Recovery · 6 min read
Hydration strategy for long training days
Hydration planning is arithmetic, not intuition. Sweat rate varies several-fold between athletes and between climates, so the same bottle plan cannot serve a cool morning run and a 40 °C afternoon session.
Measure your own sweat rate once
Weigh yourself nude before and after a one-hour session in typical conditions, correcting for fluid drunk and urine passed. Each kilogram lost is roughly one litre of sweat. That number, not a generic rule, sets your drinking plan.
Body-mass losses beyond about 2% are associated with measurable declines in endurance performance and thermoregulation, particularly in heat.
During the session: drink to a plan, not to thirst alone
For sessions under an hour in mild conditions, water and thirst are usually sufficient. Beyond that, aim to replace the majority of sweat losses with a carbohydrate–electrolyte drink, which supports both fuel and fluid retention.
Sodium concentrations of roughly 20–50 mmol/L are typical for sports drinks; heavy and salty sweaters in hot climates sit at the upper end.
After the session: 125–150% of what you lost
Rapid rehydration requires drinking 1.25–1.5 litres for every kilogram of body mass lost, because some of the volume is lost again as urine. Sodium taken with the fluid — as a drink, or simply as salted food alongside it — substantially improves retention.
Milk-based drinks perform well in rehydration trials because they combine fluid, sodium, protein and carbohydrate in one step.
Do not overdo it
Exercise-associated hyponatraemia is a genuine risk in long events when athletes drink far in excess of sweat losses. The goal is replacement, not maximal drinking. Pale-straw urine plus stable morning body mass is a practical daily check.
Sources
Where this information comes from
Peer-reviewed clinical studies, position stands and consensus statements.
- 01Sawka MN, et al. American College of Sports Medicine position stand: Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377–390. View study
- 02McDermott BP, et al. National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active. J Athl Train. 2017;52(9):877–895. View study
- 03Shirreffs SM, Watson P, Maughan RJ. Milk as an effective post-exercise rehydration drink. Br J Nutr. 2007;98(1):173–180. View study
- 04Hew-Butler T, et al. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference. Clin J Sport Med. 2015;25(4):303–320. View study
This article is general information, not individual medical advice. For a plan matched to your health history, book a consultation.
