The Importance of Understanding Sweat Rate to Optimize Your Hydration Strategy

The Importance of Understanding Sweat Rate to Optimize Your Hydration Strategy

It’s no secret that proper hydration is a critical factor in athletic performance, however, it is a bit of a well kept secret on how exactly to do that. Most athletes will be familiar with generic hydration guidelines, but to really dial it in, you need to understand something else; your sweat rate.

What Is Sweat Rate?

Sweat rate is the amount of sweat an individual loses per hour during physical activity. This rate varies significantly between individuals due to factors such as genetics, body size, fitness level, environmental conditions, and the intensity of the activity. On average, athletes may lose anywhere from 0.5 to 2.5 litres of sweat per hour, with some losing even more under extreme conditions (I have had athletes lose over 3.5L an hour before!!!).

Sweat is composed not only of water but also electrolytes, primarily sodium, which is essential for muscle function, nerve signalling, and maintaining fluid balance. As sweat rates increase, so does the loss of these critical electrolytes. This can lead to fluid and electrolyte imbalances, impaired performance and serious health risk if not properly managed.

Why Is Understanding Your Sweat Rate Important?

Understanding one’s sweat rate allows you to develop a personalized hydration strategy tailored to your specific needs in terms of both how much fluid you should consume, and how much electrolyte you should consume. Here’s why it is important to get this right;

1. Preventing Dehydration: Dehydration occurs when fluid loss exceeds intake, leading to a decrease in blood volume. Our body is fairly resilient to dehydration but it can cause detriment to many functions in the body including; decreased ability to regulate temperature, deliver oxygen to muscles, and thus maintain performance. By knowing your sweat rate, athletes can more accurately replace lost fluids during exercise, preventing the negative effects of dehydration.
2. Avoiding Overhydration: While underhydration is a concern, overhydration can be equally dangerous. The overconsumption of water without adequate electrolytes can lead to a condition called hyponatremia, a condition where blood sodium levels drop dangerously low. This is more likely to occur in athletes who are not as big sweaters but drink large amounts of water (without sodium). This is especially problematic in long-duration events. A personalized hydration plan based on sweat rate helps balance fluid and electrolyte intake, reducing this risk of this condition.
3. Optimizing Performance: Proper hydration helps maintain cardiovascular function, muscle efficiency, and cognitive performance. An athlete who understands their sweat rate can time their fluid intake more effectively, ensuring they stay hydrated without feeling bloated or waterlogged, which can hinder performance.

How to Calculate Sweat Rate

Athletes can estimate their sweat rate by weighing themselves before and after a workout, taking into account any fluid consumed during the exercise. The difference in weight, adjusted for fluid intake, represents the total fluid lost. Dividing this number by the duration of the workout gives an hourly sweat rate.

For example, if an athlete loses 1.5 kg during a 2-hour run and consumes 1 litre of water, their sweat rate would be calculated as follows:

• Total fluid loss = 1.5 kg (weight loss) + 1 kg (water consumed) = 2.5 liters
• Sweat rate = 2.5 liters / 2 hours = 1.25 liters per hour

Although this is an effective means to calculate sweat rate, there are a few more steps to make this more practically useful. Firstly, you need to do this across a number of training session which are different intensities and different durations. 

By doing this you will better understand how your body sweats in different conditions and how your sweat rate changes as exercise duration increase (as the body gets dehydrated sweat rate will naturally slow down, this is often something athletes who participate in long duration training/events forget to consider). 

Once you have calculated your sweat rate, you need to do one last thing, calculate your tolerance to fluids. 

Calculating Your Fluid Tolerance

Although this may sound simple, it is anything but, because it is this step of the process that makes creating an adequate hydration strategy complicated. That is because this is where the ‘personalization’ really comes into play and the genetics of how you sweat will determine the success of your hydration strategy. 

Take for example an athlete who is a ‘big’ sweater, say they lose 2.5L of fluid per hour of exercise. Knowing that you need to replace 2.5L of fluid is one thing, doing it is another. This is where the type of activity that you do matters. 

If the above athlete ran ultra marathons, then it would be very unrealistic to expect them to be able to stomach 2.5L of fluid each hour. Therefore recommending this person to use the same hydration strategy as someone who only loses 500ml per hour of sweat (which is easily replaced), is not advisable. 

Therefore, a new strategy has been gaining traction and popularity in the sports nutrition world, and that is the 70% rule. This states that if an athlete can consume 70% of the fluid they lose they should aim to consume 100% of the electrolytes they lose. If they cannot meet at least 70% of the fluid they consume, they should consume a much lower amount of electrolytes. 

For the examples above, if the first athlete who loses 2.5L an hour can only tolerate 1.5L per hour, which is 60% of the amount they are losing, then they do not need to replace all of the electrolytes they are losing. 

For the second athlete who loses 500ml an hour, if they can easily consume that much liquid, then it is wise for them to consume the electrolytes they lose. To assess your specific electrolyte loss during training, you would have to complete a sweat test to see how many milligrams of sodium you lose per litre of exercise. 

With our athletes we use a fairly simple rule which works very effectively when deciding what electrolyte products are best for them; if they are a big sweater (>1.5L/hour) and only exercise for up to 2 hours at a time then they should be using an Oral Rehydration Solution, like Trainade Hydration. If they are a small to moderate sweater (500ml to 1L/hour) and only exercise for up to 2 hours at a time then they should be using a high sodium product. If they exercise for over 2 hours at a time, they should consult a professional for individual hydration strategy specific to their event.

To Wrap It Up

Understanding sweat rate is a fundamental aspect of developing a personalized hydration strategy that aligns with an athlete’s unique physiological needs. By tailoring hydration to individual sweat loss, athletes can prevent dehydration, avoid overhydration, better manage blood electrolyte levels and optimize their performance across various conditions. Regularly monitoring sweat rate, especially in different environments and intensities, ensures that hydration strategies remain effective and contribute to peak athletic performance.