Written on December 7, 2009 at 7:00 am, by Eric Cressey
A while back, I attended a seminar in Houston, and while the primary topic was how to improve pitching performance, one of my biggest takeaways was with respect to adolescent physiological development. Long-time Phillies rehabilitation consultant Phil Donley presented some excellent data on when bones actually become skeletally mature. The next day, another speaker made a what was, in my opinion, an uninformed comment about how kids shouldn't strength train at young ages because it would stunt their growth.
Let's start with Donley's very intriguing numbers (which have actually been available in the literature for over two decades now); we'll stick with the shoulder girdle just to keep things to-the-point. In a baseball population, the epiphysial plate most commonly injured from throwing at the shoulder is located at the proximal humerus (Little League Shoulder); this physis (growth plate) accounts for about 80% of humeral growth, and matures by age 19 in most folks.
We've seen a lot of kids come through our door with this issue because of throwing (internal rotation of the humerus during throwing is the fastest motion in sports) and even some traumatic falls - but I can honestly say that I've NEVER seen one from strength training. So, anecdotal evidence for me shows that strength training for kids is far from what could be considered "dangerous" for developing bones.
Now, here's where it gets more interesting: bone maturation isn't uniform across the body. While the proximal humeral growth plate might mature at 19, the distal (down by the elbow) physis is finished between ages 10 and 16. The proximal and distal radius plates might mature anywhere between 14 and 23. Meanwhile, the clavicle matures at ages 22-25, and the scapula generally matures by age 22. How many of you have ever heard of a college football being held out of weight training for all four years of his participation because all that bench pressing might stunt the growth of his clavicles and scapulae? It just doesn't happen! In reality, we know that the strength training benefits of increased muscle size and strength actually protect him from injury on the field.
In other words, violent (throwing) and traumatic (falling) events far exceed any stress on a young athlete's bones that we could possibly apply in a strength training setting, where the environment is controlled and overload is gradually and systematically increased over time as the athlete becomes more comfortable with it. I'd make the argument that a young athlete should start resistance training as early as his/her attention span allows for it; the emphasis, of course, would be on body weight exercises, technical improvement, and - most importantly - keeping things fun.
If you really think about it, an athlete is placing a ton of stress (4-6 times body weight in ground reaction forces, depending on who you ask) each time he/she strides during the sprinting motion. Kids jump out of trees all the time. They lug around insanely heavy backpacks relative to their body mass. Performance, general health, and self-esteem benefits aside, it's only right to give them a fighting chance in trying to avoid injury.
Also, another great point Phil made (although it was on an unrelated topic, it pertains to us) was that as an adolescent athlete grows, his center of gravity moves further up from the ground. This is a big part of the "lapse" in coordination we see in kids during their growth spurts. A little bit of strength goes a long way with respect to maintaining the center of gravity within the base of support, and makes an athlete more comfortable "playing low" (hip and knee flexion) to bring that center of gravity closer to the base of support.
All that said, appropriate resistance training is not only safe for kids; it's also tremendously beneficial. In a review just published by Faigenbaum and Myer, the authors concluded:
Current research indicates that resistance training can be a safe, effective and worthwhile activity for children and adolescents provided that qualified professionals supervise all training sessions and provide age-appropriate instruction on proper lifting procedures and safe training guidelines. Regular participation in a multifaceted resistance training program that begins during the preseason and includes instruction on movement biomechanics may reduce the risk of sports-related injuries in young athletes.
Dr. Avery Faigenbaum has actually published a ton of great research (including position stands for numerous organizations) on the topic of strength training for kids in recent years; you can find all of it by searching for his last name at www.pubmed.com.
In the meantime, I hope this blog can help to eliminate the gross misconception in the general population that resistance training can't be beneficial for children. When performed correctly and made fun, it is safe and provides tremendous benefits to kids in both the pre-adolescent and adolescent stages.