Swimming By the Numbers: The Unfairness of Short Course – Long Course Conversion Rates, especially for Backstrokers!

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I’ll start off with the teaser. Existing one-size-fits-all course conversion rates are not remotely accurate, especially for backstroke, and there exists a sizable difference in accurate conversion rates between men and women. Finally, any swim governing body that uses a single, artificially low conversion rate is doing a great disservice to its members.

Now, on to the analysis.

A course conversion rate is used to take a time done in either a short course (25 m) pool or a long course (50 m) pool, and change it into a reasonably accurate time for the other pool. It looks like this:

Long Course Time = Short Course Time x (1 + Conversion Rate%)

Using course conversion rates is often necessary for qualifying or seeding in meets. As most North American teams do not have ready access to a 50m pool, most meets are SC, but championship meets are usually LC. Unless the governing body is willing to publish separate LC and SC time standards for individual meets to use, a conversion rate becomes necessary to allow swimmers with only SC times into a LC meet. But the process is frustrating when an inaccurate conversion rate makes a LC qualifying time so much harder to achieve than the SC time. Or when a swimmer has a great race, but doesn’t meet their converted time and thinks they did poorly.

Before the discovery of underwater kicking, conversion rates were typically 2.5%, and once the swimmer’s body adjusted to long course season it was reasonably accurate. The discovery that underwater kicking was the fastest form of swimming changed all of that. With 2 underwater phases for every 50 m instead of one, SC swimming is all about the underwater kicking. So its not surprising that different swimmers often excel at one or the other. In fact, a look at the World Records in both courses shows that only 10 of the 34 individual events has the same person holding both SC and LC World Records (5 male and 5 female).

What is the “best” conversion rate?

USA Swimming and Swimming Canada steadfastly maintain that there is no need to use any conversion rate at all. This is excellent!

“USA Swimming does not formally endorse any conversion factors between different courses. Each course (long course meter, short course meters and short course yards) is unique. For qualification into specific competition, each course has a time standard derived from a specific formula or philosophy.”

But other swim governing bodies do not want to calculate independent sets of time standards for each course, and so they just use a single conversion rate to handle everything. You’ll soon see why this is a problem.

The charts below show the SC-LC conversion rate based on records for five jurisdictions, including World, American, Canadian, European and Australian records:

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Right away we can see a big disparity between the conversion rates for men and women. The Men’s rate averages 3.6% across all jurisdictions, while the women’s averages 2.6%, and variation between jurisdictions for each gender is minimal. While the data doesn’t explain why there is this gender difference, we can speculate. This gender difference is most easily accounted for if the speed differential between men and women for underwater kicking is larger than the speed differential of their swimming. If so, men would benefit more from SC, as there is more underwater than in LC.

But let’s dig a little deeper into the data. The next chart breaks down the conversion rates by stroke, with distance freestyle (800 and 1500)separated from the shorter distances due to their minimal underwater component. The columns are the conversion rate averages for the appropriate records across all 5 jurisdictions used above.

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Here’s where it gets really interesting. What jumps out right away is the huge difference in conversion rates for different strokes: from a high of 5.8% for men’s backstroke to a low of 1.5% for women’s distance freestyle. The other thing that stands out is that both genders share the same ranking of conversion rates by stroke: from highest to lowest are backstroke, breaststroke, IM, freestyle, butterfly, and distance free.

Let’s go over each of these results to see if they make sense. I’m going to get a little geeky here. Skip to past the table if you want.

The key to the conversion rates lies in 3 areas (the assumption is that the records are all set by people with more than adequate proficiency):

  • The type of turn performed (flip versus touch). A flip turn is performed much more quickly than a touch turn, and so will lead to a larger advantage. We can guess that a touch turn (and just the turn portion) doesn’t help at all, probably contributing negligible benefit.
  • the pushoff and first 3-4 metres. This is the fastest part of the length, and for each person is pretty much constant for all strokes
  • the difference between underwater kicking speed and swimming speed. The greater the difference, the bigger the benefit as there is more underwater with SC.

This next table explores the impact of these 3 components for each stroke, and I think it explains why the conversion rates for each stroke are ranked the way they are.

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OK, now the above analysis is based on senior records. So the question might come about as to whether the conversions still hold for age group swimmers. I’ve prepared another pair of charts based on Age Group Records for both the US and Canada up to the age of 14. I’ve had to convert the US short course times from yards to metres using 11%, although the exact amount isn’t overly important as we’re mainly checking the conversion relationship between categories.

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You can see that the basic relationship holds for age group swimmers. The only exception (boy’s breaststroke conversion rate higher than their backstroke conversion rate), but I think we can chalk this up to relatively little data to work with.

So if you have to use course conversion rates, here are my recommendations.

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Earlier I said that adopting a set conversion rate may have far reaching implications. Let’s use our Swim Ontario’s blanket 2% course conversion rate as an example, and let’s imagine a swimmer trying to make a 200 qualifying time. For this example, the SC qualifying time is 2:00.00, but no SC meet is available. Let’s look at the impact of the mandated 2% conversion rate versus the actual conversion rates as determined above.

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Notice that the LC qualifying time becomes 2:02.40 irrespective of gender or stroke. The worst situation is for a male backstroker. The conversion should actually be 2:06.96, which is a brutal 4.56 seconds slower than the qualifying time! In fact, only one time becomes faster, and thats the women’s 200 fly, with a drop of 0.36 seconds. This situation is hardly fair.

The moral of this story ends up being that if this swimmer wants to qualify, he or she should only attend SC meets. Surely this can’t be the intended result of the blanket 2% conversion rate. A fair conversion rate needs to be established, or do away with the conversion rates completely and establish course-independent data-based standards. The way that Swimming Canada and USA Swimming and probably a host of other jurisdictions.

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5 comments

  1. […] Swimming By the Numbers: The Unfairness of Short Course – Long Course Conversion Rates, especially… […]

  2. Mark Goedecke · · Reply

    This is the most insightful article about the conversion rates I have ever read. Thank you!

  3. […] times, and determined real conversion rates for the different strokes, distances and genders (see here). These rates vary from a low of 1.5% for women’s distance Free to a high of 5.8% for […]

  4. There are some limitations to the data, however. For instance, the short course meters records are much “slower” comparably to the long course records because the majority of championship meets are swum in long course. Thus, swimmers are tapered and shaved for those competitions and the times will naturally be faster. Moreover, the world record holder for a short course event may not hold it for the same long course event. This may be because they are especially strong at walls or may not have a great deal of endurance. Thus, comparing swims by different individuals cannot possibly accurately depict the relationship between short course and long course swimming.

    1. Thanks Jonathan,

      You’re absolutely right about the limitations of the data, but since the conversion factors differ for each person, as you correctly point out, we cannot construct a single set of conversion factors that works for everybody. In fact, to further your point, I suspect personal conversion factors change constantly during a swimmer’s career.

      It’s very true that some will be better at LC, some at SC. (And they do have world SC championships, and many nations have national SC championships). So these conversion factors offer a good midpoint. And they are significantly different than standard conversions used by many nations and regions, while also indicating why and by how much each stroke will differ than others. As I mentioned, a standard 2% or 2.5% across the board conversion factor is just plain wrong.

      The fact that they are so consistent across age groups, nations and for world records also gives us a high confidence level in these results.

I love comments, especially when they disagree with my view.

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