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In response to the recent essay Stroke Length Loyalty (and the subsequent essay Intro to Pace Combinations) I’ve entered into an enjoyable email discussion with a retired engineer about judging efficiency of the stroke. He has been asking how we know when a change in pace combination (SPL x Tempo) is more efficient or not for a particular swimmer.

That is the golden question!

But, admittedly, judging efficiency is a tricky business in swimming.

I want to summarize some of my thoughts on this by making a proposal for how to judge an efficient stroke in swimming in a way that takes into account the multiple dimensions that affect it. And I will explain why each alone cannot reliably prove efficiency, and thus need to be used together to build the case.

First, I want to (again) carefully define what we mean by ‘efficiency’ which I think you know already, yet which I take pains to repeatedly and clearly define in my blog essays. The word is thrown around a bit too casually.

Efficiency = more work accomplished for less energy expense (for a particular swimming achievement goal).

Easily to define with words, but hard to measure in a debate-ending way by any authority or anecdote. I will discuss why below.

For land-based sports we have a lot of technological advantages for measuring input/output of performance. We can measure efficiency for runners and cyclists relatively easy (I had a little of this scientific torture done to me in a modest endurance research lab 20 years ago). Gravity is a consistent opponent which is easy for our equations and modern instruments to handle. As I describe it: Gravity Grabs Mass, while Water Grabs Shape. This is an essential difference in the swimming problem versus the running or cycling problem. Put an athlete in water and it becomes hard to measure him without restricting his natural movement patterns and without taking him out of his truly natural swimming conditions. Taking the measurements alters the subject and his performance thus puts the results into question. Furthermore, water changes its resistance as the swimmer changes his shape and velocity and this creates a very, very tricky situation for measuring swimming efficiency directly.

So, I propose that we may use a variety of indirect indicators of efficiency that take into account as many of the variables as possible involved in swimming.

#1 – Statistical Estimate

This is an external, objective measurement.

In TI we use the Height/SPL Index (SPL = Strokes Per Length of your pool) which has been developed on a great deal of observation and statistical analysis of how great human swimmers of our time use stroke length.

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This index shows us where to find a stroke length that is between 55% and 70% of a swimmer’s height (or better, wingspan). In TI we call this the SPL Green Zone (after the often green-colored efficiency zone that is positioned on some vehicle control panels showing where the best speed/fuel consumption/distance relationship is found for that vehicle). [You can read more on how to use this index and how it as constructed on my Resource page.]

Limitations: it is just an estimate based on statistics. Statistics describe what has been done – not whether it should be done. So it is not a law that the swimmer will find his efficient SPL for an event only within this Green Zone. But we have a great deal of confidence that, by far, most swimmers will find a better SPL within this zone that outside of it.

But there are exceptions we cannot ignore which urge us to keep an open mind. For example, Sun Yang, for the first 1400 of his 1500 world record swim, used a stroke length that was about 76% of his wingspan. Then shifted to a stroke length that was about 64% of his wingspan for the last 50 meters. It would be hard to argue that he wasn’t tapping into some particular efficiency at that stroke length to allow him to have so much energy to speed up like he did at the end.

Also, our statistical understanding is based on how swimmers are swimming now in these modern times. If we were to make a chart based on the common competitive swimming style of 100 years ago, we would have a different index. In 100 years from now, there may be some new breakthrough in how to compose the freestyle stroke and this chart may look different then. Though, the long-term trend seems to be going toward longer strokes, not shorter ones.

#2 – Speed

This is an external, objective measurement.

We would naturally look at how much faster the swimmer is able to go based on a change in stroke length or change in tempo.

Faster is better, right? One might quickly assume that if a swimmer can go faster with a certain stroke arrangement that must be more efficient, yes?

No. We definitely cannot make that assumption on speed result alone.

Limitations: a swimmer can produce more speed but how and at what energy cost? A swimmer can go faster by energy-expensive means or energy-efficient means. Line up two swimmers with two different stroke styles or two different SPL x Tempo arrangements and the one who goes faster is not necessarily the more efficient swimmer. We cannot see the energy cost to each swimmer because those are internal features.

There are two ways to increase speed:

  1. increase power
  2. decrease drag (water resistance)

#1 costs energy. #2 cost little or no energy (once the neuro-muscular skill for it is mastered).

If a swimmer goes faster, we cannot see by which means above he did so. It could be one, or the other, or a mix of both. Speed is measuring only time and distance, not energy consumption. Energy consumption is the central focus of efficiency and it cannot be measured from the outside.

The genuinely most-efficient stroke will be making the perfect balance between minimizing drag and adding just enough power to get the job done. To get more leverage for power a swimmer may alter body shape to suit human mechanics which increases drag because human mechanics are not suited to moving through water. (Humans are designed for working on land, against gravity). So this is the ultimate trick in swimming – to increase leverage (to increase power) but to do so in a way that keeps drag to an absolute minimum. This is not a natural exercise for humans in water.

So, the efficiency claims of a faster swimmers are always suspect until we have some way to examine the energy/power situation inside the body.

Note: Jane Cappaert and research team (1994) made a surprising discovery at the 1992 Olympics – the sprinters (50, 100, 200m) of the final round were using an average of 16% LESS energy than the swimmers who did not make it into the final round. One thing this suggests to me is that less-than-elite training programs are not understanding this low-drag approach to swimming (although everyone pays lip service to it) – they might be producing more powerful swimmers that are really good, but apparently those swimmers have higher drag too, and that is not good enough to be the best.

The world records of the future are going to push the perceived limits of both how much more power a human swimmer can generate and how much more drag he can eliminate. I wonder which one we are closer to reaching the absolute limit for.

#3 – Ease Inside The Body

This is an internal, subjective measurement.

The swimmer should feel a qualitative ease in the body when they transfer forces through the body better. When a swimmer generates power in one part of the body and transfers it through it will create sensations inside, detected by the nervous system. If the body parts are misaligned, working against each other (not in synchronized coordination) there will be collisions, tensions, tight spots, and eventually injury in conflict points of the body. If the body parts are aligned, synchronized into a harmonious whole-body action, if body tissues are properly flexible, relaxed, toned and trained to work as a team then force will flow through the body in a very smooth, even thrilling way. The difference is immediately tangible.

Genuine efficiency feels wonderful. The human brain is hard wired to seek it out, recognize it, and favor it.

Limitations: a lazy swimmer can produce a relative sensation of ease, by simply reducing the amount of effort. This would quiet down the conflicts in her body, yet make her move a lot slower (violate #2). Low energy + low speed might feel easier, but it does not equal efficiency (duh!). The absence of conflict in the body from reduced effort does not mean this swimmer has a well organized body – her low effort just means she is not doing the kind of work that exposes her problems. Only by putting the body under metabolic stress (generating and transferring more force) can the swimmer see the strengths and weaknesses of how force flows through her body. (Thank you to Dr. Kelly Starrett PhD for making this so much easier to comprehend in his marvelous book The Supple Leopard).

This analogy might help – consider your favorite (or most hated) metropolitan city, and imagine the traffic problems you have experienced there during rush hour. A poorly designed road system causes all sorts of traffic jams and congestion when more cars start pumping into the system. It is miserable to drive in it. A well-designed road system allows for vehicles to keep moving fluidly along, even in high density traffic. Keep vehicles off the road and no problems are exposed. The test is when you actually load the road system with normal traffic and then with heavy traffic. The road system is suppose to support a smooth flow of normally occurring traffic.

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In some ways our body systems are similar to a city’s traffic system. Our bodies need to be trained to deliver motor-control signals and force under the conditions we intend to swim and race in. The human (land-mammal) body does not come with these systems for swimming built-in. Longer and/or faster swimming will put heavy loads on those systems. If these systems are not made ready to handle those loads smoothly, we will feel it as (negative) stress, discomfort, pain, anxiety, and eventually as injury inside our bodies.

What we are looking for is the ability to generate and transfer more force through the body in a way that delivers in smoothly, precisely and and in a timely manner to the point where it is needed – not getting tangled up in the conflicts of the joints and tissues along the way.

I think most athletes can point to an experience where we have felt powerful and smooth and we know this is how our activity should feel at peak performance. This needs to be the norm, not the exceptional experience. This is a marvelous, tangible sign of efficiency.

#4 – Lower-Heart Rate

This is external, objective.

There are now ways to measure heart rate while swimming. (I have a Finis Aquapulse HR Monitor that clips onto the ear and have used it a bit for sprint training in the pool in the past, but not using it currently – I could see it being a useful device for calibrating one’s sense of effort, if you haven’t trained for this already.)

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Heart rate is a good indicator of metabolic expense. Yet, heart rate in swimming is affected by the mammalian dive reflex so heart rate numbers in swimming are going to be something like 15-20 beats lower than an equivalent effort on land. (I don’t have definite numbers, but this phenomena seems to be universally accepted). A swimmer needs to experiment, get some personal data, then set up his own reference points for what his training zones should be.

It is also possible (and if you will, I highly encourage) that a swimmer use a HR monitor or pulse-taking to train their perception of effort so well that they no longer need to use a monitor to confirm it. Some occasional calibration may be needed, but it is my experience that an athlete can (and should) develop a very reliable sense of heart rate (converted into a Rate of Perceived Effort scale) so an inferior external device is not needed. HR monitors do not tell the whole story of how and why HR is at a certain level, but combined with other trained subjective insight an athlete can develop intuitive control over her own body and performance.


Limitations: there is the issue I raised in #3. A person can simply use less effort to lower heart rate. But then this violates #2. Going slower is not what most people looking for in efficiency.

There is another critical limitation to point out.

Virtually every diligently practicing swimmer (and more pronounced for those who have a long history of swimming) has a neuro-muscular pattern – a rut in the road – burned deeply into their brain.

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At the time this swimmer tries to use a stroke pattern or SPL x Tempo combination that is outside their conditioned range they will experience a higher heart rate while trying it. But this immediate reaction is not a fair indicator that the unusual movement is less efficient. Why? Because the brain prefers the dominant pattern and does not have efficient control pathways set up for the new pattern yet. It has to work so much harder (the brain is already taking up 20% of the energy supply under normal, conditioned activity) to execute this new movement, and the muscle control is not established and refined to use a minimal amount of muscle to get the job done. Hence, the swimmer will experience a higher heart when he tries to perform something outside his conditioned range, whether the new movement is an improvement or not.

If you’ve seen a professional slackliner, or an acrobat walking along a tight rope you get this sense of cat-like minimalist movement – the better the walker, the less movement. Now put you or me on that line/rope and – even if we could stay balanced for 30 seconds – we are going to use a great deal of movement of our appendages to keep that balance. We will work a lot harder, much higher effort and heart rate, to maintain our position and go a lot slower while we do. The professional’s brain, through intense, deliberate training, has adapted to this activity and can perform it with extreme efficiency compared to you or me. We can intuitively understand this is not a matter of muscle power or metabolic superiority. They simply have taken the time to build the control and refine it to a calm, lower-energy state than you an I can achieve in our first few tries.

There is a similar situation in swimming. Take an accomplished swimmer with a record of success with a certain stroke style or SPL x Tempo combination – they have become ‘efficient’ at that particular style and combination because that is what the brain will do within the range of neuro-muscular conditioning the swimmer already has. But take that swimmer outside his conditioned zone even a little and his heart rate will shoot up – not because the new movement pattern is inefficient, but because the swimmer’s brain can’t handle the new patterns yet, and is in no position to compare efficiency of a new pattern to the current dominant one.

Only after a period of re-conditioning to expand the range of movement control (where the brain adapts to the point where it can lower its effort to keep control) is that swimmer in a position to test and compare different styles and SPL x Tempo combinations to see if one might hold more promise than the one he is using right now. A quick test of a significant change in the stroke without any conditioning is not a reliable test because of how the brain works to control movements. This is something that takes time (weeks if not a few months) to get conditioned for and test earnestly.

And with that, I want to acknowledge that this is one of the great psychological obstacles a swimmer (and coaches of those swimmers) may face in considering a change to their stroke style or change in SPL x Tempo (like the debate about what Ryan Cochrane must do to his stroke in order to catch Sun Yang, for example). If he has been somewhat successful with his stroke style up to this point, why risk the time and effort (in a busy and urgent training schedule!) to just see if another stroke style or pace combination might be better for him? That is a difficult and risky-feeling decision to make.

You can take this or that coach’s word for it, ‘Yes, do it!’ or, ‘No Way’, but the fact is, you’ll never know unless you go and find out yourself. (PS – I did take the leap when I discovered TI in 2001 and I am very glad I paid the price to test earnestly and eventually switch.)

Note: a new swimmer (one with few swimmer ‘ruts’) will often feel greater ease and gain more speed within a single lesson when being introduced to a better body position or movement pattern. She has no dominant pattern to work against, and her land-mammal instincts in the water are easy to improve upon. Hence, new swimmers are usually easier to teach and to persuade to make a change for they feel no risk of losing anything valuable and they experience the payoff immediately.

#5 – Reduced Turbulence

This is an external, objective measurement.

A simple but profound physics fact: sound, waves, splash, bubbles, and swirling water are products of power going into doing something besides moving that swimmer forward. These mean that force vectors are hitting the water in some direction other than the direction the swimmer needs to go. Sound, waves, splash, bubbles, and swirling water all take energy to create. Who or what is supplying the energy to create those? The swimmer.

The most efficient swimmers will be the quietest swimmers in the pool (all other things being equal).

As Coach Terry says, part of the universal human swimming problem is that most swimmer spend their time moving water around, rather than move through the water. Have you noticed how noisy it is at your pool? Especially when a club of youthful, energy-abundant (= feeling no consequence of the waste) club is practicing nearby! Just remind yourself of that next time you notice the sounds and sights at the pool: noise and splash means wasted energy.

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Smooth is beautiful. Smooth is quiet. Smooth is fast. Smooth is efficient. This is not a subjective preference in the eyes of the beholder – these are consistent with the facts of hydro-physics. The subjective features we admire in an awesome athlete and the objective features we measure are pointing in the same direction.

If it were possible to set this up, take a swimmer and have her produce two completely different stroke, but at the same speed. By simply observing the difference of turbulence created in each stroke we could confidently detect which stroke was wasting more energy. Because both strokes were producing the exact same speed we then could infer that the less efficient stroke was using more power, since it could afford to waste some of it.

Limitations: a non-moving vessel will create no sound, waves, splash, bubbles, or swirling water! But that doesn’t do us any good for getting faster, does it! The turbulence test becomes more useful at higher tempo, higher intensity swimming.

Turbulence will and must increase as velocity increases. Water simply cannot move out of the way fast enough and so it will result in more waves and splash. But there is a difference between unavoidable turbulence in a perfect stroke, and one that creates excessive turbulence. The differences between a low-turbulence style and anything producing higher-turbulence will be so much easier to notice. Yet measuring this has to be relative to that swimmer, and relative to that current velocity. During a high intensity set, a swimmer may compare against herself, and try to reduce turbulence from one repeat to another while keeping intensity level the same. This is an effective way to integrate technique and power training into one.

By the way, another great exercise is to do Silent Swimming (goal = no sounds, no splash, no bubbles) for your warm-up and cool-down swims. If you can practice a way to monitor your own turbulence (by sound and sensation) while swimming high intensity repeats that would be extremely useful too. Then you don’t need to rely solely on an outsider to tell you how turbulent you are in the water.


By now, if I have done a decent job laying out this proposal, it should be clear that any single indicator cannot be used alone to judge efficiency. A swimmer can report on the sensations happening inside her body, while the coach can be standing outside to make these external observations. It is the consensus of these internal and external indicators that give an athlete and coach confidence that a more efficient stroke is being achieved. The limitations of each indicator must be recognized and acknowledged in order to have a credible claim. Those limitations are overcome by the collaboration of the other indicators.


I realize that Total Immersion coaches are sometimes criticized for being so mindful and meticulous (thinking too much?) – but we are also praised for it by those who discovered the advantages the initial thinking effort brings to their long-term achievement. In our system of training we are working toward the accumulation of many small advantages collected all over the body, in every position and movement pattern. These efficiency indicators above reveal one aspect of the complex, multi-dimensional nature of swimming, and hence, the multi-dimensional nature of our coaching. We do a lot of thinking (observing, sensing, planning, training) in these dimensions and details in order to master efficiency in all its dimensions – physical and mental – which then frees us to move on to higher level mental activities while we swim – like just enjoying the ride! It is our mindful approach that allows us to expand the durations and intensity of our performance and our enjoyment. The mindful mastery of those underlying physical and mental skills makes for a smooth sailing vessel even under wild conditions – and a smooth sailing vessel is a result of a nicely designed vessel and well-trained pilot.

So, any one little detail in a swimmer’s overall composition – a little tilt of the head, a little tension in a muscle on the back, a misshape in the path of a recovery arm swing, a little extra splash on the entry, and extension not quite on track, a few bubbles on the kick, a slightly less-than-optimal SPL, a little inconsistency in tempo, – any of these by itself may not be so consequential. But all those corrections add up to a compound advantage that is definitely noticed and appreciated once the swimmer embraces the discipline of this approach. Hence, the meticulous nature of our coaching and our training methodology.

Efficiency is about energy. Every error in your swimming costs energy, and all those little errors add up and contribute to pre-mature exhaustion. Collect enough errors in energy use and it will add up to injury. Take the time and and make the mindful effort to examine each of these and remove them and you will conserve energy which can then be cashed in for greater distance and greater speed.

Misuses of energy are hard to detect directly in swimming. So we provide a meticulous, gradually deepening system for diagnosing then removing these errors. Our job as the TI Coach is to help you work at an appropriate pace and understanding so that you make steady progress with higher enjoyment without being overwhelmed by the unavoidable complexity of swimming mastery.

Efficiency is not just about going faster, it is about swimming in a way that aligns better with physics and physiology and those conveniently produce better health and happiness too. Good use of energy is tied directly to improved performance, and as the theory goes, tied directly to enjoyment also. Physics and psychology meet.

So, in the pursuit of greater speed I hope you will consider using a larger array of indicators for judging your efficiency than just noting if some change makes you go faster or not.

PS – if you have ideas for how to improve or expand this Efficiency Judging method I would appreciate hearing them. Send me a note any time!

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