In just over three years, Summer McIntosh has gone from a finals hopeful in the 200 fly to the most dominant swimmer in history by every metric bar one.
That metric is the World Record, still held by Liu Zige with her swim of 2:01.81 from the 2009 Chinese National Games. At the time that was a world best by 1.60 seconds, and McIntosh is still the only swimmer to come any closer than that.
After a phenomenal year in which she has reset the record books in the 200 IM, 400 IM and 400 free, she ends 2024-25 just 0.18 seconds away from the oldest world record on the women’s side – the last of the supersuited era.
If you watched the race, you may have noticed a tiny amount of frustration from the Canadian after she finished. This race is a favorite of hers, the one her mom used to swim and the world record in which has been a longstanding target. Even with narrowly missing the record, the 200 fly was actually the one event where she dropped time from Canadian Trials to Worlds.
The Changing Seasons Of Summer
We can take a look at McIntosh’s swims over the years in two ways: by the raw splits and by the percentage of the total race spent on each 50. We’ve only included finals swims at Canadian Trials and at Worlds/the Olympics, and split these out separately to look at.
Canadian Trials
Percentages
Look at her finals swims at Canadian Trials, and there’s something surprising. From 2022-24, she split the race almost identically percentage-wise, just faster overall each subsequent year.
This year, she was much faster, and more consistent, in the second half of the race. She spent 47.9% of the race on the first 100 and 52.1% on the second 100, compared to 47.1% and 52.9% in each of the preceding three years.
Splits
The consistency can be seen when looking at the raw splits. She was out almost identically to the last two years, just a hundredth faster at the 100 than in 2024, but pretty much held pace on the second half. In all three years previously she had added at least a second from the second to third 50s – this year it was just 0.31 seconds.
Worlds/Olympics
Percentages
In the summer, the story is a little different. This year was not out of line with any previous year, falling bang in the middle of where the previous years have been. That is a good sign, a swimmer calibrating how to best swim the race, and she has struck a balance between early and closing speed. She was slightly faster on the first 100 this year compared to at Trials, spending 47.881% on the first 100 compared to 47.914%.
Splits
Her splits this year were her fastest ever on all four 50s, and she was ever so slightly faster on each length that at this year’s Trials. The second 100 stands out again: even compared to last year, already far faster than 2022 and 2023 she was half a second faster, and more consistent across the final three 50s.
What Will It Take To Break The WR?
We’ve calculated the average of McIntosh’s splits as a percentage of the total race, weighing her more recent performances more heavily. Then, we have applied those numbers to some hypothetical times – including the World Record of 2:01.81.
The values either side are a two-tailed 95% confidence interval (2.5% – 97.5%)- that is, if she were to go this time, we’d expect the splits to be within this range 95% of the time (19 out of 20 swims).
Weighted percentages per split
| Weighted average | Upper Bound | Lower Bound | |
| 1st 50 | 22.26% | 22.32% (+0.6%) | 22.19% (-0.07%) |
| 2nd 50 | 25.42% | 25.52% (+0.10%) | 25.32% (-0.10%) |
| 3rd 50 | 25.99% | 26.06% (+0.07%) | 25.92% (-0.07%) |
| 4th 50 | 26.34% | 26.42% (+0.08%) | 26.25% (-0.09%) |
And here are what the splits for some hypothetical times would look like
| 2:01.81 | 2:01.50 | 2:01.00 | 2:00.50 | 1:59.99 | |
| 1st 50 | 27.11 | 27.04 | 26.93 | 26.82 | 26.71 |
| 2nd 50 | 30.96 (58.07) | 30.88 (57.92) | 30.76 (57.69) | 30.63 (57.45) | 30.50 (57.21) |
| 3rd 50 | 31.65 (1:29.72) | 31.57 (1:29.49) | 31.44 (1:29.13) | 31.31 (1:28.76) | 31.18 (1:28.39) |
| 4th 50 | 32.09 (2:01.81) | 32.01 (2:01.50) | 31.87 (2:01.00) | 31.74 (2:00.50) | 31.60 (1:59.99) |
Those first 100 meters get very fast, very quickly, but McIntosh was out in 58.41 this year. There is likely some untapped potential in her 100 fly, with a 57.35 split on Canada’s medley relay not representative of what she can truly do.
This method may undervalue her closing speed, which looks incredible this season compared to the previous three. However, she still has some way to go to match the final 50 of the world record.
The percentage breakdown looks near-identical.
Zige closed in 31.61, after a 32.12 third 50. Negative splitting the final 100 is an incredible feat, one that McIntosh, while being close in 2022 and 2023, has not managed yet.
The third 50 is McIntosh’s big advantage over Zige. If she can drop either the second of fourth 50 even slightly at Pan Pacs next summer, this record may not see its 17th birthday.
I predict Summer will break this WR in the next year.
If her time in Austin doesn’t work out as planned in any way, she has the option of going back to Fred V. in Antibes.
It’s not the same Summer every year. She is getting older and stronger. You can see it in her shoulders. That added strength is the reason she can hold on better over the final 100.
I thought the record attempt was already compromised within the first 25 meters. She was essentially even with the field. From that point I was surprised she came as close as she did.
I’ve long had two central themes on this swimming site and others — women’s distance swimming is an abomination and throughout the sport early pace is too cautious. I haven’t detected anything other than a need to double down. Summer needs to trust herself to get well under that number then… Read more »
Clearly the last 50 is where she can make up the difference. Everyone goes out too fast. Go out in 28 hold 30’s. Simple. Everyone doesn’t need to die the last 50. Seen it done. Did it myself 40 years ago. Went out slower came back much faster.
Can you stop it with the women’s distance abomination talk? 8:07 was 3rd at WCs – literally what do you wany
Maybe maybe just maybe she needs just to go .19 faster In any lap. That should do it!
I just want her to not be a pouty mcpouty pants
your wish has been fullfilled about half a week ago (minutes after her 3rd place) so it would maybe make sense to stop pouting about it yourself?
Your funny
You never swear?
Not on live tv
I think her next tapered swim is where she breaks the wr. The question is, will she be sub 2 by LA 2028?
She doesn’t have to fully be tapered. Just don’t swim any other event before 200 fly, just like what Marchand did in Singapore.
My thoughts: a little faster.
It’s wild that the splits for 1:59.99 don’t seem TOO outlandish for someone as talented as she is
you don’t need a whole article for this.. she needs to go .05 faster each 50
https://swimswam.com/sprint-guru-brett-hawke-shares-opinions-on-how-to-break-world-records/
that IG post is particularly funny when you consider how much authority BH claimed to have when ranting about pan’s WR. in the years prior, he bragged about his role in cielo’s WRs, but the best WR advice he could give in that period was merely a list of splits that anyone could hypothesise. by his own logic, the only action needed to explain pan’s 46.40 was finding the sum of 22.28 and 24.12. humanly possible
on mcintosh, the analysis here can be inferred from the split comparison in the first 2:01.99 article