Would bigger feet make you faster?

Have you ever wondered how fast you could swim if your feet were just a little bigger?  It makes sense that a bigger foot would allow you to grab more water.  But how much of an effect does it really have?  Fortunately, there is a product out there which approximates what it would be like to have bigger feet – Zoomers.  These are small fins, or flippers.  They make your foot approximately 20% longer and 70% wider at the toes.  Compare this to scuba fins, which can be 2 times longer and two times wider than the foot.  The difference between Zoomers and feet is enough to be significant, but not so much that you have to kick in a fundamentally different way.  Therefore, a comparison of Zoomer versus no-Zoomer times is a great way to see if bigger feet always make everyone faster.

So, let’s get the answer established right away.  Does Zoomers make everyone a faster sprint swimmer?  The answer is surprisingly, no.  12.5% of the individuals in this study got slower with Zoomers.  The remaining people got faster but had a huge range of performance, from 0% (Zoomers same as feet) all the way up to over 20% (Zoomers much faster than feet).  Overall, the data confirms what everyone knew.  Foot size is one indicator of swimming speed.  On average, people did get faster with Zoomers, to 95% confidence.  However, the study also confirms that the size of your feet isn’t the only thing that matters.

Presented is data from 24 individuals comparing times with Zoomers versus times without.  All times were taken over a distance of 50 yards of freestyle swimming.  Overall, the average result was +7.8% increase in speed with Zoomers, with a range of -1.5% (got slower with Zoomers), up to +21.8% (got much faster with Zoomers).  Why is the variation so high?  The individuals displayed a wide variety of skill levels, from age grouper to elite level.  In this analysis, elite is defined as someone who can swim 50 yards without Zoomers in under 30 seconds.

Swimming skill level did affect results.  Increase in speed with Zoomers was much more varied with age groupers.  By comparison, elites were more consistent at an average of +1.8% increase in speed with Zoomers and a range of -1.5% (got slower with Zoomers) up to +6.7% (got faster with Zoomers).  Age groupers had a higher increase in speed averaging +9.4% (Zoomers faster).  However, not every age grouper got the same benefit.  The range in this population was 0% (same speed whether wearing Zoomers or not) all the way up to +21.8% (Zoomer much faster).  A histogram of percent improvement as well as a chart showing sprinting times with Zoomers versus without Zoomers is shown in the figure.

This data confirms that the secrets to swimming fast are far from universal.  Adding fins to your feet, which may sound like a good idea, doesn’t always result in an increase in speed.  The range of Zoomer effects is massive (over 20% range in the data).  If the size of the hands and feet are the biggest indicator of speed, the relationship between Zoomers and non-Zoomers should be more consistent from person to person.  Something else is going on that is causing individuals to swim at different rates. 

Following below is a series of observations I have made with individuals with various skill levels with and without Zoomers.  It may seem crazy that anyone could go slower with fins.  However, moving more stuff through a thick substance like water is done at a cost of an increase in resistance.  You get more force with the same motion but it takes more energy.  Swimming with Zoomers or suddenly growing bigger feet is analogous to riding a bike at a lower gear than you are used to for a given situation.

If you are swimming well and Zoomers slow you down, chances are you have fast legs in the pool.  If you are kicking right, the leg muscles are firing when in a position to drive forward, and then quickly turn off when the leg is in recovery.  The on/off commands are being sent from the brain at the same rate as human reaction time, or as fast as humanly possible.  Those systems operate best in very specific conditions, and can be easily overwhelmed if the muscles have to work in a different way. 

Some Age groupers swim much faster with Zoomers.  Anything greater than 10% is a huge difference.  It means that you would finish a 50 yard sprint with Zoomers, but would still have 5 yards to go if you just used your feet!  If fins make you much faster, your forward motion with no-Zoomer kicking is likely low (maybe even zero).  This means you are having a tough time just keeping the feet from sinking.  Thus, the increase in water resistance that Zoomers create does not cause you to work harder.  On the contrary, you find it easier because the agony of keeping your legs afloat without fins is translated to forward movement when fins are added.  What if your speed gain with Zoomers is between zero and 10%?  Chances are your abilities in arm and leg movement are pretty normal, and you don’t have any problems with moving backwards when you are kicking with a board. 

So, hopefully you have a better understanding of the relationship between foot size and swimming.  It is true that most Olympic swimmers have abnormally large hands and feet.  But a large foot is just one of literally hundreds of factors that make an Olympic swimmer succeed.  Your shoe size is not a magical cure-all for your triathlon swim.  Your leg muscles have been grown and optimized to your physical dimensions, and may not work as well if those dimensions changed anyway.  So don’t waste your time wishing for a perfect racing body shape.  You can do plenty of things to reach your goals in the sport with the body you already have!  Until next time, happy training.