One-Hour Workout: Fast 25s

It's time to stop avoiding your top-end swim speed!

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If left to their own devices, triathletes tend to shy away from honing their top-end swim speed, even though they’re more than happy to nail tough bike and run workouts. This swim workout is designed to end all of that—these fast 25s will get you working!

Begin with a relaxed 10 minutes of easy swimming, no hard efforts at all, just moving well through the water, focusing on good stroke mechanics, and switching on your brain for the session ahead. Gradually build your effort toward the end of the 10 minutes so you can feel your heart rate and breathing rate increase. There are two “prep sets” coming up that will ensure you’re ready to go ahead of the main set.

Mixing in some medley swimming is always a good way to keep things fun and different in the pool, so embrace your inner IM (individual medley) swimmer and hit these 12 x 25 with the best fly, backstroke, and breaststroke you can manage. To be clear, you swim the first 25 as fly, the second as backstroke, the third as breaststroke, and the fourth as free. Repeat this pattern three times to total 12, taking 10 seconds rest after each 25.

Next up: 8 x 50 free, increasing effort each 50, so the first one is about 60 percent effort, the second is 75 percent effort, the third is 80 percent effort, and the fourth is 85 percent effort. Repeat this pattern on the second block. Take 10 seconds rest after each 50. This set is designed to get you amped up for the fun to come.

And now the work begins: Get ready to put yourself in the hurt locker. Follow the pattern of 3 x 25 fast (and we mean FAST!) and then 1 x 25 easy. The difference in effort here needs to be polarized, that is, the fast needs to be close to maximal, 9-10/10 RPE, while the easy should be extremely easy, 3-4/10 RPE. It’s your chance to really dial back effort before going hard again. Repeat this pattern for a total of five blocks to hit 20 x 25. Take only 5 seconds rest after each hard 25, but 15 seconds after the easy ones. This workout is best done with swim buddies (of a similar speed), so you can really put yourselves to the test and push each other to true maximal efforts.

Swim easy for three minutes, using a pull buoy if you prefer, and then repeat the 20 x 25. You should be feeling taxed and tired; this is not an easy workout, but it will pay dividends when it comes to building your swim speed.

Fast 25s


10 minutes easy swim, building pace to 6/10 RPE

12 x 25 IM (individual medley) order, as 25 butterfly, 25 backstroke, 25 breaststroke, 25 freestyle – repeat x 3, 10 seconds rest after each 25

8 x 50 free, progress 1-4, 5-8, 10 seconds rest

Main Set

20 x 25 as 5 blocks of 4 x 25, as 3 fast, 1 easy

3 minutes easy swim

20 x 25 as 5 blocks of 4 x 25, as 3 fast, 1 easy


5 minutes easy swim/pull

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