Search
  • williamtrubridge

The Underwater Marathon

A lazy Freediver

I’m not an endurance athlete. I’ve never run more than 10km or surface-swum more than 4km. As a teenager I cycled a couple of 100km+ races, but finished slower than most of my friends. And since becoming a competitive freediver I actually eschewed most forms of cardio, since freediving requires anaerobic fitness more than aerobic. So when I’m training in the pool, everything is on breath hold: I build fitness by swimming 2-3km per session, but as series of underwater laps.

This kind of training spawned the idea of ‘endurance apnea’. Could we cross a major channel like the Cook Strait only by moving underwater, and coming to the surface to breathe like a dolphin? After proving that we could in 2019 I started to wonder how far could the human body travel underwater in 24 hours with no propulsive assistance? I did a couple of trials of 2 and 4 hours swimming, and based on how those felt I devised a ‘best case plan’ that would get me as far as 50km.


There are so many things to manage in an endurance attempt: fatigue, cold, cramping, hydration & nutrition, ligament and joint inflammation are only part of the list. I expected that at least one of these would catch me out, so when I finally had a chance to attempt the record, I announced the goal as an underwater marathon: 42.2km.

Pushing off to start the swim - photo by Andre Musgrove @andremusgrove

Mental Immunity

I would have never been able to get through 24 hours if I was swimming for myself. When I devised the idea, I had decided to dedicate the swim to mental health, and also to promote a system I’ve created which I believe greatly helps in managing and even moving past stress, anxiety, depression and many of the other pressures we’re faced with in the 21st century.

The statistics clearly show we’re experiencing a mental health crisis, that has been catalysed by the Covid pandemic, even though it was gathering pace long before that. Numbers for anxiety disorders are 10 times what they were even 20 years ago, and completely incomparable with 50 years ago.

The techniques of the Mental Immune System (to be released November 24) are those I have devised to overcome similar pressures in freediving, where we have to be able to respond to stress and anxiety with equanimity and calm. Having seen the techniques at work in myself and the others I’ve taught them to, I know how powerfully they can help with similar pressures of day to day life. Most importantly they are a tool that programs the subconscious, so that we can outsource stress-control to that part of our mind that is so much more powerful and consistent.

November 5, 2022, 10:31am

I’d decided to do the swim in Nassau, Bahamas for various reasons including that there are less evening insects than on Long Island (in the heavy breathing during recoveries it’s easy to suck a mosquito deep into the lungs, prompting a fit of coughing for 10-20 minutes). The Windsor School generously donated their pool for the swim, and not knowing what she was getting herself into, Marine Sciences teacher Rachel Miller volunteered to help coordinate the team of required witnesses.

Windsor School students Adam and Skye observing underwater during the swim


So on Saturday morning, under a climbing Bahamas sun, I clipped on my neck weight, slid my noseclip and goggles into place, took a breath and pushed off for the first underwater lap. I’d decided to start the intervals at 35 seconds, meaning I would have 35 seconds to swim the lap and recover before starting the next one. At an easy relaxed pace, and with 3 stroke cycles (a push/kick plus armstroke is one cycle), I could complete a lap in just under 25 seconds, leaving me 10 seconds to recover. I had a CrossFit style countdown timer installed on the side of the pool, with a bright LED display, and a loud beep that counted me down in the last 3 seconds before the start of each lap.

Photos by Adam & Skye from the Marine Sciences class at Windsor School


To begin with, this pace was comfortable and relaxed, and I focussed on making small adjustments to my technique to ensure that I wasn’t overloading any particular muscle group. The water was 29ºC (84ºF), and I feared overheating in the strong sun, but luckily there were frequent cloud patches. After just over an hour, I took my first 3-minute break, and ate the first of the 24 bananas and energy bars I’d bought (I had no idea how many calories I would need). For fluids, in between laps I’d been sipping on a mixture of cranberry juice and water, mixed with electrolytes and amino acids. 3 minutes is barely enough time to pull off noseclip and goggles, chew down some food, quickly stretch any complaining muscle, and put equipment back on again before taking off again.


2:31pm (4 hrs in the water), 9,675m swum.

In the plan, I had scheduled dropping to an interval of 37 seconds after 4 hours, and when it came time I was definitely ready for this to happen. I was still closing a lap in 3 strokes, but on some I would have to glide a little longer at the end before touching the wall. I’d been looking forward to the extra 2 seconds of rest, but when the reward finally came there didn’t seem to be a huge difference!

Also at this time I was starting to feel the first niggles and pains in my body that indicated which zones might become a concern later on. It’s funny how the tiniest muscles can be the ones that create the biggest problem. In particular, the top surface of my right hand was becoming sore and swollen, evidently from dorsiflexing the fingers of that hand upwards in the glide position. I swapped my hand position so the left was underneath, and made similar corrections to try and help with pains I was starting to feel in the elbow, knee and ankle joints.

photo by Andre Musgrove @andremusgrove


My rhythm continued with bouts of 40-50 minutes swimming, and 3-4 minute breaks between. The banana skins piled up, and the sun slowly lowered in the sky. Smatterings of rain broke the monotony, and the support group and spectators helped to encourage me with progress reports in my breaks.

At 6:30, as the sun was setting, I took my first longer break of 20 minutes, and was able to get out of the pool and lie down for the first time, even if just for a few minutes. Arianne gave me a quick back massage, which made me realise how much I had used those muscles already, and then it was time to continue on.

As darkness took over and the pool lights came on, the novelty of swimming at night fuelled me for the first few hours (I don’t think I could have done this indoors with the same artificial light for 24 hours!). But I was wary of the fact that I wasn’t even at the halfway point, and could already feel the fatigue setting in. Laps were taking at least 3½ strokes now, sometimes 4, and my breathing was noticeably heavier in recoveries.


photo by Michael Frefields @Free_Fields


In order to try and pass time more quickly, and to give something to do to my mind, I would schedule tiny tasks to the end of each 2 laps, when I returned to the side of the pool where the timer was. “This next one I’ll adjust my swim cap to make it tighter and smoother,” “Next one I’ll take a sip of fluids,” “Now I’ll ask the team how long to the next break.” My dreamy state made me forgetful, so often a task would take 4 or 6 laps before I remembered during the actual recovery to complete it. So the laps passed, and the mini-breaks came and went, and the waxing moon took the place of the sun, climbing through the casuarina trees and into the clouds overhead.

10:31pm (12 hrs in the water), 27,050m swum.

Finally the halfway mark arrived, and I was permitted to descend to a longer interval of 41 seconds. I had been thinking about this for the last hour, and decided to try staying at 37” intervals, but with longer and more frequent breaks, thinking this might be easier. However when the time came and I completed the first 25 minute bout at this interval, I realised with a sinking feeling that I wasn’t going to be able to sustain it for another 12 hours. My breathing was just too heavy, and I was now feeling rushed in the recoveries.

photo by Michael Frefields @Free_Fields


Reluctantly, I accepted my fate at 41”, meaning I would still only be afforded 3 minutes break for every 40 minutes of swimming. The new interval felt better, and for the first time in a while I felt relaxed again. However the aches were starting to build up, and I was forced to take a Voltaren, and soon after that a second one, to try to curb the pain.

As well as the muscular problems, each time I put my nose clip on or off the constant pressure and abrasion on the nose was killing the skin there and inflaming the nose itself, so I had to loosen the clip over time. Vaseline helped a little, here and on my neck where the suit and weight were chafing the skin.

At 12:30 I took another long break, and noticed that out of the water the air temperature had dropped markedly. Rachel wrapped me in towels as I lay on one of the deck chairs, and it took the first 10 minutes of my break for my breathing to come back down to normal. My body’s physiology was starting to experience being pushed to different limits than what it was accustomed to.

I also started to feel nauseous, and wondered if this was going to be the start of 10 hours of digestive problems. For the next few bouts I didn’t eat much more than a bite or two of banana in the break, and a bucket was on hand next to the pool just in case of any gastro uprisings.

how my body was starting to feel after 15 hours in the water - photo by Michael Frefields @Free_Fields


Even though I was on the downhill stretch, I was wary of the fact that there were still over 9 hours of swimming to go, about the time it took me to swim across the Cook Strait in 2019. I was using all of 4 strokes per lap now, and well over 25 seconds.

I focused on reaching the end of each of my 40-minute sessions, then on the goal of getting to 5:30, when I would have my last 20-minute break. The threat of cramping started to loom in my ankles and calves, and I took a final Voltaren to deal with the pain in my knees, shoulders and elbows.

The moon abandoned me, and for a pair of hours I swum in a liminal state, bouncing between the tiled walls of my water prison. I willed the sky to lighten on the horizon, but time would not pass.


5:30am Daylight Savings Time (20 hrs in water), 42,275m swum

Just before my final break, I reached the goal of swimming a marathon distance underwater. I was also still on target with my schedule to be able to swim 50km in 24 hour – in fact I was about 15 laps ahead.

For the first time I started to feel confident that I would be able to swim for the full 24 hours. From here, it was just about micro-managing all the many niggles and difficulties to make sure none flared into something that would prevent me from swimming. My nausea had passed, but my intestines were complaining about the mass of half-digested banana and energy bars that had plugged it.

photo by Michael Frefields @Free_Fields

In the final break I lay silent under the towels, slowing my breathing and reminding myself of all the reasons I was doing the swim for. I yelped in pain as I slid my noseclip back into place, and then set off for the final stretch.

Day broke over the tree line, and the sun rose to find me where it had left me, but with skin as pruned as ceviche. A crowd of friends and supporters from Albany started to gather to will me on for the last stretch. I was counting down the number of 40 minute bouts: 4, 3, 2 and finally one last 40 minute swim. This is longer than the duration of an average table in my normal training, but today it felt like the home sprint. I broke past the 50km mark with about 15 minutes to go, and fuelled by adrenaline I started to accelerate. For the last few minutes Rachel gave me the exact time remaining and as I swam I calculated I could do 4 more if I didn’t take a recovery on the final lap. So at the end of the penultimate lap I turned underwater at the wall, and came back for the only 50m dynamic apnea of the entire 24 hours. In that second lap all the muscles of both legs started to cramp, and my technique deteriorated to awful as I dragged my body to the final wall.


photos by Andre Musgrove @andremusgrove


Without planning it, I had finished the swim on 2023 laps (50,575m), the number of the coming year, a year in which I will try to do my part to turn around the tide of the mental health crisis gripping our species.

I could not have completed the attempt without the support of Rachel and the crew of witnesses from Albany, my sponsors Suunto, Orca and event sponsor Frontier Supplements, and the patience and love of my family waiting for me in Japan.


with Rachel Miller, head of Marine Sciences at Windsor School in Albany


I’m no endurance athlete, but the fact I lasted 24 hours in the water must also in part be due to the power of our minds to bring us through any challenge, and I hope that with the Mental Immune System others will be able to tap into those powers to help confront the challenges, greater or smaller, that they face in their own lives.

1,737 views1 comment

Recent Posts

See All