Sweat & Hydration Assessment in London

Sweat testing measures two things about you: how much fluid you lose per hour, and how much sodium is in that sweat. The first is a sweat rate test. The second is sweat analysis, sometimes called a sweat composition test. Both are done here in one session, because either on its own leaves half the question open — a litre an hour tells you nothing about what to put in it, and a sodium concentration tells you nothing about how much of it you will lose. Sweat rate is measured twice over: continuously by the sensor, and independently from your body mass before and after with every drink weighed.

The assessment measures a normal training day, so keep the day before normal. Eat and drink as you usually would — do not deliberately overhydrate and do not restrict. Avoid alcohol in the 24 hours before and avoid unusually strenuous training the day before. Bring the kit and footwear you normally train in, the drink you normally use during exercise, and a list of any supplements or medications. Tell us if you are unwell or have recently had vomiting, diarrhoea or a fever — the assessment is better rescheduled than run on a day that will not represent you.

It gives you an individual starting point, not one fixed amount for every session. Your strategy also depends on how long the event is, the temperature and humidity, how the intensity changes, whether fluid is within reach, how much you can comfortably drink, how your gut tolerates it, and how much sodium your normal diet already provides. Replacing 100 per cent of your fluid and sodium losses during exercise is not always necessary, and drinking to excess carries its own risk.

No. A VO₂ max assessment measures cardiorespiratory fitness and progresses towards a maximal effort. This one holds a longer, controlled workload so that sweating can be measured under conditions that represent how you train or race. If you have already had VO₂, threshold or heart-rate testing, that data is used to choose the most appropriate intensity for this assessment.

No. Sweat rate and sodium losses change with exercise intensity, temperature, humidity, airflow, indoor versus outdoor exercise, clothing, heat acclimation, fitness and the sport itself. Your result is therefore reported alongside the exact conditions it was recorded in. Athletes preparing for a markedly different environment sometimes repeat the assessment — once in cooler conditions, and again before a hot-weather event.

Sodium concentration differs between areas of the body, so a reading taken at one site estimates your whole-body sweat sodium rather than measuring it directly. It is reported as an estimate for that reason, and it is still specific to you — the differences between athletes are considerably larger than the uncertainty in the method.

No urine sample is collected or analysed. You will be asked to empty your bladder before the assessment begins. If you need the toilet during the exercise period the result becomes unreliable, because urine volume is not collected and so cannot be accounted for in the calculation.

Privately, with clothing removed or in the same minimal dry clothing before and after exercise. The comparison only works if both measurements are taken the same way, which is why wet kit is removed and skin and hair are dried before the second one.

Yes, and you should drink as you normally would. Every drink is weighed so that the fluid you take in is included in the calculation rather than hidden in it. Bring the drink you usually use during exercise.

The appointment is £150 and takes about 90 minutes. That covers the initial consultation, the pre-exercise measurements, up to an hour of controlled exercise, the post-exercise measurements and the review of your results. The exercise itself is matched to your event, so the shorter end applies when a shorter effort answers the question.

At UNTIL Liverpool Street, 280 Bishops Square, London EC2M 4RB, or UNTIL Marylebone, 1 Orchard Street, London W1H 6HJ. Both operate by appointment.