Hyper-Hydration before an IRONMAN: Two Strategies, One Goal
When it comes to racing an IRONMAN in hot and humid conditions, starting the day well-hydrated can be as important as the months of training you’ve logged. Dehydration is inevitable over such a long day, but the size of your fluid ‘buffer’ at the start line can shape how far into the race you can hold pace before the heat starts to bite.
Athletes are increasingly turning to hyper-hydration strategies to expand plasma volume, increase total body water and delay the onset of dehydration. But like nutrition, there’s no one-size-fits-all. Here are two approaches being discussed in the endurance community, and why they both come with a dose of trial, error and caution.
1. The Steady Sipping Approach
This is the most widely used and best supported method:
24 hours pre-race: Aim for around 3-4 grams of sodium, spread across the day through electrolyte drinks, salty food or tablets.
How to take it: Sip slowly from 500-750 ml bottles over several hours. The key is absorption: slow sipping allows sodium and fluid to be retained rather than simply urinated out.
Evening before: One electrolyte-rich drink (~500–700 ml) with dinner.
Race morning: Another ~500 ml electrolyte drink, finished about 1.5-2 hours before the start, with light sipping until transition close.
Why it works:
Sodium helps the body hold onto fluid, topping up extracellular water and plasma volume. The gradual intake ensures it sticks, rather than just increasing bathroom trips.
Risks:
Overhydration with too much plain water can dilute sodium (hyponatremia).
Athletes with very high sweat sodium losses may need more than 3–4 g to notice benefits.
This method is safe, repeatable, and provides a reliable hydration buffer for most triathletes.
2. The ‘Supercompensation’ Strategy
A more aggressive method:
48 hours pre-race: Slightly reduce sodium intake to prime the body’s conservation systems.
Afternoon/evening before the race: Load with 5-6 g sodium, split into multiple 500-750 ml bottles and sipped slowly over several hours.
Race morning: A final preload of 2-3 g sodium in 1-1.5 L fluid, consumed gradually in the 2-3 hours before the start.
Why it might work
The theory is that after restriction, the body ‘super-compensates,’ storing more sodium and fluid than normal when reintroduced. This could expand plasma volume further than steady sipping, providing a larger hydration “reserve” for racing in the heat.
Risks
Gut tolerance: Even 5–6 g in one afternoon/evening can be hard on the stomach.
Overhydration: Pairing high sodium with too much fluid may still cause issues if not carefully balanced.
Unproven: While conceptually sound, this method hasn’t been as rigorously tested in endurance athletes as the steady sipping approach.
This is a high-risk/high-reward strategy best reserved for heat-acclimated athletes who have practiced it in training.
Which is Better?
Most athletes will benefit most from the steady sipping method: 3-4 g sodium across the day before, absorbed gradually.
High-sweat, heat-acclimated athletes may experiment with supercompensation: 5-6 g the afternoon/evening before and 2-3 g race morning.
Both strategies aim to increase plasma volume, delay dehydration and improve thermal regulation - but they differ in risk and predictability.
The Take-Home for Triathletes
Practice in training: Never try a new preload on race week.
Sip, don’t chug: Retention comes from slow absorption, not volume.
Know your losses: Sweat rate and sodium testing can guide whether you need conservative or aggressive strategies.
Don’t gamble: Stick with what your body has tolerated before.
Hyper-hydration won’t win you the race but it may give you valuable extra minutes before the heat slows you down. The right approach is the one you’ve tested, tolerated and can repeat with confidence.
Bevan McKinnon / September 2025