To clarify, let me add on this story of how these Optimal Stroke Count charts came about…

First a note: this is not intended to be an precisely chronological story. It is simply a recollection of the main events that shaped the formation of these charts, weaving each one in where it helps the story flow.  The story takes place within the span of five years from 2011 through 2014.

In order for this story to make any sense, you may want to look at these two articles about Optimal Stroke Count:


The Origin

In the original TI Coach Training Manual that many of us received (I did my TI Coach training in August of 2010) Coach Terry had inserted a text chart that gave a list of six height ranges in inches and then a recommended range of stroke counts in a 25 yard pool, something to aim for in the pursuit of efficiency. He called it the height-indexed rough guide for 25-yard SPL. Some of us coaches, having some interest in math, physics and physiology topics and with experience in working with stroke counts and tempos, were curious about how those numbers were derived and under what circumstances they applied or didn’t apply. Thus began some behind-the-scenes discussions among a  few coaches and with Coach Terry. It was a very fun time in those years thinking and talking about these concepts together, expanding, developing ideas for new materials and resources, with each person (who was a skilled professional in other areas) bringing some unique insights and expertise to the discussions. 

Being a bit geeky, some of us were not quite satisfied with the ‘rough’ guide and wondered what would be found when examining the heights (and wingspan if I could find it) and stroke counts and tempos of various swimmers in different kinds of events, both elite and ordinary citizens with great form. This began my conscious effort to collect observations and data on some swimmers and on certain recorded swims.


New Equations

Those observations led me to spend some time dissecting a single swim length (of the pool) to see what was happening at different locations and moments of time to see how changes in each section affected overall speed. Then I worked out more comprehensive math equations on a spreadsheet to include various things happening along each length of the pool, and cumulatively over many lengths, as well as taking into account the height (or wingspan) of the swimmer performing that swim.

I discussed my observations about stroke length data with Coach Terry, Coach Suzanne and a few other coaches who were interested in this topic as well. I presented my own hypothesis that obviously smooth, efficient swimmers seem to find their most optimal stroke length somewhere between 55% and 70% of their wingspan for a wide range of competitive events, though there were a few elite outliers swimming at or beyond those boundaries. Among those I discussed this with, including Terry, I felt a consensus growing that those numbers reflected our common observations, giving us a reasonable range to aim for with the wide range of people we work with. Those numbers are not based on a scientifically thorough data study, just watching and measuring different swimmers in different swims, but it was a great leap forward from any other resource we had out there at the time (and perhaps still is) for our intended purposes.


Make It Visual

Being one who processes information visually, one of my favorite products of these equations was a curve that I could calculate and then draw on a graph. The equations allow me to take different measurements from a unique swimmer and situation, and produce output that are a bit more customized to that individual. I can use the variables for height and wingspan (to derive the wingspan coefficient), push-off distance, duration of the turn, and things like that.

Somewhere along the way, I recall Terry telling a story of playing a game in his car while commuting regularly to a swim location (if you can find where he wrote about this, please send me the link and I will add it here). His car would show him the fuel economy of his commute. So he would experiment with driving the same distance each day at different speeds, which would affect time and then he’d see the trade off in time versus saving an amount of fuel. He found that he could drive slightly slower yet save a disproportionately greater amount of fuel. This provided an analogy for swimming more smoothly and calm, which might lose a minute on the swim in a triathlon, but conserve an enormous amount of energy which could then be invested back into the bike and run to make up far more time than might have been gained in the swim. This would allow the triathlete to get out of the water in much better shape to peform far better in the more demanding legs of the race. 

While living in Antalya, Turkey from 2008 to 2016, I had a wonderfully robust Honda Activa scooter which I drove around nearly every day. On the speedometer of this scooter there was a green economy zone marked out which indicated at which speed range I’d receive the most fuel economy, requiring me to drive not too slow and not too fast. I sent Terry a photo of the speedometer and pointed out how Honda conveniently provided this visual aid, and offered to create something visual like this for our swimmers. 

Keep It Simple

I am not sure if he intuited those numbers himself or got them from somewhere else. But I first encountered the idea for the index in the manual Terry provided us. It was very helpful to offer recommendations on which range of stroke count a swimmer within a height range may use. But I wanted more: a more robust explanation for how those numbers are derived, and an equation that we could plug anyone’s height (or wingspan) into and take any pool length and then calculate their estimated appropriate stroke count range with. And I wanted an equation that would work for both sides of the world, metric (meters) and standard (yards) since we often work with swimmers from all sides of the planet.

As I got deep into playing with equations I realized how many factors could influence what stroke length, stroke rate and pace the swimmer ended up using. My equations and my spreadsheet calculator expanded to take in a lot more interesting data, so I could study that for relevance if needed.

I played with more ideas for how to display some of that information. Here is one of my graphic daydreams…

There were collaborative efforts going on to update the coaches manual and various other projects Coach Terry had in mind, or that other coaches were thinking about behind the scenes. I had a particular interest in helping improve the visual aid of the manuals I was using to teach new coaches with and other products we might create. So, based on the one I had already created for my own swimmers, I offered to provide an updated and visual version of that text-based Height-Index for Terry. He approved the idea.

Though I was excited by all the potential data we could share using the things we could measure in each swimmer and swim, for everyday swimmer use, we needed to keep the tool simple. Being an experienced teacher and appreciating my own need to have information represented visually in an attractive way, I gathered the data and developed the equations and designed this graphic chart currently in use.


A New Name

I set the boundaries for curves between 55% and 70% of height (or wingspan). Then I had to make an assumption about push-off distance and time and then plotted the graph and then composed this on my vector graphic software. In honor of the Honda speedometer I colored the stroke count range green, though originally I had a gradient fill, moving from green on the edges to yellow in the middle and a dashed red line down the middle of that zone. The dashed line was there to indicate that a swimmer with an extreme Wingspan Coefficient might do better to aim for a stroke count above that line (if they had particularly short arms) or below that line (if they had particularly long arms). I don’t quite recall who, but some coach suggested I was getting a bit too complicated with the information so I removed the center line and the yellow and the zone became a simple solid green as it is now. Somewhere along the way, whether I used it first or him I don’t remember, but Terry started referring to it affectionately as the “Green Zone” in his various forum posts and blog and it stuck.

A Tool, Not A Rule

Though most people will look at that Green Zone chart and appreciate its simple clarity, they might also take it as an imperative, or a rule that they must achieve SPL within this range. However, I am burdened by knowing the assumptions behind it which do not reflect everyone’s situation. And I realize the complexity that is involved in honing in on the small range of stroke counts that will truly work best for each individual at a particular time, for a particular event. The chart is a tool (not a rule) to get you headed in the right direction, but you’ve got to do the work of fine tuning of your sense of your own optimal stroke count range, both by how what is produces and by how it feels. And working with a coach that understands how stroke length is developed can help you take those influencing factors into account and set more appropriate stroke count goals.



I composed these articles on the Optimal Stroke Count charts after recently hearing some comments and listening to myself explain some things they need to think about to adjust expectations. I realized it would be good if I laid down all this information about the charts themselves.

And after someone responded to those, wondering why I didn’t get credited for creating them, I felt I should share some of my memory of creating these and my intentions, so it would be clear that I gladly gave the time and effort on things like this, as so many of us were eager to do in the pleasure of working with Terry on new ideas and projects for TI back in those years. Many great coaches made similar contributions in little and big ways, some receiving credit some not, but that didn’t seem to be why anyone was getting involved with their skills. That was the creative atmosphere we enjoyed in those years. I sure miss our Coach.

I am pleased to know that these charts are useful and appreciated, and I just wanted to make sure that they are also understood better and used appropriately. I reserve the right to change them whenever new observations and insights urge us to improve our representation of the Green Zone. Please share those insights when you have them.


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