In August of 2019, Precision Fuel & Hydration's Andy and JP competed as a team at the ÖTILLÖ Swimrun World Championship; an event which takes place across the wild terrains of the Stockholm Archipelago and is considered to be one of the toughest single day endurance races in the world.

The ÖTILLÖ Worlds is 'the mother of all swimrun events' and the 2019 edition of the race consisted of 65km of trail running, 10km of open water swimming between 24 islands and a grand total of 46 transitions (you can find the course distances and splits here).

Our study

Swimrun is a sport which continues to grow in popularity and the number of events has increased year-on-year since the first edition took place in 2002 following a drunken bet between friends in Sweden.

It remains a relatively new sport, so research in the area is limited. To our knowledge, only one paper has been published and it focuses on the development and improvements in the standard of performances, rather than the unique hydration and nutritional challenges.

With no empirical evidence existing on specific fuelling strategies to maximise race performance, I took the opportunity to hijack Andy and JP's race and collect some field data while they did the hard work.

Using simple food recall questionnaires and pre- and post-race weighing, our aim was to gain an insight into what Andy and JP ate and drank to fuel themselves for such a gruelling day and to see if they truly practiced what they preach.

An infographic of the protocol we followed. It was interesting to see how the guys’ ‘plan’ changed over the course of the race. It also acted as a very useful prompt post-race - recalling nine hours' worth of food and drink when you’re physically ruined isn't easy!

To ensure their recall was as accurate as possible, Andy and JP were briefed on the importance of being mindful about what they were each putting into their mouths.

Image Credit: dryrobe ©

What did Andy & JP eat and drink?

Before diving into what the guys ate and drank, congratulations is in order as they finished the race in 9 hours and 4 seconds (although we don’t mention those four seconds to Andy, who clocked 09:35:14 with his partner in 2014 and 09:04:23 in 2018, and was hoping for a sub-9 hour time in 2019). This performance placed them 16th out of the 146 finishing teams and the first British team home.

We asked the lads how they felt after the race...

Andy: This one was ‘up there’ with how much I’ve suffered at points due to the mismatch between my training volume and the length of the race. 

JP: F****d.

Image Credit: dryrobe ©

Onto what we really want to know, what did they actually eat and drink before and during the race?

Andy Blow Case Study | James Phillips Case Study

Their nutritional intake was a mixture of pre-planned elements (i.e. energy gels and chews) which were carried in their wetsuits during the race, and various items that they picked up at the aid stations (e.g. cheese naan bread!).

The lads drank PH 1500 consistently throughout the race. PH 1500 - our highest strength electrolyte mix - was available at all eight of the on-course aid stations.

The fuelling strategy for a swimrun race can be considered unique compared to other endurance challenges. As it was JP’s debut at the World Championships, we asked him how fuelling and hydrating for this swimrun compare to past endurance events he'd competed in...

"It’s so long, and you really can’t carry anywhere near enough calories or fluid, so being adaptable and accepting that you have to eat and drink more than you feel comfortable with at times is ultimately for the best. If you skipped an aid station, you’d be in big trouble later on."

Nutrition - How many carbs did they consume?

Following the race, we inputted the nutritional intake questionnaires into Nutritics, an online dietary analysis software, which provided a comprehensive breakdown of their macronutrient (carbohydrates (CHO), fat and protein) consumption during the race.

Foods and fluids taken in the 30-minutes prior to the start of the race were included in the main race analysis, but breakfast was excluded and analysed separately.

The average pre-race breakfast contained:

  • 39.3g CHO
  • 18.8g protein
  • 12.7g fat

During the race, the guys consumed an average of:

  • 454g CHO (51g/h CHO) with minor fat and protein intake, resulting in an average caloric intake totalling 2,582kcal (287kcal/h).
  • An average consumption of 147mg of caffeine was also reported.

Andy’s and JP’s individual dietary breakdown can be seen in the table below:

Andy (73kg) JP (69kg)
Total CHO intake 492g 416g
CHO intake per hour 55g/h 46g/h
CHO intake per hour per kilogram of bodyweight 0.75g/kg/h 0.67g/kg/h
Total calorie intake 2917kcal 2246kcal
Calorie intake per hour 324kcal/h 250kcal/h
Total protein intake 49g 29g
Total fat intake 84g 59g

Andy and JP’s individual calorie and carbohydrate breakdown during the ÖTILLÖ Swimrun World Championship.

Typical nutrition recommendations for endurance events

It’s been suggested that a high-fat, low-carb approach to fuelling for ultrarunners is growing in momentum, but for the vast majority of endurance athletes carbs still remain 'king' and, as illustrated above, this is the clear approach Andy and JP followed.

Carbohydrate ingestion during exercise has been extensively shown to improve performance by delaying the onset of fatigue. The general consensus is that athletes who are exercising intensely for longer than ~90 minutes should target a carbohydrate intake of between 30-60 grams per hour to maintain their performance. The simple science here is that the glycogen stored in your muscles becomes notably depleted by this point and therefore further provisions of energy come in useful during prolonged exercise.

The exact amount of carbohydrate an athlete requires to fuel themselves effectively may depend on their metabolism, fitness and level of effort.

Keep in the forefront of your mind that, just like hydration, everybody’s fuelling strategy should be personalised and different.

There’s plenty of information out there about carbohydrate intakes of 90g/h maximising performance; a newer recommendation based upon the utilisation of Multiple Transportable Carbohydrates (in short, not just the intake of glucose but sucrose, maltodextrin and others, with fructose perhaps being the most notable).

In order for this strategy to be effective the athlete must have a very well-trained stomach and be aware of their intake; for instance, too much fructose can cause gastrointestinal problems.

For most athletes, a carbohydrate intake in the region of 30-60g/h is sufficient and is kindest on the stomach.

After scrutinising their numbers, both AB and JP practiced fuelling strategies which are congruent with the contemporary evidence-based recommendations.

Hydration - How much sodium and fluid did they drink?

There’s lots of variables that influence an athlete’s hydration equation and, whilst we do quantify sweat sodium concentration and try to account for sweat rates from lab or field testing, there are other factors at play - for example, differences in how much fluid/sodium a person has on board to start with being a key one, and so placing athletes in the right ‘zone’ is the best practical approach to planning a hydration strategy - which is covered in our blog: How precise does your hydration plan really need to be?.

We know that both Andy and JP have ‘very high’ sweat sodium concentrations and ‘high-to-very high’ sweat rates. Therefore, ahead of any long, hard, day of exercise, their net sodium losses can be assumed to be significant.

In addition to the PH 1500 they planned on refilling their soft flasks with at each aid station, Andy and JP chose to carry blister-packed SweatSalt Capsules, of which they each took eight (with plain water).

Over the course of the race, the pair’s average sodium intake was found to be 6,768mg (752 mg/h, which roughly equates to drinking 1 x PH 1500 an hour), with Precision Fuel & Hydration electrolytes responsible for ~80% of this and the other ~20% from their nutrition.

Andy and JP's sources of sodium intake.

Looking at it on an individual level you can see that Andy was responsible for pulling these averages up - JP consumed a total of 5,735mg of sodium (637mg/h) to Andy’s 7,801mg (867mg/h).

With previous experience of the demanding nature of the ÖTILLÖ World Championship, Andy was hyper-aware of the importance of staying on top of his sodium losses throughout the race, particularly during the latter third.

When Andy was asked how fuelling and hydrating for the swimrun compared to past endurance events, Andy replied: "I had more of a plan for this one based on prior experience and also, because I was nervous about racing with someone fitter than me, I didn't want to let energy depletion, dehydration or cramp derail things."

Shown by his food diary, Andy consistently reached for PH 1500 at all of the aid stations, while sometimes drinking smaller volumes of plain water alongside it.

In contrast, JP opted to drink mainly plain water in the final couple of hours of the race. This was what he felt he was craving at the time and he listened to his body.

In an event which is about survival and crossing the finish line, it’s difficult to determine whether JP’s performance suffered because of this or not.

It was interesting that JP recalled experiencing some cramp in his forearms in the final hour of the race - a self-diagnosed personal ‘tell’ that he was sodium-deficient.

Fluid intake

Finally, in pursuit of gaining a complete picture, we asked the guys to also record their fluid intake.

As you can imagine, recalling how much fluid you drank in a nine-hour race is not an easy feat. Fortunately, they were mainly drinking from the soft flasks they were carrying with them.

Therefore, counting back by the bottle, they estimated their fluid intake to be in the region of 4.6-4.8L, equalling an approximate intake of ~500ml per hour. The typical fluid consumption for an athlete when running is between 500-750ml/h.

The results - How dehydrated were they?

Weight loss is a commonly used indicator of dehydration. We measured AB and JP’s body weights before and after the race and calculated the change to determine their degree of dehydration.

JP lost 3.4kg in body weight (68.9kg down to 65.5kg post-race), while Andy lost a relatively small 1.4kg (72.9kg down to 71.5kg).

Andy and JP body mass change

The graph above shows JP was just shy of 5% dehydration and Andy close to 2%. This touches upon a well and long-debated topic in sports performance - how much dehydration can you tolerate before your performance suffers?

There isn't a universally accepted answer to the question, but a lot of athletes are familiar with the concept that dehydration greater than 2% body weight is detrimental to performance.

This 2% dehydration ‘threshold’ is based upon a lot of older, lab-based studies and, at the time, tied in nicely with the outdated hydration advice of ‘drink, drink, drink’. These studies have since been criticised for not accurately reflecting what really happens in practice.

On the whole, it appears that there are differences in how much dehydration different athletes can cope with before performance starts to suffer. 

We asked JP and Andy about how well they felt they approached hydration during the course of the race...

JP: I think I ended up under-doing my hydration (both water and sodium, but mainly sodium) in the last 3 hours and that had an effect on how I felt through a particularly 'rough patch' in the race.

In future, I’d make a conscious effort to take on more sodium during the back-end of the race and maybe carry more SweatSalt Capsules to take if I didn’t want anything other than water.

AB: I think that the reasons for slowing late on were more to do with lack of training volume than to do with fluid/food intake.

Limitations of the study

It’s important to highlight that all of the figures presented should be taken with a pinch of salt.

There are variables which cannot be controlled or accounted when collecting data in the field rather than a lab. For example, we had to assume that all weight lost was fluid (sweat). This assumption is unrealistic, especially in an event which exceeds two hours, as a proportion of body mass will have been lost via urine excretion, substrate utilisation (glycogen and fat stores) and respiratory water losses, to name a few. 

Furthermore, nutritional intake questionnaires, and any kind of dietary recall, is dependent on the participant’s ability to describe what they were eating and self-reporting can also be susceptible to under- or over-reporting.

Fortunately, the majority of Andy and JP’s intake were gels, chews and bars, which were consumed in their entirety and therefore made recall and input relatively simple, albeit there’s a chance that they forgot some items. Fluid intake in the field will always be particularly messy and should certainly be considered an estimation. 

We checked with them afterwards and they both felt confident in the data they reported and considered it accurate given the circumstances.

Image Credit: dryrobe ©


Both Andy and JP’s individual CHO, sodium and fluid intakes were in line with standard recommendations for typical endurance athletes.  

It's worth remembering that Andy and JP both have high sweat rates and salty sweat, so while it's interesting to look at how other people approach hydration and nutrition for endurance events, it's important to personalise your strategy to your own individual needs. 

As Andy advised after the race, "Have a decent plan based on availability of the drinks and food on course but also take a significant amount of your own tried and tested nutrition (i.e. gels you like, electrolyte capsules). Be prepared to change the plan later in the day - you need to listen to your body to do this and understand what it's telling you it needs when the going gets tough".

So, whether you're preparing for the 'mother of all swimrun events' - The ÖTILLÖ World Championship - or your own race, it's important to have a nutrition and hydration strategy in place. Just remember you need to be flexible enough to tailor those plans to how you’re feeling, the conditions and the circumstances on race day.

Further reading