Water is the most overlooked performance variable. Even mild dehydration measurably impairs training — yet the “8 glasses” rule is a myth with no strong scientific basis.
What Dehydration Does
Losing as little as 2% of bodyweight in fluid can reduce strength, power, and endurance and increase perceived effort (reviewed by Sawka et al. / ACSM position stand). Cognitive focus and mood also decline before you consciously feel thirsty.
How Much You Actually Need
A reasonable baseline is roughly 30–40 ml per kg of bodyweight per day, adjusted up for heat and training. Rather than counting glasses, use a simple biofeedback marker: pale-yellow urine most of the day indicates adequate hydration.
Electrolytes and Longer Sessions
For training under ~60–90 minutes, plain water is fine. For longer or very sweaty sessions, replacing sodium (the main electrolyte lost in sweat) helps maintain performance and fluid balance. You don’t need expensive products — salt and carbohydrate in water works.
Coach’s Note
Sip throughout the day rather than chugging all at once. Bring a bottle to the gym and drink between sets — small, consistent intake beats trying to catch up.
Takeaways
- Aim for pale-yellow urine as your daily marker.
- Add sodium for long or hot sessions.
- Don’t force-drink far beyond thirst — overhydration has its own risks.
This article is for educational purposes and summarizes current research. It is not medical advice. Consult a qualified professional before changing your training, nutrition, or supplement regimen.