What Determines Height

Today’s scientists say that height is determined by growth plates, which are located at both ends of a bone. The rate at which they grow is considered to be genetic and unchangeable. I believe scientists are overlooking the muscles surrounding these bones. Muscles have what’s known as a contractile force. This force increases as a muscle becomes bigger/more developed. If there is no muscle then there is no contractile force.

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You could say that the growth plates “push” the ends of the limb apart, while the contractile force pulls them together.


               Fact: a person’s height is the sum of the lengths of their leg, torso, neck, and head. The leg, torso, and neck contain certain muscles with fibers running vertically. These are the calves, quadriceps, hamstrings, abdominals, quadratus lumborum, and erector spinae. I hypothesize that height is primarily determined by the muscle development of these particular muscles during formative years. In other words, developing the leg and torso muscles while growing up would impede vertical growth. And loose, relaxed leg and torso muscles would facilitate vertical growth.

               How exactly would one maximize height? During developmental years, one should avoid all high-intensity (read: muscle-building) exercises of the aforementioned muscles. This means never doing sit-ups, squats, etc.—especially with heavy weights. If physical activity must be done then it should be done with low-intensity (and high repetition). This means light jogging instead of sprinting, jumping rope rather than high jumping, playing hopscotch rather than long jump, or even taking three trips to carry groceries into the house instead of one. In other words, energy should be expended via cardiovascular activities rather than short bursts. This lifestyle will minimize muscle hypertrophy and thus maximize height. It’s hard to avoid all physical activity, however, so the second part of the equation is to frequently stretch and massage the leg and spine muscles to a relaxed state. Sitting cross-legged, for example, can stretch the leg and lower back muscles. To minimize height, a teenager should engage in high-intensity leg and torso activities, and neglect stretching these muscles.

Lugging a heavy backpack around school every day is the worst thing a teen can do for his/her height. The act of stabilizing the shifting weight will strengthen the erector spinae and quadratus lumborum muscles. Walking around with extra weight will also induce hypertrophy in leg muscles.


Existing Hypotheses

               Many people believe height is genetically predetermined. A child’s height is expected to the somewhere in between the height of the mother and the father. But how do genes explain the common situation where the child ends up taller than the parents? Or shorter? I agree that genes are a definitely factor. As with all traits, the formula is genes + nurture. Most people today believe this means genes + diet, because people attribute just about every unexplained human phenomenon to diet. This is overly simplistic. Yes, I do believe malnutrition can stunt growth, but I believe this requires extreme starvation. I’m sure you know of people who grew up fat and ended up being short, and people who grew up skinny and ended up being tall. In other words, there is a very weak correlation between height and diet. I would say “diet => height” is a logical fallacy too: people believe that food (energy) goes in and out goes the resulting product—the human body. Wrong. It should be: food (energy) goes in and out goes energy in form of our actions—human behavior, which includes the body’s movements.

Every four years, people notice that the Olympic gymnasts on their TV are all short and stout. They wonder, “Did gymnastics make them short, or are they the best at gymnastics because they’re short?” Which came first, the chicken or the egg? Scientists say the growth plates cannot be influenced so gymnastics cannot make a person short. I say it can. Gymnasts use the legs with high-intensity when they leap around in tumbling, vault, and balance beam routines. Among other muscles, this induces muscle hypertrophy of the calves, quadriceps, hamstrings, abdominals, erector spinae, and quadratus lumborum. Thus, large contractile forces are working against growth plate expansion of the bones involved in height. Similarly, debates on whether weightlifting will stunt a teenager’s growth or not is a reoccurring theme on the internet. I say that it does.


Supporting Evidence: Comparing Urban to Rural

               I believe growing up in an urban environment causes teens to live more sedentary lives than their rural counterparts. Urbanization replaces fields and nature with high-rise buildings and computers. There is simply no space to run around and play in a city. I hypothesize that this sedentary lifestyle produces undeveloped leg and torso muscles, which results in a taller height. Kids in rural environments run around and play outside more often, which leads to well-developed leg and torso muscles, which leads to shorter overall height. Is this backed by any evidence? In 2013, CJ Paciorek published a study which found that urban children are taller than their rural counterparts in almost all of the 141 (low-income and middle-income) countries they researched:


               Their interpretation of this data is that the rural areas have less access to stable and affordable food supply and health care. This study is far from alone. There are countless studies that find a correlation between urbanization and height, and they all believe the same thing: better access to food and health care leads to taller humans. The truth of the matter is that there are many variables in play as humans go from a rural environment to an urban one, so using this data alone will not suffice for my hypothesis. I must find studies that narrow in on the “sedentary lifestyle” variable of urbanization.

               Many studies have found that a sedentary lifestyle is strongly correlated with myopia, a.k.a. nearsightedness. The more hours you spend doing deskwork, the worse your vision will be. In fact, 80-90% of children completing high school are now myopic in urban cities in Asia. Why am I talking about myopia? Because it has a strong correlation to deskwork. Thus I am going to substitute “myopia” with “sedentary lifestyle.” In 2002, Saw SM, et al. published “Height and Its Relationship to Refraction and Biometry Parameters in Singapore Chinese Children” after finding a correlation between height and myopia. That is, Saw SM, et al. found that the taller the child was, the worse his/her vision was. Using my substitution: the taller the child, the more sedentary his/her lifestyle.

               Centuries ago in Italy, young boys were sometimes castrated to preserve their vocal range. They were known as castrato singers. By removing the boys’ testicles, the human body would continue to develop without testosterone in the system. This led to unintended consequences in the face and body, including “a barrel-shaped chest, infantile larynx, and long, spindly legs.” Most grew to be taller than 6 feet, which is exceptionally tall for a man in the 1700s. My take on these unique data points is that testosterone plays a big role in muscle development. Unable to easily develop leg and spine muscles, these men were able to grow with seemingly indeterminate growth. Furthermore, growing up in a competitive, aggressive, or physically-demanding environment can also trigger greater production of testosterone than a sterile, incubation-room environment. In this way, the testosterone hormone can also affect height.

               The following is not concrete evidence but rather some personal observations I’ve made over the years. One, it seems like children have been getting taller and taller. That is, a 15-year-old today seems taller than a 15-year-old from 10 years ago. Most people simply chalk this up to “better diet and nutrition” but I beg to differ. Food has been plentiful for many, many decades. Two, I’ve observed that the teenagers who are tall also seem to lack muscle development at the legs. Thus, the outline of their legs are straight lines from hip to foot, like an amateur drawing. That is, there are no 3D curves at the calf and knee area. This is observable from just a cursory glance of a person’s legs. Meanwhile, shorter teenagers tend to exhibit distinct calves, thighs, and knees—or as I see it: muscle development.


Ideal Supporting Evidence: High-Intensity Legwork during Teenage Years

               One way to gather data for my hypothesis would be to conduct a survey on full-grown adults (i.e. ages 22-40). First, I would ask them what their height is. Second, I would ask them if they participated in karate, gymnastics, weightlifting of the legs, etc. as a developing child/teenager. Third, I would ask them how many months/years they were active in these sports. I expect the data to show a strong negative relationship between years spent doing high-intensity leg activities and (final) height. Karate and gymnastics qualify as high-intensity leg workouts because they involve a lot of kicking and jumping.

               Another survey possibility would be to ask how much outdoor playtime someone experienced during their developmental years. The survey would poll developing teens and full-grown adults, rural and urban. The teens would be able to give the most accurate numbers as to how long they played. I predict the rural population to have more outdoor play, and thus be shorter, than their urban counterparts. I’d say that for the majority of countries, for at least one generation now, people in rural areas have had access to the same kind of diet/calories as people in urban areas. I also predict that in mountainous regions to have more muscularly-developed legs, and thus be shorter, than people in flat plains.

               The best evidence for my hypothesis would be a survey on the heights of identical twins that lived drastically different lifestyles yet shared similar diets. For example, a twin who took many years of karate or gymnastics while his/her twin did not. Unfortunately, this scenario is very rare because most parents of twins want to give their twins have an equal and fair upbringing. However, Googling clever phrases, such as: “stunt growth weight lifting ‘twin brother’,” “stunt growth gymnastics 'twin sister',” or “stunt growth working out ‘identical twin’,” yielded many anecdotes that support my hypothesis.


Comparing Heights is Tricky

               Beware of people on the internet parroting the unproven theory that working out or weightlifting does not stunt growth. These people often cite scientists that say genetically-predetermined growth plates are responsible for overall height. End of story. Truth is, there hasn’t been a study to prove one way or the other. Also beware of people sharing their personal anecdote with no control variable. Say, for example, Jamaal from the internet says he ran track and field for all four years in high school and he’s much taller than the average American man, therefore leg workouts do not hinder height at all. I hope you see how this is incredibly flawed. First of all, he doesn’t have a control variable—he is comparing himself to the average American—America is a very diverse country with many ethnicities. It would be more acceptable for him to compare his height to the average height of his ethnicity in America. More acceptable than that would be to compare to the average of his cousins. More acceptable than that would be a blood sibling. Ideal would be an identical twin that didn’t do any physical activity in high school. Secondly, running is not necessarily a high-intensity leg exercise and thus may not induce muscle growth. Sprinting is, but long-distance running is low-intensity. Among the teenagers who do work out, only a few actually work out the calves, quadriceps, hamstrings, abdominals, or erector spinae with high intensity.

               There is currently no explanation as to why siblings differ in height. The genetic explanation may be that one sibling “got the bad genes.” My hypothesis says that the child who uses leg and torso muscles with high intensity will grow up to be “the short one.” But it gets tricky! Women are, by nature, about 10% smaller than men, and thus 10% shorter as well. For example, say a man is 5’10” and has a sister. It’s expected that his sister is around 5’3” because this is 10% less than 5’10”. If she turned out to also be 5’10”, I would conjecture that the man’s childhood involved intense leg usage, while hers did not. If she turned out to be 4’11”, I would speculate the other way around. Another factor to consider is that, in today’s society, physical activity is reserved for the male gender. The boy is encouraged or forced to do the physical labor, especially when it comes to strenuous (i.e. high-intensity) activities, because he is to “be a man.” The girl is discouraged or excused from doing physical activity because she is to “be a princess.” If a female is doing physical work, it’s advised to be low-intensity cardio activity. This is a moot point in a modern, urban lifestyle, however, where this physical labor is nearly nonexistent. But if a (rural) family strictly adhered to these gender roles, I would bet on the boy growing up to be shorter than his sister, or barely taller.


Implications If True

               Besides keeping high-intensity activity at a minimum, a less obvious way to maximize height would be a special diet devoid of protein. Since protein purportedly aids in muscle growth and recovery, kids can avoid protein-rich foods during developmental years to minimize muscle growth. Kids should also avoid getting fat, because fat is extra weight to carry around, which leads to muscle hypertrophy, which leads to stunted growth. For example, if you took twin brothers living the same active lifestyle, but gave one brother three times as much food, the fat brother will develop more muscle mass from doing the daily activities with extra weight on. So I suppose diet does affect height, but not in the way people think it does.

               The harder you work, the shorter you will grow up to be—if work is defined as high-intensity physical labor. When I see a short man—especially for his race—I often think to myself, “He must have worked hard when he was young. Maybe he helped his parents carry heavy loads every day.” And when I see a really tall man, I cannot help but think, “He’s probably never pushed himself physically. Maybe he spent his childhood sitting cross-legged in front of a TV all day.” I’m not saying the equation for height is 100% nurture. Genetics still play a role. What I am saying is that being short comes from generations of high-intensity leg and back work, and being tall comes from generations of comfortable living. Yes, this is Lamarck’s Theory of Inheritance of Acquired Characteristics. Again, before you try to disprove my hypothesis with an anecdote, you need a control variable, such as a same-sex sibling. For example, it would be a mistake to compare your level of physical activity and final height to the national average, especially if that nation is ethnically-diverse.

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