Is SWOLF (or "Swim Golf") Really A True Measure Of Efficiency?
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If you own a piece of wearable swimming technology like a swim watch, or have attended a master's or triathlon squad technique session, chances are you'll have come across the term SWOLF. You might have even wondered: What is this strange score that I get after each swim? How is it helping me become a better swimmer?
Your SWOLF score is simply your swim time in seconds per length added to the number of strokes you took to complete that length. For example, if you swim a 25m length in 25 seconds and take 25 strokes, you would have a SWOLF score of 50.
Someone else might cover that same distance in 22 seconds and take 28 strokes. Both swimmers would thus receive a score of 50 (equal "efficiency") but is the first swimmer really as efficient as the second if they take 12 seconds longer to complete each 100m interval? Is SWOLF really the best measure of efficiency for you to be tracking?
Given its prevalence as a metric across a range of products, programs and swimming literature, and knowing our own penchant for stroke analysis, you might have also wondered why Swim Smooth never refer to SWOLF. It's certainly one of the most requested topics for future blogs that we receive from our loyal followers around the world.
Today we'll help to definitively answer that question:
The idea seemed sound enough - cover a greater distance per stroke (DPS) and you were purportedly using less effort. Swimming is a cyclical sport like cycling and running and yet you'd never suggest that pushing a bigger gear on your bike or extending your run stride as far as you possibly can would make you more efficient. Yet this was the common belief in swimming at the time (and something that some still cling on to in swimming today).
So prevalent was this belief that even today, the latest technology still utilises minimum strokes as one of the two key components to ascertain a "score" for efficiency. Should we then just take it as read that this is what we should be monitoring above all else and even using it to compare elite athletes?
We are sure that every coach out there is motivated by one thing and one thing only - to help others improve. It's certainly the reason why we - as Swim Smooth coaches - got into coaching and are still as passionate about it today as we were 13 years ago.
Irrespective of whichever coach or program you follow, as different and conflicting as they might appear, they will have this basic desire to help others improve at the heart and soul of what they do. It's the driver behind what we all do as coaches and as anyone interested in the sport. However, it's also the reason that we don't hesitate to challenge the status quo if all the logic dots don't quite line up properly, especially if it means you fast-track your own education about what will likely work best for you.
Call to action: if you do know someone who still believes swimmers should take as few strokes as possible, or even coaches this way, kindly point them towards this article. Chances are they just haven't ever questioned what was told to them by their own coach.
From the video:
A classic example of how the measure of strokes per length is still utilised in swimming circles as the go to measure of efficiency and as such you'd be forgiven for thinking that it is still the holy grail. As we are about to find out though, that's not entirely true, and in many cases, simply wrong and very misleading, especially if you aren't blessed with the physique of a swimming legend like Michael Phelps.
Ironically enough, even those with god-like physiques will benefit well from this discussion too - doing so is what is allowing the likes of Katie Ledecky (multiple Olympic Champion and World Record holder), Gregorio Paltrinieri (current Olympic and World Champion) and Adam Peaty (Olympic and World Champion and World Record holder) set new benchmarks at the very highest level.
We believe it will help you too - let's get started:
For this very reason, coaches around the world used to (and in some cases still do) get their swimmers to count how many strokes they have taken, often rewarding and praising those with the lowest counts as the most efficient, despite the range of heights, builds and wingspans typically present in a squad session. How could it ever have been seen to be a logical consideration when such anthropometric variation exists naturally in society?
Take this photo of our two fastest squad swimmers in Perth:
Both Brad and Byron are two of Australia's top aspiring marathon swimmers. Brad, 27, holds the world record for the 25km Port-to-Pub swim in a time of 5h34m (or 1:20/100m average pace), which for a non-drafting solo effort is pretty remarkable - most people wouldn't be able to stay with Brad for the first 100m of his continuous 250 x 100m race! Even Australian Olympic representative, and famed Rio 2016 10km open water breakaway Jarrod Poort failed to beat Brad's time this year.
Byron, at the tender age of 15, is exactly half the weight of Brad and a full foot (27cm) shorter than him, and yet is the fastest distance swimmer we've ever had in the program. With a CSS of 1:06/100, this pocket rocket finished 5th at the national 5km open water swimming championships here in Australia, and has a hugely bright future ahead of him. During a 5500m training session, Byron is between 600 and 800m ahead of our next best swimmers in the fast lane!
Both Brad and Byron swim in our infamous Wednesday morning Red Mist Endurance session. When you watch Byron and Brad swimming side by side the obvious difference is their stroke rate (cadence) with Brad sitting around 59 SPM and Bryon revving at 90 SPM. Exactly as you'd expect given the difference in their height and builds.
Here at Swim Smooth we love our raw, unfiltered data and are massive fans of the Tritonwear Team and the brilliant data they make available for anyone interested in how the world's very best (and most efficient) swimmers swim.
Our favourite page for all the juicy data is here: www.tritonwear.com/en/race-analysis/
From there, let's examine some data from three of the world's best swimming prodigies to challenge the notion that SWOLF is a beneficial measure of efficiency. All taken from the 2016 Rio Olympic Games we have:
Ladies first:
Katie Ledecky has the highest SWOLF score (i.e. least "efficient") of the top-3 podium finishers by a count of 5, only the 2017 200m freestyle champion Federica Pelligrini has anywhere near this level of "inefficiency" within the women's field.
The phenomenon that is Adam Peaty, purportedly so much less efficient than everyone he's dominating (if we are to believe the SWOLF metric) - this race was voted by FINA as the best swim of the entire 2016 Olympic Games.
Mock him though they might, Gregorio Paltrinieri's "inelegant stroke" has now won him the two highest accolades in the sport in less than 12 months. Good job his coach, Stefano Morini, looks well beyond the aesthetics to find out what is truly efficient for him.
The Tritonwear Team offer some useful takeaways under each set which are worth investigating further:
These points are all very valid simply because the data, and the ultimate result for each swimmer, shows us that they are factual. What is interesting is how they are all in opposition to the view that a low SWOLF score gives the most efficient stroke. Of course people will argue and claim that having a more efficient stroke does not mean one swimmer will be faster than another, just that they will input less energy for a similar output. However, at the very highest level of the sport, all that matters is who crosses the line first.
Forgive us for cherry-picking the data from the Tritonwear Team's data set to demonstrate and support the findings above. Do our suggestions actually suggest an inverse relationship between a low SWOLF score and performance? Possibly. However, looking across the whole range of swims in Rio, if full statistics were run on every event we believe that this measure of so-called “efficiency” would prove to be simply “non-significant” in either direction.
That makes sense when you think about it - there are "horses for courses" and "more than one way to skin the efficiency cat" as even at the very pointy end of athletic performance there is extreme variability in body morphology and physiology allowing for such a range in data.
Acknowledgement of this and embracing people's individuality is at the heart of what our own Swim Types system is all about - be the most efficient you can be given your height, build, gender, ability level and discipline.
[Talking of horses-for-courses, the world view on stride length in horse racing has recently been turned on its head with the rise of the phenomenal Winx. More here: ab.co/2vwiqRP]
Way back in 1968 Doc Counsilman (the godfather of swimming biomechanics) discussed the dangers of adding in too much glide to lower stroke count and SWOLF score for fear of reducing efficiency:
In 1999 a detailed biomechanical study by the Australian Institute of Sport of the Pan Pacific swimming championships concluded that the perception of stroke length as being a significant and key determinant to success is incorrect:
In 2010, a study in Texas by McLean et al [1] on oxygen uptake in response to stroke rate manipulation in freestyle swimming showed that heart rate and oxygen consumption increased as stroke rate was reduced and stroke length increased to maintain a given speed.
Thus, economy was reduced significantly despite SWOLF scores being lower. Why so? All swimmers increased kicking rate to account for the pause and glide at the front of the stroke, the exact opposite of what both Katie Ledecky and Gregorio Paltrinieri do to conserve energy (as highlighted by the Tritonwear Team):
At a constant speed, if stroke rate is reduced and stroke length accordingly increases (lowering the swimmer's SWOLF score), economy reduces due to the significant increase in heart rate and oxygen consumption. All related to a swimmer being forced into kicking harder to maintain speed and compensate for the overly long stroke:
In other words, you either:
- Ignore SWOLF, do what the world's best male (Paltrinieri) and female (Ledecky) distance swimmers do which is trade-off some stroke length for a quicker turnover. This maintains rhythm and momentum, and so reduces energy expenditure from a strong kick until much later in the event.
Or:
- You seek out the lowest possible SWOLF score and come second, third or last.
And that, faithful reader, is why we never use SWOLF as a valid and reliable discussion point for efficiency.
In fact you can easily go down a cul-de-sac with your stroke and become less efficient by chasing a lower SWOLF score. Like Mark Foster says in the video above, there are many factors at play here which need to be considered, many of which are not easily measured.
So the next time your well meaning coach asks you to reduce your stroke count to match Jim who's six inches taller than you, please be wary and kindly point them to this article.
To that end we recommend performing the Swim Smooth Ramp Test as outlined here:
This has you swimming with a Tempo Trainer Pro to control your stroke rate, covering a range of cadences from slow to fast. At each we assess your speed and perceived effort to get a sense of your efficiency through the water. You will find that you have "sweet spots" in your stroke where everything clicks and you suddenly pick up speed for little or no increase in effort. Normally these sweet spots are in the middle of your cadence range, not when you are using an especially fast or slow stroke rate.
A great example of this is our development of Harold's swimming where we improved his (already very fast) speed by 12 seconds per 100m by optimising his stroke rate: www.feelforthewater.com/2017/02/when-taking-fewer-strokes-makes-you.html
For your own swimming download the test-sheet from here:
 |
| How do you think the SWOLF of these two swimmers compares? |
What is SWOLF and what does it mean for me?
Many swim watches and meters utilise this metric in their reporting. For example, Garmin state on their website:
SWOLF is a portmanteau, or blending of the terms Swimming and Golf. The SWOLF score is a measure of your swimming efficiency, and just as in golf, a lower score is better.
Your SWOLF score is simply your swim time in seconds per length added to the number of strokes you took to complete that length. For example, if you swim a 25m length in 25 seconds and take 25 strokes, you would have a SWOLF score of 50.
Someone else might cover that same distance in 22 seconds and take 28 strokes. Both swimmers would thus receive a score of 50 (equal "efficiency") but is the first swimmer really as efficient as the second if they take 12 seconds longer to complete each 100m interval? Is SWOLF really the best measure of efficiency for you to be tracking?
Given its prevalence as a metric across a range of products, programs and swimming literature, and knowing our own penchant for stroke analysis, you might have also wondered why Swim Smooth never refer to SWOLF. It's certainly one of the most requested topics for future blogs that we receive from our loyal followers around the world.
Today we'll help to definitively answer that question:
Stroke Counting: Back To The Dark Ages
Let's first go back in time. Way back. Coaches used to state that to be as efficient as possible, you had to take as few strokes as possible to complete each length. Covering a certain distance in fewer strokes was purportedly a sign of enhanced efficiency.The idea seemed sound enough - cover a greater distance per stroke (DPS) and you were purportedly using less effort. Swimming is a cyclical sport like cycling and running and yet you'd never suggest that pushing a bigger gear on your bike or extending your run stride as far as you possibly can would make you more efficient. Yet this was the common belief in swimming at the time (and something that some still cling on to in swimming today).
So prevalent was this belief that even today, the latest technology still utilises minimum strokes as one of the two key components to ascertain a "score" for efficiency. Should we then just take it as read that this is what we should be monitoring above all else and even using it to compare elite athletes?
Well Meaning Coaches
Yesterday we received this email from someone seeking to become a Swim Smooth Coach here in Australia:
"I am interested in a career change back to one of my passions - helping people.”
We are sure that every coach out there is motivated by one thing and one thing only - to help others improve. It's certainly the reason why we - as Swim Smooth coaches - got into coaching and are still as passionate about it today as we were 13 years ago.
Irrespective of whichever coach or program you follow, as different and conflicting as they might appear, they will have this basic desire to help others improve at the heart and soul of what they do. It's the driver behind what we all do as coaches and as anyone interested in the sport. However, it's also the reason that we don't hesitate to challenge the status quo if all the logic dots don't quite line up properly, especially if it means you fast-track your own education about what will likely work best for you.
Call to action: if you do know someone who still believes swimmers should take as few strokes as possible, or even coaches this way, kindly point them towards this article. Chances are they just haven't ever questioned what was told to them by their own coach.
Why it's hard to breakaway...
Here's some of that same well meaning advice from the BBC Commentary team of the men's 1500m freestyle final between Paltrinieri of Italy and Romanchuk of the Ukraine at the recent swimming World Championships in Budapest:From the video:
Helen Skelton: There's a huge difference in technique though isn't there?
Mark Foster: Yeah, it's one of those things when broken down per length, Romanchuk was taking 13 strokes less than Paltrinieri, which over 1500m is 390 strokes…
Rebecca Adlington: Good maths!
Mark Foster: Well, I'm good at maths, and I have a lot to think about in fifteen minutes, but I was observing the difference in techniques and of course Romanchuk is more efficient, but then it takes more energy to be that more efficient…Paltrinieri has taken 3 strokes each length before Romanchuk even surfaces from his streamline, but then again it takes more energy to hold your breath…so there's a lot of different things to look at that counteract one another...
Rebecca Adlington: Paltrinieri probably realises I'm never going to be good at underwater, I'm never going to be good at streamlining so he's trying to use other things to his advantage.
Mark Foster: Yeah, it's one of those things when broken down per length, Romanchuk was taking 13 strokes less than Paltrinieri, which over 1500m is 390 strokes…
Rebecca Adlington: Good maths!
Mark Foster: Well, I'm good at maths, and I have a lot to think about in fifteen minutes, but I was observing the difference in techniques and of course Romanchuk is more efficient, but then it takes more energy to be that more efficient…Paltrinieri has taken 3 strokes each length before Romanchuk even surfaces from his streamline, but then again it takes more energy to hold your breath…so there's a lot of different things to look at that counteract one another...
Rebecca Adlington: Paltrinieri probably realises I'm never going to be good at underwater, I'm never going to be good at streamlining so he's trying to use other things to his advantage.
A classic example of how the measure of strokes per length is still utilised in swimming circles as the go to measure of efficiency and as such you'd be forgiven for thinking that it is still the holy grail. As we are about to find out though, that's not entirely true, and in many cases, simply wrong and very misleading, especially if you aren't blessed with the physique of a swimming legend like Michael Phelps.
Ironically enough, even those with god-like physiques will benefit well from this discussion too - doing so is what is allowing the likes of Katie Ledecky (multiple Olympic Champion and World Record holder), Gregorio Paltrinieri (current Olympic and World Champion) and Adam Peaty (Olympic and World Champion and World Record holder) set new benchmarks at the very highest level.
We believe it will help you too - let's get started:
Too Easy Mate...
You can begin to understand where this well meaning advice comes from when you consider that counting your strokes per length is an easy metric to measure - you don't need a stopwatch, or a coach, you just need to count every right / left hand entry into the water. Simple.For this very reason, coaches around the world used to (and in some cases still do) get their swimmers to count how many strokes they have taken, often rewarding and praising those with the lowest counts as the most efficient, despite the range of heights, builds and wingspans typically present in a squad session. How could it ever have been seen to be a logical consideration when such anthropometric variation exists naturally in society?
Take this photo of our two fastest squad swimmers in Perth:
 |
| Brad (third from left) is aged 27 and 183cm / 88kg (6"0' / 194lbs) Byron (holding the series winner's trophy) is aged 15 and 156cm / 44kg (5"1' / 97lbs) |
Both Brad and Byron are two of Australia's top aspiring marathon swimmers. Brad, 27, holds the world record for the 25km Port-to-Pub swim in a time of 5h34m (or 1:20/100m average pace), which for a non-drafting solo effort is pretty remarkable - most people wouldn't be able to stay with Brad for the first 100m of his continuous 250 x 100m race! Even Australian Olympic representative, and famed Rio 2016 10km open water breakaway Jarrod Poort failed to beat Brad's time this year.
Byron, at the tender age of 15, is exactly half the weight of Brad and a full foot (27cm) shorter than him, and yet is the fastest distance swimmer we've ever had in the program. With a CSS of 1:06/100, this pocket rocket finished 5th at the national 5km open water swimming championships here in Australia, and has a hugely bright future ahead of him. During a 5500m training session, Byron is between 600 and 800m ahead of our next best swimmers in the fast lane!
Both Brad and Byron swim in our infamous Wednesday morning Red Mist Endurance session. When you watch Byron and Brad swimming side by side the obvious difference is their stroke rate (cadence) with Brad sitting around 59 SPM and Bryon revving at 90 SPM. Exactly as you'd expect given the difference in their height and builds.
At their respective CSS paces (very similar) Brad typically takes 32 to 33 strokes per 50m length and Byron 49 to 51 strokes. If you work out the SWOLF score for each, Brad is 66 to 67 and Byron 83 to 85 - does this really imply that Brad is over 20% more efficient than Byron? Of course not.
The key point here is that there's more than one way to swim efficiently and one has a higher SWOLF score than the other. Brad shouldn't swim like Byron and Byron shouldn't swim like Brad and at Swim Smooth we'd never suggest that they do.
The key point here is that there's more than one way to swim efficiently and one has a higher SWOLF score than the other. Brad shouldn't swim like Byron and Byron shouldn't swim like Brad and at Swim Smooth we'd never suggest that they do.
Separating The Wheat From The Chaff
Once upon a time it was even said that you were not at all efficient if you couldn't swim a 25m length in less than 20 strokes. Supposedly 20 strokes per length was where "the wheat and the chaff were separated". However these days some of the world's best swimmers are demonstrating strokes well in excess of this stroke count. They often take significantly more strokes per length than their rivals and are still beating them in the process. Or put another way, they are reporting SWOLF scores much higher than those they are racing closely against...Getting Into The Finer Detail
If you've been following Swim Smooth for a while, much of the above will come as no surprise to you. We've spent the last 13 years warning of the dangers of overly lengthening your stroke by adding a pause and glide to artificially lower your stroke count. We refer to this simply as "Overgliding" and at one point in the 1990s this style of swimming was at almost epidemic proportions. At least SWOLF takes into account time per length as well, but as we've seen, even that throws up spurious results too.Here at Swim Smooth we love our raw, unfiltered data and are massive fans of the Tritonwear Team and the brilliant data they make available for anyone interested in how the world's very best (and most efficient) swimmers swim.
Our favourite page for all the juicy data is here: www.tritonwear.com/en/race-analysis/
From there, let's examine some data from three of the world's best swimming prodigies to challenge the notion that SWOLF is a beneficial measure of efficiency. All taken from the 2016 Rio Olympic Games we have:
- 200m freestyle for women - featuring Katie Ledecky (widely regarded as the world's best swimmer in the post-Phelps era)
- 1500m freestyle for men - featuring Gregorio Paltrinieri (1500m freestyle Olympic & World Champion)
- 100m breaststroke for men - featuring Adam Peaty (50m breaststroke Olympic Champion and 50m / 100m World Champion and record holder)
Ladies first:
 |
| (click to expand) |
Katie Ledecky has the highest SWOLF score (i.e. least "efficient") of the top-3 podium finishers by a count of 5, only the 2017 200m freestyle champion Federica Pelligrini has anywhere near this level of "inefficiency" within the women's field.
 |
| (click to expand) |
The phenomenon that is Adam Peaty, purportedly so much less efficient than everyone he's dominating (if we are to believe the SWOLF metric) - this race was voted by FINA as the best swim of the entire 2016 Olympic Games.
 |
| (click to expand) |
Mock him though they might, Gregorio Paltrinieri's "inelegant stroke" has now won him the two highest accolades in the sport in less than 12 months. Good job his coach, Stefano Morini, looks well beyond the aesthetics to find out what is truly efficient for him.
The Tritonwear Team offer some useful takeaways under each set which are worth investigating further:
Ledecky: "is versatile across all freestyle events"
Paltrinieri: "hardly kicks to conserve energy"
Peaty: "proves to the world it's possible to maintain efficiency with a quick rate"
Paltrinieri: "hardly kicks to conserve energy"
Peaty: "proves to the world it's possible to maintain efficiency with a quick rate"
These points are all very valid simply because the data, and the ultimate result for each swimmer, shows us that they are factual. What is interesting is how they are all in opposition to the view that a low SWOLF score gives the most efficient stroke. Of course people will argue and claim that having a more efficient stroke does not mean one swimmer will be faster than another, just that they will input less energy for a similar output. However, at the very highest level of the sport, all that matters is who crosses the line first.
Forgive us for cherry-picking the data from the Tritonwear Team's data set to demonstrate and support the findings above. Do our suggestions actually suggest an inverse relationship between a low SWOLF score and performance? Possibly. However, looking across the whole range of swims in Rio, if full statistics were run on every event we believe that this measure of so-called “efficiency” would prove to be simply “non-significant” in either direction.
That makes sense when you think about it - there are "horses for courses" and "more than one way to skin the efficiency cat" as even at the very pointy end of athletic performance there is extreme variability in body morphology and physiology allowing for such a range in data.
Acknowledgement of this and embracing people's individuality is at the heart of what our own Swim Types system is all about - be the most efficient you can be given your height, build, gender, ability level and discipline.
[Talking of horses-for-courses, the world view on stride length in horse racing has recently been turned on its head with the rise of the phenomenal Winx. More here: ab.co/2vwiqRP]
The True Indicators And Proponents For Efficiency Have Always Been There
But really this shouldn't be news at all because sports scientists have been warning us of the dangers of overly lengthening the stroke length for a long time:Way back in 1968 Doc Counsilman (the godfather of swimming biomechanics) discussed the dangers of adding in too much glide to lower stroke count and SWOLF score for fear of reducing efficiency:
 |
| Extract from the Science of Swimming (1968) by Doc Counsilman |
In 1999 a detailed biomechanical study by the Australian Institute of Sport of the Pan Pacific swimming championships concluded that the perception of stroke length as being a significant and key determinant to success is incorrect:
 |
| Mason and Cossor challenge commonly held beliefs and perceptions |
In 2010, a study in Texas by McLean et al [1] on oxygen uptake in response to stroke rate manipulation in freestyle swimming showed that heart rate and oxygen consumption increased as stroke rate was reduced and stroke length increased to maintain a given speed.
Thus, economy was reduced significantly despite SWOLF scores being lower. Why so? All swimmers increased kicking rate to account for the pause and glide at the front of the stroke, the exact opposite of what both Katie Ledecky and Gregorio Paltrinieri do to conserve energy (as highlighted by the Tritonwear Team):
At a constant speed, if stroke rate is reduced and stroke length accordingly increases (lowering the swimmer's SWOLF score), economy reduces due to the significant increase in heart rate and oxygen consumption. All related to a swimmer being forced into kicking harder to maintain speed and compensate for the overly long stroke:
In other words, you either:
- Ignore SWOLF, do what the world's best male (Paltrinieri) and female (Ledecky) distance swimmers do which is trade-off some stroke length for a quicker turnover. This maintains rhythm and momentum, and so reduces energy expenditure from a strong kick until much later in the event.
Or:
- You seek out the lowest possible SWOLF score and come second, third or last.
And that, faithful reader, is why we never use SWOLF as a valid and reliable discussion point for efficiency.
So Bin SWOLF Completely?
The conclusions here are clear. SWOLF is an extremely poor way to compare one swimmer's efficiency to another - either at the elite or age-group level. You might choose to use SWOLF as a way of tracking your stroke development over time but be very wary that a lower SWOLF score doesn't necessarily mean better swimming.In fact you can easily go down a cul-de-sac with your stroke and become less efficient by chasing a lower SWOLF score. Like Mark Foster says in the video above, there are many factors at play here which need to be considered, many of which are not easily measured.
So the next time your well meaning coach asks you to reduce your stroke count to match Jim who's six inches taller than you, please be wary and kindly point them to this article.
If Not SWOLF The How Should I Monitor My Swimming Efficiency?
What you are really looking for as you develop your swimming is the best way for you to swim as an individual.To that end we recommend performing the Swim Smooth Ramp Test as outlined here:
This has you swimming with a Tempo Trainer Pro to control your stroke rate, covering a range of cadences from slow to fast. At each we assess your speed and perceived effort to get a sense of your efficiency through the water. You will find that you have "sweet spots" in your stroke where everything clicks and you suddenly pick up speed for little or no increase in effort. Normally these sweet spots are in the middle of your cadence range, not when you are using an especially fast or slow stroke rate.
A great example of this is our development of Harold's swimming where we improved his (already very fast) speed by 12 seconds per 100m by optimising his stroke rate: www.feelforthewater.com/2017/02/when-taking-fewer-strokes-makes-you.html
For your own swimming download the test-sheet from here:
Swim Smooth!
[1] McLean SP, Palmer D, Ice G, Truijens M, Smith JC. (2010). Oxygen uptake response to stroke rate manipulation in freestyle swimming. Med Sci Sports Exerc., 42(10):1909-13.
[1] McLean SP, Palmer D, Ice G, Truijens M, Smith JC. (2010). Oxygen uptake response to stroke rate manipulation in freestyle swimming. Med Sci Sports Exerc., 42(10):1909-13.