The Importance of Hydration and Electrolytes for Performance

When we become dehydrated, our blood volume will fall, reducing blood flow to our working muscles. That in turn can lead to a higher body‐temperature, a reduced sweat rate, greater muscle glycogen use, increased perception of effort and an elevated heart rate. All of these factors, alone or combined, can undermine performance as well as mental focus.

Even a loss as small as 2% of body weight due to sweat can trigger dehydration. It’s therefore vital to begin your training session or race well‐hydrated, and to strive to maintain hydration throughout the effort.

If we measure our sweat rate and combine that with the expected duration of exercise, we can better predict our fluid needs. Why use an individualised approach? Because we each sweat differently, due to genetics, sex, training status and acclimatisation. And on top of that, external factors will affect sweat rate: ambient temperature, humidity, wind and even clothing all play a part.

Before Exercise

About 2 hours before exercise, aim to drink 6‑8 ml of fluid per kg of body weight. This gives time for absorption and for the body to excrete any excess. Having sodium (and other electrolytes) pre‑exercise is also beneficial: it stimulates thirst and promotes fluid retention.

During Exercise

During the workout, aim to drink frequently enough to avoid reductions in baseline body weight greater than 2%. How much you drink depends on your personal sweat rate.

How to Calculate Your Sweat Rate

The simplest method is:

1. Empty your bladder and weigh yourself (minimal or no clothing, ensuring the same conditions after).
2. Perform your training session, note conditions, exercise intensity and amount of fluid consumed.
3. Weigh yourself after exercise under the same conditions as the first weigh‑in.
4. Calculate weight loss: weight before minus weight after.
5. Calculate total sweat loss: weight loss + fluid intake.
6. Compute sweat rate: total sweat loss ÷ exercise duration.

This gives your sweat rate for that session, though being mindful of external conditions may alter it. If you’re preparing for an event in different weather or clothing than usual, you may want to repeat the test under those specific conditions.

After Exercise

With your sweat rate calculated, you can then work to re‑hydrate efficiently. Note that bathroom losses will also affect body weight, so privilege an estimate rather than an exact measure in that respect.

A widely recommended guideline: aim to consume 1.5 L of fluid for each kg of body weight lost, this accounts for fluids subsequently lost via urine. This doesn’t need to be consumed all at once; a smart approach might be to consume 500 ml immediately post‑exercise, then regular intervals thereafter.

What Are Electrolytes and Why Do We Need Them?

Beyond fluid losses, electrolyte balance is key. Many of our body’s processes rely on tiny electrical charges transmitted throughout the system. These electrical signals play roles in hydration, muscle contraction and nerve‐function.

Our bodies must maintain electrolyte pools in order to function efficiently. The vital electrolytes we need to replenish include sodium, calcium, potassium, bicarbonate, chloride, phosphate and magnesium. Since sweat during exercise mostly removes sodium and potassium, these are especially important when maintaining hydration and performance.

Low electrolyte levels may lead to fatigue, headaches and dehydration. Over time, persistent deficits can bring more severe consequences. Think of your body as a battery: if the charge runs low, performance must be supported by replenishment.

How Can You Replace Lost Electrolytes?

There are many whole‑food sources of electrolytes. For example:

• Potatoes provide phosphorus and magnesium.
• Leafy greens such as kale or spinach supply calcium and magnesium.
• Coconut water or milk offer sodium, potassium, calcium and magnesium.

At Science in Sport we make electrolyte‐replacement easy on the go. Our two key products for hydration and electrolytes are:

SiS Hydro

Hydro is an effervescent tablet that dissolves in water. It was originally developed for the British Sailing team at the 2008 Beijing Olympics. Each tablet contains:

• Chloride: 269 mg
• Sodium: 345 mg
• Potassium: 65 mg
• Magnesium: 8.1 mg
• Calcium: 102 mg

Directions: Dissolve one tablet in 500 ml of water and consume 3‑4 hours before your event. Then drink a further 250‑500 ml in the hour prior to starting. For shorter exercise sessions without carbohydrate needs, consume 500 ml of Hydro per hour. Once prepared, use within 24 hours. Do not exceed 4 tablets per day.

SiS GO Electrolyte Power

GO Electrolyte combines electrolyte replacement with easily digestible carbohydrate. It supports endurance performance and helps protect against cramp. The formulation includes: 36 g carbohydrate (6 % solution), sodium (20 mmol/L) and fluid (500 ml serving).

Directions: Drink 500 ml every 24‑60 minutes of exercise. To prepare, add 40 g of GO Electrolyte powder (2 scoops) to 500 ml water, shake well and consume within 24 hrs.

Frequently Asked Questions

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Key Takeaways

• Even 2% body weight loss from sweat can impair both physical and mental performance.
• Start well-hydrated and maintain fluid intake throughout your activity.
• Calculate your personal sweat rate to better plan hydration for different conditions.
• Replacing electrolytes like sodium and potassium is crucial, not just fluid.
• Use tailored strategies before, during, and after exercise to stay optimally hydrated.