This series will analyze current evidence for training the general youth populations as well as for those who already consider themselves athletes. We will give a historical perspective on the state of strength training in youth and offer recommendations for training individuals and teams. These recommendations will serve as the basis for developing strength and athletic potential. Each sport involves unique constraints and, consequently, demands certain skill sets. What is undeniable is the role that physical strength plays in a wide array of sports and its utility in overall physical fitness. We will start with a discussion of the current status quo and build an argument for where programming needs to go.
Audio Version plus an interview with Dr. Miles:
Part 1: Current State of Affairs
A dogmatic approach to resistance training in the youth population has hindered the progression of a scientific consensus for decades. Axioms such as “Resistance training stunts growth” and “Resistance training damages adolescent growth plates” have stymied proper study methodology and forced an overreliance on expert opinion. Fortunately, the past 20 years have seen a slow shift away from that approach as these axioms have fallen in the research literature. We now have evidence-based recommendations that advocate resistance training for the current and long-term health of the youth and adolescent populations.
In the 2014 international consensus position statement on youth resistance training, Lloyd et al went so far as to state “misinformed concerns that resistance training would be harmful to the developing skeleton have been replaced by reports indicating childhood may be the opportune time to build bone mass and enhance bone structure by participating in weight-bearing physical activities.”
In fact, the American Academy of Pediatrics released a 2008 position statement dispelling the myth of detrimental effects from resistance training, while promoting the positive outcomes emerging in the literature. This piece presented three arguments:
- Resistance training should be an essential component of preparatory training for aspiring athletes.
- Participation in resistance training earlier in life correlates with participation later in life.
- Individuals who do not participate in resistance training are likely at increased risk of negative consequences.
To the first point, they argue:
“Developing the technical skill and competency to perform a variety of resistance training exercises at the appropriate intensity and volume, while providing youth with an opportunity to participate in programmes that are safe, effective, and enjoyable.”
This statement has multiple components that deserve further discussion. Technical skill and competency come with routine practice. In his book Outliers, Malcolm Gladwell popularized the theory that it takes approximately 10,000 hours of deliberate practice to master a skill. This idea was based off a 1993 study by Anders Ericsson titled “The Role of Deliberate Practice in the Acquisition of Expert Performance.” While the so-called “10,000 hour rule” is likely flawed for multiple reasons (the author has actually refuted Gladwell’s claim), waiting until early adulthood to begin to develop technical skills is likely placing the population at an increased risk of the negative consequences mentioned.
However, it should be noted that this is not making a case for early sports specialization (as will be discussed later), but rather a case for beginning to develop skills earlier in life. A 2018 study by Henriksson et al found that among a cohort of 1.2 million Swedish males, being “unfit, weak, and obese” was associated with an increased risk of disability. The original cohort of this study was 16-19 year old males. Another study from Varma et al in 2017 compared physical activity of individuals across the lifespan using accelerometer data. They found that on average, today’s 16 year olds participate in about the same amount of physical activity as today’s 60 year olds. Accelerometer data is not without flaws, as it does a poor job of measuring resistance training, but this study is damning for the overall physical activity habits of the general population today.
Current World Health Organization recommendations for youth aged 5-17 years is to engage in 60 minutes of moderate-to-vigorous physical activity each day. Systematic reviews and meta-analyses on the subject evaluating participation in physical education class show we are falling well short of that measure. For example, using accelerometer data, Hollis et al showed elementary students met that standard only 50% of the time, while Fairclough and Stratton found an even lower participation at 34.2%. This same trend carries on through secondary school, where only 40.5% of physical education class achieved the moderate-vigorous threshold. So while healthcare providers and trainers are frequently exposed to the perspective of an athlete who is overtraining, we must be mindful that as a whole, the adolescent population is grossly undertrained.
The current American College of Sports Medicine recommendation for the implementation of resistance training is 2-3 times per week in the adult population. In a 2016 review by Dankel et al only 18.3% of individuals met this criteria — but among those who did, a 23% reduction in all-cause mortality was observed. Consider that we have people purchasing supplements with no evidential support or a possible “single-digit” effects, when there is evidence that the addition of resistance training can generate double-digit benefits.
The reasons why this has not been adopted more readily are multifactorial, as we will discuss.
Early Sports Specialization
The American Academy of Pediatrics position statement on resistance training advocates for a variety of resistance training exercises. However, we are faced with an epidemic of 1) no resistance training, and 2) a continued push towards specificity of training earlier in the youth population.
In the United States 75% of families have at least one child who participates in organized sport. Early sports specialization continues to rise with 12% of children under the age of 7 participating in sport in 2008, representing an increase from 9% in 1997. While a 3% increase over a decade may seem small, consider how many actual children this represents who are now participating in organized sport before the third grade. According to DiFiori et al, as of 2013, 60 million youth in the US between the ages of 6 and 18 participate in organized sport.
Jayanthi et al define “early sports specialization” as: “intense, year round (>8 months) training in a single sport with the exclusion of other sports.” A recent review by Post et al sought to examine the association between early sport specialization and risk of injury. While athletes exceeding greater than 8 months of participation in a single sport experienced the greatest risk of injury, athletes who participate in greater than 8 months of any organized sport were also at an increased risk of injury. Two other variables also correlated with increased risk:
- Participation in more hours of organized sport per week than the age of the child (i.e. a 12 year old participating in more than 12 hours/week), an
- Greater than 16 hours/week of organized sport in general.
This would seem to call into question the current trend in youth sports for organized sports at an increasingly young age.
According to the National Collegiate Athletic Association (NCAA), the belief that early sports specialization will lead to increased probability of playing at the next level is fallacious. In their 2018 report, high school males have a conversion rate (i.e., progressing from high school to collegiate sport) varying from 12.4% in lacrosse to 2.9% in wrestling. For females, the highest rate is 24.5% for ice hockey, while the lowest is 3.8% for basketball. It should be noted that even these numbers may be inflated, as many athletes in high school do not play for their school, but instead opt to play for travel teams that would not be accounted for in these data.
If a child does have the ability to play in college, the average scholarship is only $10,400 per year, with many of the athletes in this report not receiving a scholarship at all. Conversely, it is not unheard of for parents to spend $1000/month on coaching, tournaments, travel, and food for their kids. Considering that these expenses can begin as early as age six, that seems to cancel out the average scholarship benefits fairly quickly.
What is more interesting is the mounting evidence that those athletes who do go on to play in college are actually less likely to specialize early. Another study by Post et al examined a cohort of athletes from a major Division I university. Of their athletes, only 16.9% specialized by their freshman year and 41.1% by their senior year. This means that of the athletes at this university, over half were multi-sport athletes coming out of high school.
Buckley et al surveyed 3090 high school, collegiate, and professional athletes in 2017 and found respectively that 45.2%, 67.7%, and 45% of those athletes had quit another sport to focus solely on one. While there is the possibility that those athletes had only played one sport all along, it still appears that less than half of the professional athletes surveyed participated in only one sport.
The Buckley paper presents other data that can be framed through the early sports specialization lens as well. The average age for professional and collegiate athletes to specialize was almost 15, while high school athletes specialized just before age 13. With high school athletes specializing almost two years earlier, it is easy to hypothesize that this early specialization could lead to an increased risk of burnout in sport. In this light, we may be exposing youth to a type of survivorship bias, where only those who do not get injured or burn out “survive” to make it to the next level.
Consider: how many excellent 12 year old athletes end up becoming amazing 18+ year old athletes? Baseball pitchers who throw at a higher velocity early are at an increased risk of injury. Volleyball players who jumped higher were at double the risk of injury as their less talented peers. Coaches, parents, and peers could be placing these talented athletes under a “Damoclean sword” by continuing to showcase their success at an early age.
Bell et al performed a meta-analysis in 2018 examining the risk of injury associated with sports specialization. Compared to non-specialized athletes, highly specialized athletes were 1.81 times more likely to suffer an injury (CI 1.26-2.60). In layman’s terms, specialized athletes were almost twice as likely to get injured as athletes who did not specialize. McGuine et al conducted a prospective study on the association of specialization and injury risk in a cohort of over 1500 high school athletes. Those who were either moderately or highly specialized were at an increased risk of suffering a lower extremity injury than their less-specialized peers.
It is therefore difficult to advocate for youth training to become the best on the field at a very young age, when research increasingly suggests that their time on the field may actually be more limited due to injury. Quite possibly, taking baseball players, swimmers, volleyball players off the field, out of the pools, and off the court and getting them in the gym can make them better athletes. Post et al showed that highly specialized athletes were more likely to report an injury of any kind in the previous year compared to their less-specialized peers. O’Kane et al demonstrated that among risk factors for female soccer players sustaining a lower extremity injury, playing on more than 1 soccer team increased the risk of injury by 2.5, while participating in multiple physical activities decreased the risk by 61%.
This has also been demonstrated at the elite level. Rugg et al examined 237 first-round NBA draft picks from 2008-2015. Of those athletes, 201 (85%) had specialized into one sport by the time of high school. Among these specialized athletes, 42.8% had suffered one major injury compared to 25% in the non-specialized group. While this does not account for contact versus non-contact injuries, it still accounts for a significant difference. This means that athletes who were specialized had an over 50% increase in the likelihood of having suffered an injury.
DiFiori et al recently released a position statement on overuse injuries in youth sports, with estimations that 45-54% of youth injuries are directly related to overuse (68% in running). This likely means that youth are not getting injured because of their sport, but rather because of how much they are participating in their sport. Of course, there are multiple contributors to an overuse injury besides just participation in one sport. Overscheduling and under-recovery are also factors contributing to injury risk. Athletes who participate in more practices within 48 hours of competition and athletes getting less than 6 hours of sleep the night before a competition are also at increased risk. Similarly, athletes averaging less than 8 hours of sleep are 1.7 times more likely to suffer an injury based on data from Milewski et al.
We must emphasize that early sports specialization is disadvantageous for all sports, including those focused on resistance training. While there are no specific longitudinal studies looking at injury risk for youth powerlifting or weightlifting, we must assume from the general heuristic that even these athletes need variability in sport. While we are strongly advocating that youth athletes need to resistance train, this is not all they need to do to become well rounded, resilient athletes. A 2019 study by Bush et al looked at American weightlifters and found that 75.9% of those surveyed did not specialize before the age of 21. It was a retrospective study with only 141 athletes submitting so it is not without flaws. However, the odds ratio for youth specialization in weightlifting versus non-specialized athletes was 23.9 (95% CI 4.1-138). Even on the low end of that confidence interval, youth specializing in weightlifting were over 4 times as likely as their non-specialized peers to have sustained an injury.
These overuse injuries do not solely manifest in physical form either. Psychological burnout is another repercussion of the movement towards early sports specialization. Psychological burnout as it relates to sport has been defined as:
- Sport-related exhaustion (persistent fatigue related to overtaxing in sport)
- Sport-related cynicism (indifference or distal attitudes towards sports)
- Feelings of inadequacy (perception of not performing as well as one used to).
Similar to the physical overuse injuries described above, psychological burnout correlates with the amount of time athletes participate in sport, but also with the expectation of sport. This introduces the concepts of expectations and the goal of sports participation.
Many parents view early specialization as a means to increase the likelihood of their child progressing to the collegiate or professional level of sport. These performance-based goals are based on demonstrating normative competence (e.g., superiority or winning), and have been shown to increase the likelihood of athletes suffering burnout.
Padaki et al sought to quantify the influence of parents on early sport specialization in 2017. When queried, 20.4% of the parents in their cohort had hopes of their child playing at the professional level, and 36.4% hoped they would play at the collegiate level. These parental expectations often translate into increased pressure on the youth. In this cohort, the average age of the athlete was just under 14 years, with 72% already suffering an overuse injury and 16.6% already having undergone surgery.
The psychological state of an athlete can also influence physical injury risk. Athletes often feel pressure to perform with perfection. This may involve winning, or coaches demanding a specific pattern of movement or skill execution. Perfectionism is defined as striving for a flawless performance and setting exceedingly high standards of performance, accompanied by tendencies for overly critical evaluations of one’s behavior. Madigan et al looked at the association between perfectionism and risk of injury in junior athletes and found “the likelihood of sustaining an injury was increased by over two times for each one standard deviation increase in perfectionistic concerns.” Once again, psychological dispositions can manifest as increased risk of physical injuries in the athlete.
Instead of taking a perfectionist approach, Sorkilla et al recommend setting goals directed towards mastery; that is, goals primarily motivated by improvement or mastering a task. Athletes who are more “mastery-driven” are likely demonstrating adaptive behaviors, persisting in the face of failure and exhibiting more positive emotions than those who are strictly performance-oriented.
Growth and Injury Risk
Childhood and adolescence is a time of rapid growth and development. The structural integrity of physiological structures can be affected during periods of rapid growth. Stress only has a positive or negative connotation when viewed through the lens of the adaptation it is inducing, which introduces some nuance to the concept of “load” in an athlete’s training.
While progressive loading generally elicits positive adaptations, the repetitive loading typically seen in early sports specialization can cause adverse adaptations. This is still context-specific, however. For example, the humeral head retroversion typically seen as advantageous in the youth throwing athlete is caused by essentially the same mechanism as seen with the development of cam impingement in youth hockey players. That being said, Wilhelm et al surveyed 102 professional baseball pitchers and those who specialized early were twice as likely to have suffered a serious injury than their non-specialized peers. What is more interesting is that the more specialized cohort specialized at just 8.9 years of age (SD 3.7 yrs).
In the context of individual sports, there does appear to be a correlation between periods of rapid growth and an increased risk of injury. Read et al demonstrated that recent increases in body mass index (BMI), leg length, and stature were correlated with injury rates in youth soccer players, particularly among U14-15 age cohort. Kemper et al demonstrated quantifiable variables correlating with an increased risk of injury in youth soccer players: those players who grew >0.6 cm, increased BMI >0.3 kg/m2, or presented with body fat <7% in athletes 11-16 and <5% in athletes over age 16.
So far we have discussed the current state of affairs in youth sport, discussed the prevalence and problems of early sports specialization, as well as unique psychological and biological considerations with respect to injury risk in the youth athlete. In the next part of this series we will dive into the Long-Term Athletic Development model.
Edited by Austin Baraki, MD, and Michael Ray, MS, DC