[samldev]

I was a college swimmer, qualified for Olympic Trials in 2012 and 2016. There are absolutely slow and fast pools. It basically comes down to two things:

1. The depth - which is only 7ft in Paris, unusually shallow for a competition pool.

2. The sides. Does the water spill over the sides into the gutters, or smash into a wall and bounce back, creating more chop.

A trained eye can see all the swimmers in Paris struggling in their last 10-20 meters (heck, an untrained eye can spot some of these). Bummer that it makes the meet feel slow but at least it generally affects all the swimmers equally

[madaxe_again]

I actually did a fairly lengthy research project on pretty much exactly this as a physics undergraduate - I wasn’t looking at swimming specifically, but rather boundary separation and Reynolds number in an open channel of varying depth.

The setup was simple - a constant head vessel to provide a constant but adjustable flow of water in from one end, and a little plastic boat sat in the middle of the channel, attached to a force gauge at one end of the channel. The outflow of the channel had a gate with an adjustable height in order to vary the depth. Also, a couple of dye injectors at different heights in the channel in order to see turbulent vs laminar flow.

The key finding was that at shallower depths, turbulent flow began much more rapidly and resulted in erratic but overall higher resistive forces on the boat. Deep water remained laminar for much longer, and could flow much faster before turning turbulent near the surface. This was the expected result, but it was nice to experimentally prove it.

So in short, the pool depth almost certainly impacts the point at which turbulence kicks in, and therefore athletic performance. It’s probably the dive/entry that is being most impeded, as that’s when the swimmer will largely be experiencing laminar flow.

[bonestamp2]

Is there a formula to calculate the ideal depth at which going any deeper results in diminishing returns? In other words, how deep should future competitive swimming pools be built to provide the most world record opportunities (and perhaps more excitement for spectators due to increased world records)?

[bjoli]

Does it manifest directly? The water has had some time to settle when they start.

[madaxe_again]

Yes. An object moving through water is more or less equivalent to water moving around an object, and the moment you cross a boundary condition, be it depth, velocity, viscosity, the phase transition is instantaneous to all intents and purposes.

I’d have entire days of experiments screwed up just by the water being slightly too warm or cold, or there being dust, or not enough dust, or sunshine, or… fluid dynamics are finicky.

[LorenzoGood]

Yes, but there will be no turbulence at the start of a swimming race.

[askvictor]

At some (shallow) point, does a 'ground effect' kick in? Or any sort of constructive interference?

[madaxe_again]

Yes, in a very shallow flow you retain laminar flow - but you wouldn’t be able to swim in it, as we’re talking 15mm or so.

[conductr]

My untrained eye has noticed. But I also think it's not really a big deal. There are so few events where the conditions are exactly the same every 4 years. Just kinda the luck of the draw if you happen to be competing in the most ideal conditions for WR setting in any event

[kergonath]

Also, the important bit is fairness for all competitors. As the OP said, the same conditions affect everybody. I have little sympathy for the (few) swimmers complaining. They are not owed a world record and if they’re that good, they’re going to get one anyway.

[teractiveodular]

Wouldn't the sides affect swimmers on the edge lanes next to them more? And is this one reason why the strongest swimmers are usually placed in the center lanes?

[jseutter]

Swimmers on edge lanes get affected more, and they leave the outside lanes unoccupied except for the first stage of qualifying.

[killingtime74]

From the races I saw they specifically had the edge lanes (left most, right most) empty probably for this reason. I.e. 8 out of 10 lanes are used. I think one of them did have someone in one of those lanes because one of the qualifying heats was a dead heat.

[aqfamnzc]

Given the other comments I must be missing something, but wouldn't it be pretty much fair? The end swimmer gets one real neighbor and one simulated (reflection) neighbor from the wall. The middle folks have two real neighbors creating chop.

[lupusreal]

Correct.

[trhway]

> But I also think it's not really a big deal.

the difference of the resulting turbulence from the wave bounced back from the bottom surface at 2m here and from the more traditional 3m is a big deal. The water is pushed by the swimmer's hands with the speed of something on the scale of 2 meters per second, so, as the swimmer moves forward, that turbulent movement of the water reflected by the pool bottom may as well come behind the legs in the 3m depth case while in the 2m depth case it would catch the legs decreasing the efficiency of their movement.

[myworkinisgood]

It's not a big deal in terms of competition as long as all players are affected equally. People are just being whiny.

[LargeWu]

Additionally, anybody good enough to be prevented from setting a world record because of this pool will undoubtedly have multiple chances in other competitions with faster pools.

[nl]

This isn't really the case. You need a fast pool and good competition.

The Titmus vs Sanders vs Ledecky 400m could have been a world record race in another pool, but there's a pretty good chance we'll never see the three of them race each other again.

[LargeWu]

Counterpoint: Ledecky has never had anybody even close to her level in the 1500 and she has broken her own WR half a dozen times. I think good competition can help, but that effect is likely far less than pool conditions.

[nl]

Yes, this is absolutely true.

In Ledecky's case the clock is the only competition, and she's just so much better than anyone else it's currently impossible for someone to race her.

In Athletics at non-Championship meets they have pacemakers who provide a pace for the eventual winners to chase when they are going for fast times.

It'd be interesting to see what Ledecky could do if she swam (for example) with male pacemakers as competition.

Or maybe Summer Sanders will move up to the 1500m and we'll see a real race before Ledecky retires.

[Rastonbury]

Wouldn't any of these people not try for a WR in other comps without strong competitors? WR seems more prestigious than just a win and going for it and getting it means you win that race too

[thaumasiotes]

> There are so few events where the conditions are exactly the same every 4 years.

The Olympics used to be held at Olympia. It's not difficult to make the conditions the same every four years.

[lordnacho]

On that note, I should mention the idea of having a permanent Olympic city. Perhaps a new one.

That way, there's no circus that goes around at great expense each time, and the Olympic city becomes a centre for sports science during the interim.

Perhaps have separate summer and winter cities.

Only drawback is the ioc doesn't get to choose a city every four years.

[RandomThoughts3]

The circus is the point of the Olympic.

If there is no big event happening somewhere, the Olympic have no point. There are already permanent venues and international competitions happening for each of the sports of the Olympic.

[lostlogin]

> Only drawback is the ioc doesn't get to choose a city every four years.

That’s a massive drawback which is probably insurmountable.

They to love kickback.

[mrgoldenbrown]

Imagine the bribes they would get when choosing the permanent city though!

[tweetle_beetle]

I'm no expert, buy there also seems to be loads more stuff lying on the bottom of the shallow floor than I remember from previous Olympics. Not even sure exactly what it is - large white panels and other equipment that the swimmers don't look that far off touching when underwater (not the robot cameras which are relatively unobtrusive).

[ranie93]

digital lap counters to help the swimmers keep track

[creaghpatr]

Thats pretty nice, when I swam the 500 I would have to lift my head to see the lap counter dropping the sign in the pool which messes with your head position

[jonhohle]

Wouldn’t the underwater camera on a track cause currents?

[bhandziuk]

I could be fully enclosed for the full length and just have a glass top

[mysterydip]

Would the swimmers in the center lanes have any advantage by being furthest away from the wall-induced chop?

[etempleton]

Yes, those on the outside will have choppier waters as the water bounces off the sides of the pools. The modern competition pools do a pretty good job of reducing this effect, but it is always there.

[rurban]

Plus, you'd have a big advantage later if you start fast and gain a few meters from your two neighbors. Their waves would slow you down. Gliding is much faster than fighting through rough waters.

[renewiltord]

Could probably increase fairness by doubling the width and throwing away the last few lanes (leaving them empty). But would that incentivize the edges? I don't know.

[eru]

They could get almost perfect fairness in any kind of Olypmic-style race by just letting competitors all use exactly the same lane, one after another.

In earlier times, measuring equipment wasn't accurate enough, so races had to be done in parallel with people starting at the same time. Today, that's no longer necessary. In fact, people racing one after another is exactly how we hand out world records.

Of course, the Olympics and other events like them aren't there to find the best athletes in some absolute sense; these events are there to entertain spectators. Otherwise, swimmers could just do time trials at home and mail in times.

And spectators like people racing each other at the same time.

[jimktrains2]

There's something to be said for racing _someone_ and not just the clock, for the swimmers/racers, not even thinking about the audience.

Additionally, it would make races take 8x to 10x amount of time.

[eru]

> There's something to be said for racing _someone_ and not just the clock, for the swimmers/racers, not even thinking about the audience.

Yes, it's more fun.

> Additionally, it would make races take 8x to 10x amount of time.

Well, that's not a problem, they can run different events in parallel. Eg swimming and running shouldn't interfere at all with each other.

[skeeter2020]

It's not supposed to be fair (as in equal) though, lane assignment goes inside-to-out based on qualifying times. The easiest way to avoid the chop is to get out in front and stay there.

[Micanthus]

> The easiest way to avoid the chop is to get out in front and stay there.

While that's technically true, the drafting effect actually means that being a bit more than a body length behind the swimmer next to you is beneficial to you. That's another part of the philosophy why the fastest swimmers are assigned the center lanes, and the slowest the outermost lanes, to balance out the choppiness of being by the sides with creating a potential for drafting. Of course intentionally drafting is not a strategy that will win you the race, especially in short events, but in longer events it can be important to keep pace with the swimmer next to you while they need to expend more energy and you draft off of them either with the intention to eventually pass them or to stay ahead of the swimmers on your outside.

[renewiltord]

Makes sense.

[SECProto]

They do throw away one lane on each side already, FYI (in addition to positioning competitors to minimize influence on results, as others discussed)

[elevaet]

They put the most favoured (by entry times or heat results) swimmers in the center lanes, slower ones out from there. You've probably noticed that you usually see the race leaders in the middle, and you hardly ever see the edges winning.

In cases where there are less swimmers than lanes, they leave the edge lanes empty.

[water-data-dude]

Alternately: a swimming pool on the interior of a cylinder - rotated to provide artificial gravity.

[hgomersall]

Supposedly, that's why the fastest qualifiers get the middle lanes.

[jschulenklopper]

And having a better view on the competition in the neighboring lanes (just like in track running). There's even some applied psychology here, that competing swimmers 'push' each other to higher speeds because they can see each other more clearly (and 'feel' the push from someone just lagging).

Putting the faster qualifiers in the middle lanes is also a better view for the spectators on both sides of the pool.

[iknowSFR]

Interesting to see the 400m and 200m track and field athletes starting to favor outside lanes.

[rurban]

That's because of the drag in the inner curves. There the outer lanes are faster.

[johnp314]

It would be interesting to see a comparison of lane effect, say for instance, re-running a race after let's say a weeks rest with the top finishers now nearest the side walls and the lowest finishers in the center lanes. Oh and for incentive, let's say the average of their two times determines the winners.

[sandworm101]

The human factor would make this very difficult. A more scientific test might be to use RC boats with tightly regulated power outputs, with a wave machine to ensure consistency.

[dredmorbius]

The fact that swimming competitions are so very close, often down to 100ths of a second, doesn't much help.

Olympic and similar competitions are timed to the nearest 1,000th of a second, but any result within the same 100th is considered a tie as that last bit is just entirely arbitrary, in part because pool dimensions themselves are not accurate to this degree. (The FINA standards mentioned in my earlier comment addresses dimensions accuracy standards.) The Olympics did break ties at the 1/1,000s standard in 1972, but has since judged any result within 1/100th as a tie:

<https://olympstats.com/2014/02/12/timing-accuracy-at-the-oly...>

[dr_dshiv]

Random assignment should make it easy to detect, depending on the size of the effect

[ldng]

Supposedly, all the Paris 2024 new accommodation were designed with re-usability for the general public after the Olympics. Is it possible that had an impact the swimming pool on design choices ? Put differently, are performance design at odd with more general/accessible design in the case of a swimming pool ?

[tw04]

Given the pool was put on top of a rugby pitch, which resulted in the shallower depth because they didn't want to destroy the pitch (a full depth pool would have weighed too much) - unlikely. The pool isn't a permanent structure, it's not going to remain there after the olympics are done.

I would be very surprised if they re-use it at all - an "above ground" pool of that size seems like it would be more trouble than it's worth to maintain over the long run.

A timelapse of the pool being put together: https://www.youtube.com/watch?v=jTuFidqy0yI

[QuarterReptile]

I can't speak to the French ecosystem, but in the US these pools often (usually?) get resold to swim clubs who find some land and build buildings around them.

[xhkkffbf]

Sometimes they just move the pool to a new city and set it up in an arena for another championship.

[physicsguy]

Given the abandonment of olympic venues all the way round the world, I don't think this is a bad thing.

There's a lot in the book Soccernomics about how the economic value promised by politicians lobbying for hosting things like this rarely pan out.

[wildzzz]

There's definitely economic value but it really only goes to the companies building facilities, the suppliers, and the hospitality industry immediately surrounding the events. In an already well-developed city, they aren't going to be building many new permanent structures. Many will be temporary that will eventually be torn down or just converted back to what they were originally. The money is spent, distributed to the companies that directly participated in the build up and run of the Olympics but there's little gain made after.

A more interesting way of doing the Olympics would be to only allow for developing countries to participate in the selection process. Each country would be required to meet a certain level of funding to guarantee they can support the entire Olympics. Foreign investment would be encouraged. There would be a requirement for some aspects to be permanent construction, you couldn't just build a tent city for the athlete village. Then a name is picked randomly. The host country then receives major foreign investment, not just in sporting arenas, but in many areas of its economy. The Olympic committee could also collect dues from participating countries based on GDP that would go to the host country for economic development. It would basically create a lottery system for the economy of developing countries. The build up to the Olympics would create the infrastructure needed for future investment. This would likely require host cities to be selected much further out in advance. An oversight committee would observe the development and if milestones are not met, a host city from a developed country that does have the infrastructure necessary would instead be chosen.

[femtozer]

In this case, the pool is temporary. La Défense Arena is usually used for rugby (Racing 92) and concerts.

[Scoundreller]

Dumb question I never thought about: do the circulation/filtration pumps get turned off during races? And for what minimum time before hand to let things settle?

If so, I guess this would be a serious competition only thing because you wouldn’t want them off for hours.

[dredmorbius]

FINA competition pool standards have recirculation minimum standards, and pumps run continuously. Further, "water distribution has to be such that no appreciable current or turbulence is created. 'Appreciable current' is defined as water movement that can move a floating basketball (filled with 6 litres of water to obtain the right buoyancy) in one direction for more than 1,25m in 60 seconds."

<https://resources.fina.org/fina/document/2022/02/08/77c3058d...> (PDF)

Most competitive swimming pools have a large number of inlets with diffusers on them, laid out every 2m or so across the pool floor.

Those are circular disks about 10cm in diameter, looking vaguely like this:

  __________
  \________/
   |      |

    ^^^^^^

The carets indicate inlet water flow beneath the diffusers. The effect is that water entering the pool largely moves perpendicular to the pool floor, and slowly diffuses upwards. Water return is through the (large, wide, deep) gutters.

Because the gutters are continuously removing water from the pool, circulation needs to be on to maintain a consistent fill level.

[sandworm101]

They do, but circulation cannot be totally stopped. This is a greater problem in outdoor pools but any pool will have some sort of temperature gradient that will inevitably result in circulation. Any water movement means slower times, at least in those events longer than 50m (1 length).

[OJFord]

Surely that has far less effect than that of all the other swimmers? Naïvely I would think we should be running time trials of a single swimmer at a time before caring about any of this?

[croes]

>A lot of this is perception vs. reality,” he said. “If you were to talk to many very accomplished coaches, they would say the pool has to be a minimum 3 meters deep. Most of our research shows that anything over 2 meters is frivolous. … Obviously, some depth is very important. But after a certain point, it's diminishing return.

Maybe it's just the swimmers and not the pool as such

[lou1306]

But a lot of the swimmers themselves are not able to go anywhere near their personal bests: this is a sharp reversal from past Olympics, where many athletes reached new personal records.

Plus, they are the worldwide foremost experts on competitive swimming. Definitely I would be more interested in their evaluation of a swimming pool rather than trust "research results" from the company that built the pool in question.

[viraptor]

> they are the worldwide foremost experts on competitive swimming

On swimming, sure. But not fluid dynamics. It's a bit like music listeners shouldn't be treated as experts on music quality, or you'll get the audiophile nuts who need gold connectors. Some combination of personal experience for comfort and objective measurements for performance would be much better.

[dsr_]

It's strange that you would pick on gold connectors. Gold is an excellent conductor and does not corrode in air, so it makes a great plating material. In the quantities needed for plating, it's not too expensive, either.

Silver corrodes relatively quickly and is expensive; that's a bad tradeoff against copper, which is much cheaper and nearly as conductive. So: gold-plated connectors on copper wires are extremely common.

None of that makes an audible difference, as it turns out: humans can't tell the difference between silver, copper, gold, aluminum, or even iron wires at audio frequencies and realistic (sub-kilometer) lengths with comparable resistance. All the advantages are material costs vs longevity without maintenance.

Also, most music listeners are not experts on music quality or sound reproduction quality (two very different things). Many music listeners are experts on their own preferences. Everyone is entitled to their own preferences.

[viraptor]

Picking on it exactly because there's no difference in sound, but the extreme audiophiles will claim they hear it anyway. https://ventiontech.com/products/toslink-to-mini-toslink-opt... - "gold-plated connectors resist corrosion for optimal signal transfer over time." - it's an optical cable!

[mensetmanusman]

There is an audible difference after being in a high temp high humidity environment for 5 years :)

[kergonath]

> It's strange that you would pick on gold connectors. Gold is an excellent conductor and does not corrode in air, so it makes a great plating material. In the quantities needed for plating, it's not too expensive, either.

It’s not strange at all. Gold plating improving quality sounds truthy but is absolutely false. I have yet to read a serious study, at least single blind, showing any meaningful difference. And I have yet to read a serious engineering study showing any meaningful difference in characteristics. Steel plated jacks are just fine, and optical connectors make the whole thing irrelevant. As you write yourself:

> None of that makes an audible difference, as it turns out

> Also, most music listeners are not experts on music quality or sound reproduction quality (two very different things). Many music listeners are experts on their own preferences. Everyone is entitled to their own preferences.

Indeed. But their preference have no effect on Physics. If they are happy to get gold-plated ruthenium cables with diamond coatings, more power to them. It does not make these cables any better.

Theo are entitled to their own preferences, not their own reality.

[SoftTalker]

"I reject your reality and substitute my own!"

[teddyh]

> Gold is an excellent conductor

Actually, gold is a worse conductor than both copper and silver, and only a little better than aluminum.

> and does not corrode in air

This is the real reason for plating contacts in gold. But gold wires would be a bad idea, since they would be worse than both copper and silver wires.

[Gud]

Parent didn’t say gold was a better conductor than silver or copper though. How does gold compare to copper- or silver oxide? Which was the point parent was making.

[ssl-3]

Aluminum is also an excellent conductor.

[BoringTimesGang]

You're comparing the science of electronics and sound (well understood, rigorous) with sports science (cesspit of low-N, hard to study well). In sports, anecdata are valuable - putting guff in a journal doesn't make it any less guff.

[aleph_minus_one]

> Plus, they are the worldwide foremost experts on competitive swimming. Definitely I would be more interested in their evaluation of a swimming pool rather than trust "research results" from the company that built the pool in question.

But they are very prone to psychological effects.

[mrguyorama]

Professional athletes are MORE superstitious than other people, and are prone to serious amounts of bias in how they attribute outcomes.

[croes]

Maybe they all change their behavior because they know the pool is less deep as they are used to.

Some kind of placebo effect or fear of coming to close to the ground.

Many athletes are superstitious.

[AtlasBarfed]

There's Olympic gold medals on the line.

People are going absolutely as hard as they can.

There's no way an Olympic pool for the actual Olympics should be that shallow. If athletes prefer a deep pool, the pool should be deep.

Swimming is one of the premier sports at Olympics. It's also a facility that has one of the most reuse if built properly.

You don't think a Paris aquatic center wouldn't get tons of reuse in world championships and other types of top end level events if they'd built a fast pool

It's a mystifying decision. Especially since one of the standout athletes on the French Olympic team is a swimmer, and it appears that their decision now cheap out on the pool cost him a world record on the Olympic stage on his home soil

[swores]

Placebo or fear can absolutely be a possibility regardless of how badly they want to do well because it's the Olympics.

Firstly, if a swimmer were to wrongly worry about hitting the floor even if there is 0% that any of their races ever saw them go as low as this floor, it could be in the back of their mind that going as low as they usually do might cause them problems and therefore seem logical to avoid.

Secondly, humans are not perfectly rational machines. Many a football (soccer for any Americans) player has come back from a nasty injury and found themselves unable to play as boldly as they used to, even though the odds of getting injured haven't changed just their perception of it.

I do agree that if the athletes feel it's needed then they should be listened to, just explaining that it's possible for both things to be true, that the depth doesn't create any physical problems yet still lead to changed behaviour from the swimmers.

[RaftPeople]

> Placebo or fear can absolutely be a possibility regardless of how badly they want to do well because it's the Olympics.

But it seems unlikely all swimmers would be impacted equally by psychological effects. Some thrive some wither, lots of variation.

[stingrae]

> It's also a facility that has one of the most reuse if built properly. You don't think a Paris aquatic center wouldn't get tons of reuse in world championships and other types of top end level events if they'd built a fast pool

They didn't build a dedicated aquatic center. "The pool here in suburban Paris — a temporary vessel plopped into a rugby stadium"

[AtlasBarfed]

So you agree they cheaped out?

Paris allegedly spend 1.5 billion to clean up the Seine presumably for fringe events like open water swimming and triathlon.

Again: premier top-of-program sport in Olympics primetime. All they had to do was dig a hole in a rugby field.

[Someone]

> People are going absolutely as hard as they can.

Not necessarily. If they think the pool is slower, they’ll think they will have to swim for a bit longer, and may (possibly subconsciously) adjust their power output to allow for having something left when they have swum for as long as they think it would take them in a fast pool.

[bobthepanda]

In fact a lot of the upcoming olympics specifically don’t have as much new construction because of the white elephant criticisms of the Olympics leading to most developed host candidates declining and/or having hosting referenda rejected.

The Athens 2004 and Rio 2016 venues in particular are not doing very well post-Games.

[bregma]

> There's Olympic gold medals on the line. People are going absolutely as hard as they can.

They don't have to outswim the bear. They just have to outswim the silver medalist.

[duggan]

As much as it's about winning the medals, this is about setting personal and world records, too.

[a_c_s]

Right, if you are swimming in multiple events then it doesn't necessarily make sense to swim as hard as you can in the early events if that is going to tire you out for the latter events.

[beAbU]

The pool is a temporary structure, La Defence is a multi purpose venue. The pool is literally a tub on top of a rugby field.

Perhaps this is why its shallower than normal.

[Kon-Peki]

All major competitions will be in temporary pools from now on. It’s a major spectator sport with growing popularity, but as seen in 2008, 2012, 2016, etc purpose-built facilities for that crowd size are failures.

Paris is swimming in a rugby stadium. It is loud and exciting. The US trials this year were in a temporary pool at the NFL stadium in Indianapolis with 60,000 seats filled! LA 2028 has already announced that they will be using a temporary pool in an NFL stadium and will have 38,000 seats. Brisbane 2032 hasn’t said anything as far as I’ve heard, but you can bet that’s also what they will do.

Edit - I was wrong about LA swimming capacity. It is going to be at the NFL stadium in Inglewood, but as of now they are only aiming for 38,000 seats

[ben7799]

I had read in one of the other articles about this issue that you are correct, that is exactly why the pool is shallower than usual.

The building was going to need structural modifications to make the pool standard depth.

[xhkkffbf]

Experience shows that the pools don't get much reuse. Look at the abandoned venues in Beijing. After all, there's only one world championship each year and dozens of very nice pools already on the planet.

BTW, it's not clear the decision was purely monetary. Raising the water level means ruining the view of the closest seats. The spectators would be that much further away.

[s1artibartfast]

When you measure human performance, placebo matters.

[stonemetal12]

Considering touching the bottom results in disqualification it isn't a superstitious fear.

[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.

[BoringTimesGang]

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

[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.

[_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.

[freejazz]

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

[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?

[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?

[derbOac]

At the end of the article it notes thqt quote is coming from the company who built the pool.

On some swimming forums competitors were complaining about the bidding process for the pool construction and giving a different opinion, noting that the depth is less than what was recommended by international standards bodies. There's also something about video equipment at the bottom of the pool?

I'm not sure what to think, as there are things to consider both ways, but there's a bit more out there than swimmers versus pool officials.

[ianburrell]

The Olympic swimming is held in temporary pools in an indoor arena. Temporary pools explain the shallow depth and high walls. It isn't construction problem but decision to not use permanent pool.

Temporary pools seem to be thing recently. The US trials were held in one.

[SoftTalker]

You can set up a temporary pool in a huge venue such as a football stadium and get higher attendance, or stated differently, you can accomodate a one-time need for that much spectator capacity for an event like the Olympics when you will never need that again in the lifetime of the facility.

[toast0]

Maybe not the same level of attendance, but you can build a permanent pool with temporary stands for the Olympics, and use the larger than necessary deck in other ways after the Olympics.

[qzw]

Notice the “most of…” and “diminishing returns”. The vagueness is doing a lot of heavy lifting in that statement. Since world records are often broken by mere tenths or hundredths of a second, I would think that an Olympic games would err on the side of extra spending for exactly those diminishing returns. The excitement and extra viewership from having many new WRs would more than offset the added cost anyway.

[Xcelerate]

I doubt that. What is P(set of slower times across swimmers | pool is not slower)? Seems like it wouldn’t be too hard to calculate if we make a few reasonable assumptions about observational data.

And if you don’t like inferring causation, one could just directly perform an experiment to test this pool vs another pool using swimmers who didn’t quite make the Olympics.

[etempleton]

There are more things that influence if a pool is fast or slow than just the depth.

How the pool gutters neutralizes or doesn’t neutralize waves; water temperature; the design of the lane lines; design of the starting block; the electronic touch sensors(how hard are they - do you get a good solid feel for push off?); etc

Depth is probably only part of the reason the pool is slow. It would be very unlikely everyone happens to be slow at the Olympics this year.

[rscho]

Perception is everything. If the pool 'feels fast', you'll feel like you're on your way to your best, which is a huge boost to your motivation. The converse is also true.

[roughly]

I mean, "diminishing effects" - these folks are the absolute apex of swimming struggling for the absolute maximum speed in the water that any person has ever achieved (under the watchful eye of someone with a stopwatch, at least). Small effects don't matter unless you're going for a world record, and then they might.

[dredmorbius]

The one aspect which isn't equal at least amongst Olympic and other competitions is that a slower (or faster) pool will generate fewer (or more) records overall. One measure of the current games' bias would be the number of new Olympic and world records set as compared with other events --- prior or subsequent Olympics, and other world-level competitions within the current year, say. I expect the quants at sites such as 538 would be looking at this.

[alistairSH]

Are records generally evenly distributed over time? Or do we see massive spikes due to single generational talents?

[dredmorbius]

The more general tendency that I've seen and which has been noted in articles/studies I'm familiar with is generally technique and technology.

Two examples of technique I'm aware of are the Fosbury Flop (1968) in the high jump, in which the jumper goes backwards over the bar (previously jumpers had gone forwards and feet-first, by 1968 with a sissors step), and heads-down technique in Australian Crawl "freestyle" swimming. Both dramatically improved results.

The Fosbury Flop was enabled by the technological introduction of foam mats on the landing side of the high-jump. Without mats, landing on your back after clearing a 2m+ bar position was somewhat undesirable.

Heads-down stroke in freestyle was in conjunction with freshwater (rather than salt) in swimming pools. Swimming heads-down without goggles in a salt-water pool burns the eyes quite strongly. With freshwater, and acrylic plastic goggles (acrylic being invented in the Great Plastics Boom of the 1930s). I'm not entirely sure when plastic swim goggles became widespread, though it may not have been until the 1970s, and the Montreal Olympics (1976) were the first to permit goggles.

Track generally has also seen tremendous improvements in the track composition (loose cinders to rubberised surface). Swimming pools have hugely reduced wave action through wave-absorbing lane lines, deep gutters, inlet diffusers, and laser-guided construction ensuring accurate and consistent distance.

That's on top of vast improvements in training, other equipment, doping (which has a very long history), professionalisation of sport (including the Olympics), and other factors.

Talent is a component, but the overall phenomenon is highly multidimensional.

[lostlogin]

> Or do we see massive spikes due to single generational talents?

Various types of doping could cause this too. More positively, tech, diet and science changes could too in some sports too.

[rightbyte]

> Bummer that it makes the meet feel slow but at least it generally affects all the swimmers equally

Shouldn't the middle swimmer be worse off with "fast" pools? There would be less waves on the side lanes, compared to a "slow" pool where there are reflections.

[pdpi]

> at least it generally affects all the swimmers equally

> 2. The sides. Does the water spill over the sides into the gutters, or smash into a wall and bounce back, creating more chop.

My only experience with competitive swimming is playing some water polo some 25 years ago, but wouldn't that effect disproportionately affect the swimmers on the outermost lanes?

[davidmurdoch]

To a lesser effect, there's also the surface tension of the water, which can be adjusted with salt and borates.

[HPsquared]

Density and viscosity must also play a role, or are those managed via temperature control?

[davidmurdoch]

Seems very plausible. I haven't noticed a speed difference in my own pool with temperature changes, but that might just be because the temperature itself can be so distracting. But I do feel like a salty pool makes me faster (maybe from buoyancy), and borates makes the water feel smoother and less "sticky" (something about surface tension changes with borates, it even makes the surface look different).

[HPsquared]

Oh and of course the cooling effect. That's a factor for long distances especially if the water is too warm.

[ClassyJacket]

This is yet another reason on the huge list of reasons to keep the Olympics in Athens and just use the same facilities each time.

[adolph]

Why aren't swimming lanes stadium shaped like running tracks or speed skating? Floor mounted LED indicators could advise competitors of the relative distance ahead and behind of nearest adversaries.

[sschueller]

Shouldn't that be part of the standard "Olympic Pool" definition? Depth, water height on side and overflow etc. seem to be as important as the nittting of a football goal net.

[manojlds]

Why doesn't it affect more the people closer to the sides?

[mb7733]

It does. This is why the fastest qualifiers get to swim in the middle lanes.

[notatoad]

this is the reason that the leftmost and rightmost lanes of the pool aren't used for competition.

[jmalicki]

For point 2, wouldn't the reflections off the sidewalls create more issue with chop on the outer lanes than the middle?

[palijer]

The outer lanes are where the slower swimmers are placed already anyways, so if they were having more chop, it wouldn't likely impact a medal contender and cause a big upset... Not saying that outer lanes haven't come out on top in the last, but less likely.

[myworkinisgood]

All swimmers are affected equally so I don't see a problem.

[Yawrehto]

Off-topic but congratulations for qualifying for trials!

[croes]

So now that two swimming worlds records have fallen, we can't blame the pools anymore, can we?

[umanwizard]

Why does it matter how deep the pool is?

Edit: the article addresses this, so if anyone else is curious like I was, I suggest clicking.

[creshal]

Because it means waves bounce off the bottom faster (less distance travelled) and much more importantly, with far more energy (square cube law works against you). So the waters far more choppy far faster, since you have 50% less water volume to absorb all the energy.

[defrost]

If it's too shallow the swimmers arms hit the bottom ...

Slightly deeper and there's drag from the floor as their arms barely miss it. That effect persists until it doesn't .. now it's deep enough.

It needs to be deep enough that vortex's created by swimmers have disapated by the time they reach bottom and reflect back to the surface so as to not interfere with following swimmers or swimmers returning.

[sshine]

> If it's too shallow the swimmers arms hit the bottom

Is it’s deep enough, the gravitational mass of the water will form a black hole and squash the swimmer to death.

[defrost]

    Big whorls have little whorls
    Which feed on their velocity,
    And little whorls have lesser whorls
    And so on to viscosity.

~ Lewis Fry Richardson

    and then to an event horizon.

~ sshine

[expression1sh]

Well before that the hydrogen atoms would fuse into helium and release vast amounts of energy, killing all the swimmers, spectators, and many people in Paris.

[HPsquared]

Edge effects affecting the flow field around the swimmer. I suppose the floor might trap turbulence near the surface rather than dissipating into the depths.