I have been lifting weights for the past year and I was interested to know if it would stunt my growth. I would love to keep growing in height since I stand at an average of 5’9”. My friend back home told me that he typically tries to avoid heavy weight lifting because his older brother tried it when he was young and has not grown ever since. Of course, this is just one case or one anecdote, which implies a weak inference when determining if lifting weights stunts growth. I decided to investigate because getting stronger and getting taller are some of my goals. I also want to find out if it was okay for me to start lifting at an earlier age since I do have some regrets starting just the past year. So does lifting weights actually stunt growth?
This meta-analysis explains the results of 60 years worth of studies of children and weightlifting. All the subjects from these studies were within the ages of 6-18. The scientists that conducted the meta analysis study pondered if weight training would stunt the growth of children while they were already in the stages of growing through puberty. While evaluating all 118 of these studies, the scientists chose studies that fit their criteria best suitable for the meta analysis. Only 42 out of the 118 fit their criteria. One of the criterion that I thought was most important was that “the study design had to include a resistance-training intervention (Behringer).” This meant that the putative causal variable (“x” variable) had to be manipulated in the study in order to be included into the meta analysis. In this case, the x variable is the amount of weight training. Observational studies were not used in the meta-analysis, which is good because you can have a lot less uncertainty in figuring out if weight training stunts growth when you use well conducted experiments. The manipulated training programs that the children went through in all 42 studies ranged from 4 to 60 weeks with a mean average of 9.9 weeks, a mean of 2.7 sessions per week, and a mean of 41.1 minutes in each session. A vast majority of the studies (83.3%) reported that they used free weights and resistance machines. The scientists found an overall weighted effect size of 1.12, which explains that “the ability to gain muscular strength seems to increase with age and maturational status. Furthermore, study duration and the number of performed sets were found to have a positive impact on the outcome (Behringer).” In other words, they found as the older you get and the more you put into your weight training, the more muscular gains you received.
The conclusions were based off the results of randomized and non-randomized controlled trials. For the randomized trials, researchers randomly assigned the children to a treatment group where they went through some sort of weight training, or a control group where they went through no training. They integrated the results from both types of study designs into one conclusion. We know that randomization is used in controlled experiments to reduce the impact of confounding variables and give subjects an equal chance of either being assigned to the control group or the experimental group. Can results vary greatly whether they came from randomized or non-randomized trials? And by how much? I believe there should be some sort of consistency when evaluating studies in a meta analysis and that researchers should use studies with the same designs. A possible confounding variable could be that the children who were chosen for the study may have had prior experience with weightlifting before the experiment. The experiment would show clearer, and unbiased results if they used subjects with little to no experience with weight training to better see the effects. 79.4% of the studies did not even report training status or experience with training of their subjects. So could this meta-analysis be guilty of the Texas sharpshooter problem? They found the positive results to their liking, but most of the studies failed to mention if their subjects were affected by a pretty important confounding variable that I explained above. There could be a chance that the scientists made a false positive decision in concluding that weight training helped with the overall growth of children. Also, the scientists stressed that only one of the 42 studies actually focused on how exactly the hormones of puberty were affected by weight training, and that more studies would have to be done to figure out the physiological mechanism in response to strength stimuli (Behringer).
Well can’t one argue that when you lift weights, you have a higher chance of injuring yourself if something were to go wrong? You could end up breaking a bone or two if you’re not careful around heavy weights. According to this article, a study by the National Strength and Conditioning Association (NSCA) was mentioned which showed that after observing children over a one year period, fewer than 1% of injuries occurred from weight resistance training (Fell). Even though this was observational, I believe that in this case the observational study is the best way to go about finding out if children are more likely to get injured from lifting weights without running into a bunch of ethics. Of course, adult supervision should be required when children are near weights. I believe that there is an extreme minimal chance of getting injured if there are professionals who supervise and guide children in performing lifts with good form. Although it was not mentioned in the article, it is safe to assume that the children that were lifting weights in the study were supervised. We shouldn’t be testing to see if children are more likely to get injured on their own without supervision.
Even though I mentioned some flaws of this meta analysis, I still have confidence in the overall results. The fact that there was a meta analysis instead of a single study helps too. I concluded from the observational study that children will be less likely to get injured as long as they are supervised. Overall, I’m not going to stop lifting heavy weights because I still want to get stronger and gain mass. The meta analysis didn’t directly mention height, and there weren’t many studies I could find that only concentrated on height. If I were to conduct an experiment, I would look for height as the dependent variable. Of course, I would have to replicate the studies and get some nasty mean peer review. What do you guys think?
Picture source: http://www.muscleandfitness.com/workouts/legs-exercises/deadlift-step-step-optimal-results