Nutrition - Hydrate with Water & ?

Maintaining hydration during training and racing isn’t just about drinking water - it’s a precision balance between fluids and electrolytes, especially sodium.

Hydrate - with just water?

Why it Matters: The Research Speaks

A fluid loss of just 2 % of body weight significantly impairs endurance performance, even in moderate climates. That same 2 % deficit can raise heart rate, decrease muscle endurance, and impair temperature regulation. But beware over-hydration is a genuine danger. Drinking too much water dilutes blood sodium, potentially leading to exercise-associated hyponatraemia (EAH). Studies of endurance athletes who collapsed showed fluid intake of 1.2–6 L above needs, with morning-after blood sodium falling from ~135 to ~122 mmol/L.

What We Learn From Experimental Trials

• Sweat sodium loss varies between individuals - research shows huge variability (30–50 mmol/L), increasing with exercise intensity; some athletes may lose over 4.5 g of salt per hour.

• Responses to controlled rehydration strategies show that fluid intake guided by thirst is sufficient to prevent both dehydration and hyponatraemia.

  
  

How to Hydrate Smart:

Experimental Steps from Lab to Field

1. Sweat-Test Simulation

   • Set up: 60–90 minutes at race intensity in training gear.

   • Measure: Body weight pre/post, noting sweat and fluid intake.

   • Repeat: 2–3 times across different days to account for variability

2. Electrolyte Tracking Trial

   • Alternate between water-only, carb-electrolyte drinks, and added sodium tablets.

   • Observe urine colour, bodyweight change, and how you feel during and after.

3. Hydration Strategy Validation on Long Ride/Run

   • Mixed hydration group (water + sodium/carbs): perform vs. water-only group.

   • Monitor bodyweight, cramps, energy, recovery and temperature response.

   
   

Waimakariri river, Coast to Coast, New Zealand

Practical Takeaways

• Weigh before & after sessions - every 0.5 kg = ~0.5 L fluid loss. Aim to refill about 80–100% of that during recovery.

• Test different mixes during long sessions - find what your gut tolerates best.

• Sip regularly, matching thirst - not gulping. Over-drinking is just as risky as under-drinking.

• Dial in sodium based on your sweat test: include gels, salted drinks, or salt tabs if you’re a heavy “salty sweater.” Normal athletes lose 30–50 mmol sodium per litre sweat, but those who sweat more intensely may lose much more.

Coach’s Tip: Hydration is an experiment. Your aim is to hit the hydration sweet spot - enough to stay cool and avoid cramps, but not so much that blood sodium becomes dangerously low. Practising this in training sets you up for race-day reliability and safety. Let hydration be a tool, not a guess.