About the author – Bert Flier
For this article, we asked triathlon coach and nutrition specialist Bert Flier to share his insights.
Bert has been active in endurance sports for more than 30 years as a triathlete, coach, and author. During that time, he has guided countless triathletes, cyclists, and runners in their training and nutrition strategies for long-distance events.
His approach is practical and based on real-world experience: testing during training so that on race day you know exactly what works.
The hydration mistake many triathletes make (and how to avoid it)
In the final hour of the 1999 Almere Triathlon, I was leapfrogging with Guido Gosselink. We were both having a tough day. My calves kept cramping.
Every time I stopped at a lamppost to stretch, Guido passed me. A little later, he had to stop himself, and I caught him again. We kept alternating all the way to the finish.
It was over thirty degrees. During the race briefing, one piece of advice was repeated again and again: drink a lot. And I did. With what I know now, far too much. After the finish, I ended up in the medical tent. The diagnosis was hyponatremia: water intoxication caused by too much water and too few minerals.
That day, I drank nearly two litres of water per hour. The sodium deficit that followed caused my cramps.
That’s when I started measuring
The lesson from that hot race in Almere stayed with me.
On warm days, I weighed myself before training and again afterwards. Without clothing, since everything was soaked and would affect the measurement.
During training, I carefully tracked how much I drank. This allowed me to calculate my net fluid loss. On hot days, that turned out to be more than two litres per hour. But that still wasn’t the full picture.
Sweat analysis: how much sodium do you lose?
Today, you can have your sweat analyzed for mineral loss. I recommend this to all athletes racing four hours or longer. The amount of sodium you lose per liter of sweat is highly individual. It can vary from 0.5 grams per liter to 2.5 grams per liter. That’s a fivefold difference.
How I applied the lesson
The lesson from that hot race in Almere was simple: you don’t just need to replace fluids, you also need to replace minerals. My sweat analysis showed I lose more than 1.5 grams of salt per liter. That’s higher than what most sports nutrition products typically replace.
Since then, I always check how much sodium is in my sports nutrition. If needed, I supplement with mineral tablets or even regular table salt.
Improvising in the heat
A few years later, I rode a 180 km cyclo in France that included two climbs of Mont Ventoux. It was extremely hot. Thirty-five degrees. My starting bottles contained enough minerals, but at the aid stations there was only water with syrup and sweets. No minerals.
After 100 kilometers, the first cramps started. I just managed the second climb, but during the descent toward Bédoin both legs locked up in severe cramps. My hamstrings felt like tightly stretched elastic bands.
In Bédoin, I passed a terrace filled with cyclists. I stopped and asked just one question: is there any salt? Someone handed me a salt shaker. I poured far too much into both bottles. It tasted saltier than seawater.
But it worked. Within ten minutes, my legs started turning again. For the final forty kilometers, I was able to push hard once more.
The hydration triangle
During long efforts, you need to replace three things: fluids, carbohydrates, and minerals.
Fluids help compensate for sweat loss and regulate body temperature.
Carbohydrates provide the fuel your muscles need during prolonged effort.
Minerals, especially sodium, help your muscles and nervous system function properly and ensure the fluids you drink are actually absorbed.
Many triathletes focus mainly on drinking but forget that sodium is essential to make hydration effective.
5 practical tips for hydration during long triathlons
Want to avoid cramps and performance loss during long training sessions and races? Keep these guidelines in mind.
Measure your sweat loss
You can take a sweat test at a professional sports lab. Another option is to weigh yourself before and after training to understand how much fluid you lose. Especially during long races, this can make the difference between maintaining performance and gradually fading. Once you know your numbers, hydration becomes a strategy instead of a guess.
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Drink regularly
Spread your fluid intake throughout the effort so your body can absorb it more effectively. -
Don’t forget sodium
You lose minerals through sweat. Sodium helps your body absorb the fluids you drink. -
Test your strategy during training
Use training sessions to discover what hydration strategy works best for you. You don’t want surprises on race day. -
Adjust hydration to temperature and intensity
The warmer it gets and the harder you go, the greater your fluid and sodium loss.
Which Amacx products fit this hydration strategy?
In this article, Bert explains the importance of replacing fluids, carbohydrates, and sodium during long efforts. Within the Amacx range, several products can help support this strategy during training and racing.
Amacx Energy Drink
An isotonic sports drink with carbohydrates and sodium to help replenish both energy and fluids during prolonged effort.
Amacx Hydro Tabs
Electrolyte tablets containing sodium. Useful when you mainly drink water or want to add extra minerals, for example in hot conditions or when you sweat heavily.
Amacx Energy Gel
A practical carbohydrate source to help maintain energy levels during training and races.
With this combination, you can replenish fluids, carbohydrates, and minerals simultaneously during long efforts.
