Triathlon Training Explained | What Is Critical Swim Speed?

In association with TrainingPeaks - gtn.io/Training...
On this week's Triathlon Training Explained show we're looking at threshold swim pace and calculating your critical swim speed. Once your CSS is computed, this can be used to accurately pace your swim leg.
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On this episode of TTE, we're looking into swim pacing for triathlon and effectively using your critical swim speed. We explain how to work out your CSS and then show you how to put this to use. Mark also shares his top threshold swimming sessions the T.T.T.T.T!
Some triathletes may have a very quick short swim speed but a much slower longer one, other athletes could be the opposite. Your CSS figure will give a more accurate representation of your threshold pace and will enable you to work out your training zones.
Have you worked out your critical swim speed? If so, let us know what it is! 👇
For more information on this topic, check out the following links from training peaks:
- Early Season Workouts for Improving Race Pace - gtn.io/TPEarlyS...
- How to Best Calculate Swim Zones in TrainingPeaks - gtn.io/TPSwimZone
- Reasons You're Not Swimming Any Faster - gtn.io/TPNotSwi...
If you'd like to contribute captions and video info in your language, here's the link 👍 gtn.io/az
Watch more on GTN...
📹 TTE Bike Pacing - gtn.io/TTEBikeP...
📹 Lucy Charles 5 Swim Tips gtn.io/SwimFast...
Music: Epidemic Sound
4 - Oldschool Leavers
Photos: © Triathlon / Getty Images
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[@barryfield9300]

Great photography in this video! A 4:36/400M, damn that's fast!

[@gethynfriz]

Impressive swimming Mark, especially as you seem to be wearing a White t-shirt and shorts 😉

[@ruilucena3017]

little math correction, your CSS its not a 1 minute and 12 seconds, its a 1.12 minutes which equates to 1 minute and 7 seconds. other than that, great video. keep up the good work.

[@nicolajc]

So after 400meters that is 4minutes and 28seconds - but that is faster than his 400meter timetrail qualifying the CSS ??

[@marsert123]

@@nicolajc yes, because the css pace contains the 200m time aswell. building the average leads to this effect

[@kareemdayes6703]

Thank you cos I've been trying to reverse engineer this and I can't see how he's got 1min 12 secs? I keep getting 67secs too......I'm a bit baffled

[@kareemdayes6703]

Ok so i figured out what's wrong here. His Minutes : Secs time don't match with his seconds conversion. If we go with the first Minutes : Secs time then 1:12 is the CSS, if we go with the seconds he quotes second then 1:07 is his CSS. He's used two different sets of time at two points in the video. But the point is I've figured out how to convert my m/s into s/100m. Confusion solved. This is a really useful exercise! Thank you. Will be doing this bi-monthly from now on I think to track my progress. Really useful tool and great explanation.

[@kareemdayes6703]

If we go by the time in seconds (2nd time he quotes) then he swam the 400m in 4:21 and the 200m in 2:07 ;)

[@danielbyrne9349]

I've been disappointed with GTN content recently, but this was really useful and hopefully by implementing it I can finally see my swim times go down. I'd love to see a video about using a Tempo Trainer to help pace in training.

[@alanjackman5729]

Another good test we did in college was a T-30 but done differently you would do 200 threshold (going off heart rate) with 30 seconds rest doing that for 30 minutes then you average out your times and boom thats your threshold pace too. It is a 30 minute swim...but I felt it got a good accurate reading.

[@markthrelfall3577]

Alan Jackman you’re very right. A T-30 is another good option. I’ve not heard of it broken before, but that’s maybe one to explore

[@stug45]

Great explanation....for my athletes it just needs the tempo trainer and how it helps to pace! For me as an ex swimmer, these sets are the ones that get me from sitting on poolside with a fast 100m but terrible pacing, to the fastest swim of the day in 6 weeks. I'm now back training full time and I'm getting myself ready for some important races!

[@markthrelfall3577]

stug45 I couldn’t agree more. You get so much bang for you buck with these sessions. That’s exciting, all the best. Let us know how you get on

[@stug45]

Mark Threlfall I forgot to say great times btw..... would be frustrating to be slightly ahead of you, knowing that you will fly past on the bike and you run like I'm standing still!

[@MattDion]

I prefer Tito's Totally Tubular Time Trial Taco Training as it typically involves mixed drinks, but this TTTTT sounds good too I guess.

[@kevinlavery6194]

Today I learned that division is complicated math 😂😂 Joking aside, thanks for the info. As a new swimmer I had never heard of CSS. I'll have to figure mine out!

[@sebastiangrievous1]

More swimming workout videos please!

[@Kariwable]

Learned so much. Love GTN.

[@hhhhhhh817]

Great Video GTN. More content like that please!!!

[@ironmantooltime]

Athlete B in da house! ☹️😂

[@yavormihaylov8711]

Hi GTN great vid. How do u convert mins in sec? 4:36 are 276 sec, right? Or is there another convert in between?

[@johnnguyen270]

Any chance you can do a video on Improving Your Max Swim Speed ?

[@Paul_Paulson]

If I am taking a lot longer to swim 200m (about four minutes), would I be better taking a test over a shorter distance, such as 200 + 100, or 150 + 300? Could you also give some guidance on determine my pace for aerobic swimming? I often set off too fast (for my level) and then die once I get up to 300 or 400m.

[@yousufasmal2429]

Whats your opinion on doing other strokes (like breast stroke or back stroke) during your swim training ? Since we (triathletes) dont use those strokes in races, so does it benefit us ?

[@abhishekavhad8077]

Great question !

[@maikholzhey6167]

it is wasted time...

[@juliaburmeister2038]

I'm a competitive swimmer focusing on the middle and longer distances and also butterfly but find it useful to practice the other strokes as well. E.g. Backstroke and Butterfly use simmilar muscle groups and therefore train those as well. It also helps with keeping that range of motion in the joints since it is never good to train something only in one way. Variety in training is as important as consistency but keep in mind that you need to have at least decent technique for it to work. But it defenitely helps with keeping these boring swim sessions a bit more exciting

[@alanjackman5729]

I second this as well. I was a butterflier in college so I love me some butterfly but I do find that when I get aerobically fit in butterfly it helps my freestyle too.

[@maikholzhey6167]

Alan Jackman You get aerobically fit in butterfly? Please post your actual heart rate after 1500m butterfly^^ - This is what I think is exactly the problem with swim training, you're not training purely aerobically with a decently low heart rate to build endurance and you're also not doing speed work or strength training either. You sit a very difficult point in your zones. For me it is all about technique and efficiency to get less fatigued out of the water and fresh on the bike. Triathlons are not decided in swimming...

[@yuriadanperez9419]

Should I give it my all in both 400 and 200 or should I pace myself?

[@martin.B777]

Thanks for sharing! Mark, what is your weekly swimming volume?

[@0Spagetty0]

This one was really helpful

[@leohewett3041]

Marks tan lines in his speedos go very well 🏊‍♂️🚴‍♂️🏃‍♂️

[@akdrn3624]

During recent races I was able to sustain a 1:43/1:45 pace for around 2000m (wetsuit open water at sea), while in the pool I wouldn't be able to use this pace for a 10x100 with short rest. I am more around 1:55. Earlier in the season I struggled to swim 2:10 in open water with a wetsuit and my pool times were pretty similar to the actual ones 🤔

[@glenngundermann2433]

The calculations seem to be screwy. You swam 4:36 and 2:12 for the 400m and 200m respectively. This works out to 276 and 132 seconds. The calcs used 261.6 and 127.2 seconds. Strange. You calculated 1.49 m / sec, which works out as CSS = 1.12 min / 100m or 1:07 / 100m. Your final verbal answer though was CSS = 1:12 / 100m, which is the correct answer had you used the correct number of seconds. 200 ÷ 144 = 1.39 m / sec, which arrives at CSS = 1:12 / 100m.

[@dermotmarronify]

He over-complicated it. Easiest way to do it is subtract the 200 time from the 400 time and divide by 2: (4.36 - 2:.2)/2 = 2.24/2 = 1.12

[@velo1337]

where did alistar brownlee explain this? i wanna watch the whole video of him

[@henrymasters8319]

The Brownlees came out with a book: Swim, Bike, Run

[@alexiisenbrandt2161]

Holy **** mark have some serious skills in swiming

[@ARodenas]

I just didn't get this: one has to swim at the absolute max (sustainable) pace possible for those 400m, and 200m ?

[@oneaweekmulti-sportclub8230]

Yes you do

[@pierce9128]

#gtn Did a CSS test today and both 400 & 200 times resulted in the same pace of 1:58 and the online calculator said this isn't possible. What do i do now

[@aaronroeck1]

How do you use css for those sets? Swim all of those interval examples at css? Also when pacing a race how do you know what percentage of css to go at? Obviously I know shorter than 1500 you can go >css but on longer ones, how much less that css should you go?

[@markthrelfall3577]

Aaron Roeck for those sets explained in the video, you should swim at your CSS pace. Just take the relevant recovery. In terms of longer swims over 1500m it depends really. Half Ironman/middle distance - there shouldn’t be much drop off. Very minute. It’s only an extra 400m. I’ve just done a little math on my own times to gauge any difference for an Ironman swim - I reckon it’s around 2-3s/100 slower. But could differ a little depending on ability. I will investigate this further for you

[@likemarksee]

Mark Threlfall, how does your CSS test result compare to your 1500m TT time? Which test result should be used for CSS swim sets. Is it possible to swim CSS sets at a pace which is too hard?

[@chocolatefairy1822]

Although an explanation of CSS is really well done, you then give examples of doing swims with x amount of rest (at 10.45) which completely voids the whole point of establishing the CSS pace. You could do you 20x100 with 5 sec rest, 10 secs, 44 seconds....etc. You are supposed to set the rest based on the CSS test. Please can you comment on this?

[@allisonscanlan4144]

Yes especially for intervals swimming should be based on CSS or swimming just on a specific time. More relaxed swims could just be with rest

[@stephaniexyz3781]

Very helpful video, thank you! I am type A (sprinter). I always struggle in distances longer than 750m. I have the same problem when I am running, and can't hold my 5k pace longer. So my question is, if there is a similar rule for training longer runs?

[@markthrelfall3577]

Stephanie xyz absolutely. I would recommend including one longer and easier run per week. As well as a specific threshold run. A similar format to the swim. We have a video on it if you search for Threshold Run in our videos

[@stephaniexyz3781]

Mark Threlfall Thanks!!!

[@akdrn3624]

Mark what pace were you swimming your 20x100? 1'12"? Short rest like 10"?

[@markthrelfall3577]

Alessandro de rinaldis my CSS pace used to be about 1:07/1:08, so I would have 12 second recovery. If I swam short course, I would often go off 1:15 turnaround, and come in on more like 1:06

[@TheGeotube23]

Define: Turnaround - How much time it is expected to complete a set

[@NeouItier]

Hi, can you explain in detail how to use CSS please? ;)

[@jwv5330]

How do you move from a profile like athlete B to athlete C? I seem to not be able to gain any speed over duration and all my shorter intervals seem to be a “race pace,” but I’m having a hard time increasing my threshold.

[@maikholzhey6167]

Really nice swimming!

[@Wilsonwill89]

Couple of questions... does it matter if done in a 25m or 50m pool? One problem I've found with Training Peaks with swimming is I've done my CSS test in the pool and TSS scores are appropriate but then when I do an open water session where I'm much faster my scores (TSS, ATL, CTL) are way higher, what can I do about this?

[@markthrelfall3577]

Will Wilson it doesn’t really matter. Times tend to be faster in 25m, particularly if you do tumble turns. I’d try and do it in the distance pool you will be doing the sets in regularly. For me, I would normally swim 50m. If I ever swam a CSS set in 25m, then I would just take roughly 1-2 seconds off per 100m. With regards to scores in TP, that isn’t something I’ve ever thought about, but you’re right. If you’re wearing a wetsuit, you’re going to swim faster. I guess you can just manually tweak the results. I’ll have a look into this - great question

[@Wilsonwill89]

Mark Threlfall the tumble turn is really something I need to work on. Thanks for the swift reply!

[@unjovenfinanciero]

4:36 on a 50 mts pool??? daaaammnnnn

[@kareemdayes6703]

Ok having played with this equation I've come to the conclusion it is flawed.........by swimming a slow 200m the CSS dramatically falls. I can't see how in any scenario swimming a slower 200m means I'm improving? Am i missing something?

[@diogoalmeida8211]

So, most AG triathletes that don't come from a swim background swim at above 2'/100m. They can manage a top speed of 1:50 on a 100m. Probably a 1:40/100 on 25's (numbers just average and for arguments sake). So, mostly Athlete B. I think they should work on getting to the top speed from 1:50 to 1:40/45 first, on the 100, ahead of thinking of working their Threshold pace from 2' to 1:55. I really believe they need to work on the top speed first (short, hard efforts with lots of rest), then threshold, then again the top speed, and so on. You always need a little "room to work with" between top and endurance speeds... Unless you are at the top of your game like the Brownlees or the guys from the 10k swim marathons. Not too much, or you'll end up being athlete A... but a little. Find the balance. Having said that, Threshold sessions have been my main tool for the past 20 years. Absolutely love them. I specially love 1x800 @ 12' (aim 11:35) + 2x400 @ 6' (aim 5:45) + 4x200 @ 3' (aim 2:45) + 8x100 @ 1:30 (aim 1:22/24)... so that'll take you 48' of grinding no matter how fast you swim...

[@JakobThusgaard]

Hey Diego, I'm admittedly late to the party here. Just wondering: what's the point of working top speed if one can't maintain it? What if that top speeds wears off too soon and the threshold speed ends up being faster over the course of the full distance?

[@donflorione2285]

I guess the calculation is a little bit wrong. 1,49 m/sec is a time of 67sec/100m. It is correct for the actual times he swam, but he hasn't used them in his calculation. 4:36 min = 276 sec not 261 etc. 200/(276 - 132) = 1.39 m/s = 1.12 /100m

[@taylore7102]

lol

[@christopherfry7456]

DonFlorione, forgive my lack on mathematic skills they are not good and I get confused easily but how do you convert 1.39m/s into your CSS pace of 1.12/100m?

[@donflorione2285]

Kn Office 1.12 means 72 sec. (1/1.39)*100=71,942 sec ~ 1:12 min

[@christopherfry7456]

Thank you.

[@jonathanhacker6913]

Really impressed with your swimming Mark. However I couldn't help but notice your straight arm recovery stroke. Coming from swimming, I was taught all my life to swim a high ellbow - low hand recovery, yet in triathlon a lot of people seem to be swimming a straight arm recovery. Can you enlighten me on why this stroke is commonly used in triathlon?

[@markthrelfall3577]

Jonathan Hacker I need to do a video on this. It’s not something I taught myself, more it just happened over time. I used to have a lovely pool stroke. The straighter recovery is handy for getting in close to other swimmers to draft. Also, for making sure hands clear any waves or chop. I’ve also found that straighter arms helps a little for arm rate

[@whittenmethod]

Gary Hall has an amazing book on details of stroke physics. The fast straight arm recovery increases of force the arm enters the water with and provides a coupling motion that increases the power of the pulling arm because it causes the shoulders to rotate more quickly.

[@frankeeeej]

interesting vid also Goddamn those are some impressive times Mark

[@magnusalexander2617]

Nice video!

[@gtn]

Thanks!

[@joesaunders4194]

Hi guys can you do a video on paratriathlon as I would love to do a triathlon but I can’t run or ride a normal bike I am 13 so would I be to young.

[@markthrelfall3577]

Joe Saunders hi Joe! We would love to help you. We have some good ideas in the pipeline, so keep an eye out. If there’s anything specifically you want us to cover, or you’d like to know, please shout

[@joesaunders4194]

Mark Threlfall hi Mark these are the main things how would I do the run as I can’t run due to my disability and the bike as I can’t ride a normal bike . I also can’t walk without my splints that I wear so from the swim to T1 would be tricky how would I do that? If you don’t know what splints are just google AFO’s. That would be helpful. From Joe

[@joesaunders4194]

Mark Threlfall Hi Mark I was thinking about a wetsuit mainly because I wouldn’t be able to use a full wetsuit as my disability allows very little flex in my feet which means I have very little calf muscle. And from the swim into t1 would be hard as I can’t walk barefoot or without my splints because I am very unstable. Could you include this in the paratriathlon video please.

[@jackrigal9085]

How does the CSS link to the beepers.

[@Goerkiwuns]

Hey Marc, is it important which pool length i am using to do the 400-200 test ? I mean it's obvious that you swim faster in a 25m pool

[@KookinHaole]

Just mutilple

[@kofio7581]

So I just did a CSS Threshold session taken from the swimsmooth book. My CSS is 2:10 but I managed to average a 2:05 for the whole session. Does that mean my CSS is not actually 2.10?

[@kelyip4163]

Makes sense since you get many more breaks during the session

[@prabo123]

i am very slow in swimming, there is no swimming pool here..... i do 2 km the hour open water very slow......

[@mustaphab.1190]

prabo123 respect for your dedication

[@joeyc8546]

What about being an ok swimmer but having terrible turns affecting your pace for all the distances? I dont tumble turn so i am slow and dont push off particularly aggressively. Is there a way other than open water swimming that could account for it?

[@markthrelfall3577]

Joey C yeah, that’s an interesting one. But I think that would be shown by a slightly slower 400 to 200 relatively, due to there being more turns. I imagine it would come out with a CSS score in the right ball park that would project well to the longer distances. Give it a go, and let me know what you think

[@joeyc8546]

Mark Threlfall i get what you mean now. So the difference between the two distances almost takes account of the turns, so as long as they are consistent then it cancels them out, and the curve will be correct for drop off for the different distances. Thank you for replying! The video was excellent too, good to see the test in action and the results explained.

[@ponderingfox]

A good topic would be warmups and cooldowns.

[@LaMartiLoca]

What swim watch did you recomend?

[@markthrelfall3577]

Fernando Miralles Delgado I’m using the Polar V800. It auto laps and stops in the pool. It’s a great option

[@Bubblymonkey833]

Hi Mark what watch are you wearing when your swimming

[@jarodkylevanblerk5968]

Polar v800

[@JasonFonger]

How often to do these CSS sessions for a pro or high level age group athlete?

[@markthrelfall3577]

Jason Fonger we would do one per week. Never more than once, although some sessions may include short stints as well. But if you only do a couple of swims per week, I would try to do one at least every other week

[@JasonFonger]

Thanks for the response, Mark. I currently swim 3 times a week but my swim is by far my weakest link so I'll be upping it to 4. Maybe one CSS, one endurance, one high end/sprint, and one recovery/technique. Does that sound reasonable?

[@kajet666]

400 metres in 4:21.6... not bad Threlfall, not bad.

[@toddholmes1719]

How do I connect CCS to the training sets? Should I always be swimming at my CCS, and only the recovery time increases with distance?

[@markthrelfall3577]

Todd Holmes hi Todd. I normally recommend doing a CSS/Threshold swim once per week if you can. If you only swim a couple of times a week, then aim for at least once every other week. The idea is that as you progress, you can sustain the pace more easily over longer reps, so you just build that up with time. But it is a little more taxing, so we tend to allow a touch more recovery for the longer reps

[@tandersson]

So athlete C is just a faster athlete B?

[@scotthumphreys4157]

So, as athlete A I just need to reduce my max speed a little and I'll be a threshold superstar? Thanks, got it!

[@likemarksee]

Wow 1:12/100m. IMO the CSS test is flawed. Using the calculation, your CSS pace is the pace you maintained for the second 200m of the 400m. The flaw is, most people can’t maintain that for a 1500m, it’s not even close. So using CSS calc. pace, you’ll end up swimming anaerobic for the first few reps. and you won’t be able to maintain that pace for the subsequent reps. However, you’ll find threshold pace by the end of 20* 100m.

[@markthrelfall3577]

Mark w I see what you’re saying, but the way the calculation works projects that time whilst factoring in the pace drop. It really has worked for myself and many athletes I know for calculating threshold pace. I hear your concerns though

[@timehlers841]

Love how Mark converts his times into seconds wrongly, then complicates things, does not explain how he converts m/sec into CSS, but the result is correct. "I enjoyed doing the maths here" 🤣🤣🤣

[@andresarango7653]

Translate to Spanish please

[@mustaphab.1190]

Athlete Bs here 😂🐢🐢

[@markthrelfall3577]

Mustafa Bircan a Diesel engine? 😊

[@mustaphab.1190]

Mark Threlfall not exactly, diesel engines are torque power houses. 1,2 ecoboost at my best maybe? 😁💪🚗🚵🏊🏃

[@VaeVictisVII]

Your swimming makes me depressed, maybe just fake your times for moral sake? :)

[@markthrelfall3577]

Robin V 😛 I lived and breathed swimming from a very young age. It’s all relative, so just do the best you can. Let me know how you do

[@Panda74gofaster]

Have you win many swims or Tri’$?