Can you remember from your younger years being told not to do weights because you might become “muscle bound” or weights will “stunt your growth”? It was never quite explained what the term muscle bound meant, but it was certainly scary enough to ensure that weights weren’t a big part of most adolescents fitness programs! There was also a general thought that not only was strength and resistance training potentially harmful in young children, but also that it was ineffective anyway in producing strength gains in this age group.
The risk of injury in adolescent children is one main reason why parents (and health practitioners) would steer children away from strength raining – the thought being that an immature skeletal 
system, in particular the growth plates, would be unable to cope with the stress placed on it by weight training.
What Are Growth Plates?
Growth platesare located towards each end of the long bones (limb bones, including foot and ankle) of children and adolescents. Whilst it would probably make more sense, growth of these bones does not come from the middle of the bone – new bone tissue is developed within these growth plates at the end of bones, which then determines the exact size and shape the bones will reach by adulthood. When young people finish growing, solid bone replaces the cartilage growth plate, and the growth plates “close” and one calcified bone is formed (as distinct from two separate bone pieces separated by a vulnerable cartilage plate. Whilst enormous individual variance does occur, girls tend to reach skeletal maturity before boys: approximately 15 – 16 years of age compared to 16 – 18 years of age.
The growth plates are relatively flexible, made of cartilage, and therefore are a susceptible zone for injury under certain circumstances. The growth plate is the weakest area of the growing skeleton, weaker than the nearby ligaments and tendons that connect bones to other bones and muscles. In a growing child, a serious injury to a joint is more likely to damage a growth plate than the ligaments that stabilize the joint. An injury that would cause a sprain in an adult can be associated with a growth plate injury in a child.
If a growth plate is injured, the growth of the bone may be effected, potentially resulting in deformities, poorly shaped bones, reduced growth in a limb, or even future degenerative joint change. Hence the thought that weight training may damage the vulnerable growth plate and result in “stunted growth”.
What we do actually know now about growth plates is that they have a great capacity to deal with load, and are in reality quite resistant to many of the forces children put them in daily life and normal sporting activities. Many of the growth plate injuries that occur are actually acute traumatic injuries, resulting from a fall or single higher impact incident. Far less common (but still possible) is growth plate injury due to repetitive overload, such as strength training exercise. Having said that, some sports, gymnastics being a prime example, where high loads are placed repetitively through the limbs, can result in an overload growth plate condition.
As with any training, controlled and sensibly progressed loads will result in adaptation of a tissue or body part to that load, rendering it more able to resist load over time. For example if you go to the gym regularly you will know that the same exercises become easier over time, allowing you to lift more weight or do more repetitions. Similarly, the first time you run 3km is tough, but as you get fitter and progress up to 10km, the 3km becomes “a piece of cake” because your body has adapted.
In a similar way, placing loads through the body of growing children is not only good, but critical for normal development. The big issues arise if the loads are simply too high, or more commonly if the tissue hasn’t had time to adapt to the increasing load!
What Role Does Strength Training play in Children?
As a start, let’s change the terminology! Strength training does tend to give the connotation of being in the gym and lifting heavy weights. Resistance training is probably a much better term to use, as resistance can be in the form of body weight, elastic bands, pilates reformers, water…or even weights!
Here are some facts supported by research:
* Adolescent and pre-adolescent children CAN gain strength improvements of up to 70% over an 8 – 12 week resistance training program, with 30-50% being typical gains.
* Strength gains are two-fold between the ages of 7 and 12, suggesting that this may actually be a time to benefit from some form of controlled resistance training.
* Resistance training places stress, loading and demand on muscles that is all important for bone modelling. In other words, the (correct) stress placed on bones by muscles during resistance training actually stimulates growth.
* This effect on bone and bone density is critical in pre-adolescent children, as our maximum bone density capacity as an adult is actually determined by the density levels we achieve during these adolescent and pre-adolescent years. This has been a big issue in swimmers in the past (low bone density and density related medical conditions as adults) due to the focus solely on swimming laps for training – non weight bearing exercise. Now that research and medicine has progressed so far, swimmers now do a significant component of “land based” training to complement their swimming, thereby ensuring improved strength, improved neuro-muscular control, and critically – improved bone density!
* The stresses of resistance training are no worse (and in fact possibly a fair bit better) than the enormous stresses of running, jumping and other vigorous activities that children participate in.
* Much of the strength gain from resistance training in adolescents is thought to come from “neuro-muscular” adaptation. In other words, through repeating a certain exercise or skill, the body will recruit more nerves (and use the existing nerve pathways in better fashion, resulting in improved muscle performance). So the apparent improvement in strength in adolescents is often an improvement in nerve recruitment. This principle is critical in growing children – exposing them to different forms of exercise, across different conditions, and within different sports, allows greater development of skill level, fitness, co-ordination, strength etc.
* Research even indicates that injury rates are lower in children who participate in resistance training, compared to their peers who do no resistance training.
So it would seem that the term “muscle bound” really has no relative importance with children and there is no evidence to suggest that children who do strength training will end up with over developed, inelastic and slow to react muscles. You need only look at ballet dancers, who do an incredible amount of strength and resistance based training, and they certainly don’t have overdeveloped inelastic muscle tissue!
Conversely “stunted growth” (or altered growth) does have meaning, and is a potential outcome of a poorly managed or misdiagnosed growth plate injury in an adolescent. It is unlikely that this injury has been due to resistance training however – it is far more likely to be caused by a single traumatic injury during sport.
One of the biggest issues we see in younger children these days is volume and intensity of activity – both training and competition. In many cases, “load management” is the key: reducing the amount of training and game sessions per week that the child does. However there is also an argument that a well designed resistance training program will better prepare the child for the intensive programs that tend to be a part of junior sport these days.
In summary, there is an abundance of research to support resistance training in pre-adolescents and adolescents. Programs should be sensible, progressive (never increasing by more than 10% from one session to another is a good general guide to follow), have adult supervision, be focussed on technique rather than weight or repetitions, and involve a variety of resistance training methods.
