The Determining Factor for Height

                It seems that if there’s anything you don’t like about yourself, you can work on it or get it fixed. If you’re fat, you can diet and exercise. If you have a uni-brow, you can pluck it. If you’re short, though… sorry, not even surgery can help you there. Teens often wonder if weightlifting will stunt their growth, as if humans are supposed to be tall and anything less is suboptimal. I believe a man that is 5’5” is neither unhealthy nor malnourished. In today’s society, however, being short is a huge disadvantage for men: studies have shown that height is strongly correlated with income; furthermore, a tall man can derive self-confidence from being able to literally look down on other people; and of course, a tall man has a greater selection of women since most women only date men taller than themselves. Life seems very unfair for the short man. But what if I told you height is not 100% genetic and can be nurtured? Well, it’s probably too late for you anyway.

                A person’s height is the sum of the lengths of their leg, torso, neck, and head. Today’s scientists say height is determined by growth plates, which are located at both ends of a bone. Scientists say nothing can be done to alter their growth rate (because they are “very internal”). I believe these scientists have overlooked the muscles that surround these bones. I hypothesize that height can be manipulated through development of the leg and torso muscles. (I’ve disregarded the lengths of the head and neck because they are insignificant compared to the leg and trunk.) Muscles contract and have a contractile force. As the muscle becomes bigger/more developed, the contractile force increases. If there is no muscle then there is no contractile force:

CREATOR: gd-jpeg v1.0 (using IJG JPEG v62), default quality

                As you can see, this muscle’s contractile force goes the opposite direction of the growth plate force. Thus, leg and torso muscle hypertrophy should impede vertical growth. It is possible to sufficiently stretch a muscle to a relaxed state. At that point in time, the contractile force would be weak. To maximize height, I believe one must eliminate all the contractile forces that contribute to height. These are all the muscles with fibers that run vertically: the calves, quadriceps, hamstrings, trapezius, abdominals, and erector spinae. If any of these muscles hypertrophy, they would have a contractile force, which would resist growth plate expansion, which would retard vertical growth, as my hypothesis goes.

                How exactly would one maximize height? From birth until 18 or so, one should avoid all high-intensity (i.e. muscle-building) exercises of the aforementioned muscles. This means never doing sit-ups, squats, etc. If physical activity cannot be avoided, it should be done with low intensity (and high repetition). This means jogging instead of sprinting, jumping rope rather than high jumping, or even taking three trips to carry groceries into the house instead of one. In other words, one should do cardiovascular activities rather than expend energy in short bursts. This will minimize muscle development and thus maximize height. Muscles will always exist, however, so the second part of the formula is to stretch the leg and spine muscles to a relaxed state as often as possible. The bridge stretch is a good example. Even sitting cross-legged for some time will stretch the leg and lower back muscles. To minimize height, one should engage in high-intensity leg and torso activities, and never/rarely stretch these muscles.

 

Existing Hypotheses

                Many people believe height is genetically predetermined. I definitely agree that genes are a factor. But for many conditions—not just height—I see the role of genes as defining an individual’s default/expected value and the possible range of deviation. Thus, I often visualize the effect of genes as a normal distribution, or a box-and-whisker plot:

boxplot

                I believe genes define how tall one is expected to grow. Basically, a daughter is expected to be the same height as her mother and a son is to be the same height as his father. I believe genes also define the minimum and maximum degree of deviation allowed. I hypothesize that nurture determines how far a person deviates from the projected value—how far one travels along the whiskers of the box plot.

                So it’s nature + nurture. Most people believe this means genes + diet. People today attribute just about every unexplained human phenomenon to diet. I think this is absurd. Yes, I do believe malnutrition can stunt growth, but I believe extreme starvation is required for this to occur. I’m sure you’ve encountered short people who eat too much food, too little food, only healthy food, etc. and tall people who eat too much food, too little food, only healthy food, etc. In other words, no one has observed a correlation between height and diet. Why, then, do so many people believe diet determines height? Simple. It’s because food is what is physically put into our bodies. It’s a very simplistic, caveman-like way of thinking. Many people do not acknowledge that food doesn’t go directly to the limbs bur rather passes through the digestive system. I believe there is something that more directly affects the height-determining growth plates, and that is the muscle that surrounds it.

                Every four years, people notice that Olympic gymnasts are short and then wonder: did gymnastics make them short, or are they the best at gymnastics because they’re short? The chicken or the egg dilemma; is selection bias at play? Scientists say the growth plates cannot be affected, except from injury, therefore gymnastics cannot make a person short. I say it can. Unlike long-distance runners, gymnasts use the legs with high-intensity as they leap around in tumbling, vault, and balance beam. This induces muscle hypertrophy of the calves, quadriceps, hamstrings, trapezius, abdominals, and erector spinae, among other muscles. Thus, a large contractile force is working against growth plate expansion of the limbs involved in height.

 

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. Through urbanization, fields and nature have been replaced 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 muscularly-undeveloped legs and torsos, which produces taller overall 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:

                The study’s interpretation of these findings 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 quite a few variables in play going from a rural environment to an urban one, so using just this data will not suffice for my hypothesis. We must narrow it down to the “sedentary lifestyle” component of the urban environment as the determining factor of height.

                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, 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. Now, invoking the substitution method: the taller the child, the more sedentary his/her lifestyle.

                The following is not hard evidence but rather a few things I’ve noticed over the years. One, it seems like children have been getting taller and taller. That is, a 10-year-old today seems taller than a 10-year-old from 10 years ago. Most people simply chalk this up to “better diet and nutrition” but I beg to differ. Two, I’ve observed that the teenagers who are tall also seem to lack muscle development at the legs. That is, if you were to outline their legs, there would be no curves whatsoever at the calf and knee area—it’d just be straight lines from hip to foot, like a bad drawing. Shorter teenagers, on the other hand, show distinct calves and knees.

 

Ideal Supporting Evidence: Teens Doing High-Intensity Legwork

                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.

                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 did not do any sports growing up while his/her twin took many years of karate or gymnastics. Unfortunately, this scenario is very rare because most parents of twins ensure their twins have an equal and fair upbringing. However, I Googled clever phrases, such as: “stunt growth weight lifting ‘twin brother’,” “stunt growth gymnastics 'twin sister',” or “stunt growth ‘working out ‘identical twin’.” Searching these phrases yielded many personal accounts that align with my hypothesis.

                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 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. Long-distance running is low-intensity/high-repetition. Among the teenagers who do work out, few actually work out the calves, quadriceps, hamstrings, trapezius, abdominals, or erector spinae with high intensity.

 

Comparing Height across Genders is Tricky

                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 wait, 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 important factor to consider is that in today’s society, in just about every country in the world, 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. I hypothesize that a family that strictly adheres to these gender roles would see the boy grow up to be shorter than his sister, or barely taller.

 

Implications of my Hypothesis

                The harder you work, the shorter you will grow up to be—if work was to be defined as high-intensity physical labor. So when I see a man that’s short, especially relative to his race, I often think to myself, “He must have worked hard when he was young. Maybe he took karate…” And when I see a really tall man, I cannot help but think, “He must’ve sat cross-legged in front of a TV all day as a kid. He’s probably never pushed himself physically.” I’m not saying the equation for height is 100% nurture, though. I acknowledge that genetics are involved. I would say that being short comes from generations of high-intensity leg and back work, and being tall comes from generations of comfortable living (i.e. without high-intensity leg and back work). This is assuming you believe in Lamarck’s Theory of Inheritance of Acquired Characteristics, which is gaining steam today as scientists understand more about epigenetic inheritance. And again, before you try to disprove my hypothesis with an anecdote: you need a control variable, such as a same-sex sibling; it is futile to compare your level of physical activity and final height to the national average, especially if that nation is racially diverse.




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