How to work out your sweat rate

How to work out your sweat rate

Sweat Rates and Dehydration

Our sweat mechanism is our natural and most efficient way of cooling our body down. When our bodies heat up and reach a threshold we begin to sweat.  Sweat rates are quickly becoming a hot topic in sport as part of your hydration and fuelling strategies during training and racing. 

Other than sweating, we also have a thirst mechanism. However, factors such as stress or other external stimulus may cause us to overlook those thirst signals when training and racing. Mild dehydration where you can experience weight loss of 1 – 2% is relatively common during sustained exercise. It is usually expected and preferred than overcompensating and trying to drink to replenish exactly what you have lost or more. 

In contrast, overcompensating on the fluids you have lost is not advisable. You don’t need to be drinking more fluids than you sweat when exercising. Being mindful about your fluid intake prevents you from overly diluting your blood sodium concentration from excessive fluid intake during exercise leading to hyponatraemia

With greater levels of dehydration comes higher chances of excessive plasma volume depletion. This plasma depletion means the heart must work harder to supply the working muscles. Plasma depletion also has an impact on how efficiently your body is at cooling itself.

 

Lady standing on scales measuring body weight for sweat rate test Image: i yunmai on Unsplash

Benefits of Knowing Your Sweat Rate

Knowing your sweat rates is a start in mastering your hydration and fuelling strategy for training and racing. You’ll understand how much fluid replacement is needed under varying conditions, so that you can perform at your best.

Adding the knowledge of your sodium concentration loss to your tool kit will help determine the electrolytes needing replacement when exercising. Therefore, knowing these two aspects puts you in a solid position to kick starting a robust hydration and fuelling strategy.

As a result, you are less likely to carry extra fluids. Train with less weight, less effort and less cumulative wastage.

Knowing your sweat rate can help prevent larger weight losses that lead to more severe levels of dehydration, which can impact your performance - particularly in hotter and humid conditions. 

Getting a few sweat tests under your belt will create a better awareness of your fluid intake needs during exercise. You will reduce over or under compensating on your fluid intake, particularly when you are in more vulnerable hot and humid climatic conditions.

Triathletes running sweating on road in race 

Sweat Test Best Practice

Testing should be done in multiple scenarios ranging from hot, dry and humid conditions to cooler, colder climates. Testing your sweat rate a few times and in these variable conditions means you will become more efficient at the procedure, and you will become fine-tuned at guesstimating your sweat rates in different climates even without doing a test.

Everyone has different sweat rates. There are some seriously high volume sweaters out there who have been reported of sweating >3 litres per hour. 

There are a handful of factors that influence your sweat rate and some of these are:

  • Your genetic makeup (some people just sweat more than others).
  • Your effort in the activity (cycling power, running speed, etc.).
  • The external environment, i.e., hot, humid, or cooler climates.
  • The gear you are wearing and carrying.
  • Your fitness level and degree of acclimation (fitter athletes who are better acclimated are likely to sweat more in a response to regulate their body temperature better).

Test in a session that lasts longer than 45 minutes but less than 2 hours. Shorter sessions may not result in peak sweat rates and therefore cause errors in calculations. Sessions longer than 2 hours mean that you will also need to consider what fuels (carbohydrates and fats) you are burning that contribute to your weight loss. You can expect weight losses of up to 0.5kg or 1 lbs in sessions lasting 2 hours or more, with greater losses in longer sessions.

Try avoiding going to the toilet when testing. However, as the sessions might be 2 hours in duration you may end up needing to go. If you do, then you can assume that any fluid loss is roughly 250ml – 300ml (250g – 300g) per toilet stop. Note how many times you went to the toilet and subtract this total from your sweat rate calculation; otherwise you will be overestimating your sweat loss by the amount of fluid you lost when going to the toilet.

Other corrections for non-sweat body weight changes such as the consumption of food or any bowel movements should also be considered in your calculations. These figures should be deducted from your overall sweat loss.

Your sweat rate calculations will be estimations at best. There can be 5 – 15% variation of results even under the strictest replicated testing conditions. Athletes are recommended to follow a categorical scheme where their sweat rates are categorised into low, moderate, or high levels. These levels would then dictate their recommended fluid replacement. The rationale of categorising can also be applied to athletes’ sodium concentrations lost in sweat once you’ve had a sodium sweat test – how much sodium you lose when sweating.

Not many athletes know how to measure their sweat rates and can be put off thinking you need a lab to conduct your test. There are complex ways to measure your sweat rate but we like to keep things simple at ACTIVE VITA so we will walk you through an easy option.

Below you will see a list of things you will need to measure your sweat rate.

 

Sweat sign for cyclist

Image: claudio-schwarz-unsplash

Equipment needed to test your sweat rate

  • Digital body weight scales (to weigh your body and any drink bottles if you decide to drink during the session you are doing the sweat test).
    • Digital scales give more accurate readings when measuring your drink bottles.
  • A dry towel.
  • Something to record your data on or use our online sweat rate calculator.

How to Calculate Your Sweat Rate

The simplest and most accurate method to assess sweat rate is via changes in nude body weight from before to after exercise. There may be occasions when going nude may not be an option. In this case the use of as little and light clothing as possible is recommended. You will need to consider the weight of your garments and the sweat retained in the garments after exercise and account for this in your calculations.

For a quick and easy way to determine your sweat rate then use our online sweat rate calculator. Just pop in the figures and hit calculate and you’ll receive the results. There is an option to enter your sodium levels if you’ve had your sodium concentration test done. If not then don’t worry you can still get some pretty good results to help guide your hydration requirements.

Here is a spreadsheet to help you record your sweat rate data. Keeping your rates recorded is a great way to highlight patterns and build your overall hydration and fuelling strategy to help determine your optimal hydration, fluid and electrolyte requirements.

The spreadsheet is a great tool to spot patterns and give you a consensus on your sweat rate over varying conditions and activities. There are two tabs both with sweat rate calculators. Choose the one you prefer.

You may also get body composition scales (image below) that measure muscle, fat and your water levels. You could consider using these - however, it is suggested you still use the changes in body weight method at least once to validate the accuracy of the body composition scales. Once you have determined their accuracy then you could use the scales going forward. 

 Body composition scales measure muscle fat sweat rate water loss

 Body Composition Scales 

Steps to Measure Your Sweat Rate

  1. Void all urine, then weigh-in wearing little to no clothing, in order to obtain the most accurate reading.
  2. Following the weigh-in, exercise for at least one hour while keeping track of the quantity of fluid consumed.
  3. After exercise, dry yourself off, and step onto the scales again. Make sure to wear exactly what was worn when measuring your weight before you exercised.
  4. Subtract the post-exercise weight from the pre-exercise weight in kilograms or pounds, and convert the difference to millilitres (1g = 1ml) or fluid ounces loss (1ml = 0.03 floz).
  5. Then add to that number the amount of millilitres or fluid ounces of fluid that were consumed during the exercise. This will determine how much sweat was lost during exercise.
  6. Divide the total sweat loss by the total duration of the exercise to determine total fluid loss per hour of exercise.

Sample of Sweat Rate calculator in tab 1

sweat rate calculator  

Sample of Sweat Rate calculator in tab 2

 sweat rate calculator

 

Q: How do my sweat rates compare? 

This study shows athletes with sweat rates ranging from 0.5L/hr up to 2.5L/hr and more. It is generally accepted that sweat losses of 1L – 1.5L/hr are considered an average/moderate sweat rate. Whereas anything less than 1L/hr would be considered a lower sweat rate and anything around 2.5L/hr would be a higher sweat rate. Over 2.5L/hr would be a very high rate.

While comparing your sweat rates to others can provide a general perspective on where you stand, it is more important to view your sweat rates in relation to your own body size, weight and effort level. These are significant factors that can influence your sweat rates. For example, a sweat rate of 1.5L/hr for a petite female cyclist could mean she is a heavy sweater. Whereas the same output for a 7ft male rugby player could mean he is on the lower end of sweat rates. In general men tend to sweat more than women and the very high sweat rates of >2.5L/hr tend to be seen in those with higher body mass exercising in very hot and humid conditions. The key takeaway is knowing your own sweat rate and not worrying over how you compare to others. 

Q. I have my sweat rates. What’s next?

Once you have your sweat rate data, you can start thinking about your hydration and fuelling strategy. Remember, a mild state of dehydration when training and racing is acceptable and you can still perform. This tends to be the preferred approach when it comes to hydrating during exercise as opposed to replacing all the fluids you lose (which can lead to hyponatraemia). If you are replacing your fluids then a reasonable benchmark is to replace around 80% of the fluids loss. That is for every 1L of fluids lost you can aim to replace around 800ml. This is a guide and every person is likely to differ with the amount they can replace when exercising. 

A hydration and fuelling strategy can be key in making or breaking a PB, topping podium or dodging a DNF. However, it’s important to remember that you may need to be flexible with your strategy. Being prepared and willing to be flexible when those unforeseen situations occur such as dropping or losing your water bottle on the course can help you stay on course.

Knowing your sweat rates can take your training and racing to the next level. You no doubt train hard but do you Fuel Smart? Remember for a quick check on your fluid loss use our online sweat rate calculator

At ACTIVE VITA we offer a range of sports nutrition to help you replenish lost fuels from sweating. Pop on over to see how we can help you master your hydration and fuelling strategy and reach out if you have any questions on how best to use our products.  

 

Athlete running in desert sweating and drinking active vita drink mix

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