Research Review By Dr. Brynne Stainsby©

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Date Posted:

February 2019

Study Title:

Developmental changes in the youth athlete: implications for movement, skills acquisition, performance and injuries

Authors:

Corso M

Author's Affiliations:

Department of Graduate Studies, Canadian Memorial Chiropractic College, Toronto, Canada.

Publication Information:

Journal of the Canadian Chiropractic Association 2018; 62(3): 150-160.

Background Information:

While there has been a rising rate of youth (ages 6-18) participation in competitive sport over the past decade, there has been a concurrent drop in school-based physical education in America (1). Due to this fact, many competitive athletes are not exposed to various sports during childhood, and the topic of early sport specialization (ESS) has gained increasing attention in the media and sport communities (2). Defined as intensive, year-round training in a single sport, ESS has gained popularity among competitive athletic populations; with up to 91% of athletes believing specialization is essential for their future success (2, 3).

Athletes are stratified in the literature based on three criteria to determine their degree of specialization:
  1. training more than eight months per year,
  2. choosing a single main sport, and
  3. quitting all sports to focus on one sport (2, 4, 5).
The degree of specialization increases with the greater number of criteria that may be applied to the athlete; however, it is important to note that the criteria do not account for an athlete who has only ever participated in one sport (i.e. cannot respond “yes” to question three), and coaches and clinicians should account for this.

In general, athletes with a low specialization (1/3 of the above factors) have a low risk for injury, but a moderate risk of acute injury. Moderate (2/3) and highly (3/3) specialized athletes, on the other hand, have a moderate and high risk of injury, but a low risk of acute injuries (2, 4, 5). It should also be noted that participating in over 16 hours per week of organized activity (regardless of the number of sports) is also associated with an increased risk for injury (2, 4).

In the United States alone, sport and recreation-related injuries account for 8.6 million consultations in the emergency department annually (6), with basketball, football and soccer representing the most common injuries in patients under the age of 18 (7). In sports medicine clinics, 67% of injuries occurred in the lower extremity, with serious overuse injuries most commonly affecting the knee, and serious acute injuries most commonly affecting the ankle (8).

It has been proposed that the risks of ESS include a greater risk of injury, limiting overall motor skill, sociological and psychological development, and possibly even burnout. In addition, it has also been identified that success at a young age does not necessarily predict long-term athletic success, and in some cases (such as swimming), it may limit future achievements (2, 5).

Given the increasing number of youth athletes participating in competitive sport, the purpose of this review is to examine the changes that are occurring in young athlete’s development and the relevant implications on movement, performance and injury.

Summary:

Growth, Maturation & Development:
  • Average age of peak height velocity (PHV or ‘growth spurt’) is 12 years old in girls and 14 in boys (9). Typically, peak leg length growth occurs prior to or during PHV, while peak trunk height growth occurs during or after.
  • It is important to note that peak growth velocity for body mass occurs approximately one year after PHV (10). This increase in bone growth requires increased strength, resulting in a greater demand on muscles that are not fully developed (11). As increases in muscle spindles and moment arms occur with growth, more muscles gain mechanical advantage over time (12, 13).
  • Tendon length and cross-sectional area (CSA) increase through athlete growth and development (14). In addition to physiological changes, increased loading of the tendon (such as resistance training) also contributes to tissue maturation (15-19).
  • Fascia develops in response to load, however, no studies have been conducted to outline the changes that occur through growth/development of young athletes.
Implications for Movement:
  • It has been suggested that in order to refine postural control and movement, humans require the ability to quickly integrate sensory information appropriately, and this increases with age (20, 21).
  • In order to perform a task appropriately, integration of the sensory and neuromuscular systems must occur. Given the number of changes which occur through the period of growth, motor patterns must be adjusted.
  • Throughout childhood, the contractile properties of muscles, lower neuromuscular efficiency and musculotendinous stiffness, and greater electromechanical delay (EMD, the time between muscle activation and force production) contribute to lower voluntary muscle activation (12, 16, 22-25). During development, these factors change and athletes become more able to activate muscles and produce more rapid, coordinated movements.
  • In the pediatric population, learning a new task (particularly multi-joint, complex movements involved in sport) requires controlling body mass, opposing and taking advantage of gravity as required, and matching muscular and non-muscular forces (26). Coaches and athletes should be aware this means children require more time for training and skill acquisition.
Implications for Skill Acquisition:
  • Open kinetic chain skills (throwing, striking, kicking, etc.) require linear and rotational translation of energy through proximal to distal sequencing of segments (27, 28). Optimizing the timing of this sequence allows for greater recovery of stored elastic potential, reduces torque and improves the quality of movement (29, 30).
  • Coaches, parents and trainers should be aware that, given how children learn tasks, focusing on functional outcomes (rather than performance cues) allows athletes to explore movement and their preferred or optimal method of performance (28). Changing environmental constraints (while keeping the task consistent) may also facilitate the learning of movement outcomes (27).
Implications for Performance:
  • Changes in body size, muscle mass and the neuromuscular system during the developmental period for athletes can contribute to movement, coordination and performance. Typically, this process is improved through adolescence, and changes in EMD and the rate of force development improve power production during multi-joint tasks (31-33).
  • During growth spurts, the relative lengthening and resting tension of muscles, the increased mass of the muscles and delay in muscle development limits the amount of force that can be produced. Additionally, altered neuromuscular control during this time can lead to impaired coordination (‘adolescent awkwardness’), during and up to one year following rapid growth (34-38).
  • During this phase, performance may plateau or deteriorate while the athlete adapts to perceptual, spatial, physiological and biomechanical changes caused by growth (39).
Implications for Injury:
  • The delay of muscle hypertrophy and length (relative to bone growth) may place young athletes at risk for injury, particularly traction apophysitis (11, 40-42).
  • Decreased neuromuscular control, strength imbalances and uncoordinated biomechanics may also lead to injuries (43).
  • Differing rates of development between individuals may also contribute to injuries, particularly in contact sports where athletes are grouped by age. For example, in a study of 13-15 year old ice hockey players, differences between the smallest and largest players were 53 cm and 53 kg (44). These differences in anthropometrics can create significant differences in force production and potential for injury (45).
  • Increased training during periods of rapid growth may increase injury susceptibility (46).
  • Equipment must also be considered, as it is possible to overload an athlete or lead to negative impact absorption or energy transfer if it does not fit the athlete correctly (43).

Clinical Application & Conclusions:

Given that many growth and developmental changes are occurring in youth and adolescent athletes, coaches, trainers and clinicians should be aware of periods of growth, which can impact loads on all body tissues. It is important to note that muscle and fascial growth is delayed relative to bone growth, and is not related to concurrent improvements in strength. Typically, the year following peak height velocity (the ‘growth spurt’) is a year of adaptation, with increased muscle length, cross-sectional area, muscle and tendon stiffness and bone mineral density. This typically relates to impaired or altered coordination of movement following the growth spurt. Coaches, athletes and parents should be aware that skill acquisition may be challenging at this time, and performance may plateau or deteriorate.

The period following growth is also a time period where overuse injuries are likely to occur. Clinicians, trainers and coaches may adapt training volume and/or intensity, as required, as well as provide additional opportunity for skill acquisition and/or re-learning.

Study Methods:

Methods were not reported, as this was a narrative review.

Study Strengths / Weaknesses:

Strengths:
  • This study provided an interesting overview of the physiological changes occurring in the body systems during periods of growth and development for young athletes.
  • This review highlights the implications for movement, skill acquisition, performance and injuries in young athletes, and highlights areas of awareness for athletes, parents, coaches, trainers and clinicians.
Weaknesses:
  • The greatest weakness of a narrative review is the lack of methodology reported, including the search strategy, or if or how the included articles were appraised. Without this sort of detail, we cannot be confident that the results and conclusions were not subject to a high risk of bias.
  • Given only a single author conducted this review, again, we cannot be confident that the results and conclusions were not subject to high risk of bias.
  • Though the content of this review focuses on developmental changes of youth athletes, the introduction focuses on ESS but does not revisit this concept, nor how ESS specifically may affect growth and development, or alter injury rates.

Additional References:

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