[echoangle]

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.

[defrost]

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]

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]

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.

[TylerE]

Feels like you're missing a variable here. If your nieces time in a fast pool would be 25th in Paris, that means her time in Paris will be slower than that, because now she's in the slow pool, right?

[_heimdall]

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.

[thaumasiotes]

> 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.

This is a weird standard. Out of 200 people doing anything, how many do you expect to set a personal record? Say you drive to the grocery store. Are you setting a time record for the trip more than 0.5% of the time?

[Scarblac]

These athletes plan their whole training and fitness regime for years so that they are at their absolute best at this particular day.

Tbh I don't do much of that sort of thing for my grocery store trips at all.

[thaumasiotes]

> These athletes plan their whole training and fitness regime for years so that they are at their absolute best at this particular day.

The only way this could actually happen is if they intentionally sandbag their performance starting several years in advance -- and continuing indefinitely -- which would prevent them from qualifying for the Olympics in the first place. It's not a possibility.

[BoringTimesGang]

Or it could happen that the training, diet and injury-avoidance regime for long term success is different from that for short term optimisation. As it is for many, many sports.

[thaumasiotes]

All right. The 2020 Olympics were canceled and a replacement event was held in 2021. According to this theory, there should have been a shocking drop in personal records set at the 2021 event. Was there?

[Scarblac]

Sure, there could be multiple peaks. That doesnt really subtract from my argument that this isn't a day like any other for these athletes, form and fitness wise.

[BoringTimesGang]

The motivation of a commute is not comparable to the motivation of a swimmer in 4th place of a medal event, etc.

[thaumasiotes]

So what? Is the motivation of a swimmer in 2nd place in a non-Olympic event comparable? Is the motivation of a swimmer who wants to work toward the Olympics comparable? Is the motivation of a swimmer trying out for the Olympics comparable?

Every Olympic athlete, with the possible exception of the Jamaican bobsled team, has been equally motivated at dozens or hundreds of officially-measured points in the recent past. Why do we expect personal records at the Olympics?

[BoringTimesGang]

Well, for one thing, world records don't get ratified in a local pool.

And athletes are competent enough to achieve the time needed for qualification without going all-out. Look at the finish times of the heats. Pan Zhanle was over a second slower.

[echoangle]

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.

[mmmrtl]

Explain to us how water "tension", density, and viscosity are variables that would change? It's just water, and temperature is set at ~25 C. The shape of the pool and gutter setup are the only major factors at play, assuming the filtration system isn't causing major currents.

[echoangle]

It’s not demineralized water though, have you ever added a tiny bit of soap to water and it immediately reduced the surface tension? I’m not saying there’s soap in the water in France obviously, but there’s a lot of other additives that could theoretically affect water properties even with a fixed temperature.

Edit: for example, compare salt and fresh water properties here: https://ittc.info/media/4048/75-02-01-03.pdf#page2

At 25 degrees, fresh water has a Viscosity of 0.000890 Pa⋅s and sea water has 0.000959 Pa⋅s. That’s an 8% difference in viscosity by adding NaCl to water. Is it that strange that there could be a 1% difference in viscosity for example by having different additives in the pool water?

[ff317]

Yeah but it's not just "water", as in plain H2O. All water has different things dissolved or mixed into it. In pools there's commonly several chemicals added to that water: to correct the pH for humans, to sanitize, control corrosion of metal, avoid calcium deposits on other surfaces, etc. It's entirely possible that the additives in the water could be way off of normal and somehow affect things like viscosity or surface tension.

[throwaheyy]

No, it isn't.

[_heimdall]

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]

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]

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]

So to be clear, you have no idea, you just insist on discounting the experiences of the swimmers because you can?

[_heimdall]

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]

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

[echoangle]

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]

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]

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.

[fullspectrumdev]

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.

[sdwr]

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

[CoastalCoder]

Even CFD analysis is a model though, with all that implies.

Would a large, blind empirical study be more trustworthy?

[Eddy_Viscosity2]

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.

[echoangle]

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.

[lou1306]

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.

[tanewishly]

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]

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.

[MrPatan]

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

[echoangle]

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]

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]

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.

[Xcelerate]

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]

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.

[djtango]

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.

[Scarblac]

Wouldn't they notice the extra turbulence affecting their legs?

[echoangle]

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.