Ape Index — My Thoughts on It

One of my clients sent me a link to an article in Triathlon Competitor magazine called Do you know your Ape Index?  The article talks about how arm length can affect your cadence — short arms yields a higher cadence and long arms yields  a lower cadence. He asked me if the information was new or true.  Read the article and take a look at my reply:



No, it’s not really new.  It’s a little bit more nuanced than what they say in the article.

To fully understand what they are talking about consider the equation:

V = SL x SR

Your speed (V) in the water is a product of your stroke length (SL, how far you travel on a stroke cycle) and your stroke rate (SR, the tempo, cadence or arm turnover).  What I’ve been telling swimmers is that there is no right or wrong answer about your stroke rate and, in fact, you choose your stroke rate from a range of options depending on what you are doing — much lower for a recovery swim or a 2.4 mile swim and much faster for a 50 yard sprint.

There are also other factors that affect your stroke rate:  your gender (women generally are higher), your muscle mass (more makes it lower), and your make-up of quick and slow twitch fibers (more slow twitch usually means a higher rate).  And, yes, arm length is definitely a factor in the equation.  That’s why generally people who are taller have lower stroke rates because they have longer arms.

What you are looking to do is to find the slowest stroke rate and the most stroke length that you can to go a given speed and heart rate.   Stroke rate is the part that makes you tired — to high a turnover and you are putting a lot of stress on your body.  So even though you will have a faster stroke rate if your arms are shorter, that doesn’t mean that you need to turn it over.  If you have poorer techique, you will swim with a higher stroke rate to go a particular speed because you simply lack a lot of the SL.  What we don’t want to confuse is higher SR because of your body composition and higher SR because your stroke sucks.  🙂

Here would be my strategy and way to think about it:

1)  Get your swim golf score and time/stroke combo.  Calculate the SR while doing this — time 10 strokes and divide by 10 to get the seconds per stroke (actually the inverse of SR)

2)  If your stroke count is above the range on the table that I showed you, work on your form to increase your SL.  Your SR will go down because of it but it will be based on what is proper for your body

3)  As your golf score goes down, start playing around with using different stroke rates, faster and slower, to find out what which yields a better V

4)  As you become more skilled, start looking at the heart rate that you need to do your swim at and compare it to the V = SL x SR that you can do for the distance.  You might be able to hold an SR for 100’s at a heart rate, but it might be too fast for a long swim and your heart rate will start to spike.  When you go anaerobic, that’s when you start to get less V for your SR

I strongly disagree that only tall people need to choose a longer or shorter stroke. What you are looking to do is to find the slowest stroke rate and the most stroke length that you can to go a given speed — in other words, the longest stroke that you can do based on your body, the distance you need to go, the pace you want to do, and the heart rate intensity you want to devote to it.  This thinking is at the heart of how we teach swimmers to understanding training and improvement.  You can “swim long or swim hard” and might get some improvement but it’s a shot in the dark.  Alternatively, you can take this approach and be more scientific about it.


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