Human Limits

Exploring performance and health with Michael J. Joyner, M.D.

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Size Makes a Difference: Gymnastics and Swimming

Today’s post is a bit more technical.

During the first week of the Olympics gymnastics and swimming will be two of the featured events.   I get a lot of questions about how much of elite athletic performance is due to genetic factors and how much is due to environmental factors: the classic problem of nature vs. nurture.

So why not start with gymnastics and swimming.   Gymnasts tend to be short and swimmers tend to be tall.   In the case of gymnastics it is important to have a high strength to body weight ratio.   A major factor that determines the strength of a muscle is its cross sectional area.

As people get taller the cross sectional area of their muscles gets bigger and they get stronger.  However, their body weight (essentially body volume) goes up faster.  Area is essentially a squared function of height and volume a cubed function.  There is a whole area of biology called allometry or scaling that considers these relationships for all sorts of things.

The practical effect is that as people get taller on average their strength to weight ratio gets lower and that makes it harder to do all of the tricks that the top gymnasts do.   This is one of the reasons that the top women in gymnastics have gotten younger and as a result shorter and lighter as the tricks required to compete at the highest level have gotten harder.

In 1968 26 year old Vera Caslavska dominated women’s gymnastics at the Mexico City Olympics.  She was reportedly 5’3’’(160 cm) and about 128 pounds (58 kg).  Caslavska, a Czech, was also a hero in resisting the Soviet invasion of Czechoslovakia in 1968.

Watch this video of her and compare it to what you will be watching on TV during the next week.

In swimming, a bigger surface should slow things down and make it harder to move through the water.   However, streamlined body positions like that seen in the Michael Phelps video posted yesterday, can limit the negative effects of size.  Swimmers are also in the water and essentially floating so there isn’t much penalty for getting heavier.

This general line of reasoning also applies to oxygen transport systems and when you add that to more muscle strength, taller swimmers have an advantage.  In general smaller people do better in things that are weight dependent and taller people do better in things that are weight independent.  This is especially true in endurance sports.  Compare the size of the distance runners with the swimmers and rowers you will be watching over the next couple of weeks.

So how much of this is “genetic”? It is known that height is about 80% heritable and there are excellent equations that use parental height and other factors that are pretty good at predicting the adult height of children.   However, at this time, there are no clear genetic explanations for why some people are tall and some people are short.  This has been studied extensively in hundreds of thousands of people and no answers have emerged.

I am attaching a link to a summary article on this topic and also a recent scientific article.   One idea is that as we learn more about how genes are turned on and off and how they interact with environmental factors the genetics of height will become clearer.  The other idea is that so much of what and who we are is so complex that there will never be clear genetic answers for most of it.

One Response to “Size Makes a Difference: Gymnastics and Swimming”

  1. July 28th, 2012 at 1:27 pm

    B. Joyner says:

    Interesting! Read the article while watching Olympic swimming.

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