Hydration, Fuelling & Heat for Women
Sims' hydration-physiology playbook for endurance and heat: get sodium and fuel right around training so you actually perform, instead of sipping plain water and bonking.
This is Sims' core expertise as an environmental exercise physiologist. The practical message from ROAR: a normal sports drink does not carry enough sodium to matter, so for longer or hot sessions she favours a higher-sodium pre-load to hold plasma volume, real food or functional carbohydrate during, and prompt refuelling after. Hydration needs also shift across the cycle and into menopause as plasma volume and heat regulation change. Heat and cold acclimation are trainable, and the gut can be trained to tolerate fuel. None of this requires plain water-chugging, which can backfire.
Why it works▼
Pre-load with a higher-sodium drink for long or hot sessions
Sodium pulls fluid into the bloodstream and supports plasma volume and heat tolerance.
For sessions under an hour, water is usually enough
Fuelling needs scale with duration and intensity; short sessions do not need carbohydrate drinks.
Take in fluid and carbohydrate on longer efforts
Replaces sweat losses and sustains intensity; the right amount depends on heat and sweat rate.
Rehydrate and refuel promptly
Restores plasma volume and starts recovery; women are especially sensitive to delayed refuelling.
Practise race fuelling in training
The gut adapts to tolerate fuel; surprising it on race day causes GI distress.
Build heat tolerance gradually
Heat acclimation expands plasma volume and improves cooling, a real and trainable adaptation.
Account for the cycle and menopause
Plasma volume and thermoregulation shift with hormones, so fixed numbers will not fit every week or every age.
- Endurance athletes and long-session trainers
- Anyone training in heat
- Women who bonk or cramp on plain water
- People prepping for a race or event
- Some of Sims' female-specific hydration claims are debated in the research; treat the sodium and fluid numbers as a tested starting point to personalise
- Very high sodium intake is not for everyone: blood-pressure, kidney or heart conditions should clear it with a doctor
- Over-drinking plain water during long events can cause hyponatraemia (low blood sodium), which is dangerous; sodium matters
- Sims sells no hydration line; the items here are generic categories, confirm any specific product yourself
- Educational only, not medical advice
- July 3, 2026 Protocol published.
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Not medical advice. This page is for education only and is not a substitute for professional medical care. Consult a qualified clinician before changing your health routine.
Independent curation. YourProtocol.ai is an independent platform. This protocol is based on the publicly available work of Stacy Sims and is not created, reviewed, endorsed by, or affiliated with Stacy Sims or Author, ROAR & Next Level.