Weight or resistance training in children and adolescents has been somewhat of a contentious topic throughout history. One of most prominently discussed topics is the claim of resistance training stunting growth, due to injuries related to stress on the growth plates of immature bone. Yet, children and adolescents are allowed to participate in sports that involve high-impact, high-force movements (think long jump in track and field, cutting, etc.) as well as physical contact sports (football, soccer, etc.) - all of which require the body to withstand a significant amount of force and stress. The purpose of this article is to take a look at the research on resistance training in youth athletes and discuss how we can utilize this extremely beneficial tool to create strong, resilient humans that can perform at their highest level.
Background
Resistance training can take many forms. The most common one we think of is using weights - whether in the form of free weights (dumbbells, barbells), machines, cables, or bands. Resistance training can also involve utilizing one’s own body weight to induce a stress stimulus. The primary purpose of weight training is to improve one of the following characteristics: muscle size, strength, power, endurance, or a combination of any of those. Since this article is focused on weight training in youth athletes, this point is important to understand because those are all characteristics that we can modify which help perform athletic movements and prepare the body for the forces placed on it during play.
Now that we understand what resistance training is and what the purpose of it is, we can discuss the world of resistance training in the youth population. As mentioned in the intro, there have been many myths about resistance training in youth, with the most prominent one touting it as harmful to physical development including stunting overall growth. This idea is based on the fact that in growing children and adolescents, their growth plates are not fully closed and placing stress on them through external resistance (resistance training), will cause the growth plates not to close because they are constantly being tugged on by the tendons as muscle contracts. We will get into what the research has to say on this specific topic in the next section, but something we need to understand is how the body adapts. As mentioned above, the primary purpose of resistance training is to improve muscular size, strength, power, endurance. This happens because a stress inducing stimulus was placed on the body, which causes physiological changes to happen in the muscle tissue as well as the nervous system. When these changes occur there is actually an acute period where that tissue's ability to operate how it normally would decreases, and our body does not like that. With adequate recovery, the body will respond by making that tissue stronger so that the next time a similar stimulus is placed on it, it is better prepared to handle it. This can be said about virtually every body system, our hearts get stronger and more efficient from doing cardiovascular exercises (running, cycling) so that it can be better at performing that job in the future. If we think about this principle in the context of tendons and growth plates, realistically, we can take advantage of that to not only make the muscles of children and adolescents stronger, but their tendons, growth plates, and other soft tissues stronger as well in order to be able to withstand the demands of sporting activities.
This brings us to the next point. As mentioned, there is this unfounded myth about the harm resistance training can have on a child’s physical development but this fails to take into account that these same tissues and structures (tendons, growth plates, etc.) are undergoing a high amount of stress during sporting activities. It is estimated that when humans run, it is 2-3x your body weight of force going through each individual leg when your foot contacts the ground. This same principle applies to activities that involve any sort of acceleration and force production - sprinting, jumping, cutting, resisting contact from external force (another child’s body), and more. This means that when youth athletes are participating in sports, they are already placing high amounts of load/force through these same structures and most likely at a higher intensity than they would with resistance training. If we go back to college coursework and remember our physics classes, force is a product of mass x acceleration, so while the mass may or may not be higher during resistance training, the acceleration is usually at a significantly lower level compared to running, jumping, cutting, etc.. Wouldn’t it make sense to utilize controlled and specific work (resistance training) to make these tissues and structures stronger so that when our youth athletes are performing high-velocity, high-force movements (sprinting, cutting, jumping) their bodies are able to withstand these impacts? We think so, but don’t just believe us, let’s look at the research.
The Research
The first article I want to discuss is this review from the American Academy of Pediatrics (AAP) that focuses on the global benefits of resistance training in children and adolescents as well as injury risk in youth athletes and the claim of inhibiting physical development. In this article they mention that there has been a steady increase in the amount of youth participating in sports but also a steady decrease in regular physical activity in those children and adolescents not participating in sport. Additionally, with the youth population as a whole, there is evidence of decreasing measures in muscular fitness over the years. They cite many studies that demonstrate a relatively low injury risk when proper supervision and technique are the cornerstones of a youth resistance training program and mention that there has been a primary shift of focus from the injury risk during resistance training (which, as mentioned, is quite low) but the injury and health risks associated with not having adequate strength to keep up with sport, training, and regular life demands. In addition to these benefits of increased muscular strength, power, and endurance, there is evidence of improvements with cardiovascular fitness, body composition, bone mineral density, blood lipid profiles, insulin sensitivity in youth who are overweight, resistance to injury, and mental health. With that many benefits listed, why would we not want our children and adolescents participating in resistance training?
A direct quote from this article states,
“Injury rates in youth resistance training settings that adhere to qualified supervision and proper technique are lower than those occurring in other sports or general recess play at school.”
This is consistent with the injury rates with resistance training even among adults. More people get seriously hurt stepping off of a curb than they do when participating in a solid resistance training program (there are specific statistics on this, but that may be for another article). Continuing with the topic of injuries, and now addressing the claim of inhibiting physical development, this article states,
“Appropriately designed resistance training programs have no apparent negative effect on linear growth, physeal (growth plate) health, or the cardiovascular system. Explosive contractions of the muscle-tendon attachment at apophyseal (growth plate) areas during active play, sports, or lifting weights may increase the risk of avulsion fracture until closer to skeletal maturity.”
This quote directly supports that point we discussed at the end of the Background section. We apply this concept to college and elite level athletes without question, and the research has demonstrated that the same benefits can be achieved in youth athletes. This is exactly why we have decided to take on this challenge of implementing properly supervised and progressed resistance training programs for children and adolescents with our Youth Athlete Development program.
The other two articles I want to mention both discuss similar concepts with one through the lens of general resistance training and the other through weightlifting (also known as olympic lifting - clean, clean and jerk, snatch, etc.). Along with the previously mentioned article from the AAP, these articles also point out the relatively low injury risk with properly supervised and structured training programs. One of the unique points from the article that focuses on weightlifting is a focus on physical literacy in children and adolescents. Physical literacy involves the development of proficiency in fundamental movement skills (walking, running, and jumping) and fundamental athletic skills (catching, hopping) which are the basis for more skilled movements that would occur in sport. This article discusses how participating in a variety of activities, including a resistance training program can help improve all areas of physical literacy and if children/adolescents specialize too early, they often lack the full spectrum of physical literacy because adolescence itself is a window of opportunity where a majority of the adaptations from resistance training and improvements with physical literacy occur.
This brings us to the last article which along with other two articles mentions the long list of benefits that resistance training has for developing children and adolescents and the relatively low risk of injury. Uniquely, this articles also discusses the concept of the difference between chronological age (how old a child or adolescent is in years) and biological age (relating to the onset and completion of puberty) and what types of training are most beneficial for the child/adolescent depending on what stage they are in. To breakdown which type of training is more beneficial, we first need to understand the concept of peak-height velocity, which is where the peak rate of skeletal growth occurs, and peak-weight velocity, which is where the peak rate of maturation-associated skeletal muscle accumulation occurs. This article found that the majority of the adaptations from resistance training prior to peak-height velocity occur from neuromuscular adaptations (the nervous system becomes better at contracting the muscle) and due to this, lower-load, higher velocity movements such as squat jump, medicine ball work, and other properly dosed plyometric exercises tend to produce the greatest gains in power and force development. On the flip side of that, the greatest gains from a skeletal muscle growth and hormonal perspective occur during peak-weight velocity which is ~6-12 months after peak-height velocity and high-intensity strength training is the best method for improving power and force development. This again, points back to the notion that the best resistance training programs for youth are those that are properly supervised and progressed by coaches that understand these facets of growth and development, not just a blanket program that assumes every person is at the same stage of biological age and has the same training background.
Discussion
The research is pretty clear on the low risk of injury with resistance training and the benefits that can be had from it in the youth population. I am hoping that we can finally put to bed the myth that resistance training stunts growth. As with exercising in any population, proper supervision and progression can make all of the difference with the outcomes from participating in a resistance training program. Knowing where a child or adolescent is in terms of biological age can help guide what exercises and programming make the most sense to get the best gains. We take all of this into account with our Youth Athlete Development and believe that this is the best way to reduce injury risk, become stronger and more resilient, and perform at the highest level in sport. If you’re interested in learning more, click the button below.