The numbers to know
- Dehydration of roughly 2% of body mass degrades endurance, sprint repeatability, decision-making and heat tolerance.
- Rehydrate with about 16-24 oz (450-700 ml) of fluid per pound of body weight lost during training.
- Aim for roughly 5-7 ml per kg of body weight 2-4 hours before a session — about 12-20 oz for most high-school athletes.
- During training, roughly 4-8 oz every 15-20 minutes, adjusted to sweat rate and heat.
Between two sessions
- Weigh before and after each session, in dry clothes. The scale is the most honest hydration monitor an athlete owns.
- Add sodium (a sports drink, electrolyte tab, or salted food) for sessions over 60-90 minutes, in heat, or if you are a salty/heavy sweater.
- Include carbohydrate and protein in the between-session meal — rehydration and refueling happen together.
- Urine that is pale straw colored is the target. Dark, low-volume urine before a second session means you are behind.
- Never use fluid restriction or sweat suits to make weight. That is a heat-illness pathway, not a training method.
