On science in marathon swimming

In marathon swimming, there’s very little in the way of credible science – that is, methodologically rigorous, experimentally controlled, peer-reviewed science. It’s not hard to understand why: Open-water swimming, especially the marathon variety, is a tiny market compared to land-based endurance sports. Market size is related to the potential for making money, and the potential for making money is, in turn, related to funding and motivation for scientific research. Even in triathlon (an enormous, lucrative market), swimming is often seen merely as a warm-up to the bike and run, so there’s little effort to understand it.

As a result, marathon swimmers are left with approximately four strategies for acquiring knowledge about their sport – specifically, the physiological demands of long-distance swimming, and the nutrition required to fulfill those demands:

  1. Figuring out what is known, scientifically, about land-based endurance activities, and applying it to swimming.
  2. Figuring out what is known, scientifically, about pool swimming (in which races last anywhere between 20 seconds and 15 minutes), and applying it to marathon swimming (in which a race or solo event may last 10 or 15 hours).
  3. Word of mouth – finding out what works for other marathon swimmers. This is how most people discover Maxim – because that’s what they use in the English Channel.
  4. Individual trial-and-error. Penny Palfrey likes watered-down porridge and chocolate ice cream. Who knew?

Most successful marathon swimmers use each of these strategies at some point. The problem with the hybrid approach, however, is that it neglects one very important thing: actual, science-based knowledge about marathon swimming. As science has continually shown since at least Galileo, there’s a lot we don’t know – and much of what we think we know might actually be totally false.

A few rhetorical questions, off the top of my head:

  • How are nutritional needs affected by the environment in which the activity occurs? E.g., how is running a marathon in 60-degree air different from swimming a marathon in 60-degree water?
  • By corollary, are products designed for land-based endurance activities sub-optimal for water-based endurance activities?
  • Is digestion during an endurance event affected by physical orientation? E.g., swimming horizontally vs. running vertically?
  • How does electrolyte loss differ between running and swimming? Are supplemental electrolytes necessary while swimming in a saltwater (i.e., electrolyte-rich) environment?
  • How should fluid consumption be adjusted for cold-water swims vs. warm-water swims?

Any others?

The first in a three-part series. See Part 2 and Part 3. Also see this post by Donal Buckley on choline supplementation.

17 thoughts on “On science in marathon swimming”

    1. What would the experiments be like? I would volunteer as a guinea pig too. My husband’s a doctor–I’m sure he’d be willing to take some readings on me.

      1. In a way, most marathon swimmers do their own “mini-experiments” whenever they try new things. That’s what I mean by individual trial-and-error. To do real, you know, “science-y” experiments, though, you’d probably need the lab infrastructure of an exercise physiologist with a big research grant. And probably a nutritionist as co-investigator. I don’t happen to know any personally.

  1. Love this post. It’s been on my mind for a while, I mentioned it to Steve Munatones in a discussion.


    -Are maximum carb absorption rates increased in cold water? I don’t think anyone knows the real answer to this, but it seems to me the figures don’t add for an 18 hour cold water.
    -How best to improve marathon swim feeds, taking count of the drawbacks of the medium?
    -Few of us have found a way to get in the 4:1 carb/protein ratio, because of salt water ingestion. I myself can’t use Hi5 4;1 from more than 4 hours (tested it). Though some people have no problem with Hi5 (or equivalent).
    – Why aren’t we discussing specific additions like Choline or Vitamin E on long swims?

    I had this on my To Do list but you’ll do it better than me. Really looking forward to the next instalment.

    On this separate note, why don’t you enable WordPress to autoTweet when you write a new post? It’s in the Sharing settings on the dashboard. BTW, I owe your responses to your emails as soon as I get it done, I’m not ignoring you!

    1. Great questions Donal. What do you find promising about Choline & Vitamin E? I just set up auto-tweet, though I’m pretty sure it’s not in the core WP installation and requires & plugin (there are many).

      1. The Choline research seems to indicate it is useful in events lasting > 2 hours. It’s used for muscle control. Vitamin E seems indicated for asthma control, something prevalent amongst swimmers. I’ve written the choline one, I though I’d have it up this week, but the queue was full.

        I was moaning about lack of scientific studies (on cold swimmers especially) & Steve mentioned to me that the US military have done a lot of studies, Unfortunately, not widely available.

  2. When I was national coach in the 1980’s we did a research project at the flume in Colorado Springs. We had two groups of swimmers swim four hours rest two days then do it again. Randomly one group was given water the other was given gatorade. The latter group was able to maintain pace and speed for both tests. The water group had to stop. We feed every 15 minutes and took blood every 30 minutes. They were breathing and exhaling into a mask. Some swimmers did muscle biopsies. The swimmers felt the tests were very painful. The results were published by Marion Cassidy. USA swimming should have a copy or you could find Marion. The goal was to test water versus gatorade and recovery time. The biopsies showed a breakdown but I can’t remember the chemical. The 15 minutes seemed to help each group which is why the national team switched to 15 minutes in the 1980’s for feeding irregardless of salt or fresh water. We could feed in 6 seconds with a quick chug of 4 to 6 ounces.
    I hope this helps.

    1. Penny, I’m honored that you found my site. That’s great info on the Co. Springs study – I’ll have to check it out. I’d love to see further studies, comparing, e.g., gatorade vs. maltodextrin, and whether gatorade leads to gastric distress over longer periods (10-15 hrs instead of just 4), and especially in saltwater. Not sure how much will there is in USA Swimming at the moment for such research…

  3. The USA is not where you are going to find the answers. British Swimming and Russia Swimming are where the most research is being done. They are far ahead of anyone else from my perspective. In the USA, Dr. Peter Attia can probably best answer your questions. He will give a free one-hour introductory webinar on nutrition for marathon swimmers on November 14th.

  4. This is not on this topic, but I wonder if somebody can forward this to Penny Dean, since I don’t have an email address for her, obviously. I am a radio historian writing about early Los Angeles radio in the 1920s and ’30s.

    I have a .jpg image of a picture of George Young, winner of the Wrigley Catalina Ocean Marathon. The photo shows Young next to the microphone of Hollywood radio station KFWB (owned by Warner Brothers Pictures) at Grauman’s Egyptian Theater to accept his prize money for winning the Catalina Channel swim contest, on the night of January 18, 1927.

    Just in case Penny Dean would like me to send her a copy of this magazine photo from Radio Doings in January 1927, please forward this message to her or have her email me at


    Jim Hilliker
    Monterey, CA

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