Quick estimate
The sweat per hour the estimate starts from
How we calculate
With scales. This is the method recommended by scientific societies 2 4: the weight you lose plus what you drink is what you sweat. Divided by the hours of training, that is your sweat rate per hour.
Quick estimate. We start from 0.5, 0.9 and 1.3 litres an hour for a light, moderate or hard session for a 70 kg person at 15-25 °C. We chose those values based on the published averages, which range from 0.8 to 1.5 litres an hour depending on the sport 3. We then adjust them for your weight and the temperature, and keep them within the real range of 0.3 to 2.5 litres an hour 1. Your figure may be quite different: that is why we recommend the scales.
Sodium. We multiply your sweat by 920 mg of sodium per litre, the average from data on more than 1,300 athletes 3. If you get salt marks, we use 1,380 mg per litre, a higher value for people who lose more salt.
Your plan. We apply the recommendations of the German Nutrition Society 1:
- Before: 5-10 ml per kilo of body weight in the 2-4 hours beforehand.
- During: for less than an hour, water if you are thirsty. For longer, according to thirst and without exceeding 80% of what you sweat, with 400-1,100 mg of sodium per litre and 30-60 g of carbohydrate an hour from 90 minutes onwards. Which type of drink suits you in each case is covered in isotonic, hypotonic or hypertonic drinks.
- After: 1.5 litres for every kilo of body weight you have lost.
Your plan
How much to drink before, during and after
How to use the result
Do the scales calculation on two or three different sessions, in hot and cold weather, and keep your figures. They will help you plan your long runs, your bike rides or a competition, such as the Barcelona Half Marathon or the Empúries Marathon.
And remember that drinking too much is also a problem: if you weigh more when you finish than when you started, you have drunk too much. The safest strategy is to drink according to thirst 5.
Frequently asked questions
Is the quick estimate reliable?
It is a guide. Everyone sweats very differently, from 0.3 to 2.5 litres an hour. To find your real figure, weigh yourself before and after a session and use the scales method. Repeat it in hot and cold weather, because it changes.
Why does it not tell me to replace everything I sweat during training?
Because current recommendations advise drinking according to thirst and not replacing more than 80% of what you sweat while you train. Drinking too much can cause hyponatraemia. The rest is replaced afterwards.
How do I know if my sweat is salty?
If white marks are left on your clothes, cap or skin when your sweat dries, or it stings your eyes, you probably lose more sodium than average. To know exactly, you need a sweat test.
How many servings of Nitrus do I need?
The calculator tells you how many servings the fluid you should drink during training is equivalent to, and how much sodium and carbohydrate they provide. Each serving is 25 g in 400-500 ml of water, with about 195 mg of sodium and 15 g of carbohydrate.
Sources
- 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
- Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377-390. View publication
- Barnes KA, Anderson ML, Stofan JR, et al. Normative data for sweating rate, sweat sodium concentration, and sweat sodium loss in athletes: an update and analysis by sport. J Sports Sci. 2019;37(20):2356-2366. View publication
- Baker LB. Sweating rate and sweat sodium concentration in athletes: a review of methodology and intra/interindividual variability. Sports Med. 2017;47(Suppl 1):111-128. 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
A varied and balanced diet and a healthy lifestyle are important.