In 30 seconds
- In long trail and mountain races, the guideline is to drink 450-750 ml per hour, about 150-250 ml every 20 minutes, with 500-700 mg of sodium per litre.
- Carbohydrate: 30-50 g per hour in ultras, from foods and drinks you have already tried in training.
- At the Ultra Pirineu (100 km and 6,600 m of elevation gain), the longest stretch without an aid station is 15.1 km, and you must carry a minimum reserve of 1 litre of water.
- Drinking too much is a real risk: in 161 km ultras, hyponatraemia has been found in between 5% and 51% of runners.
In long trail and mountain races, the guideline is to drink 450-750 ml per hour, with 500-700 mg of sodium per litre and 30-50 g of carbohydrate per hour 6. In the Pyrenees, you also need to plan each stretch between aid stations and allow for the cold and the altitude.
We explain it using the figures from the Ultra Pirineu 2027 and a plan you can start testing in training right now.
Per hour, in long races
Your reference figures in the mountains
Why the mountains change the way you drink
A mountain race is not a road marathon with more climbing. You spend many hours out, at a slower pace, carrying your water on your back, with aid stations kilometres of trail apart.
That changes the strategy. In ultras, the most common plan is to drink to a personalised schedule, not only when you are thirsty 6. Drinking only to thirst can leave you short of sodium and electrolytes 6.
Conditions matter too. In heat or humidity you sweat more and find it harder to cool down 6: we cover this in training in heat and humidity. In the cold, thirst is blunted and you can still become dehydrated 6. And altitude increases water losses 8.
The Ultra Pirineu and the Pyrenean season
The Ultra Pirineu takes place on 1, 2 and 3 October 2027 in Bagà, in the Cadí-Moixeró Natural Park, with races over several distances 1. These are the figures for the two longest 2 3 4:
| Ultra 100K | Marató 42K | |
|---|---|---|
| Start | Saturday 2 October, 5.30 am, in Bagà | Saturday 2 October, 9 am, in Bagà |
| Distance and elevation gain | 100 km and 6,600 m of ascent | 42 km and 2,800 m of ascent |
| Highest point | Niu de l'Àliga, at 2,520 m (km 16.4) | Niu de l'Àliga, at 2,520 m (km 16.4) |
| Aid stations | 10, plus the finish | 4, plus the finish |
| Cut-off time | Sunday 3 October, 8 am | Saturday 2 October, 7.15 pm |
| Mandatory water | Minimum reserve of 1 litre and a reusable cup | Minimum reserve of 1 litre and a reusable cup |
Source: official Ultra Pirineu website (race pages and mandatory kit). The organisers reserve the right to change the content and distribution of the aid stations.
Look closely at the stretch from Niu de l'Àliga, at 2,520 m, to Serrat de les Esposes: according to the official table, it is 15.1 km without an aid station, the longest stretch of the Ultra 2. At the aid stations you will find water, sparkling water, cola, an isotonic drink and chicken and vegetable broth 2.
The season starts earlier. Val d'Aran by UTMB runs from 7 to 11 July 2027, with races from 10 to 163 km 5. In July, the challenge is the heat: we cover it in exercising in hot weather.
In October, it is the cold and the weather. The Ultra requires a thermal layer, waterproof trousers, a hat and gloves, and the final kit list is published on the Friday based on the latest forecast 4. The organisers do not give a reference temperature, so be ready for both extremes.
Your plan: before, during and after
| When | What to do |
|---|---|
| 2-4 hours before | Drink 5-10 ml per kilo of body weight: 350-700 ml if you weigh 70 kg. Aim for pale yellow urine. |
| During: fluid | 150-250 ml every 20 minutes, about 450-750 ml per hour, depending on thirst, heat and pace. |
| During: sodium | 500-700 mg per litre of fluid. More if you sweat over 1.2 litres per hour for more than 2 hours. |
| During: carbohydrate | 30-50 g per hour, from drinks, gels and food you have already tried. |
| After | If you are not running again within 24 hours, meals and water are enough. To rehydrate quickly, about 1.5 litres per kilo lost. |
Sources: Tiller et al., 2019 (ISSN); Mosler et al., 2020 (German Nutrition Society).
Fluid: with a plan, but without overdoing it
The International Society of Sports Nutrition (ISSN) guideline for ultras is 450-750 ml per hour, about 150-250 ml every 20 minutes 6. Adjust it to the heat, your pace and your sweat.
In the mountains, you do the maths stretch by stretch. If it takes you 3 hours between two aid stations and you drink 500 ml per hour, you need 1.5 litres: more than the mandatory 1-litre reserve 4. To find out how much you sweat, weigh yourself before and after a long run and use the hydration calculator. If you are running the Ultra Pirineu, the race hydration planner works out how much to carry between aid stations.
Sodium: more than many drinks contain
In long races, the ISSN suggests 500-700 mg of sodium per litre of fluid, a higher concentration than many commercial drinks 6. The German Nutrition Society puts the range at 400-1,100 mg per litre and recommends extra sodium if you sweat more than 1.2 litres per hour for more than 2 hours 9.
The broth and salty food at the aid stations count too. If you want to know how much you lose, read how much salt you lose in sweat.
Carbohydrate: whatever your stomach tolerates
In ultras, the ISSN recommends 30-50 g of carbohydrate per hour, from food and drinks; reaching 90 g per hour may be unrealistic in races of more than 6 hours 6. Extreme temperatures and altitude increase your needs 6.
Your gut can be trained too: gradually increase what you eat on your long runs 6. You will find the full plan in the running nutrition guide.
Cold and altitude: you dehydrate there too
Niu de l'Àliga, at 2,520 m, falls within the band researchers call moderate altitude, between 2,000 and 3,000 m 8. Altitude increases water losses, partly through breathing, and can reduce thirst 8.
The cold adds to this: it also blunts thirst 6. So, on high ground and in the small hours, follow the reference plan even if you are not very thirsty. Check the colour of your urine: the goal is pale yellow 9.
The big risk in ultras: drinking too much
Hyponatraemia, a fall in blood sodium, is mainly caused by drinking more than you lose through sweat and urine 7. In 161 km ultras, it has been found in between 5% and 51% of runners 7.
The international consensus highlights these risk factors 7:
- Efforts of more than 4 hours and a slow pace.
- Having drinks to hand at all times.
- Gaining weight during the race: almost all cases with symptoms occur in runners who maintain or gain weight.
- Little experience or little training.
Dizziness, nausea and swelling are the first signs; headache, vomiting or confusion are an emergency 7. The sodium in drinks does not prevent it if you drink too much 7. Drink to thirst and do not empty your flask at every aid station out of obligation. You will find everything in drinking too much water during exercise.
How to use Nitrus in the mountains
Each 25 g serving of Nitrus Isotonic provides about 195 mg of sodium and 15 g of carbohydrate, plus potassium and all 13 vitamins. This is how it works out depending on the water you use:
| Preparation | Sodium per serving | Sodium per litre | Carbohydrates per serving | Carbohydrates per litre |
|---|---|---|---|---|
| 25 g in 400 ml | 195 mg | 488 mg | 15.1 g | 37.8 g |
| 25 g in 500 ml | 195 mg | 390 mg | 15.1 g | 30.3 g |
Each 25 g serving contains 0.488 g of salt (about 195 mg of sodium), 148 mg of potassium and 15.13 g of carbohydrates.
In a 400 ml soft flask it comes to 488 mg of sodium per litre, within the German Nutrition Society's 400-1,100 mg range 9 and just short of the 500-700 mg the ISSN gives for ultras 6. One serving an hour gives you the base. Top it up with water to thirst, gels or food up to 30-50 g of carbohydrate and, if you sweat a lot, add the broth or something salty at the aid stations.
Carry pre-weighed servings in small bags and refill your flask at every aid station. It contains no caffeine, so you can take it at night too. If you are preparing for an ultra, the Hydration Pack brings together two tubs of Nitrus and BCAA 2:1:1 for €53.90, with free delivery. We are a Girona company, with our own formulas made in Spain with IFS Food and BRCGS certification.
Frequently asked questions
How much water should you drink in a mountain race?
In long races, the guideline is 450-750 ml per hour, about 150-250 ml every 20 minutes, adjusted to thirst, heat and your pace. Weigh yourself before and after a long run to find out what applies to you.
How much salt should you take in a trail race or an ultra?
The International Society of Sports Nutrition suggests 500-700 mg of sodium per litre of fluid, more than many drinks contain. If you sweat a lot, the broth and salty food at the aid stations help you get there.
How much water do you need to carry at the Ultra Pirineu?
The rules require a minimum reserve of 1 litre in the 100K and the 42K, and a reusable cup in every race. Work out each stretch: if it takes you 3 hours and you drink 500 ml per hour, you need 1.5 litres.
Do you need to drink in the cold too?
Yes. In the cold, thirst is blunted and you can still become dehydrated, and altitude increases water losses. Follow the reference plan and check that your urine is pale yellow.
Can you drink too much in an ultra?
Yes, and it is dangerous. Hyponatraemia is mainly caused by drinking more than you lose, and the risk rises in efforts of over 4 hours and at a slow pace. Drink to thirst and be wary if you finish weighing the same or more.
Sources
- Salomon Ultra Pirineu. Official race website: 2027 edition (1, 2 and 3 October 2027, Bagà). View publication
- Salomon Ultra Pirineu. Salomon Ultra Pirineu 100K: race information, timetable and aid stations. View publication
- Salomon Ultra Pirineu. Salomon Marató Pirineu 42K: race information, timetable and aid stations. View publication
- Salomon Ultra Pirineu. Normativa: material obligatorio. View publication
- Val d'Aran by UTMB. Official race website: 2027 edition (7-11 July 2027). View publication
- Tiller NB, Roberts JD, Beasley L, et al. International Society of Sports Nutrition position stand: nutritional considerations for single-stage ultra-marathon training and racing. J Int Soc Sports Nutr. 2019;16(1):50. View publication
- Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Br J Sports Med. 2015;49(22):1432-1446. View publication
- Stellingwerff T, Peeling P, Garvican-Lewis LA, et al. Nutrition and altitude: strategies to enhance adaptation, improve performance and maintain health: a narrative review. Sports Med. 2019;49(Suppl 2):169-184. View publication
- Mosler S, Braun H, Carlsohn A, et al. Position of the working group sports nutrition of the German Nutrition Society (DGE): fluid replacement in sports. Dtsch Z Sportmed. 2020;71(7-9):178-184. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
