Swimming watches for triathletes are ubiquitous. These tools contain an accelerometer that can count strokes, detect how many lengths of the pool we’ve swum and keep track of our pace and time for every lap and repeat. Triathletes and swimmers are now asking questions about what they can do with the information obtained.
The two most popular sites that currently track and report this type of data are the sites of the watch makers themselves, Garmin and SwimSense. Training peaks also can import this data but as of this writing they lack a robust reporting feature.
The most easily obtainable and somewhat interesting metric reported is the SWOLF score. SWOLF is an abbreviation for “Swim Golf”, and is a score obtained by adding together your strokes per length, and the time for the length.
e.g. 25 yards swim at 30 seconds in 20 strokes is a SWOLF score of 50.
Below is a screenshot of such a reported metric from Garmin Connect:
And here is a similar example from Finis, the makers of the Swim Sense.
What does SWOLF tell us?
Many coaches believe that SWOLF is a measure of efficiency…that a lower SWOLF score is a more efficient stroke and we should strive to get SWOLF as low as we can. However, two things must be kept in mind when comparing SWOLF score and efficiency. Let’s talk about these two reasons and I’m sure you’ll also discover new ways to use SWOLF during your workout analysis.
The first reason that the SWOLF score is not a very good measure of efficiency…if it can be considered a measure at all, is that efficiency is the relationship between the amount of work energy that goes into an activity relative to the work output, or forward movement achieved. For example, if we could measure how much oxygen a swimmer was consuming while swimming in a flume at a specific speed, then we could measure his or her efficiency. External measuring tools of oxygen consumption are needed. So while we can’t get an actual efficiency number from a swim watch, what we can do is incorporate certain clues that may tell us something about the efficiency of the stroke.
But more interesting is the second reason that SWOLF can’t tell us much about the efficiency. Even though SWOLF is derived by adding two parameters together…namely Strokes per length (SPL) and the time in seconds for the length, we still need to know both the SPL and the TIME independently to make any sense of the SWOLF number.
Time and SPL Matrix = Swim Golf Variations
Let’s create a two by two box of SPL and Time, to keep it simple let’s just use HIGH and LOW for SPL and time and see what may happen to SWOLF and what it means. If it seems confusing at first, take the time to read through each scenario and you’ll create new ways to think about the metrics as well.
Here are four hypothetical scenarios which I describe in a bit more detail after each one.
If if SPL * rate = time, then we are curious about what SPL + time or SWOLF can tell us?
A) SPL is high and time is high = high SWOLF and inefficient swimming
B) SPL is high and time is low = medium SWOLF and improved efficiency
C) SPL is low and time is high = medium SWOLF and very efficient swimming
D) SPL is low and time is low = very low SWOLF and inefficient swimming
A) high spl and high time (ie slow) suggests a lot of drag and or inefficient catch. Scenario A swimmers can learn a lot from tracking SWOLF and watching it improve because experiencing either a lower SPL or a faster speed suggests they are improving swim efficiency
B) as speed increases an expected and normal response of efficient swimming is for SPL to increase (SWOLF may stay the same). Scenario B swimmers can expect to see a lower SWOLF for their easier swimming and a higher SWOLF for their faster swimming, and should strive to find a more sustainable faster speed…and be happy with a higher SWOLF. (but to discover what it is, or more specifically what their SPL & Pace targets are for various training distances and /or race settings
C) suggests very low stroke rate with lots of glide…little energy being put in compared for forward movement. Physiologically speaking a very efficient stroke (SWOLF may be the same is in scenario B). Scenario C swimmers should strive to increase their SWOLF, more specifically by increasing their tempo as they already have a very efficient stroke.
D) The ability to swim quickly and hold a low SPL requires high power, high strength swimming, and can be seen in Jai’s 2nd video here: SWOLF will be low but true efficiency is low. However if this is a race, fastest time, not highest efficiency wins. Scenario D swimmers are very skilled, fast powerful swimmers, and can pick and choose the stroke suited for their task.
In that video Jai swims two lengths. Both have the same SPL, but in the 2nd length he adds effort and speed to reduce his time. He is working much harder to get from one end to the other. He gets faster while still keeping the same number of strokes. But don’t take my word for it, go ahead and count them when you watch.
Here are the numbers:
Length 1: 16 strokes 31 seconds SWOLF 47
Length 2: 16 strokes 18 seconds SWOLF 34
The slower length is actually the more efficient stroke considering the amount of effort compared to the forward movement. it takes Jai more energy to swim the faster length. Even without having the external measuring tools to determine true efficiency, it should not be difficult to believe that Jai could sustain the first length’s effort for quite a long time…the second length for possibly 100m or less.
A graph would be interesting here… plotting combinations of Speed vs. SWOLF at different SPLS/rates and seeing if there actually is a relationship we can glean that would be useful as a self-coaching tool. My guess is that there is not…we still need to know each metric…at least two out of the three (SPL, Time or Speed) in order to analyze data and know how use it to improve our swimming practices.
I find SWOLF most as a quick measure of consistency, rather than a measure of efficiency. When i look at my athletes watch data, the SWOLF graph can reveal if they are swimming with too much rest or too easily. Or conversely if they are improving their ability to be consistent with a given set (eg. 10 x 100 as an example). Pace alone doesn’t tell us, SPL alone doesn’t tell us, but SWOLF alone does not tell us either.
e.g. if I see a set of 10 x 100 with a SWOLF that does into change AND an SPL that does not change, they are swimming consistently which is good. I still need either pace or SPL along with SWOLF to learn anything about their swimming, it doesn’t stand alone. If I want them to swim faster and get fitter as a triathlete (my main market). SO I can reduce the rest, increase the repeat distance, increase the pace (which is possibly going to change the SWOLF ).
Hopefully that gives you more insight as to what some of the metrics mean and what you can do with the information.
I still find that practicing SPL ranges at will, finding your SPL, changing your SPL and holding your chosen SPL, layered with the use of the tempo trainer (steady, ascending, descending, etc) gives the coach and athlete much more control and direction than SWOLF had the possibility to do.
IN a follow up article I will use some specific watch data graphs to help walk through an analysis of a swim set’s execution and plan further practice sets for improved skill.
Please let me know in the comments section what your thoughts are and how you use the watch data you collect.
you wrote : “The slower length is actually the more efficient stroke considering the amount of effort compared to the forward movement.”
What I understand is : You seem to define efficiency by dividing the effort (energy spent) by the distance covered. Of course he could sustain this pace for a long time, it’s slow.
I think it should be efficiency = effort / time for a specified distance
and we should have different target SWOLF for each race distance. for example (from the video) : 200 m race (swolf 34), 20 km race (swolf 47)
What if you combine heart rate data from a swim HRM with the SPL and Time?
Do you mean combine it as in add it in? At least one other coach has written about al “alternative swim golf” adding in HR. I don’t think it’s as useful as SPL & time because there’s little reason to think that a heart beat and a stroke are equivalent or temporally related as a stroke and a second are much more tightly correlated. However, being observant of your HR at various speeds and efforts is a good metric to track over time. Swimming the same speed at a lower HR indicates improved efficiency, and can be done within a single session by searcing for ways to swim easier, adjusting technique or focus.
we add in # of breathes taken as well, not HR. allows for some tracking of effort higher efforts = more breathes reduced (SWgolf) score working in all 3 (time+strokes+breathes) helps look at swim efficency at different efforts
I agree with you Dimitri. We can go back and discuss what we understand by “efficiency” in swimming. The way I see it a very efficient swimmer will swim a given distance with the lowest SPL in the shortest time possible.
Efficiency has a definition in exercise physiology defined as the ratio of work generated to the
total metabolic energy cost. Work is defined as force that creates displacement, or travel. In the case of swimming that displacement needs to be in the direction we want to travel. Lowest SPL and shortest time both increase the workload which can actually reduce the efficiency, even if it results in a faster speed.
Good job, you are understanding just the point that SWOLF threatens to obscure. And if a swimmer is going to use SWOLF, they should be aware that there will be different combinations that allow them to swim different distances at their own ability & fitness limits.
Efficiency has a scientific definition however, I’m not making it up, and it is the ratio of work done (forward movement) to the energy used.
So intuitively both lengths in the video cover the same distance, yet the faster one uses more energy, it is less efficient. Yet it also has a lower SWOLF score.
For those not understanding what SWOLF is and isn’t measuring, this could be very misleading.
As you suggest, a lower SWOLF is not necessarily better if your target distance is a 20k race any more than if you are training for a sprint. It’s incomplete information.
Thanks for the comment and for prompting me to clarify.
Hi Coach Suzanne,
Thank you for covering this and for the great explanation….I only have 16 months of self-taught TI under my belt and got a 910XT for my recent birthday and the SWOLF was driving me nuts because it was getting higher even though I was feeling more efficient in the water…the stroke counter may not be perfect either as I am currently testing it’s accuracy.
I agree a lot with the points made here and totally agreeing with Dimitri. I would like to add though that:
1. The definition of efficiency you are talking about is not the correct one I think. It is true that scientifically we also can say that for example an engine is more efficient when it uses a single liter on 100km as opposed to 2.0 liters on 100km. We would say it’s twice as efficient. But under the covers something must have changed.
Over time people will also gain a better physical condition. All of a sudden the same 225 kcal that you had to spend 5 months ago for a single length all of a sudden is giving you 1.5 lengths. Same energy but both better time and spl. It is your body that has changed to improve on the energy consumption.
2. SWOLF is EVER ONLY a PERSONAL number and to NEVER COMPARE other than to yourself under the same circumstances!
A. It cannot be compared to other swimmers (which you seem to be doing)
B. It cannot be compared to other stroke types (and distances)
C. It cannot be compared to different size pools and especially open water.
One person is never B and C at the same time. A person’s SWOLF on 50m front crawl will be different in a 25m and 50m pool. Probably not by much…. but it is not the same.
I think still every individual should strive to reach ‘D’.
If you are a ‘B’ swimmer you should work on maintaining your time but improve your number of strokes. Whatever you need to change to improve the quality.
If you are a ‘C’ swimmer you should work on your on adding more power to the stroke but maintain the stroke quality.
2. I agree with your table a bit but there is a ‘hidden’ relationship in the formula.
Higher stroke power implies lesser stroke count and frankly with a little bit of nicer stroke you spare energy!
The movie clip of Jay is a nice visual however I would like to add though that if he would even add a little bit more power you cannot even make stroke 16 anymore. Putting this extra power (not necessarily effort, as muscle power grows when we train) into the stroke he would actually also lower the stroke count. The little bit of extra power then is reflected in both numbers. Even though this is a these are figurative numbers:
220 kcal => 16 strokes, 17.80 => 33.8
225 kcal => 15 strokes, 16.70 => 31.7
This brings us to the point where we could say (and agree): if we have 900 kcal to spend on a race it is important what race that is. Is that freestyle 400m in a 25 meter pool or is that 50m in a 50m pool. Without a doubt the SWOLF values for both these races will and should never be the same.
To achieve improvement though you want to look at yourself and say:
1. I am on 1.04.53 right now
2. Set a target: by the end of the season I want to be on 1.00.00
3. That is 15s/length (25 meter pool)
4. Determine your current SWOLF
5. Determine which component of it is easier to change at the moment (lets say 1st from 22 to 21 strokes)
6. Train and measure
7. repeat 5 and six. Anytime a different minor improvement
Thank you for your interesting article.
I was wondering if adding (a part of) heartrate to the swolf wouldn’t be a better indicator for the efficiency. Heartrate is in my perspective a good indicator for the energy output.
One could look at the evolution of the SWOLF at a given heartrate.
Can you comment on that ?
yes, HR can be a good indicator of energy spent. In the big picture speed vs. HR would be the most helpful tool. But improving economy as measured by Same effort or speed with a lower heart rate can be a nice thing to add. The Finis AquaPulse has been used by several coaches to see if they can maintain tempo or SPL while lowering the HR by focusing on various skills during the swim, eliminating the need to stop and check HR manually (during which time HR drops and focus also wanders)
Well I guess my point is that swolf is not really a measure of efficiency. Certainly adding HR or perceived effort is a good way to calibrate your efforts to make sure you are actually saving energy. I don’t think a direct comparision of swolf to HR is as helpful as simply comparing your pace or speed to HR as a measure of your energy use.
Hi, have you made a mistake in your Scenario C when you say “Scenario C swimmers should strive to increase their SWOLF, more specifically by increasing their tempo as they already have a very efficient stroke.” ?
Surely if a swimmer increases their tempo they will reduce their SWOLF, as shown in your video of Jai where he increases his tempo in length two and reduces his SWOLF from 47 to 34.
My Garmin Forerunner 735 watch calculates SWOLF. The watch definites ONE stroke as the right arm pull AND the left arm pull. To me that is TWO strokes. As it is in your video. I wonder what the standard definition of a stroke is?
Hi Bill, The majority of professional coaches (and athletes) count the way I describe in my articles. You can decide what you want to do with the data and how to use it, and make up your mind about the best way for you to count.