Do Long Arms And Short Legs Help Swimming?

In triathlon, we all have a sport which we excel, and a sport that really challenges us.  Some athletes excel in running and cycling.  For others, the swim portion of a race is just never long enough.  Great swimmers do have one thing in common:  they all started swimming at a very young age.  Very few began swimming after the age of 25 and became competitive on a world stage either in pool swimming or triathlon swimming.  So, what makes a good swimmer?  Is it lifelong training, or just getting lucky enough to be born with long arms and short legs?

The intent of this article is to see if longer arms and shorter legs can explain the differences in performance between Duane Dobko, a former Division-1 swimmer/backstroker, and David Thompson, professional triathlete and run/bike specialist.  In a sport that doesn’t come easy, it is logical to think that performing the movement correctly is all that matters.  But how much are you born with?

The table below compares the dimensional characteristics and swim/run performances of Duane Dobko and David Thompson.  Both athletes have attempted to master swimming and running as best as they possibly can. The difference is that David began swimming much later (age 24 versus age 6 for Duane), whereas David is a lifelong runner and Duane started running at age 26.  The data is below.

This comparison is a good apples-apples comparison.  Both athletes are the same height, and have the same size feet and hands.  The only difference is arm & leg length and years of experience in swimming and running.  The difference in arm length (if you count the difference in shoulder width) is 1.25 inches per arm with Duane having the longer arm.  The difference in leg length is 2 inches with David having the longer leg length; though it is an odd result that the difference is all below the knee (femur length is the same).

The data confirms that Duane’s physical dimensions are more “fish-like” than David’s.  But the figures do not explain the time gap.  The following calculation illustrates.  Assume that Duane’s stroke allows him to travel 2.5 inches further than David at the same stroke rate (strokes per minute).  The 2.5 inch value is twice the 1.25 difference in the table above (1.25 inch at the front of the stroke, and 1.25 inch at the finish).  Also assume that David and Duane take the same number of strokes per pool length.  Duane’s travel distance per stroke is approximated as 3 feet 9.5 inch (using a rough estimate of 15 strokes over 19yards of swimming).  David’s travel distance per stroke at the same effort would then be 3 feet, 7 inches.  In this model, the benefit to Duane would be 3 feet 9.5 inch / 3 feet 7 inch = 5.8%.  This result goes halfway to explain the difference between David and Duane over 500yards (at 10% in the above table).  However, it is nowhere near the difference between David and Duane over 50yards (at 18%).  Something else is at work.

Could the difference in leg length explain the remaining time gap?  It is widely accepted that great swimmers have short legs and long arms.  There have been many theories that explain why short legs matter.  A good one is that a longer leg equates to more mass (and drag) under the water.  This might be true.  My own logic (it is just logic – I have no data) is that longer legs are more difficult to move in a thick medium like water.  It is hard to estimate what this effect could be, so I will not even try to create a numerical model.  However, I will explain my logic.

In running, longer legs allow an increase in stride length, which means that you can go further for the same stride and effort (like running on stilts!).  In swimming, it is the opposite.  In optimal flutter (freestyle) kicking, your feet are moving no more than 16 inches up and down.  If you kick deeper, you wear out your legs and increase your drag.  Long legs in kicking will not provide the equivalent of “longer stride length”.  On the contrary, a longer leg will require more energy to get the same propulsion just because you have to move more mass.

So, excluding the possible effects of leg length, the differences in upper body dimension between David and Duane don’t add up to their performance difference in swimming.  How do the numbers look with running?  Let’s assume David’s stride length is an even 5 feet at full speed (this is a rough estimate).  Assume that David’s 2-inch advantage in leg length (taken from the table above) gives him a 4-inch advantage per stride (2 inches at foot-strike and 2 inches when the foot leaves the ground).  This assumes that Duane is traveling at a modest 4 feet 8 inches per stride at full speed.  Thus, Thompson’s advantage due to leg length = % difference of 5 feet to 4feet 8 inch = 7.1%.  This is much less than the actual advantage of David Thompson in the table above (25%).  Clearly, leg length does not explain the difference in running performance.

What else is at work when body dimensions aren’t the answer?  I hypothesize it is the years of swimming for Duane and years of running for David has optimized their systems for the sports of their specialty and at the exclusion of other non-similar sports.  I have had the unique opportunity to train swimming with David Thompson for the past two years.  The differences of how David and I maintain swimming fitness after any time off is very revealing. 

When David is forced to take 2 weeks off of swimming, he experiences a very dramatic loss of swimming performance that takes a long time to regain.  On the other hand, a 2 week break for Duane is not nearly as significant, and any time loss can be recovered more much more quickly.  This effect has occurred despite David’s performance improvements in swimming.  It is as if David’s system can be trained to perform at an elite level, but it does not develop the memory that Duane’s system has for the water.

What is the moral of this story?  This article does confirm for a single pair of athletes a set of dimensional characteristics that are “typical” of elite swimmers and “typical” of elite runners.  However, the dimensions don’t explain the difference in performance.  Somehow, David Thompson has overcame great odds and found a way to swim with the best pro triathletes in the world.  He accomplished this despite learning swimming at a late age.  Thus, this article cannot conclude if David’s dimensions help or hinder.  Maybe he has overcome swimming with extreme willpower.  Or maybe he’s found a way to move through the water that is optimal for his system.  I suppose only David Thomspon knows for sure. 

Never let your physical dimensions hold you back from your performance goals.  Your system might be suited for running, swimming, or some other sport.  But body dimension is only one of many possible characteristics that affect your final race time.  Alone, dimensions did not explain the difference between David and Duane.  It is likely that good old fashioned hard work and dedication matters much more than what you were born with.  That’s my logic, and I’m sticking with it until someone proves me wrong!  Until next time, happy training.