Everything you need to calculate your sweat losses inc. a free downloadable spreadsheet, plus a guide on how to use the data to optimise your hydration plan!
"}},"slug":"how-to-measure-your-sweat-rate","blogTags":"Hydration","featuredPost":false,"author":{"name":"Andy Blow","slug":"andy-blow","facebookHandle":"https://www.facebook.com/andy.blow.3","twitterHandle":"https://twitter.com/andybl0w?lang=en","instagramHandle":"https://www.instagram.com/andyblow","linkedInProfile":"https://uk.linkedin.com/in/andy-blow-47b90133","stravaProfile":"https://www.strava.com/athletes/6999012","bio":{"childMarkdownRemark":{"html":"Andy Blow is a Sports Scientist with a BSc Honours degree in Sports and Exercise Science from the University of Bath. An expert in hydration, he has co-authored a number of scientific studies and books.
\nHe was once the Team Sports Scientist for the Benetton and Renault Formula 1 teams and remains an adviser to the Porsche Human Performance Centre at Silverstone.
\nAndy has finished in the top 10 of IRONMAN and IRONMAN 70.3 races, as well as winning an XTERRA Age Group World title. It was his own struggles with cramp that led to him specialising in hydration and founding Precision Fuel & Hydration.
"}},"title":"PF&H Founder and Sports Scientist","headshot":{"file":{"url":"//images.ctfassets.net/428xzyjdw7rf/2LTns8O1ZGOHSfDQGv2jZz/f6470d62f0c1f14e7239432f60a0b765/Andy.png"}}},"scientificallyReviewed":null,"image":{"resize":{"src":"//images.ctfassets.net/428xzyjdw7rf/Iv9C02n0g6vN5PVQFnxna/ade0d779afc9d9ae62570c0c367cbb9b/Weighing_scales.jpg?w=1200&h=630&q=70&fit=fill","width":1200,"height":630}},"socialMediaImage":{"resize":{"src":"//images.ctfassets.net/428xzyjdw7rf/6xwFUIJ1xGivxhTbLTX5TA/2ee383b22b077beecac52faa38f2856f/resized-Measuring_your_sweat_rate.webp?w=1200&h=630&fl=progressive&q=90&fm=jpg&fit=fill","width":1200,"height":630}},"body":{"childMarkdownRemark":{"excerpt":"Estimating your sweat rate can be a useful exercise when you’re trying to figure out how much and what you need to drink during training and events. Sweat rate…","html":"Estimating your sweat rate can be a useful exercise when you’re trying to figure out how much and what you need to drink during training and events.
\nSweat rate varies considerably from person-to-person due to body shape, size and fitness level. Your own sweat rate can also vary quite a lot as a multitude of factors - including how hard you’re working, the ambient temperature and humidity, wind speed, your clothing and heat acclimation status - all play a role in determining how fast and how much your body perspires.
\nIdeally, sweat rate measurement should be done on several occasions and in a range of conditions. So, you can then extrapolate the results and use them as a guide to dial in your fluid and electrolyte intake for an upcoming race...
\nEquipment needed:
\nMethod:
\nThis is slightly adapted from Asker Jeukendrup’s excellent mysportscience...
\n2. Perform your session (or event) and record exactly how much you ate and drank.
\nThis is easy if you drink from a single bottle or two.
\nWeigh your bottles before (That’s X) and after (Y) and record the difference. 1 gram = 1 millilitre.* (Z)
\n* If you use different measurement units, e.g. fl oz, you’ll need to convert all values to litres (via Google!). Make sure all units are in kg or litres
\nWeight lost (C) = A-B
\nWeight of fuel and hydration consumed (Z) = X-Y
\n6. You can now calculate your sweat rate…
\n(C+Z) / your exercise duration (in minutes)/60 minutes.
\nNote: It’s best not to use the bathroom at all during these sessions as this can skew the results. If you do have to go, in an ideal world you’d weigh yourself before and after to measure urine output, although a decent estimate is to assume a fluid loss of ~0.3L (300ml / 12oz) per bathroom stop.
\nYou then just need to subtract 300ml (0.3kg) from your estimated sweat rate at the end.
\nI’d generally recommend trying to limit data collection to sessions lasting at least 60 minutes to 2 hours long. This is because anything shorter than that can be prone to errors of multiplication in the equations and doesn’t account for the time it takes to reach steady state sweating and may underestimate fluid losses over longer durations. Anything longer can start to be skewed by other non-sweat related sources of body mass change, including fuel utilisation (you inevitably burn glycogen during exercise and this can affect your body weight results), and respiratory water losses (a function of the amount of air moved in and out of your lungs as you breathe).
\nTo make the above calculations really easy, you can collect all of the data into this spreadsheet along with some relevant notes about your session (mode of exercise, duration in minutes, rough intensity, temperature, whether it was outside or inside etc).
\n\nThe sheet will then spit out a % bodyweight loss figure for that workout and also an estimate of your sweat rate expressed in litres per hour. Like this:
\nYou can record numerous sessions in the sheet and this will help you to get a handle on what kind of range of sweat losses you see for different sports, in different weather conditions and at different intensities.
\nThough these calculations likely won’t be 100% accurate, they give you a good estimate of your sweat losses and will help categorise how sweaty you are. If you do this enough, you’ll become very good at ‘guesstimating’ your sweat rate in the future; a dinner party trick of dubious value if nothing else!
\nPlus, if you’ve also had a Sweat Test with us, you can add your sweat sodium concentration data in and it will estimate your hourly and total sodium loss numbers too, helping you get a good idea of what you’re losing so you can more adequately replace it.
\nWe often get asked what constitutes a low, moderate or high sweat rate by athletes taking our Fuel & Hydration Planner and it’s a tricky question to answer as there are a lot of variables involved.
\nA recent paper helpfully looked at a range of sweat rate data collected in a variety of sports and the graphs below show something of the trend in the data from 102 athletes in 340 trials:
\nThe range of sweat rates in the data was about 0.4 litres per hour to close to 3L/h (we have also observed as high as 3L/h in the Precision Performance Lab.
\n\nAnother study done at the 2003 Hawaii Ironman in Kona came up with a very similar range of sweat rate figures in athletes a few days before the race.
\nDepending on your body shape and size (individuals with smaller body weights will typically sweat less than larger individuals as smaller people have lower absolute rates of heat production, which requires less sweat to keep you cool), anywhere from 0.5-1.5L/h are low-to-moderate sweat rates. These are common and relatively easy to manage from a fluid loss and hydration standpoint.
\nAnything much less than 0.5L/h would be on the low side for race intensities in mild conditions. Anything above 2.5L/h means you will start to run into issues with taking on enough fluids to remain hydrated during prolonged exercise in warm conditions.
\nWhilst we’ve seen those very high sweat rates of upwards of 3L/h in a handful of athletes, it tends to be in very, very big guys (men do tend to have higher sweat rates than women as men tend to have more muscle mass and therefore higher rates of metabolic heat production), and/or those working incredibly hard in oppressively hot and humid conditions.
\nDo bear in mind that body weight and size factor into all this, so if you’re a small female distance runner but you’re sweating at 1.5L/h, that might be considered a high or even very high sweat rate for you. On the flip side, the same number might be deemed quite low for a 6ft 11in (210cm), 150kg (330 lbs) Offensive Lineman in the NFL. But, I’m sure you get the general idea.
\nOnce you’ve collected a reasonable amount of sweat rate data, the obvious question is \"what can you do with the numbers?\" And unfortunately the answer is not as straightforward as many athletes would like it to be.
\nOften you’ll see athletes performing these kinds of sweat rate tests and then proceeding to work out that an example sweat rate of 1L/h when running hard means they obviously need to drink 1L/h when running (i.e. to replace 100% of their losses).
\nThere’s a nice simplicity to the concept of ‘1 out = 1 in’ and for a long time it was assumed that 100% sweat loss replacement during exercise was likely to deliver an optimal performance.
\nBut time and research has shown that this logic is fundamentally flawed (the maintenance of performance in an exercising body is way to complex) and few, if any, credible sports scientists or nutritionists would advocate ‘like for like’ replacement of sweat losses during activity these days.
\nIn fact, as 100% replacement often requires drinking beyond the body’s natural thirst instincts, it can be very dangerous. It carries the risk of hyponatremia (low blood sodium levels resulting in some nasty symptoms) if taken too far and this alone is enough to strongly discourage 100% fluid replacement as something to shoot for.
\nYou can actually tolerate quite a bit of dehydration (as defined by body weight loss) during training and competition - assuming you start well hydrated. The exact amount you need to replace throughout your race is dependent on a few factors. The percentage of your sweat losses you should replace increases as your event duration increases (for example, when stepping up from an IRONMAN 70.3® to a full distance IRONMAN®) and as environmental conditions get more challenging. We know that dehydration exacerbates the impact of heat on exercise performance. In other words, the hotter you get and the conditions are the more important hydration is for performance.
\nThis blog on how much dehydration you can tolerate is well worth a read as it gives some pointers on how much sweat you can probably lose before your performance is compromised and should help get your head around how much fluid you might want to be replacing.
\nIt’s not productive to try to use sweat rate data to try to create a pre-determined, inflexible strategy for fluid and electrolyte replacement.
\nMeasuring your sweat rate should be about getting to a pretty decent ‘ballpark’ figure for how much sweat (and sodium if you know your sweat composition) you’ll likely lose over a period of time, at a certain intensity and in a particular set of environmental conditions.
\nThe reason we can’t use sweat rates from training and testing for hydration plans without question in races is that sweat rates are dependent on multiple factors, such as your power output or running speed/grade, environmental conditions (ambient temperature, relative humidity, solar radiation and wind speed), and clothing.
\nAnd so, without keeping these factors exactly the same between testing/training and racing, you can’t be certain of your sweat rates in different combinations of those factors. If you do enough of this testing in and around the type of scenarios you encounter in training and competing, it can be very helpful in working out the approximate levels of fluid and sodium intake that you’ll then go on to experiment with to optimise your performance.
\nIt's worth noting that calculating sweat rate should be used as a GUIDE, and you should always defer to your body's signals in the moment to make adjustments. It's unrealistic to strictly follow a plan all the time because racing is dynamic (with fluctuations in speed, race temperatures, and physical conditions affecting metabolic rate and sweating rate/fluid loss in real time).
\nIf you need some help with putting a hydration plan together to test in training, take our free Fuel & Hydration Planner. If you do that after getting some sweat rate data you’ll be able to answer our question on sweat rate with more confidence/accuracy.
\nLet’s say you’re losing ~0.5L of sweat per hour. It’s unlikely that you’re going to benefit from doing much more than drinking to thirst as, even over several hours, your total fluid and sodium losses are unlikely to get especially high.
\nBut, if you’re losing more than 1.5L per hour then, during prolonged exercise, you’re likely to benefit from getting in front of the dehydration/sodium depletion curve with a pretty aggressive approach to hydration.
\nTaking proactive action during the early stages of big sessions and long events will help mitigate your inevitably high losses over the long haul. That’s especially the case if you also have a high sweat sodium concentration.
\nBy measuring your sweat rate (and sweat concentration) and using this as a guide with differing levels of intake, you’re much more likely to iterate your way to the kind of hydration plan that will serve you well when it matters most.
\nThis is just one part of the hydration equation...
\nDr Tamara Hew-Butler is an Exercise Physiologist and Associate Professor of Exercise and Sports Science at Wayne State University in Detroit, Michigan. She is a Fellow of the American College of Sports Medicine (FACSM) and specializes in both sports medicine and exercise physiology. Her expertise is in exercise-associated hyponatremia and the endocrine regulation of water and sodium balance. She has published over 80 scientific articles and her work has been highlighted on radio shows (Science Friday, National Public Radio), television (The Weather Channel), podcasts (CJSM), newspapers (New York Times, Washington Post, CNN), a comic strip (xkcd) and reality television show (Adam Ruins Everything). Dr Hew-Butler is an avid runner and sports fan. She enjoys spending time with her husband, Bill, and pet ducks on their 10-acre hobby farm. Tamara obtained her BS in Kinesiology at the University of California at Los Angeles, CA. As well as her Doctor of Podiatric Medicine (DPM) at Temple University in Philadelphia, PA; and her Philosophy Doctor (PhD) at the University of Cape Town, South Africa. With more than 80 published scientific works to her name, Dr Tamara Hew-Butler is a leading figure in the field of hydration and hyponatremia. Considering exercise-associated hyponatremia as a continuum (BMJ Case Reports, 2018) Exercise associated hyponatremia: 2017 update (Frontiers in Medicine, Lausanne)Exercise Physiologist and Professor
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