Swimming pace training and prediction

[Fabien]

To provide some background before diving into details, I started learning freestyle in August 2023, mainly through SwimGym videos, in preparation for my first sprint triathlon in July 2023. In October 2024, I began following an Athletica training plan for my Ironman-distance race. Additionally, in September, I started training once a week with a masters class focused on technique.

Given this background, I now find some of the slower training paces quite unnatural—specifically, the very slow pace of 2:18/100m. I’m unsure if this is expected, especially when I see my swimming pace profile showing 2:43/100m.

From here, I’m not sure what to do next:

• Stick with it and adapt to the slower pace, as it might be expected for Ironman-distance training.
• Re-do the swimming test.
• Follow the swimming pace profile’s recommendation when selecting the last six weeks, which currently displays no data. It suggests completing at least three maximal efforts in the 3-minute and 15-minute ranges (e.g., three maximal efforts at 200m, 400m, and 800m), which is different than the swimming test.

Given my limited swimming experience, I’m mainly looking to understand what to expect and plan correctly for race day. While I feel confident about the running and cycling aspects, I’m much less certain about swimming.

[Prof]

Hi @Fabien ,
Thanks for this. Based on your historic data the critical speed looks appropriate in your settings. However to your point, its possible that the Zone 1 and 2 paces in the water medium might need adjustment in the future. From a practical standpoint you might want to:

1. Do a longer time trial that lasts at least 20 min. Note how your curve of actual movement speed falls after about 13 min. Try perhaps a 1500m TT. If this raises your critical speed then your Z1 and 2 should move up as well.
2. Trust feel in these zones. Recovery means recovery. Steady means steady. Use the paces to help guide you but let your brain override the mechanical limitations as needed. If you can move faster and more efficiently with the same feel then you’re doing something right.

My 2c

[Fabien]

Thanks for your reply, I’ll give a go to a 20min swim non stop and follow up by 1500m, see if it impact things and will report!

[Fabien]

So, I did a 1.5k session in 30 minutes and 27 seconds, which gives me a pace of 2:02 min/100m. From what I observed, this didn’t change anything on Athletica’s side. The Swimming Pace Profile still only displays data under the 2024 tab, showing a predicted pace of 2:43 min/100m.

So, I decided to run a new swimming test (the same one used when you first set up Athletica) with the following results:

50m time 39 seconds (T1) // was 40 
400m time 7:07 = 427 seconds (T2) 
CSS: (400-50) / (427-39) = 350 / 388 = 0.9 m/seconds 

Now, convert this to mins/100m 
100m/1.06m/s = 111s which equals 1:51 min/100m

So I updated my critical swimming from: 2:07 to 1:51

Zone before:

Zone after:

So the Zone 1, 2, 3a increased the pace where 3b, 4, 5, 6 decreased.

The Swimming Pace Profile is still with the previous data, so I would expect to be updated later one, same for the different swimming session planed

[Prof]

Thank you @Fabien … that’s great work. Cc @Andrea and can you also please share with Stef who I know will be chipping away with swim optimization in the near future.