photo from: kidsexercises.net
Okay, so I love football, specifically the Denver Broncos so as you can imagine (if you follow football) its been an exciting season with lots of controversy! As a result of all my football watching recently, I can’t help but notice the extremely large muscles on the guys on the field! It started me thinking about strength training and how important it is for function at any level, from pro sports to a child trying to learn/relearn how to walk.
At our clinic we do a lot of strengthening with kids. This includes functional strengthening as well as targeted muscle specific strengthening. For the targeted strengthening we use the Universal Exercise Unit, because it works well for our needs. We tend to do high repetitions and low weight/resistance for the strength training we do with the kids. This can cause a lot of questions from parents who are used to traditional strength training for adults because many trainers and physical therapists recommend fewer repetitions and larger amounts of resistance for maximum strength gains in adults. The reason for the low weight/resistance and high repetitions lies in the developmental differences between how children and adults make functional strength gains.
(In general strengthening is done to improve function in day to day life which is why I keep mentioning functional strength gains.)
Strength training in adults causes the muscle fibers to get thicker or hypertrophy. These bigger muscle fibers are the reason adults who are strength training develop bigger muscles (which they can flex and show off to their friends) and thereby make functional strength gains. For adults to maximize muscle hypertrophy and their ability to “build” muscle, heavier weights at lower repetitions are recommended over the course of 6-8 weeks of consistent strength training.
On the flip side, strength training in children, uses improved motor unit recruitment (or muscle fiber recruitment) to cause functional strength gains. This process does not result in muscle hypertrophy and while we may see improved definition in the muscle when contracted, the overall size of the muscle does not grow. By using high repetitions in each strengthening exercise the child has more opportunities to practice a movement against a set amount of weight/resistance. This practice provides the opportunity to produce the motor learning that allows them to more effectively and efficiently recruit their muscles when a task demands increased strength. The lighter weights, allows a child to actively participate in more repetitions or opportunities for practicing calling on specific muscles for specific movements prior to fatigue.
Kids don’t begin building muscle through fiber hypertrophy until puberty but depending on the goals of strengthening and/or a child’s diagnosis a pediatric physical therapist may continue to use higher repetitions and lighter weights while working with children that have already entered puberty if their goals are not necessarily purely strength based, but rather motor control, selective muscle activation, or endurance based.
Hopefully I made this understandable and not too confusing but feel free to ask for clarification if something wasn’t clear! I also included some references for those of you that like to look things up!
References:
1) Faigenbaum A, Kraemer W, Blimkie C, Jeffreys I, Micheli L, Nitka M, Rowland T. Youth resistance training: updated position statement paper from the national strength and conditioning association. J Strength Cond Res. 2009;23(Supplement 5): S60-S70.
2) Raynor AJ. Strength power and co-activation in children with developmental coordination disorder. Dev Med Child Neurol. 2001; 43:676-684.
3) ACSM’s Guidelines for Exercise Testing and Prescription, 7th Ed. Baltimore, MD: Lippincott Williams & Wilkins; 2006.