SIMS Swimming Pool (Photo credit: Wikipedia)
I’ve written about this before.
I went to check my old calculation today at the pool with my trusty old Polar s720i – which, like many old Polars, work in the pool.
I had a few issues with the unit not picking up the HR track all the time but largely it was OK.
5 TRIMPs per 100m
To cut a long story short I said before that 5 TRIMPs per 100m was about right. That was ages ago. Having retried it today I get the same result. A good efficient swimmer not doing a maximal effort might be 1 TRIMP per 25m length. Then again I set my zones conservatively. So 5 TRIMPs per 100m seems about right.
<Edit> It’s April now and I still have this nagging doubt that 5 is too high. So totally arbitrarily I now use 4. The reason being that I came up with a figure of, let’s say, 80 TRIMPs for whatever the swim length time was. It (80) just seemed higher than an equivalently hard 80-TRIMP run session over a similar period. ie an 80 TRIMP run felt much harder.
Last Updated on 11 April 2026 by the5krunner
My favourite kit and nutrition
- Maurten — the race nutrition trusted by elite athletes. Gels and drink mix engineered to be easy on the stomach.
- Garmin 90-degree charging adapter — the small adapter that keeps your charging cable tidy at the stem. Essential for race day.
- Garmin charging puck — the fastest and most reliable way to top up your Garmin before a session.
- Ravemen FR300 — front light that mounts directly under your Garmin or Wahoo head unit. Keeps your bars clean and your beam pointed where it matters.
- Garmin Varia RTL515 — radar rear light that alerts you to vehicles approaching from behind. Pairs with your Edge or Garmin watch.
- Stryd — the footpod that brings running power to your Garmin. The single most useful running upgrade I have made.
- Favero Assioma Pro RS2 — the power meter pedals most serious cyclists end up choosing. Accurate, easy to move between bikes.
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tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors. ID
