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Background:
There are three competitive swimming courses: 25 yard pools (short course yards - SCY), 25-meter pools (short course meters – SCM), and 50 meter pools (long course meters). Conversion factors for each of the 18 short course swimming events were developed to convert between any of these courses.
The USA Swimming page contains the all-time fastest performers lists for SCY and LCM. From these lists, I looked at each event and extracted times for swimmers who appeared on both the SCY list and the LCM list. The average ratio between the swimmers SCY and LCM times was taken as the conversion factor. Below is an example for the men’s 50 free:
|
LCM |
SCY |
NAME |
|
21.81 |
19.05 |
Tom Jager |
|
22.04 |
19.07 |
Roland Schoeman |
|
22.05 |
19.08 |
Neil Walker |
|
21.80 |
19.05 |
Anthony Ervin |
|
21.85 |
19.12 |
Matt Biondi |
|
22.23 |
19.14 |
David Fox |
|
22.18 |
19.16 |
Brett Hawke |
|
22.06 |
19.17 |
Brendon Dedekind |
|
22.60 |
19.20 |
Shaun Jordan |
|
22.36 |
19.25 |
Aaron Ciarla |
|
22.41 |
19.35 |
Brian Kurza |
|
22.54 |
19.36 |
Robin Leamy |
|
22.05 |
19.36 |
Bart Kizierowski |
|
22.32 |
19.38 |
Steve Crocker |
|
22.50 |
19.38 |
Adam Schmitt |
|
22.00 |
19.44 |
Jason Lezak |
|
22.37 |
19.45 |
Ricky Busquets |
|
22.32 |
19.47 |
Sabir Muhammad |
|
22.51 |
19.51 |
Matt Busbee |
|
22.53 |
19.53 |
Greg Busse |
|
22.55 |
19.64 |
Tom Williams |
|
22.18 |
19.67 |
Peter Williams |
|
22.51 |
19.67 |
Matthew Macedo |
|
|
|
|
|
|
average ratio: |
0.868554233 |
This process was followed for each of the events for which all time data was available. Data was not available for the 50’s stroke and 800/1000 free. Based on the results from the events where full data was available, I decided to use the conversion factor for the next greater or lesser distance in each of the above events. See full conversion factor table below, for SCY to LCM:
|
SCY / LCM |
WOMEN |
MEN |
|
EVENT |
RATIO |
RATIO |
|
50 free |
0.87329 |
0.86855 |
|
100 free |
0.87938 |
0.86595 |
|
200 free |
0.87863 |
0.86877 |
|
4/500 free |
1.11928 |
1.10688 |
|
8/1000 free |
1.11928 |
1.10688 |
|
15/1650 free |
0.98127 |
0.97191 |
|
50 back |
0.86601 |
0.84941 |
|
100 back |
0.86601 |
0.84941 |
|
200 back |
0.87367 |
0.85783 |
|
50 breast |
0.87793 |
0.86408 |
|
100 breast |
0.87793 |
0.86408 |
|
200 breast |
0.88046 |
0.86708 |
|
50 fly |
0.89085 |
0.87711 |
|
100 fly |
0.89085 |
0.87711 |
|
200 fly |
0.89199 |
0.87870 |
|
100 IM |
|
|
|
200 IM |
0.87654 |
0.86245 |
|
400 IM |
0.88390 |
0.86947 |
There are two major factors that affect a swimmers time conversion from SCY to LCM:
- the fatigue factor: how much does the swimmer slow down with distance?
- Turn quickness, power off the wall: swimmers with quicker turns and a more powerful push off the wall will do better in a short course pool.
There is a reasonable sample size in the method used above, so the conversion factors should capture some middle ground between better short course and long course swimmers, at the elite level.
One observation from the conversion factor table above: the conversion factors for women are higher than those for the men. Looking at a conversion example, let’s say a woman and a man both swim 57.00 seconds for a 100 free LCM. The woman’s converted SCY time is 57 * .87938 = 50.12; the man’s converted SCY time is 57 * .86595 = 49.36. So the time difference between SCY and LCM is greater for men than women. This is due to a combination of two factors:
- the women’s pace drops off less with increasing distance
- men have greater power off the wall, so turns help men more
The next conversion I considered was from SCM to LCM. I could not find an all-time best performances list for SCM, so things were more challenging. For reference I calculated the ratios between the SCM and LCM world records. Here the sample size is only one swim per course, unlike the 20 or so used above for the SCY to LCM conversion.
Comparing the SCY to LCM conversion to the SCM to LCM conversion, the only difference is that the shorter course is 9.36% longer. Both SCY and SCM have the same number of turns. So I chose to calculate the SCM to LCM conversions from the SCY to LCM conversions using a straight distance conversion, plus an additional fatigue factor. I chose the fatigue factor such that the average difference between the SCM/LCM conversion factor calculated from SCY to LCM (with distance ratio plus fatigue factor), and the SCM to LCM world record ratio, was nearly zero. The result follows:
Men: SCM/LCM = SCY/LCM + distance conversion + 2.0% fatigue factor
Women: SCM/LCM = SCY/LCM + distance conversion + 1.4% fatigue factor
SCM/LCM |
Women |
Men |
|
Event |
Ratio |
Ratio |
|
50 free |
0.96841 |
0.96886 |
|
100 free |
0.97516 |
0.96596 |
|
200 free |
0.97433 |
0.96910 |
|
400 free |
0.984 |
0.973 |
|
800 free |
0.984 |
0.973 |
|
1500 free |
0.984 |
0.973 |
|
50 back |
0.96034 |
0.94751 |
|
100 back |
0.96034 |
0.94751 |
|
200 back |
0.96884 |
0.95690 |
|
50 breast |
0.97356 |
0.96387 |
|
100 breast |
0.97356 |
0.96387 |
|
200 breast |
0.97636 |
0.96722 |
|
50 fly |
0.98788 |
0.97840 |
|
100 fly |
0.98788 |
0.97840 |
|
200 fly |
0.98915 |
0.98017 |
|
100 IM |
|
|
|
200 IM |
0.97201 |
0.96205 |
|
400 IM |
0.98018 |
0.96988 |
The final conversion to consider is from SCY to SCM. Again I wanted to calculate the SCY to SCM conversion factors from the SCY to LCM factors, since the SCY to LCM data is the most solid. In this case the distance ratio is the same as the SCY to LCM data, but the number of turns differs. The following turn factors added to the above to the SCY to LCM conversions provided pretty good correlation with the SCY record to SCM US national record ratio:
Men: SCY/SCM = SCY/LCM + 3.0% turn factor
Women: SCY/SCM = SCY/LCM + 1.2% turn factor
|
SCY/SCM |
Women |
Men |
|
Event |
Ratio |
Ratio |
|
50 free |
0.88377 |
0.89461 |
|
100 free |
0.88993 |
0.89193 |
|
200 free |
0.88917 |
0.89483 |
|
4/500 free |
1.13495 |
1.13676 |
|
8/1000 free |
1.13495 |
1.13676 |
|
15/1650 free |
0.99501 |
0.99815 |
|
50 back |
0.87640 |
0.87489 |
|
100 back |
0.87640 |
0.87489 |
|
200 back |
0.88416 |
0.88357 |
|
50 breast |
0.88847 |
0.89000 |
|
100 breast |
0.88847 |
0.89000 |
|
200 breast |
0.89102 |
0.89310 |
|
50 fly |
0.90154 |
0.90342 |
|
100 fly |
0.90154 |
0.90342 |
|
200 fly |
0.90269 |
0.90506 |
|
100 IM |
0.88706 |
0.88832 |
|
200 IM |
0.88706 |
0.88832 |
|
400 IM |
0.89451 |
0.89555 |
Finally, for your own time conversions it is worth considering your own turn power and proficiency, and your own stamina. The conversion factors used in the online calculator are based on the performance of elite swimmers. If your turns are less proficient, then additional turns will increase your speed less. If you think your pace will drop off with increasing distance more than an elite swimmer’s, then you should add more time to your LC conversions.
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