Why Tall Swimmers Have An Advantage
Alan Couzens, M.Sc. (Sports Science)
Jan 30th, 2017
Horses for Courses – Gold Medal Swimmer, Missy Franklin (6'2") & Gold Medal Gymnast, Shawn Johnson (4'11")
As we get a little deeper into EC’s annual swim challenge, the lats get sore, the paces slow and the reflections start…
Coach, if I’m putting so much time into swimming, why are my swim splits still so slow? Why do I suck in the water? The answer is, it might not be your fault!
Have you ever wondered why Olympic sailing competitions divide boats into classes based on length?
You don’t see 12 foot dinghys lining up against 12 meter super yauchts for the same reason that you don’t see flyweights lining up against heavyweights in boxing – they’d get their proverbial butts kicked!
Similarly, if you look at the boats lined up in a rowing regatta, how come none of them look like the squat, wide little things that we used to row around the pond on?
On a more specific note, if you happened to get a ticket for the Men’s Olympic 100 Free final in Rio, you could be forgiven for thinking that you’d accidentally walked into the Basketball final by mistake! The top 3 guys were 6’4”, 6’6” and 6’7”! And this trend of super tall athletes swimming fast isn’t isolated.
When I was growing up in the pool, the 2 superstars of the time were American Matt Biondi & German Michael “The Albatross” Gross (pictured below) – 2 guys who both happened to be 6’7”!
Then we had the reign of Alex Popov (6’ 6”). Lately, you might have heard of a guy by the name of Sun Yang who is dominating Men’s distance swimming – also 6’6”. Or, a couple of U.S. ladies who are household names in the pool – Katie Ledecky – 6’0” or Missy Franklin – 6’2” (pictured above).
Closer to our world, 2 of the perennial fastest swimmers in Kona each year - Andy Potts and Jan Frodeno are 6'3" and 6'4" resp.
If you’re on the less height endowed side, when it comes to swimming, the guy you should blame for your ‘challenges’ is a bloke named Froude.
Froude discovered that the wave drag of a vessel increases exponentially as the ratio between speed/length increases. His formula is expressed as…
Where u0 is the flow velocity, g0 represents the shape of the swimmer and l0 represents the swimmers length. According to the formula, the faster the vessel is moving, the longer it has to be to keep wave drag manageable.
The importance of this law when it comes to swimming can’t be overstated. In a 2004 study by Kjendlie & Stallman, height was 2x more important as a predictor of the oxygen cost to swim at a given velocity than hand slippage, i.e. technique!
Anyone who has been around age-group swim squads for a while can confirm this - the arrival of the freakishly tall kid (I was in that boat myself so I'm allowed to say that :-) who, despite sub-optimal technique does very well. I remember back to one of my first high school swim meets, a guy named Brad – big dude - 99th percentile sort :-) over 6’ at 14, decided he’d give this swim thing a try. First meet, lines up for the 50 free, belly flops off the blocks and gets those arms cranking, splash flying in all directions. Let’s just say swim technique wasn’t his strong suit. Touches the wall first in 29s, surrounded by a heat full of much shorter, much more polished swimmers who, despite spending many hours polishing clearly superior techniques, simply couldn’t keep up. And, thanks to Froude, there is a good ol’ physics based reason for this…
Below you’ll see the difference in wave drag (in Newtons) when we plug 3 different heights into Froude’s formula to get a coefficient of wave drag for each that we can then apply to calculate the total wave drag for a given swim speed. In this case, a competitive Ironman swim speed of 1.3m/s
Through no fault of their own, the short swimmer has to deal with about 40% more wave drag to swim at the same speed as the tall swimmer!
More practically, let’s look at what this means in terms of speed, i.e. here is the data rejigged to look at what Ironman swim split would be obtained by each swimmer height at the tallest swimmers level of wave drag (16N) assuming all other factors – power output, propulsive efficiency etc. are equal.
At the same level of wave drag, the 2 meter tall swimmer swims almost 6 minutes faster. Thanks a lot Froude! :-)
But, if you’re of the shorter persuasion, don’t despair. Contrary to the Olympic 100m swim final, if we cast our eyes across the Ironman winners, we’ll see a lot of different body shapes and a good number of them on the short side. And there is good reason for this: While height is a great thing to have in the water, it’s not a great thing to have when running long distances, especially running long distances in the heat. And, considering the Ironman World Championship is about 3x longer duration running than it is swimming and that the running takes place in a furnace(!), shorter athletes have historically done very well! Remember a little Aussie by the name of Greg Welch? Or another (5'3") athlete by the name of Rinny?
The point of this post then is about one word – context. When comparing yourself as a “sucky swimmer” be sure that the comparison is against athletes of similar height (&, according to Froude’s equation, similar shape). It can be tempting to devote a lot of time & energy trying to ‘fix a weakness’, sometimes to the extent that you let your strength slip. Hopefully the above adds some context to that. The reality is that, if you are a shorter athlete, to bring your swim speed up to the ‘same level’ of taller athletes, you would need to become a far superior swimmer in propulsive efficiency &/or pure fitness/power terms.
While this is not to say that most triathletes could not stand to devote some time to polishing up the technical aspects of their stroke, keep it in context. If your morphotype is more Gebresellasie than Phelps, the time & energy that you might devote to keeping up with the super fish could be better spent exploiting areas that are natural strengths.
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