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Being good at swimming doesn’t mean you can evaluate the pool performance better than everyone else. I trust someone running a CFD analysis of a pool more than

Being good at swimming doesn’t mean you can evaluate the pool performance better than everyone else. I trust someone running a CFD analysis of a pool more than a competitive Olympic swimmer when it comes to the effect of pool depth. It’s very hard to make accurate statistical assessments from intuition. Edit: maybe I’m not making myself clear: I don’t doubt they are slower in the current pool than they were before. But I doubt they can accurately tell you that it’s because of the pool depth. There are other factors that could also influence the performance, and I’m not sure the swimmers can accurately determine which factor is the primary difference.

CoastalCoder 2y ago
Even CFD analysis is a model though, with all that implies. Would a large, blind empirical study be more trustworthy?
- echoangle 2y ago
  Only if the depth is the only variable that’s changed. You can’t just use two entirely different pools at different times and locations and conclude that the depth is the reason for different performance.
- Eddy_Viscosity2 2y ago
  Yes and no. The empirical study could identify correlations and the strength of those correlations, but does nothing to say why they are correlated (maybe just spurious). But a CFD analysis may give you insight into what may be happening to cause the issue, which can then lead to a hypothesis that can then be tested further. All models are wrong, but some are useful.
_heimdall 2y ago
You don't necessarily need to do an in depth study of the pool when every Olympic swimmer in it fails to meet their own personal records. A study may be useful to understand why depth still matters beyond the 2m point, but a study isn't needed to show that swimmer performance is impacted.
- echoangle 2y ago
  Or maybe there’s something else going on? There are a lot of other variables in a pool except depth, no? Maybe water tension, density, viscosity? Someone else mentioned the walls of the pool also influencing the wave properties in the pool. Just noticing the pool being more shallow and people swimming slower doesn’t mean that’s the reason.
  - _heimdall 2y ago
    Rereading your last comment and I think I just misunderstood it, sorry! I first read it as saying a study would be needed to know if something about the pool was anything them down, but you were still specifically talking about whether the depth is the issue.
    - echoangle 2y ago
      Yes, I think a lot of people misunderstood the point, I’m ESL so maybe i didn’t write it up properly. I was just talking about the effect of pool depth, not doubting that something is different this time.
      - _heimdall 2y ago
        For what it's worth, my misunderstanding wasn't actually due to your message at all. I simply focused on the first sentance and lost the next sentance that tied it back to pool depth. Your English is actually very, very good! I wouldn't have guessed that it is a second language for you.
  - freejazz 2y ago
    So to be clear, you have no idea, you just insist on discounting the experiences of the swimmers because you can?
    - _heimdall 2y ago
      I misread the earlier posts here when I started dow this comment path, but I actually agree with them. There seems great evidence, including the swimmers', experience to say that something about the pool slows them down. It seems less clear that the depth is the issue, it could be something else or a combination of factors related to the pool that cause it.
boringg 2y ago
While part of it may be true. The athletes who spend 1000s of hours can probably intuit something being different.
- echoangle 2y ago
  The can maybe intuit being slower, but I doubt they can accurately tell you that it’s because of a different pools depth. There are a lot of other variables that could be the reason.
  - AnthonBerg 2y ago
    Do you have links available to any peer-reviewed scientific literature on which you base your theory that – just to make sure we’re on the same page — the theory that it is difficult to the point of impossibility for people to correctly ascertain that the depth and construction of the pool they swim in has no effect on their swimming dynamics, efficiency, and competitive performance?
    - echoangle 2y ago
      Isn’t that the null hypothesis? I have these data points: 1) The pool is shallower than normal in this Olympic 2) The pool seems to be slower this Olympic 3) swimmers seem to think it’s because the shallower depth 4) people responsible for building the pool say the effect of depth is negligible 5) there are other things that can be different about the pool except depth because the pools aren’t strictly standardized in their properties My only claim was that point 3 doesn’t tell me a lot because I find it very plausible that you can’t really detect the reason for the slowness just from swimming. I don’t have positive proof of that though.
Xcelerate 2y ago
I trust the swimmers’ intuition far more than an ad-hoc CFD analysis. Plus the shape of the pool itself isn’t necessarily the only variable that might be affecting the race times. The gold standard would be an empirical randomized controlled trial to compare two pools, assuming you could hide “which pool” from the participants.
- echoangle 2y ago
  I don’t doubt that they are slower, I doubt that it’s the pool depth. To be more accurate, i have no idea if it the pool depth, but a swimmer saying that it is doesn’t tell me a lot. I’m not sure if the intuition of a swimmer can differentiate between the pool depth effect and other effects that could influence performance. I don’t doubt that something is making them slower, but i don’t believe it’s pool depth until there’s better evidence.
  - Scarblac 2y ago
    Wouldn't they notice the extra turbulence affecting their legs?
    - echoangle 2y ago
      Looks like they don’t if you look at the quotes in the article. Nobody said “I can feel the turbulence reflected from the bottom of the pool slowing me down”, they just said they notice they are slower and the article claims they think it might be depth-related.
  - djtango 2y ago
    It's pretty amazing that people here are willing to wade into a field and contest what is accepted amongst practitioners. Olympians literally spend around 40 hours a week in the pool if not more. Places like team USA and other well funded teams have an army of coaches and scientists trying to eke out every basis point of performance as their full-time job. As a swimmer, I remember everyone lauding over how cool the Beijing Water Cube was because it was a uniform 3m deep which made it excellent for racing in - this was 16 years ago in 2008. Since the Paris Olympics were accepted the regulation recommendation for pool depth has been revised from 2m to 2.5m So clearly people vested in the sport and live and breathe it have seen enough evidence (including the sleepy regulatory board) to advise deeper pools. If you wanted another possible explanation for how depth may affect the swim - a crucial part of the swim is the dive and also the underwater kicking. Both of those may have separate dynamics to swimming on the surface.
fullspectrumdev 2y ago
I was always told that CFD is not a substitute for “actually going and testing”. It will get you a fair amount of the way there, but at some point you have to go and actually do the thing to validate your model.
defrost 2y ago
Competitive Olympic swimmers in G20 countries aren't always rocket scientists and brain surgeons ... BUT .. thay are frequently coached by teams that include leading sports scientists with degrees in fluid dynamics | applied mathematics | etc. Australia, as one example, took swimming (and a few other sports) next level with a plethora of studies on all things performance related. Any theorectical results from, say, CFD, would be parallel tested in real conditions and|or modelled in a scale pool (like a wind tunnel for water). Those who competed at that level in sport in the larger countries almost certainly heard first hand bleeding edge results from cutting edge sport science.
- Kon-Peki 2y ago
  The powerhouse swimming nations (USA, China, Australia, Canada, UK, etc) are so far ahead of everyone else it isn't even close anymore. My niece was not fast enough to be invited to the trials this year (missed by .03 seconds in her favorite event), but her time would have put her into the second heat in Paris. She's the ~150th fastest person in the USA, but would have come in ~25th place in the Olympics. It's the same situation in China, Australia, Canada, UK, etc. Most countries only have a small handful of elite swimmers. The power nations can each provide 20-50 swimmers fast enough to get to the semi-finals in every single event. They're analyzing and optimizing for everything. This is why most of the elite swimmers not from these countries go and train in the powerhouse countries. And why the powerhouse countries don't care that they do. I'd bet that 90% of all the medal winners this year do their training in 5 countries.
  - toast0 2y ago
    If she's likely to continue to be fast again in 4 years, it might be time to venue shop her team? Have any connection to other countries not in the top? Even if not, 4 years might be enough time to develop a connection. Being 25th in the Olympics is way cooler than being 150th in the USA, even if they're objectively the same speed. Also, you may need to adjust her speed if the Olympics pool is slower than the trials speed; but still it's way cooler to be any place in the Olympics than 150th faster in the USA --- maybe unless you're in the know for swimming. Venue shopping might feel ick, but I don't think it's too bad if you're in the competitive envelope, as opposed to what's perhaps a tradition of less then competitive entrants in some events.
MrPatan 2y ago
Intuition forms because it works. When it doesn't it's remarkable to the point of writing books and movies about it.
- echoangle 2y ago
  Intuition is a heuristic that lets you form decisions fast without a lot of effort. But I wouldn’t say having a wrong intuition is that uncommon that I would write a book every time I had a wrong intuition. I have intuitions all the time about stuff and when I check, it turns out I was wrong. That’s also why I wouldn’t make important decisions based purely on intuition. Intuitions form because sometimes, you need quick decisions and it’s better to do something wrong some of the time than take longer to make a better decision.
- Rayhem 2y ago
  When it works we call it intuition. When it doesn't we call it superstition. There are all sorts of availability biases at work here; none of which really support the use of intuition as a valuable, predictive resource. After all, if your intuition fails to predict something, there must be some lurking variable somewhere that you failed to account for. Not that the intuition is wrong /s.
  - djtango 2y ago
    The thing is, depth discussions have been going on for decades and these swimmers literally live in the pool. When people spend literally 40+ hours a week in water I trust them well before I trust scientists because it takes scientists so much longer to catch up and measure what the practitioners are observing. Like this reminds me of Beckham/Ronaldo doing free kicks. They had a deep understanding of controlling the ball well beyond what scientists knew how to measure and explain what they're doing.
lou1306 2y ago
Sure, it is not necessarily the pool depth. But that is almost surely the one factor that deviates the most from the "average". Paris is 50-100m above sea level which is pretty unremarkable gravity- and pressure- wise. Its water is unlikely to be macroscopically different from that of other French or Western European cities. I am aware the above may be proportionality bias, but at the same time there is some kind of "reverse proportionality bias" at play here: the assumption that since the effect of a shallow pool are too small, they can't significantly affect the athletes. Human behaviours are very nonlinear, and even very small sensory inputs may very well "throw off" an experienced swimmer.
sdwr 2y ago
I trust someone who's life is getting that 2/10 of a second to know when the 2/10 of a second is impeded. The how can be argued
tanewishly 2y ago
A CFD analysis is based on a model - an abstraction of reality. If the CFD analysis found everything is okay, yet reality shows it isn't, I wouldn't trust the competency of the person behind the analysis.
- echoangle 2y ago
  But CFD didn’t say that everything is ok, it said that pool depth has a very small effect. So either CFD is wrong or something else is wrong with the pool that’s not depth.

CoastalCoder 2y ago

Even CFD analysis is a model though, with all that implies. Would a large, blind empirical study be more trustworthy?

echoangle 2y ago
Only if the depth is the only variable that’s changed. You can’t just use two entirely different pools at different times and locations and conclude that the depth is the reason for different performance.
Eddy_Viscosity2 2y ago
Yes and no. The empirical study could identify correlations and the strength of those correlations, but does nothing to say why they are correlated (maybe just spurious). But a CFD analysis may give you insight into what may be happening to cause the issue, which can then lead to a hypothesis that can then be tested further. All models are wrong, but some are useful.

_heimdall 2y ago

You don't necessarily need to do an in depth study of the pool when every Olympic swimmer in it fails to meet their own personal records. A study may be useful to understand why depth still matters beyond the 2m point, but a study isn't needed to show that swimmer performance is impacted.

echoangle 2y ago
Or maybe there’s something else going on? There are a lot of other variables in a pool except depth, no? Maybe water tension, density, viscosity? Someone else mentioned the walls of the pool also influencing the wave properties in the pool. Just noticing the pool being more shallow and people swimming slower doesn’t mean that’s the reason.
- _heimdall 2y ago
  Rereading your last comment and I think I just misunderstood it, sorry! I first read it as saying a study would be needed to know if something about the pool was anything them down, but you were still specifically talking about whether the depth is the issue.
  - echoangle 2y ago
    Yes, I think a lot of people misunderstood the point, I’m ESL so maybe i didn’t write it up properly. I was just talking about the effect of pool depth, not doubting that something is different this time.
    - _heimdall 2y ago
      For what it's worth, my misunderstanding wasn't actually due to your message at all. I simply focused on the first sentance and lost the next sentance that tied it back to pool depth. Your English is actually very, very good! I wouldn't have guessed that it is a second language for you.
- freejazz 2y ago
  So to be clear, you have no idea, you just insist on discounting the experiences of the swimmers because you can?
  - _heimdall 2y ago
    I misread the earlier posts here when I started dow this comment path, but I actually agree with them. There seems great evidence, including the swimmers', experience to say that something about the pool slows them down. It seems less clear that the depth is the issue, it could be something else or a combination of factors related to the pool that cause it.

boringg 2y ago

While part of it may be true. The athletes who spend 1000s of hours can probably intuit something being different.

echoangle 2y ago
The can maybe intuit being slower, but I doubt they can accurately tell you that it’s because of a different pools depth. There are a lot of other variables that could be the reason.
- AnthonBerg 2y ago
  Do you have links available to any peer-reviewed scientific literature on which you base your theory that – just to make sure we’re on the same page — the theory that it is difficult to the point of impossibility for people to correctly ascertain that the depth and construction of the pool they swim in has no effect on their swimming dynamics, efficiency, and competitive performance?
  - echoangle 2y ago
    Isn’t that the null hypothesis? I have these data points: 1) The pool is shallower than normal in this Olympic 2) The pool seems to be slower this Olympic 3) swimmers seem to think it’s because the shallower depth 4) people responsible for building the pool say the effect of depth is negligible 5) there are other things that can be different about the pool except depth because the pools aren’t strictly standardized in their properties My only claim was that point 3 doesn’t tell me a lot because I find it very plausible that you can’t really detect the reason for the slowness just from swimming. I don’t have positive proof of that though.

Xcelerate 2y ago

I trust the swimmers’ intuition far more than an ad-hoc CFD analysis. Plus the shape of the pool itself isn’t necessarily the only variable that might be affecting the race times. The gold standard would be an empirical randomized controlled trial to compare two pools, assuming you could hide “which pool” from the participants.

echoangle 2y ago
I don’t doubt that they are slower, I doubt that it’s the pool depth. To be more accurate, i have no idea if it the pool depth, but a swimmer saying that it is doesn’t tell me a lot. I’m not sure if the intuition of a swimmer can differentiate between the pool depth effect and other effects that could influence performance. I don’t doubt that something is making them slower, but i don’t believe it’s pool depth until there’s better evidence.
- Scarblac 2y ago
  Wouldn't they notice the extra turbulence affecting their legs?
  - echoangle 2y ago
    Looks like they don’t if you look at the quotes in the article. Nobody said “I can feel the turbulence reflected from the bottom of the pool slowing me down”, they just said they notice they are slower and the article claims they think it might be depth-related.
- djtango 2y ago
  It's pretty amazing that people here are willing to wade into a field and contest what is accepted amongst practitioners. Olympians literally spend around 40 hours a week in the pool if not more. Places like team USA and other well funded teams have an army of coaches and scientists trying to eke out every basis point of performance as their full-time job. As a swimmer, I remember everyone lauding over how cool the Beijing Water Cube was because it was a uniform 3m deep which made it excellent for racing in - this was 16 years ago in 2008. Since the Paris Olympics were accepted the regulation recommendation for pool depth has been revised from 2m to 2.5m So clearly people vested in the sport and live and breathe it have seen enough evidence (including the sleepy regulatory board) to advise deeper pools. If you wanted another possible explanation for how depth may affect the swim - a crucial part of the swim is the dive and also the underwater kicking. Both of those may have separate dynamics to swimming on the surface.

fullspectrumdev 2y ago

I was always told that CFD is not a substitute for “actually going and testing”. It will get you a fair amount of the way there, but at some point you have to go and actually do the thing to validate your model.

defrost 2y ago

Competitive Olympic swimmers in G20 countries aren't always rocket scientists and brain surgeons ... BUT .. thay are frequently coached by teams that include leading sports scientists with degrees in fluid dynamics | applied mathematics | etc. Australia, as one example, took swimming (and a few other sports) next level with a plethora of studies on all things performance related. Any theorectical results from, say, CFD, would be parallel tested in real conditions and|or modelled in a scale pool (like a wind tunnel for water). Those who competed at that level in sport in the larger countries almost certainly heard first hand bleeding edge results from cutting edge sport science.

Kon-Peki 2y ago
The powerhouse swimming nations (USA, China, Australia, Canada, UK, etc) are so far ahead of everyone else it isn't even close anymore. My niece was not fast enough to be invited to the trials this year (missed by .03 seconds in her favorite event), but her time would have put her into the second heat in Paris. She's the ~150th fastest person in the USA, but would have come in ~25th place in the Olympics. It's the same situation in China, Australia, Canada, UK, etc. Most countries only have a small handful of elite swimmers. The power nations can each provide 20-50 swimmers fast enough to get to the semi-finals in every single event. They're analyzing and optimizing for everything. This is why most of the elite swimmers not from these countries go and train in the powerhouse countries. And why the powerhouse countries don't care that they do. I'd bet that 90% of all the medal winners this year do their training in 5 countries.
- toast0 2y ago
  If she's likely to continue to be fast again in 4 years, it might be time to venue shop her team? Have any connection to other countries not in the top? Even if not, 4 years might be enough time to develop a connection. Being 25th in the Olympics is way cooler than being 150th in the USA, even if they're objectively the same speed. Also, you may need to adjust her speed if the Olympics pool is slower than the trials speed; but still it's way cooler to be any place in the Olympics than 150th faster in the USA --- maybe unless you're in the know for swimming. Venue shopping might feel ick, but I don't think it's too bad if you're in the competitive envelope, as opposed to what's perhaps a tradition of less then competitive entrants in some events.

MrPatan 2y ago

Intuition forms because it works. When it doesn't it's remarkable to the point of writing books and movies about it.

echoangle 2y ago
Intuition is a heuristic that lets you form decisions fast without a lot of effort. But I wouldn’t say having a wrong intuition is that uncommon that I would write a book every time I had a wrong intuition. I have intuitions all the time about stuff and when I check, it turns out I was wrong. That’s also why I wouldn’t make important decisions based purely on intuition. Intuitions form because sometimes, you need quick decisions and it’s better to do something wrong some of the time than take longer to make a better decision.
Rayhem 2y ago
When it works we call it intuition. When it doesn't we call it superstition. There are all sorts of availability biases at work here; none of which really support the use of intuition as a valuable, predictive resource. After all, if your intuition fails to predict something, there must be some lurking variable somewhere that you failed to account for. Not that the intuition is wrong /s.
- djtango 2y ago
  The thing is, depth discussions have been going on for decades and these swimmers literally live in the pool. When people spend literally 40+ hours a week in water I trust them well before I trust scientists because it takes scientists so much longer to catch up and measure what the practitioners are observing. Like this reminds me of Beckham/Ronaldo doing free kicks. They had a deep understanding of controlling the ball well beyond what scientists knew how to measure and explain what they're doing.

lou1306 2y ago

Sure, it is not necessarily the pool depth. But that is almost surely the one factor that deviates the most from the "average". Paris is 50-100m above sea level which is pretty unremarkable gravity- and pressure- wise. Its water is unlikely to be macroscopically different from that of other French or Western European cities. I am aware the above may be proportionality bias, but at the same time there is some kind of "reverse proportionality bias" at play here: the assumption that since the effect of a shallow pool are too small, they can't significantly affect the athletes. Human behaviours are very nonlinear, and even very small sensory inputs may very well "throw off" an experienced swimmer.

sdwr 2y ago

I trust someone who's life is getting that 2/10 of a second to know when the 2/10 of a second is impeded. The how can be argued

tanewishly 2y ago

A CFD analysis is based on a model - an abstraction of reality. If the CFD analysis found everything is okay, yet reality shows it isn't, I wouldn't trust the competency of the person behind the analysis.

echoangle 2y ago
But CFD didn’t say that everything is ok, it said that pool depth has a very small effect. So either CFD is wrong or something else is wrong with the pool that’s not depth.