Training in the heat: estimate sweat loss to inform your hydration plan
Use a practical sweat estimate without confusing fluid loss with sodium loss.
Disclosure: this article contains True affiliate links. Enduran-se may earn a commission on purchases made through these links. Code: TRUEVICTORMATHOS, subject to store terms.
A soaked shirt indicates sweating, but it does not tell you how many liters you lost. A simple estimate can help identify differences between sessions and provide better information for a dietitian.
How to make an estimate
Weigh yourself before and after a session, ideally on the same scale, wearing dry clothing or without wet clothing. Record fluids consumed and any urine produced during that period. For a field approximation, use:
Estimated sweat in liters ≈ weight before − weight after + fluid consumed − urine.
Enter weights in kilograms and volumes in liters. Divide by duration in hours to estimate liters per hour. This is approximate: food intake, respiratory exchanges and other factors affect the calculation, especially during long sessions.
A numerical example
Someone starts at 70 kg, finishes at 69.5 kg, drinks 0.6 L and does not urinate during one hour. The estimate is 70 − 69.5 + 0.6 = 1.1 L of sweat during that hour. This does not mean they must drink 1.1 L per hour next time.
Tolerance, water access, pace and clinical context also inform planning. Repeat observations under similar conditions to identify patterns rather than extrapolating a cool training session to a hot race.
This calculation does not measure sodium
Losing a liter of sweat does not reveal its sodium concentration. Do not derive an exact salt dose from the scale or white marks on clothing. These observations can guide questions, but do not replace specific assessment when needed.
True Hydration Electrolytes is one replacement product to evaluate within a plan. Choosing a brand does not establish your losses or how much you need to replace.
<!-- BANNER:hydration -->
Turn the record into decisions
Bring duration, approximate temperature, weights, drinks and symptoms to your next professional appointment. This makes it easier to discuss carrying capacity, refill points and tolerance using information from your routine.
Do not treat the scale as an obligation to finish every session at exactly the same weight. Gaining weight by drinking beyond losses can also be dangerous. If confusion, fainting or significant illness occurs in the heat, stop and seek help; do not try to resolve it only with an electrolyte packet.
Educational content for adults; it does not replace individual assessment and planning with a qualified professional.
References
Cada um no seu ritmo. Juntos no caminho.