Measuring hydration: body mass, urine and sweat

Three measures, three different questions

Studies on archers' hydration use three tools, and each answers a question of its own. Scales, before and after shooting, tell you how much weight was lost in that session. Urine, through its density or its colour, tells you how concentrated it is at one particular moment of the day. Sweat, collected from the skin, tells you how much is lost per hour and with how much sodium and potassium. The three measures complement one another, but they do not convert into one another: a specific gravity of 1.025 says nothing about how many grams were lost, and a 400 ml drop says nothing about the state an archer arrived in. To read any figure on dehydration, then, you need to know which of the three it comes from.

Weighing before and after

The most thorough use of the scales is in the 2025 Turkish study of eight national-team archers at a World Cup: a digital scale, minimal clothing, bladder emptied before both weighings, urine passed during the session collected and weighed, drinks and food weighed before and after. Only with all of that does a change in body mass become an estimate of sweat lost. During competition the average loss was 0.58% of body mass, 0.75% in the men and 0.33% in the women, with 0.66 litres drunk per hour.

The 2026 Jakarta study uses the scales more simply: eleven archers weighed before and after an outdoor qualification round, one kilogram counted as one thousand millilitres, with neither the fluid drunk nor the temperature recorded. What it measures is therefore the net drop in weight, 390.9 ml on average, from 200 to 700, not the total fluid loss, and without the starting body mass it cannot be expressed as a percentage. The figures also have a problem: the reported standard deviation is 7.348 ml, which cannot coexist with values spread between 200 and 700, and the t of 168.491 that the authors derive from it inherits the same error.

The percentage matters because thresholds are expressed that way. The authors of the 2020 Cypriot experiment refer to 2% of body mass, but they list among their limitations that they did not weigh the archers during the trials, and they read dehydration in urine alone.

Urine: specific gravity and colour

Specific gravity tells you how concentrated urine is compared with water. The Cypriot group measured it with a refractometer on a first-morning sample, and the Turkish group with a digital one, four times a day: on waking, half an hour before competition, a quarter of an hour after it and before bed. The 2026 Surabaya study used reagent strips instead, on a midstream sample taken before and after the session. Strips read in steps of 0.005, 1.020, 1.025, 1.030, so many archers land on the same value, which weakens the test. The authors say so, together with a second limitation: the final sample was taken as soon as shooting ended, before what had been drunk could reach the urine.

The first trap is the threshold. The Cypriot study calls an archer dehydrated at 1.025 or above; the Turkish group calls an archer euhydrated below 1.020, "minimally hypohydrated" between 1.020 and 1.024, and hypohydrated above that. An archer at 1.022 is therefore hydrated by the first study's standard and minimally hypohydrated by the second's. The second trap is the time of day: in both Turkish studies urine is most concentrated on waking, more than before or after competition (p = 0.004 and p = 0.029 against the pre-competition sample), so a morning sample and one taken before a session do not measure the same thing.

Colour is the simplest version of the same measure. At the 2023 Grand Prix it was always read by the same researcher on a scale from 1 to 8, and it agreed with specific gravity. In a 2023 Indonesian study each archer compared a morning sample against a card on their own, but the paper publishes neither the average colour nor the score on the two days. As for specific gravity itself, the Cypriot authors write that it may not be the best reference, and the Turkish group calls for sweat to be measured as well.

Sweat

Only the 2025 Turkish study measured sweat, with absorbent patches on the shoulder blade and the thigh for the whole session; the sweat was drawn out with a syringe and analysed with electrodes for sodium and potassium. Sodium averaged 45.2 ± 9.7 mmol/l, about 416 mg per hour, with no difference between men and women; the men sweated more (p = 0.002). The 416 mg per hour come from a multiplication, concentration times litres of sweat per hour, so they hold only if the weighing that gives the volume holds.

When urine is used for something else

Two Ukrainian papers, from 2024 and 2025, measure lactate and urea in the urine of sixteen archers, before and after shooting, in training and in competition. These are concentrations taken from single samples, and neither paper reports urine specific gravity or creatinine alongside them; the 2025 authors themselves suggest adding creatinine. Without a measure of dilution, a difference in concentration between two days cannot be separated from a difference in how much was drunk. The entry on urine lactate, which stays at "reported", should be read with that limitation too.

What these figures support today

The cleanest experiment is the Cypriot one: ten archers at 36 to 37 degrees, specific gravity 1.032 ± 0.005 after twenty-four hours on 1.25 litres of fluid against 1.015 ± 0.004 when hydrated, all ten past the 1.025 threshold. The score does not drop, 562 points when dehydrated against 550 when hydrated, and this is the basis of the entries on dehydration and score and on alertness in competition. The 0.66 litres per hour drunk in competition sit in the entry on hydration in competition, the median pre-session specific gravity of 1.025 in the one on archers arriving dehydrated, and the comparison of two drinks in the one on isotonic drink and water.

The shared limitation is that the three measures almost never appear together. The only study that weighs the archers, reads their urine and collects their sweat was carried out at 23.7 degrees, with meals planned by a nutritionist; the only one with measured heat, 36 to 37 degrees in Cyprus, looked at urine alone. The findings in chronological order are in the article on sleep and recovery.

What to check

• which of the three measures was used, and whether the figure is in millilitres, as a percentage of body mass or as specific gravity;
• for the scales: whether fluid drunk, food and urine were counted, and whether the starting body mass is given;
• for urine: refractometer, strip or colour, what time the sample was taken and which threshold the study uses;
• for sweat: where the patches were and for how long, and which weighing the volume comes from;
• the temperature on the field, and whether the archers drank to a plan;
• whether the means, the spread and the test values are consistent with one another.

How design and sample are weighed is explained in How we read a study; how heat on the field is measured, in the page on wind, heat and humidity; what all this means for a competition day, in the article on hydration and nutrition on competition day.

@misc{campagna2026_enresearchmethodsmeasuringhydration,
  author = {Campagna, Matteo},
  title = {Measuring hydration: body mass, urine and sweat},
  year = {2026},
  howpublished = {Research, matteocampagna.com},
  url = {https://matteocampagna.com/en/research/methods/measuring-hydration},
  note = {accessed 2026-10-16}
}