40. Hewett T, Myer GD. The mechanistic connection between the trunk, hip, knee, and anterior cruciate ligament injury. Exerc Sport Sci Rev 39: 161–166, 2011.
41. Hewett TE, Ford KR, Myer GD. Anterior cruciate ligament injuries in female athletes: Part 2, a meta-analysis of neuromuscular interventions aimed at injury prevention. Am J Sports Med 34: 490–498, 2006.
42. Hootman JM, Dick R, Agel J. Epidemiology of collegiate injuries for 15 sports: Summary and recommendations for injury prevention initiatives. J Athl Train 42: 311–319, 2007.
43. Hrysomallis C. Balance ability and athletic performance. Sports Med 41: 221–232, 2011.
44. Jayanthi N, LaBella C, Fischer D, Pasulka J, Dugas LR. Sports-specialized intensive training and the risk of injury in young athletes: A Clinical Case-Control Study. Am J Sports Med 43: 794–801, 2015.
45. Jemni M, ed. Cardiovascular and Respiratory Systems of Gymnasts. Oxon, United Kingdom: Routledge, 2011.
46. Jemni M, ed. Energetics of Gymnastics. Oxon, United Kingdom: Routledge, 2011.
47. Jemni M, ed. Specific Physical and Physiological Assessments of Gymnasts. Oxon, United Kingdom: Routledge, 2011.
48. Jemni M, Friemel F, Le Chevalier JM, Origas M. Heart rate and blood lactate concentration analysis during a high level men’s gymnastics competition. J Strength Cond Res 14: 389–394, 2000.
49. Jemni M, Sands WA, eds. Training Principles in Gymnastics. Oxon, United Kingdom: Routledge, 2011.
50. Katrichis NE, Moca A. Sports performance series: The planche. Natl Str Cond Assoc J 14: 6–9, 1992.
51. Kawamori N, Newton RU. Velocity specificity of resistance training: Actual movement velocity versus intention to move explosively. J Strength Cond Res 28: 86–91, 2006.
52. Khamis HJ, Roche AF. Predicting adult stature without using skeletal age—The Khamis-Roche method. Pediatrics 94: 504–507, 1994.
53. Kochanowicz A, Kochanowicz K, Niespodziuski B, Mieszkowski J, Aschenbrenner P, Bielec G, Szark-Eckardt M. Maximal power of the lower limbs of youth
gymnasts and biomechanical indicators of the Forward handspring vault versus the sports result. J Hum Kinet 53: 33–40, 2016.
54. Komi PV. Stretch-shortening cycle: A powerful model to study normal and fatigued muscle. J Biomech 33: 1197–1206, 2000.
55. Lesinski M, Prieske O, Granacher U. Effects and dose-response relationships of resistance training on physical performance in youth
athletes: A systematic review and meta-analysis. Br J Sports Med 50: 781–795, 2016.
56. Lloyd R, Cronin J. Plyometric development in youth
. In: Strength and Conditioning for Young Athletes Science and Application. Lloyd RS, Oliver JL, eds. Oxon, United Kingdom: Routledge, 2014. pp. 100.
57. Lloyd R, Cronin J, Faigenbaum A, Haff G, Howard R, Kraemer W, Micheli L, Myer G, Oliver J. The national strength and conditioning association position statement on long-term athletic development. J Strength Cond Res 30: 1491–1509, 2016.
58. Lloyd R, Oliver J, Hughes M, Williams C. The effects of 4-weeks of plyometric training on reactive strength index and leg stiffness in male youths. J Strength Cond Res 26: 2812–2819, 2012.
59. Lloyd RS, Faigenbaum AD, Stone MH, Oliver JL, Jeffreys I, Moody JA, Brewer C, Pierce KC, McCambridge TM, Howard R, Herrington L, Hainline B, Micheli LJ, Jaques R, Kraemer WJ, McBride MG, Best TM, Chu BA, Alvar BA, Myer GD. Position statement on youth
resistance training: The 2014 International consensus. Br J Sports Med 48: 498–505, 2014.
60. Lloyd RS, Meyers RW, Oliver JL. The natural development and trainability of plyometric ability during childhood. J Strength Cond Res 3: 23–32, 2011.
61. Lloyd RS, Oliver JL. The youth
physical development model: A new approach to long-term athletic development. J Strength Cond Res 34: 61–72, 2012.
62. Lloyd RS, Oliver JL, Faigenbaum AD, Myer GD, De Ste Croix MBA. Chronological age vs. biological maturation- implications for exercise programming in youth
. J Strength Cond Res 28: 1454–1464, 2014.
63. Lloyd RS, Radnor JM, De Ste Croix MBA, Cronin JB, Oliver JL. Changes in sprint and jump performances after traditional, plyometric, and combined resistance training in male youth
pre- and post-peak height velocity. J Strength Cond Res 30: 1239–1247, 2015.
64. Louder T, Bressel M, Bressel E. The kinetic specificity of plyometric training: Verbal cues revisited. J Hum Kinet 49: 201–208, 2015.
65. Malina R, Bouche R, Bar-Or O. Growth, Maturation, and Physical Activity. Champaign, IL: Human Kinetics, 2004.
66. Malina RM, ed. Growth, Maturation and Development: Applications to Young Athletes and in Particular Divers. Indianapolis, IN: Diving, 2007. pp. 3–29.
67. Marina M, Jemni M. Plyometric training performance in elite-oriented prepubertal female gymnasts. J Strength Cond Res 28: 1015–1025, 2014.
68. Marina M, Rodriguez FA. Physiological demands of young women's competitive gymnastic routines. Biol Sport 31: 217–222, 2014.
69. McLaughlin PA, Geiblinger H, Morrison WE. Take-off characteristics of double back somersaults on the floor. 13 International Symposium on Biomechanics in Sports, Canada, 1995.
70. McKay D, Broderick C, Steinbeck K. The adolescent athlete: A developmental approach to injury risk. Pediatr Exerc Sci 28: 488–500, 2016.
71. McMahon JJ, Comfort P, Pearson P. Lower limb stiffness effect on performance and training considerations. Strength Condl 34: 94–101, 2012.
72. McNeal JR, Edgerly S, Sands WA, Kawaguchi J. Acute effects of vibration-assisted stretching are more evident in the non-dominant limb. Eur J Sport Sci 11: 45–50, 2011.
73. McNeal JR, Sands WA, Shultz BB. Muscle activation characteristics of tumbling take-offs. Sports Biomech 6: 375–390, 2007.
74. McNitt-Gray JL, Munkasy B, Welch M. External reaction forces experienced by gymnasts during the take-off and landing of tumbling skills. Technique 14: 10–16, 1994.
75. McNitt-Gray JL, Yokoi T, Millward C. Landing strategy adjustments made by female gymnasts in response to drop height and mat composition. J Appl Biomech 9: 173–190, 1993.
76. Meyers RW, Oliver JL, Hughes MG, Cronin JB, Lloyd RS. Maximal sprint speed in boys of increasing maturity. Pediatr Exerc Sci 27: 85–94, 2015.
77. Mitchell C, Cohen R, Dotan R, Gabriel D, Klentrou P, Falk B. Rate of muscle activation in power- and endurance-trained boys. Int J Sports Physiol Perform 6: 94–105, 2011.
78. Mkaouer B, Jemni M, Amara S, Chaabène H, Tabka Z. Kinematic and kinetic analysis of two gymnastics acrobatic series to performing the backward stretched somersault. J Hum Kinet 37: 17–26, 2013.
79. Moran J, Sandercock G, Rumpf MC, Parry DA. Variation in responses to sprint training in male youth
athletes: A meta-analysis. Int J Sports Med 38: 1–11, 2017.
80. Morin JB, Bourdin M, Edouard P, Peyrot N, Samozino P, Lacour JR. Mechanical determinants of 100-m sprint running performance. Eur J Appl Physiol 112: 3921–3930, 2012.
81. Mostafavifar AM, Best TM, Myer GD. Early sport specialisation, does it lead to long-term problems? Br J Sports Med 47: 1060–1061, 2013.
82. Myer G, Ford K, Paulumbo J, Hewett T. Neuromuscular training improves performance and lower-extremity bio in female athletes. J Strength Cond Res 19: 51–60, 2005.
83. Myer G, Jayanthi N, DiFiori J, Faigenbaum A, Kiefer A, Logerstedt D, Micheli L. Sports specialization, Part II: Alternative solutions to early sport specialization in youth
athletes. Sports Health 8: 65–73, 2016.
84. Myer GD, Ford KR, McLean SG, Hewett TE. The effects of plyometric versus dynamic stabilization and balance training on lower extremity biomechanics. Am J Sports Med 34: 445–455, 2006.
85. Myer GD, Lloyd RS, Brent JL, Faigenbaum AD. How young is “too young” to start training? ACSMs Health Fit J 17: 14–23, 2013.
86. Myer GD, Sugimoto D, Thomas S, Hewett TE. The influence of age on the effectiveness of neuromuscular training to reduce anterior cruciate ligament injury in female athletes: A meta-analysis. Am J Sports Med 41: 203–215, 2013.
87. Nashner LM, ed. Practical Biomechanics and Physiology of Balance. San Diego, CA: Singular Publishing Group, 1997.
88. O'Brien TD, Reeves ND, Baltzopoulos V, Jones DA, Maganaris CN. Strong relationships exist between muscle volume, joint power and whole-body external mechanical power in adults and children. Exp Physiol 94: 731–738, 2009.
89. Oliver J, Brady A, Lloyd R. Well-being of youth
athletes. In: Strength and Conditioning Consideration for Young Athletes: Science and Application. Lloyd R, Oliver J, eds. Oxon, United Kingdom: Routledge, 2014. pp. 214–223.
90. Pasulka J, Jayanthi N, McCann A, Dugas LR, LaBella C. Specialization patterns across various youth
sports and relationship to injury risk. Phys Sportsmed 45: 344–352, 2017.
91. Piazza M, Battaglia C, Fiorilli G, Innocenti G, Iuliano E, Aquino G, Calcagno G, Giombini A, Di Cagno A. Effects of resistance training on jumping performance in pre-adolescent rhythmic gymnasts: A randomized controlled study. Ital J Anat Embryol 119: 10–19, 2014.
92. Pion J, Lenoir M, Vandorpe B, Segers V. Talent in female gymnastics: A survival analysis based upon performance characteristics. Int J Sports Med 36: 935–940, 2015.
93. Quatman-Yates CC, Myer GD, Ford KR, Hewett TE. A longitudinal evaluation of maturational effects on lower extremity strength in female adolescent athletes. Pediatr Phys Ther 25: 271–276, 2013.
94. Radnor JM, Lloyd R, Oliver J. Individual response to different forms of resistance training in school-aged boys. J Strength Cond Res 31: 787–797, 2017.
95. Ratel S, Bedu M, Hennegrave A, Doré E, Duché P. Effects of age and recovery duration on peak power output during repeated cycling sprints. Int J Sport Med 23: 397, 2002.
96. Rubini EC, Souza AC, Mello ML, Bacurau RF, Cabral LF, Farinatti PT. Immediate effect of static and proprioceptive neuromuscular facilitation stretching on hip adductor flexibility in female ballet dancers. J Dance Med Sci 15: 177–181, 2011.
97. Sands W. Injury prevention in women's gymnastics. Sports Med 30: 359–373, 2000.
98. Sands W, McNeal J, eds. Mobility Development and Flexibility in Youth
. Oxon, United Kingdom: Routledge, 2014.
99. Sands W, McNeal J, Jemnic M, Delonga T. Should female gymnasts lift weights? Sportsciorg 4, 2000. Available at: http://sportsci.org/jour/0003/was.html
100. Sands W, McNeal J, Stone M. Vibration, split stretching, and static vertical jump performance in young male gymnasts. Med Sci Sports Exerc 41: 80, 2009.
101. Sands W, McNeal J, Stone M, Russel E, Jemni M. Flexibility enhancement with vibration: Acute and long-term. Med Sci Sports Exerc 38: 720–725, 2006.
102. Schoenfeld B. The mechanisms of muscle hypertrophy and their application to resistance training. J Strength Cond Res 24: 2857–2872, 2010.
103. Seely MK, Bressel E. A comparison of upper-extremity reaction forces between the yurchenko vault and floor exercise. J Sports Sci Med 4: 85–94, 2005.
104. Sheppard J, Hobson S, Barker M, Taylor K, Chapman D, McGuigan D, Newton R. The effect of training with accentuated eccentric load counter-movement jumps on strength and power characteristics of high-performance volleyball players. Int J Sports Sci Coach 3: 335–363, 2008.
105. Sobera M. Maintaining body balance in extreme positions. Sport Biol 24: 81–83, 2007.
106. Stratton G, Oliver JL, eds. The Impact of Growth and Maturation on Physical Performance. Oxon, United Kingdom: Routledge, 2014.
107. Suchomel T, Sands W, McNeal J. Comparison of static, countermovement, and drop jumps of the upper and lower extremities in U.S. Junior national team male gymnasts. Sc GYM 8: 15–30, 2016.
108. Theodoropoulou A, Markou KB, Vagenakis GA, Benardot D, Leglise M, Kourounis G, Vagenakis AG, Georgopoulos NA. Delayed but normally progressed puberty is more pronounced in artistic compared with rhythmic elite gymnasts due to the intensity of training. J Clin Endocrinol Metab 90: 6022–6027, 2005.
109. Tonson A, Ratel S, Le Fur Y, Cozzone P, Bendahan D. Effect of maturation on the relationship between muscle size and force production. Med Sci Sports Exerc 40: 918–925, 2008.
110. Valovich McLeod T, Decoster L, Loud K, Micheli L, Parker J, Sandrey M, White C. National Athletic Trainers' Association position statement: Prevention of pediatric overuse injuries. J Athl Train 46: 206–220, 2011.
111. Van der Sluis A, Elferink-Gemser M, Coelho-e-Silva M, Nijboer J, Brink M, Visscher C. Sport injuries aligned to peak height velocity in talented pubertal soccer players. Int J Sports Med 35: 351–355, 2014.
112. Viru A, Loko J, Harro M, Volver A, Laaneots L, Viru M. Critical periods in the development of performance capacity during childhood and adolescence. Eur J Phys Educ 4: 75–119, 1999.
113. Vogler C, Bove KE. Morphology of skeletal muscle in children. An assessment of normal growth and differentiation. Arch Pathol Lab Med 109: 238–242, 1985.
114. Wicke J, Gainey K, Figueroa M. A comparison of self-administered proprioceptive neuromuscular facilitation to static stretching on range of motion and flexibility. J Strength Cond Res 28: 168–172, 2013.
115. Wilson G, Wood G, Elliott B. Optimal stiffness of series elastic component in a stretch-shorten cycle activity. J Appl Physiol 70: 825–833, 1991.