Heat Acclimation Strategies with Julien Périard PhD | Koopcast Episode 97

trail and ultra runners what is going on what's happening welcome to another episode of the KoopCast as always i'm your humble host coach Jason Koop and this episode of the podcast is about a topic that we seem to revisit time and time again and the reason we do is because i always get a lot of questions on this it is about how to train and prepare for events in the heat i have a real treat for you guys today in our next guest who is julian perryard who's a research professor at the university of cambria research institute for sport and exercise where he leads the environmental physiology research group there you guys know that i like people that are in sports science that are also practitioners and julian is one of those he works with a number of different sports including with fifa the uci world athletics and world triathlon he's also a national level triathlete in his own right or used to be a national level triathlete in his own right we talk a little bit about that at the early parts of this podcast but i came across julian's work when i was doing a lot of research in how to incorporate different heat acclimation protocols for athletes and his name kept coming up time and time and time again and just most recently there is this fantastic behemoth of a

paper titled exercise under heat stress thermal regulation hydration performance implications and mitigation strategies and it is one of the most comprehensive papers that i have ever seen on a topic is one that i will give to a lot of our coaches and is one that i will continue to personally use and professionally use as a resource for times for times to come that paper the link to that paper will definitely be in the show notes so go ahead and check it out but be forewarned is a big one it is really meaty and it'll take you a while to get through it took me about three days to get through we tried to distill a lot of the pertinent information down into the hour plus of this podcast and i think we did a really good job with it and i hope that everybody comes away with some practical ways that they can implement some of these heat acclimation protocols and what is actually going to increase their body temperature to a range where it's actually going to affect their performance so here we go i need to get right out of the way here's my conversation with julian perriard it took me i don't know maybe three days to actually kind of weed through it all and it's all material that i'm you know familiar with for the most part yeah but it was hefty it was yeah and to be honest i don't think we intended for it to be that large but it takes so long to make these things to write these things it took us well you get two years but it took us two and a

half because we got delayed and then um yeah we keep talking we kept talking and say oh yeah well maybe we should have this bit to make that later on yeah and i was doing the bulk of the writing so i was like well yeah it was but yeah it's written now so it's all good it's good to know that project creep happens in academia as well oh yeah for sure i mean it's one of those things as well i don't think you know like that you read from start to finish in one go i think it's one of those things that you grab you know bits and pieces that you need hopefully um yeah well congrats on it i mean this is easily a book this is easily a book chapter in a graduate level exercise phys course i'm sure you'll get tapped for something like that and just amend what what is here because it's it's very very comprehensive yeah well thanks for that yeah it was that was that was the idea so i'm glad that it it's perceived to be so so that's this kind of like leads into like my first question it's like describe a little bit about the work that you do at the university and like what was the genesis of this this behemoth of a paper that we've just been talking about sure yeah yeah well i can tell you a bit about my journey as well like how i got here i'm i'm canadian so as you can tell i don't have an australian accent um so i'm canadian i did uh i did my undergrad and my master's at the university of ottawa and then um i kind of got the triathlon bug as many people do once they do a triathlon so i kind of got into that and then for a while i did all right so i won our national age group championship so i thought oh i can try my hand and being a pro which yeah which i did so i went to our

national training center and um um i trained for five years and did like world cups and continental cups and things like that which was which was which was amazing um but then i realized all right i this is very fun and enjoyable but i'm not going to the olympics so i thought okay well what else can i do so um i was very much obviously at that point interested in performance and performance in the heat um so i found a great place to a PhD at the university of sydney and i was looking at that time at the mechanisms that kind of mediate performance so what are the pathways by which performance is impaired under heat stress so at the time you know there was the cardiovascular element to cardiovascular function and then that critical core temperature i don't know if you've heard about that so when you reach a really high core temperature you know the i guess neuromuscular activation is reduced the muscles therefore your performance is decreased and then another one was anticipatory fatigue so i kind of looked at those aspects um once i finished that i went to aspatar sports medicine hospital in qatar and as you might know the world cup for soccer or football is in qatar next year and they were going to have it in august and obviously august qatar is like it's literally to 48 degrees celsius 50 degrees and um so we tried different things to see how well people locomotize or acclimate and so forth and we're like well it's the difference between 36 37 40 degrees and 50 degrees so it's quite hot so they've moved that then after six years there i moved to i moved back to australia so in canberra where i am now at the research institute for sport and exercise

and i've continued my research there so looking at mechanisms of fatigue in the heat but also kind of pathways to mitigate that or to reduce the impact of heat stress so heat acclimatization heat acclimation cooling strategies ensuring proper hydration and i'm kind of venturing a little bit as well into the heat therapy side of things for older individuals and people at risk of falling so that's kind of where my my area sits but um i still have a very big passion for for sport obviously in performance particularly in sports it's interesting that you went through that journey because that's basically what our outline is going to be right we're going to talk about like what are the things that make you hot to start out with and then how do you mitigate them because ultimately that's what the athletes are interested in we can get into a lot of the underpinning physiology as it as it comes along but the end part of it what do you do to actually mitigate it i feel like this is an area that's starting to actually come around where we're starting to find things that have really good efficacy that are reasonable to implement which is always important with athletes right you don't want to be running around like a chicken with your head cut off doing all these interventions that don't work and or interfere with training and we see it in the playing field whether it's on rugby pitch or out in the olympic you know track and field venue and things like that like i'm starting to feel like we're we're getting a good grip on it where we're seeing some of the same mitigation and acclimation strategies kind of over and over and over especially at the high level sports that's right that's right i think

one of the points that you underpin there that's quite important is not interfering with with training because a lot of the the research that we do in the lab it's very controlled you know you're like okay let's put people in the in the hot room for 90 minutes and 10 days straight which which is ideal for looking at you know the adaptations the mechanisms and so forth but for an athlete who's who's tapering like naturally you're not going to heat acclimatize six months before your big competition so it's it's tailoring your training or more so your intervention around your training so that you keep your training optimized then you kind of supplement that with with whatever intervention you'll do to ensure that you are properly um prepared for your race so you're right and then kind of tailoring that for different sports whether it's team sports or even individual sports or endurance sports so yes we are we have different very many different strategies to use now so it's kind of using a combination of those yeah well we're going to come back to that because i always have this most hilarious story about my introduction to ultra running being at badwater which is kind of a that is trial by fire in every sense of the word and i use it as a point to illustrate some of those facts but let's back up a little bit and kind of set the table with this the one one of the things that this paper did a really really good job of is starting is outlining everything that can make you hot and most people think of it as the environment especially in ultra in ultra running we think about races like the western states 100 which typically gets uh temperatures of in excess of 100 degrees especially the canyons or the bad water 135 that i just mentioned and that's while that

environment is a dominant player there are also other things that athletes need to take into consideration when they're looking at the landscape of how how like how hot could i potentially get during these events and is it going to be a failure point so let's let's set that up first what are the things that athletes need to look at within the events that they're training for yeah that's a very good point and i think as you highlighted the environment obviously is probably the first thing that you that you look at and i think when people think of the environment they think of all right how hot is it going to get and maybe after that they think well how humid is going to get is it going to get so those are obviously the primary factors um so what's the temperature going to be what's the environmental relative humidity going to be and i think one of the first things we need to remember with with temperature is when you look at the temperature gauge you know when you look at the bureau of meteorology or whatever when they when they tell you what temperature it is that temperature is always measured in the shade so that's temperature in the shade so it's the first thing to remember that's quite important because the other factors that affect the thermal environment in addition to temperature and relative humidity are solar load or solar radiation so the heat emitted from the sun and oftentimes in degrees celsius um you can have a certain temperature outside in the shade let's say 30 degrees but it could be 10 15 degrees warmer in the direct sun so if there's not if it's not cloudy whatsoever and you're in direct sunlight it can be a lot hotter than what the temperature gauge tells you because once again that's that's measured in the shade and the way we measure um temperature um like exposed temperature is with a black globe so essentially you stick a thermometer in a black

globe because that attracts all the radiative heat and so forth so it's very important to understand as well like will it be cloudy will it be um will it be completely clear and i guess the fourth aspect of the environment is is wind speed and wind speed is quite important because that helps with thermal regulation as well um and those are kind of the um the four parameters of the environment that are important so the temperature the relative humidity um the solar radiation and the and the wind speed and the reason they're important is because they affect thermal regulation and there's two kind of ways that we thermal regulate one is through like autonomic responses or automatic responses essentially so as we get hot um we send more blood to the periphery to the skin and that's essentially a way of taking blood that's really hot in the central circulation sending it to the skin and then we can lose that to the environment but the important thing there is that there needs to be a gradient between the skin and the environment right so if your skin is is warm and it's cooler outside and that's not a problem you can lose heat via convection so the kind of wind flowing over your skin to the environment but if it's really hot outside and the air temperature is warmer than your skin temperature then you actually gain heat via convection um having said that that pathway to losing heat or heat exchange is is important but it's not as important as sweating so sweating especially in hot conditions is the primary avenue of heat loss especially again like if if it's hotter outside and your skin temperature then obviously you're

not losing heat via convection so it's really at some point becoming the the primary avenue for heat heat loss um so obviously with sweating being very important you want those beads of sweat to evaporate and that's one of the things that people might not necessarily realize is that you know if you're sweating and those beads of sweat are simply just kind of trickling down your skin and fall into the ground you're just basically getting dehydrated right so that bead of sweat that forms on your skin needs to evaporate for it to kind of cool your skin and kind of start cooling you down so um if we go back to the environment if it's very humid then the air around the body is kind of saturated has a lot of water vapor content within it so it's more difficult for those beads of sweat to evaporate so if it's really dry you might be sweating quite a lot but not even realize it because the beads of sweat are evaporating more readily um and i guess another thing with that is the wind speed so if you have a bit more wind that kind of helps with the evaporation of sweat because it kind of removes that layer of maybe saturated water vapor around the on the skin so it helps with uh with sweating so a lot of things a lot of moving parts there and things to consider it's it's i'm glad that you mentioned the clothing and the sweating uh piece of things because this is a piece of advice that we see thrown thrown around a lot on both sides of the fence in coaching circles and also athletic circles is what type of clothing should you actually wear in these environments and i always kind of come back to that fundamental piece that you just mentioned is you want the water to evaporate because that's what makes that's

what creates the temperature gradient you spend a little bit of time talking about that in the paper what did you guys come up with when you were evaluating the right clothing properties to actually wear in hot environments yeah that's a good point and i think there's several um um most of the clothing that you can get for um performing in the heat i guess is quite good but the issue becomes the well the issue becomes or arises i should say at the point where um whatever garment you're wearing becomes saturated because initially when you're exercising you start sweating i think those garments are quite good at wicking the water from your sweat putting it through the um the garment and then kind of evaporating but once you're sweating a lot and that garment becomes saturated with with water then it becomes less effective about kind of evaporating the water from its from the fabric i guess so um yeah so you want obviously a fabric that's that's wicking that can take the sweat off and bring it into the surface of the garment to then kind of be uh evaporated or or or you can lose heat and with convection by cooling the garment down i guess but um so i think it's very important to keep that in mind and what about in that same vein the use of cold water and or ice at the same time because that that almost has it has an effect where yes you're you're actually putting the temperature gradient on these pieces of skin right through the through the ice or through the water but at the same time you're not allowed you can't you can put get yourself in a situation where you're not allowing it to evaporate

yeah well that's an interesting one because people also think sometimes about using cold water or um or ice to kind of cool you down but it doesn't really cool you down like if you think of cooling we're thinking of cooling down your core temperature so if you're just putting a bit of water cold water on your head um it might make you feel better for a little bit because it feels cooler um and it might cool your skin down a little bit but it certainly won't cool your core temperature down um if you're continually doing it and then maybe at some point it'll kind of um slow down the rate of rise in in temperature but it'll still go it'll still go up um because the surface area that you're covering is quite small and you know you're putting a small amount that's not continuous um so in terms of evaporating itself yes you're right that's that's another side of it um but i think in terms of cooling you down it would it wouldn't necessarily do it make you feel better um and in terms of cooling the temperature of the skin for evaporation it might have a bit of an effect there but i think you're you'd get back up at temperature relatively quickly unless you keep doing it yeah and you mentioned that if it's not evaporating all you're doing is you're just losing water through sweat and you're becoming dehydrated which is another one of the key ways that your body thermal regulates right as you've got you have to keep your plasma volume up and i want to spend a little bit more time talking about this because this is particularly in the ultra marathon world but also in your kind of previous experience in triathlon this becomes a big issue because of the duration and unlike the the some of the uh

heat acclimation protocols that you know i was raving about earlier that we're starting to get a good fix on this has been an area where you still see the these big discrepancies in terms of how to hydrate and people kind of fall into two camps right do you want to hydrate on a schedule or do you want to hydrate based on thirst and that might be beyond the scope of this right here but i want to know or i guess the listeners are going to be curious to know why is maintaining your hydration status so important in thermal regulation yeah well i think there's two things there's the there's thermal regulation and then the cardiovascular response which are intimately linked but as i mentioned like sweat becomes the primary avenue by which we lose heat when it's hot outside so obviously if you think of sweating you're thinking of losing body water so as you dehydrate you can think of having less body water to use towards towards sweating and there is some research out there that's demonstrated that both skin blood flow and the sweating response are impaired after certain levels of dehydration so the more dehydrated you get um you can think of you know the body trying to conserve water and then sending a bit less to um to the sweat glands and so forth of the sweat glands producing less um less fluid and secreting less fluid for evaporation so um that's part of it so if you get very very dehydrated and you're in hot conditions then you might compromise your ability to thermoregulate and lose heat via sweating which kind of compounds things right because you're already very hot and then if you're sweating less then you're going to get

even hotter because your avenue or your ability to dissipate heat um is impaired and then in terms of performance obviously if you get quite hot um being hot and having a high core temperature and and your blood being warm kind of exacerbates or increases your heart rate for a given workload for example so there's um the pacemaker cells for example in the heart kind of sense that there's an autonomic response so for a given workload your heart rate is going to be higher and then if you lose quite a lot of fluids then you'll have less blood volume as you mentioned so your plasma volume is going to go down so oxygen carrying capacity is going to be somewhat compromised so you'll have to increase your heart rate to kind of bring blood to the working muscles so your cardiovascular response will be exacerbated as well so again for the same workloads or running at the same speed you'll have an even higher heart rate and that's because once again thermoregulation cardiovascular function and you know blood flow they're all intimately linked it but i keep coming back to this this kind of discrepancy between how much body water it would it be appropriate to lose depending upon the duration of the event and you know i mean the the long-time listeners for this podcast will remember i had a i had a stavros kavaros on who i'm sure you're you're very familiar with and he's pretty adamant that listen you know you can tolerate kind of up to a two percent dehydration and that's you know we can we can function normally but we really don't know in an ultra situation how much more dehydration you can actually tolerate based on these other fluids that

just naturally get lost that aren't really contributing to the plasma the plasma volume that you're talking about it's so integral to these to these physiological functions and you see that the the the the real life manifestation of not knowing that comes out in how the medical team at different races manages themselves and i've been around ultra running enough where i have been at two different hundred mile races in the same year that were separated by three weeks and in the pre-race meeting before one of them one you know one medical one medical doctor that is responsible that is responsible for the race is telling us that you cannot drink enough that you just need to drink and maintain your body weight as much as possible and the other one is saying listen you we can tolerate up to an eight percent amount of dehydration and you'll be totally fine and the athletes that kind of like that are at those races they're they're going to be like okay that's exactly what i'm going to do right and so i kind of worked through this with a lot of academic type of practitioners to try to get to try to have the listeners understand that it those are hard answers to kind of come by and it's the duration that compounds the whole issue right it's are you running for five hours or 10 hours or 15 hours or 20 hours that we all lump into this ultra marathon group that kind of makes things really complicated yes yes you're i think you're absolutely right it's it's very very complicated i don't think there's

a straightforward answer i think the other thing too is that you know in terms of tolerating i mean yes we can tolerate eight percent dehydration i don't think anything too dramatic will happen in terms of health you might not feel great but you can tolerate it but then it comes down to what are your goals so you know i'll finish in the best state possible do you want to optimize your performance throughout your run and you're right there's a very big difference between a four-hour run and a 15-hour run because naturally you know given everything being the same the environment course and so forth you'll be out there for much longer so um you'll be producing less heat likely in the 15-hour run than the four-hour run because you'll be running at a lower metabolic heat production and i think that's the other thing i forgot to mention earlier um you know within the environment obviously that creates thermal stress but probably the most important avenue of of well i guess the bad the the greatest level of heat that we can gain is from metabolic heat production and exercising ourselves right because if you think of someone lying on a beach and it's 40 degrees or 100 degrees outside it's not too much of an issue but if someone's doing an ultra on that same beach 40 degrees or 100 degrees that's very different because we produce heat right and as humans we're very inefficient so some of that heat or that energy is directed towards movement but you know 10 15 percent maybe but the rest is released as heat so we produce lots of heat and the harder we go the harder the run the more heat we produce so again if you're running four hours you're probably going to run slightly harder than if you're running 15 20 hours so those are some of the

things that we should consider as well so how long is the race how much heat am i going to produce do i want to optimize my performance um and i guess my answer to to all of that to come back to your to your question is um i agree with with sarvos you know it's like after a certain point of dehydration um your performance and thermoregulation are going to start to be impaired i would i would say though that it's not like you know you're reaching a cliff and it just kind of falls it's kind of progressive so someone might get to a two three percent body mass loss but because they're running at a relatively somewhat sub-maximal intensity performance might not necessarily be impaired you know but if you're doing like a really hard 30 40 minute one hour run where you know you really need to be on on top of everything and everything needs to be optimized and maybe you'll see some performance decrements there but if you're you know a few percent dehydrated and you're running at you know running walking running walking then i don't think your performance per se is going to be impaired or your thermoregulation but i think that does become a point depending on again how long you've been out there how much you are dehydrated how hot it is so i think it's it's very context specific and i think in terms of those recommendations when we did kind of a bit of a historical look at that i think that's what i think the recommendations nowadays are becoming a bit more um tailored to i guess the content in which exercising you know initially in the 50s and well initially when people started doing marathons it was seen as a weakness you know to eat and run and that's obviously changed a lot to as you said you know

drinking a certain amount over a certain amount of time um drinking to to fully offset sweat losses which i think is a bit was a bit dangerous and they saw some cases of hyponatremia where you kind of have fluid overload which can lead to cerebral edema to then to then being a bit more specific because again the other thing we have to think about is within a certain sport you know it's easy to say drink as much as you can or drink like this but depending on the constraints of the sport whether you can carry fluids or whether there's aid stations that x number of kilometers or miles i mean obviously those things come into play when you're trying to plan or not or drink to thirst you know your fluid strategy so i think newer recommendations kind of think of that a little bit more um and i think you know the good well the good ones i guess the balanced ones i should say um you know are the ones that look at the sport per se and you know and then kind of contextualize it so if you're going to exercise in hot conditions maybe in you know for more than 60 90 minutes then maybe it is worth having a fluid hydration strategy um especially if you're exercising at a high intensity if you're exercising in cool conditions at a slow um at a slower um slower speed for example then you maybe you can drink to thirst but i think for ultras isn't this is just my opinion but for ultras given that there's so long and there's so much preparation that goes into it especially with nutrition right so if you're thinking just of nutrition well why wouldn't you think of hydration as well so it's understanding your body understanding

the pace at which you'll be going the environment in which you'll be and how much sweat you lose um and i guess the other thing to that is with running as opposed to cycling for example there's a lot less bouncing around in cycling so you can probably drink more in cycling whereas running you don't want to have too many things in your stomach sloshing around so there's gastric um gastric comfort that comes into play so um well as you can tell it's a very complex answer yeah totally but here's what i keep coming back to and you touched a little bit of you touch on this a little bit about your paper the consequences for losing too much plasma volume losing too much of your body water are exacerbated the performance related consequences are exacerbated when it's hot because you can't thermoregulate as well and or when the intensity is high because the thermal load is higher in both of those cases so you stay well hydrated in the heat your performance will be impaired because your cardiovascular response um is kind of exacerbated yeah exactly and so i look at those two situations and i'm like that's when you really have to have it nailed that's when you really have to have this whole strategy dialed if you're exercising in you know 50 degrees fahrenheit or whatever like where they set all the world marathon majors right and there's a lot of the tales of these athletes that are that get six percent dehydrated eight percent dehydrated that still have phenomenal marathons highly gebersaw assy comes to mind that story gets regurgitated every time we start talking about dehydration it's like yeah he's a good athlete and he was only eight eight percent dehydrated at the

very end of a marathon that was in like 47 degrees you know fahrenheit type type type of weather that's not the case when you're exercising or trying to compete in really hot conditions or when the duration is a whole lot longer that's right and i think to be honest i think one of the things we can expect is that people will be dehydrated like especially you know in a race like that it's it's so long it's so hard and again the fluid depending on what your sweat rate is and your intensity and so forth it's very difficult to consume enough fluids to to remain you hydrate or not lose any body mass firstly and secondly like i said if you're running if you're trying if you're sweating a lot like you know 1.5 liters per hour for example it's pretty difficult to consume a liter and a half of fluid for a few hours in a row so i think that's one of the things that people need to be aware as well of as well and and and be okay with well and you know i might be five percent dehydrated which yes might affect my performance to a certain degree and my thermal regulation but again if you're exercising at a very submaximal rate for a long time the the difference in performance is not going to be a major one i wouldn't suggest especially because you're not at that you know that high intensity where everything needs to be a bit more optimized than at some maximal intensities you mentioned this really interesting you had this really interesting quote a few minutes ago that i want to elaborate on is is that a lot of athletes they have a plan for their nutrition and normally that's i'm going to take in 250 calories an hour i'm going to take in 300 calories an hour but they fail to have a plan for their hydration and i think the the one of the roots of that is

because it should change depending upon the temperature right one of the things that we do with our athletes to try to get a fix on it and i'm not sure that this is the best one so maybe you can you know give me give me a better tool to use in my toolkit here is we just have the athletes athletes do a simple sweat test they go out and they run for an hour in a certain environment and they weigh themselves before and afterwards and we try to get a gauge on their sweat rate but i do it in 10 degree fahrenheit increments to try to set some parameters across what we could use during an ultramarathon inevitably what happens is is we kind of go on like two hour chunks almost throughout the ultramarathon so from eight to ten this is your hydration or this is your fluid replacement rate from ten to twelve this is your fluid replacement rate and we try to get some boundaries off of it and sometimes it's two x from beginning to end sometimes it's like two and a half x you start out with half a liter and you end up with a liter and a half you know at the high points of the day i'm trying to come up with is that a good way is that a reasonable way to do it or is there a better way to do it based on your research and and do the do we need to get those temperature gradients any finer or does it even matter no i think what you're doing is actually quite good because that's you so you've thought about it and you know that you know for running at a similar hour at a certain speed um you'll be sweating more obviously if you're in a hot condition and the cool conditions i guess the thing i would say is maybe you'd also want to maybe tailor the the speed at which you're running um for example if you say okay run at i don't know eight miles an hour or something like that then you probably want to

say run a bit slower when it's harder because you probably will run slightly slower when it's when it's hotter you're probably still going to sweat more anyways um but just kind of um doing the incremental rise in temperature and maybe adjusting that to um to the speed at which you'll be running during your event um because if you're just doing an hour run you might go a bit quicker than you normally would obviously producing a bit more heat and sweating a bit more and then you you'd think that you'd need more fluid than you actually need during the race so maybe just thinking about that but i think from a starting point it's it's actually perfect because you've thought about the different environments and how they affect um potentially affect sweat rate yeah well we can't get the environment that's when it's the complicating factor because you got to extrapolate you got to like you plot it out on excel and try to extrapolate it to a certain extent if that's going to be the case fortunately in ultra running everything's at the same intensity so it's like you just go out and do a run and that's your ultra running it that's here it's pretty or it's pretty darn close yeah and i think the other thing you have to bear in mind as well is you know at some point you have a maximum sweat right right so you're not going to sweat more than a certain amount and the other thing to consider is uh fluid absorption you know so and there's there's some research on there but you know you're not going to absorb you know two liters let's say at some point you calculate that someone needs to drink two liters per hour well they're not going to absorb that so that's fluid is just going to be sloshing around in their stomach so you probably want to tailor that to you know probably know much more than a liter and a half for example or something like that and the other thing associated with that is people probably want to try uh try that in

training which i'm sure you you have them do but just to see how they feel because if it's the for the first time they do it in training or in the race as i'm sure you're right about right if you never try something for the first time in a race then you know they get halfway and they get some gastrointestinal issues and so forth so you probably want to try that strategy on a long run just to see how how um how the acid can cope with it okay so i'm going to put you on the spot because this wasn't in the outline on the on the absorption issue because i i know and because these people are going to email me afterwards if i don't ask this question i know people who are in excess regularly of two liters an hour of sweat loss they live in the florida panhandle where it's a bazillion degrees and we've done these sweat tests on them before and they come back and it's like three liters an hour three and a half liters an hour to which it's like i look at them i go i ain't got nothing for you like i don't have anything like i don't because i know what the maximum absorption rate is i know we can change it a little bit to a certain extent but we're not going to get close to this four liters an hour absurdity that you're that you're sweating out i fail to have an answer for them so help well yeah there's a range so you probably probably arrange this from one to one and a half liters per hour you know but the other thing you have to remember as well is um if you're exercising at a higher intensity then you have less blood going to the gut and you know the gastrointestinal system which kind of slows down absorption as well so another one is even if you're exercising in a lower intensity but in the heat because you need so much blood to go to the periphery for skin blood

flow and so forth again there's less blood in the central circulation to help with with gastric emptying so when it's hot and you're running at a high intensity your gastric emptying rate is going to be lower than if you're running in a cool conditions at a lower intensity so there's all those things so um you know if someone is sweating two three liters per hour um they're probably they probably physically can't dream or they can physically drink enough to replace that but they won't be able to um to absorb it and i guess the other thing too i don't know i don't know if those athletes have tried but if they've tried to actually consume that much fluid if they can even handle having that much stomach sloshing around because i mean two three liters per hour running or just well two liters per hour running you'd have a lot of fluids sloshing around in there that's about the maximum that in my it just in my scope of practice and our other coaches scope of practice that's about the maximum that we can see being tolerated but once again in some situations we have this really big just you if the discrepancies not that big then i just kind of i'm kind of like what you mentioned earlier it's like okay you're going to have to deal with being a little bit dehydrated and that's fine but it's you know when i ask an athlete to go out and do a five-hour run and i know that they're going to have a sweat rate of three liters an hour and they can only take in two they're five liters down at that simple math right so they're five liters down at the end of that run that actually becomes kind of kind of problematic from a lot of different perspectives and i've tried to throw everything at this problem like we've tried you know the preload hydration uh products which a lot of those work

really well for a lot of athletes in uh uh in those conditions but outside of that it's i've it's always been a stumper yeah i mean i think there's two things there i mean if someone is running five hours um i'm assuming they're running at a relatively sub-maximal intensity fast and so three liters so a sweat rate of three liters per hour for someone running for five hours that is that is a very very very very high sweat so there'll be people in the world that sweat that much um so it might be just a matter of making sure that that's really their their actual um sweater because that's quite a lot oh i know i'm trust me man they're out there i know they're at the edge of the bell curve but they're out there i guess the other thing too you talked about pre-hydration so one of the things that maybe they can do is hyperhydrate um meaning you know doing some fluid um overload so fluid intake a bit more before with some sodium in there uh to kind of um to kind of retain a bit more one of the projects we're going to do soon is um hyperhydration with glycerol um so you retain a bit more fluid so they can maybe do some of those things so they'll start off their run obviously a bit heavier than they would normally um but you know by the two hour mark they'll still maybe be dehydrated but they'll be less dehydrated than they would if they were they weren't hyper or if they weren't hyperhydrated yeah we've used um both the scratch hyperhydration product which is just give the listeners a little bit of a perspective on that i think that's like 1.6 gram oh man i'm gonna have to look this up i'm

gonna chop this up really quick do you know off the top of your head what the grams is or the milligrams of sodium per liter is on that one oh no i don't know i think it's three it's like it's yeah hold on i'm gonna look it up really quick well i mean when i was in catar for example we do bike rides right so we'd start at 5 30 in the morning to be done by 8 30 because already at 8 30 it was over 45 degrees celsius so we'd start very very early in the um in the day and what i would do is i would actually take some oral oral rehydration solution so you know when you when you're sick for example you can take those so i would actually take that in my bottles and um and drink that because it was high in sodium and the fact that um you know you can drink that and it doesn't feel salty it's because you actually need the salt yeah yeah we've used that as well i just looked it up so it's 1720 milligrams per half a liter so that's 34 40 for a liter which you know a normal a normal electrolyte drink is going to have 800 or 600 milligrams of sodium per liter so it's literally you know double or triple that um we've we've used those products before but it's always been in kind of like a acute setting right we know we have these athletes that are going to this hot weather event or maybe it kind of sprung up on us we're doing a camp like a cross-country type of camp and then we don't have time to do that whole acclimation process and some i would say most athletes have a pretty good pretty good response to that how much of that is placebo or not who knows but it we we tend

to have good good results with it and we see that in other practices as well where they're you know hyper hydrating with some other type of commercial product yeah well to be honest i would imagine ultra runners are pretty dialed in i mean maybe i'm wrong but you'd be surprised i'm gonna have the story of what we're not so dialed in we're gonna bring that up next but continue hydration nutrition especially nutrition because you're out there for so long i mean you know after you bonk a few times you think all right i need to work on this i don't know maybe you'd be surprised at how how long it's taken us to figure out so we've gone over like some of the acute nutritional interventions let's one of one of the other really remarkable pieces of the paper was the very incredible amount of detail on the acclimation and the acclimatization protocols that you can use to get ready for hot weather events and i tell the story all the time because it was kind of my indoctrination into into ultra running and the physiologists they just kind of chuckle you know about it um but when i first started coaching ultra running i i had a literal trial by fire and the event that i was working with athletes in was the bad water ultra marathon which is really famous for being super hot and i didn't know you know i didn't know anything at the time so i was trying to figure out what the athletes were doing to get prepared for this and what i what i stumbled upon was almost all of the athletes in the field had this combination of acclimation methods that was kind of like the

frankenstein version of what you presented in your in your paper they were wheeling their uh treadmills into their laundry room they were turning up the some sort of like oil heater or something like that in the sun in their laundry room as well to make it hot they would disconnect the dryer vent from the dryer and turn it on full blast and put it in their face to kind of simulate the you know the hot winds that death valley is so notorious for and then they would put on a sweatsuit and a rain suit kind of over at over that so you have all of the acclimation methods right you're trying to exercise in the environment you're trying to increase your torque core temperature with uh controlled hyperthermia you're trying to make a hot you know hot sauna kind of in this exact room and and for whatever reason whether they were just intimidated by bad water or you know it was just cultural or whatever a lot of the athletes in this in the field many of the athletes in the field had this like combination of all these things where they just kind of were thrown in the kitchen sink all at the same time at the problem that kind of solved it and you you peeled apart all of those different methods quite well and almost kind of rank ordered them a little bit uh in the paper in terms of how effective they can be and also which ones are going to be the the the kind of the least intrusive into an athlete's uh training environment and fortunately we've got a lot smarter on that so to your credit and all this the sports scientists ahead of you but let's get let's give that outline a little bit on the different acclimation

methods that we've learned since this terrible bad water time that we're starting to see kind of crop up in all sports and then we can kind of like tailor it down into an ultra marathon situation so the bad water idiots don't do this anymore well well you know what i think i don't think it's a bad idea you know like the thing a lot of the things that i often that i want on the paper for example you need a certain certain infrastructure to do right for some of them so yeah i don't know if i'd tell someone to disconnect the dryer and put the vent in your face that's the tipping point the dryer is the tipping point yeah where you kind of have to work with what you have right so i mean i guess the first thing to talk about is acclimation versus acclimatization right so acclimation is you know adapting to the heat in an artificial setting so you know that's ideally if you have an environmental chamber which i'm sure very few people have in their homes um where you can control temperature and humidity or you sit in a sauna so any kind of artificial way to do to get adaptations is acclimation whereas acclimatization is what we get from being outside in a hot environment so if you are living in a hot area then that's fine you can just go outside and train for example the men that people that you mentioned earlier in the florida panhandle where it's hot and humid obviously they'll be acclimatized to that hot and humid environment um even people living in you know in the northern united states you know they get acclimatized through the summer by training outside so that's acclimatization compared to acclimation um so there's kind of a combination of things you can do so the protocols that i'll talk

about some of them are purely acclimation protocols so you need a very structured environment in which to do it and some are acclimatization and kind of some cross over so i guess the first one is kind of self-paced exercise so you go outside you do your workout you do your run um and whatever you know your workout is that day that's what you do and essentially you get you can get eat adaptation from running outside if it's hot but you can also do that on inside right so if you have a a certain workout or a long run you could also jump on the treadmill so that's one you can do both as acclimation and acclimatization um and that you know doesn't interfere too much obviously with your training program but if you're supposed to hit specific speeds for example during a run or you know those intervals will be compromised in the heat so you need to know that um but if you will do that in a hot environment maybe do the intervals at the beginning of the workout where you know your your performance will be less compromised because your thermal strain is less elevated and then you just kind of do the rest of the run afterwards probably at a lower speed but you'll still be in the hot environment um then the other one is constant load exercise so that's a bit easier to do in the lab um because you say okay i wanted exercise at 60 of my vo2 max or at a given um speed well which which will equate to a given speed so if you're running at i don't know six seven eight ten miles an hour whatever it is you put that on the treadmill and you just run at a constant rate um and you'll find that in the heat your obviously your core temperature and heart rate are going to creep up

so it's going to get harder and harder and harder um and then obviously if you want to do that outside it's going to be a bit more difficult depending on you know if you're running on a flat surface because of terrain changes and so forth so it's hard to keep a certain speed but it's it's doable um then the other one is you can think of controlled hyperthermia or isothermal heat acclimation and that that was developed in the 60s by a researcher named fox and he was trying to basically look at um eliciting a similar core temperature every day because his thoughts were that um during the constant load adaptation protocol if you're running at the same speed every day as you adapt you know your core your core temperature might not increase as much towards the end of your protocol of acclimation after 10 days for example your heart rate may be lower so the stimulus for adaptation is maybe a bit lower but having said that oftentimes with the controlled hyperthermia protocol we talk we target a core temperature of 38.5 but during constant load exercise by the time you finish exercise you're well above that so even after day 10 you're well above 38.5 so in the controlled hyperthermia the idea is to get to a certain core temperature and then as quickly as possible you know 38.5 degrees celsius which i'm not too sure how much that is 90 high 90s i guess in terms of fahrenheit so you get to that core temperature and then you maintain that now the issue with that though is that you might find that you have to slow down quite a lot when you're in the hot environment because to maintain that core

temperature if you keep running you'll you'll you know you'll you'll keep increasing your core temperature so you might have to stop running start again stop again after you reach that um so from a workout perspective it'll be a bit uneven but it definitely does induce adaptations um so a few years ago we kind of suggested the method of controlling heart rate um because of that intimate relationship that i talked about before with core temperature and and heart rate so if you're exercising at a given work rate or speed your core temperature will go up but your heart rate will be a linear increase with that so if you're exercising in the heat at a given heart rate so for example the heart rate associated with holding i don't know eight miles per hour for example then you start off at eight miles per hour obviously because your heart rate doesn't go up but you run like that for 15 minutes and after that you adjust the treadmill speed to maintain that heart rate now naturally you know your the treadmill speed will decrease throughout your session if it's 90 minutes two hours to maintain that heart rate but as you adapt as the days goes up the days go on then that speed will kind of creep up um for that same heart rate and that's probably logistically a little bit easier to do for someone who doesn't have um you know core temperature monitoring system um because when you want to when you measure core temperature you want an accurate measurement so those those tympanic temperatures those guns for the ears that's not the most accurate under the tongue is not the most accurate so um you can do esophageal temperature which is a probe through the nose down the esophagus i don't think people are

gonna be doing that at home um erectile temperature maybe they can do that not always pleasant when you're wearing a workout to check your rectal temperature um or if you have a bit more money you can buy like um those systems with pills so you swallow a pill um and then you can monitor your core temperature that way having said that the systems are you know a couple thousand dollars and each pill is probably going to be maybe 75 us dollars so you know it's pretty expensive um per per running so if you're if you go by by heart rate you'll probably get to um a higher heart or a similar core temperature every day and then do that now the alternative to that if you don't have a hot environment in which to train is you can use either son of bathing or hot water immersion so you can do your workout outside in cool conditions if you can't acclimatize and then obviously if you do that you don't compromise your workout then after your workout you can jump into a hot bath of roughly 40 degrees celsius which is around 100 degrees i think fahrenheit and you know for the first time maybe stay in there for 20 minutes and then try to build that up you know to to 40 minutes and there's some nice research from a colleague neil walsh who's demonstrated that kind of actually works quite well um so you kind of work with what you have you can also go into a sauna afterwards you probably spend a bit less time in a sauna because that's very hot so you're probably not gonna spend 40 minutes in there um but that's another way to induce um heat adaptation so there's quite an array of of methods or protocols that you can use

and fundamentally you've kind of got two categories right you've got the active category where you're doing something right you're doing the exercise and both the exercise and or the environment is what's causing the rise in core temperature and then you have the passive modalities which is mainly sauna bathing and uh hot water immersion bath where you're not doing anything inside of there that's why i always get a crack out of the bad water people because they're trying to do them all they're trying to do both the passive and the active kind of at the same time but that that's not neither here nor there there there's been a lot of a reasonable amount of consternation around okay which one is better which one is going to produce the most amount of adaptation if handling the heat is mission critical to whatever event that that uh that uh that i'm doing and i think we're starting to get like like i mentioned earlier i think we're starting to get some like reasonable consensus developed developed around there that's actually and what i mean by reasonable is like athletes can actually implement it sometimes we get these things from sports science and they're just completely they're just they're they're not practical at all but i think in this case we're starting to get some things that are actually implemented that are actually implementable for even everyday athletes not just athletes that have access to a core core temperature pills like we do over the training center that's right behind me um so what would you advise athletes in terms of how like how to navigate that and what modalities are are the better ones to pick out of that array that you just mentioned yeah that's a good question

and i would say that you know um any heat acclimation is better than no heat acclimation right so that's the first thing so if you can't heat heat acclimate and then it's better than not doing it so whatever is available to you is probably the first port of call right so like i said before and i think like you've mentioned you know not everybody has access to environmental chambers so there's certain things that some people won't be able to do um and having said that you know there was a meta-analysis from another colleague chris satter a few years ago and he compared the controlled hypothermia protocol with constant load protocols and you know the adaptations of several papers put together and they showed that there wasn't any difference so i think you know if you acclimatize or acclimate you will get some benefits um and the other thing too is that you know we think of either doing the passive or the active approach and obviously the active approach is very specific and you have endogenous so you know internal heat production and exogenous external heat production to kind of increase your core temperature compared to just the passive one which is the environment um but sometimes if athletes are very very fit they don't necessarily need to exercise in the heat because you know that's not part of exercising in the heat as well could improve performance but if you're already very fit and you just want the heat adaptations then maybe you just do the passive approach for example right and then then you don't compromise your workout so you can do that so i guess for bringing all that together i would say first thing is well again acclimate if you can secondly use what you have so if you don't if it's not if it's hot outside well then go outside and acclimatize you know if you're doing a key workout we'll do it early in the morning or in the evening

where it's cooler and you can hit your target brace times and if you're doing a heat acclimatization session we'll go in the hottest part of the day make sure you're well hydrated and so forth they use that environment that you have at your disposal if it's cool um then maybe it is a matter of buying a few heaters you know put it in the room with your treadmill and um putting on maybe an extra layer and trying to get your core temperature up that way or do your workout in cool conditions jump into your bath just go to a local hardware store or something get like a thermometer for your bath and then just jump in there afterwards um i think it's important to note though that there'll be a lot of blood cooling in the legs so when you jump out of the bath take your time if you're not because blood pressure will drop so you don't want to you want to fall and bump your head um you know or if it's a case of you know then you're exercising on your treadmill in a hot room just put on your heart rate monitor and try to hold you know the heart rate that's that's um associated with a low intensity that you can hold for a while um and adjust the the pace that way so i'd say that and that's even what we're recommending for athletes now you know it's not necessarily one protocol per se it's kind of an amalgamation of those because if you're exposed to the heat then you will induce with adaptation so it doesn't have to be that one protocol so for example you know even if it's hot outside uh you can do you know your acclimatization run but then on another run on the weekend you can just jump in the bath after after your run so it's just maybe looking at what's available to you and kind of tailoring it to your to your unique circumstances

i mean you're almost channeling verbatim you don't know this but i'm laughing my ass off right now you're almost channeling verbatim one of my longtime colleagues uh lindsey gollich and i don't know if you've had any interaction with her she runs the high altitude uh uh and high altitude and environmental performance center it's always a mouthful to say here at the olympic training center and i've known her for years and so she's got all the tools that you just mentioned right the the pill thermometers she's got a room that she can bring into any you know any altitude heat and uh humidity combination that on earth that she can kind of set things to she can wheel in equipment you know ad nauseum do kind of do whatever and she's just like listen if we can get people just to do heat acclimation stuff that's the win they can integrate it into the life that's a second win and then we look at how much does it affect training and for the really high level athletes that's a huge consideration huge consideration if you impact the quality or and or the quantity of training that they're doing but for you know mid-pack blokes like you and i you know who have no shot at making an olympic team it's probably the impact the impact that doing something in an artificially hot environment a few times or several times a week is probably not that much we're still going to gain fitness from those types of sessions yeah absolutely and that's a good point because i mean we're um our labs are two three kilometers away from the australian institute of sport so ahead of the olympics we

have a lot of the athletes coming even the paralympics you know they come in and train and again it comes back to what we were mentioning before like yeah the ideal protocol might be 10 days but they're never going to do that right because usually you're implementing this you know a month or two out and then it kind of coincides with your taper and your build phase so you have to be careful and and do that so what they do even is like two three months out they come in just twice a week and do a run so you know is that optimal no it's probably not optimal to do it twice a week for eight weeks relative to maybe 10 and 14 days in a row let's face it but again you know you have to get your training right because that's the other thing too i mean if it's fine to acclimatize and acclimate but i know a lot of these a lot of these things like you know the technical technological advances and these little kind of training pools or the little kind of things to optimize performance they're great you know that one but if you don't get the 99 right you know underneath that there's no point improving by one percent if you get improved by 50 by just getting your training right so i think the first thing you know in anything is just getting the training right getting your base right being prepared and then those kind of little tweaks you get you know towards the end so in terms of acclimation that's what i would tell someone initially i mean make sure you're training you can you can acclimatize passively all you want but you know if you're going to run 100 miles and you haven't run 100 miles before you know just work you know and it kind of it kind of seems intuitive but you know

we're bombarded by all these kind of ways to optimize performance whereas you know we have to think of the important stuff first so i think yeah so in terms of when you're planning your your heat acclimatization or acclimation use what you have and then do it progressively because there's different ways of doing it as well right i mean you you either do you know for example twice a week for a few months leading in or you can do maybe let's say you're six weeks out of your major competition and you're in a down week or something like that then you can do maybe five six days of intense heat acclimation then you top it up once or twice a week and we kind of go through that a little bit in the review so and that's just also trial and error you know like how people kind of react because if you acclimate um for like really well you can spend you know a month keeping training because if you train you'll still maintain some of that acclimation because you are training you're sweating you're increasing your core temperature and so forth and then if you top it up just before your competition the week before with two or three sessions in the heat then you'll regain some of those acclimation adaptations so just kind of thinking big picture as well so working back from you know your competition and then working back to see what's available to you and what you can do it's probably the best approach i'd say i started using that protocol that two-phase protocol one like one one heat acclimation block like six weeks out ish six to eight weeks out and another one the week of but honestly i'm gonna i'm gonna sound like i'm patting myself on the back a little bit i'm really not honestly i was i was and i did it before a lot of this research

came out a lot of the practice came out as well that's what that was the pat on the back that i was trying not to do but honestly i was doing it because i or i switched over to doing that more because i was afraid of screwing it up all at the very end because i didn't know how the athlete was going or i felt like i was guessing too much on how the athlete was going to react by putting in this hot and heavy heat or sauna or whatever i was going to use at the time protocol like during the taper or in the last week of the race or whatever and so i implemented that two-phase just to almost do a trial run even without i mean we knew a little bit about the residual effects at the time but not nearly enough to where i was going to take credit for being that smart now it comes out to where it's like okay if we can do these kind of top off sessions i think that that's that can be quite effective and this is this is where the rubber meets the road i think because everybody's going to we we've kind of made the case that everybody needs to do something people always want to know how much for how long right how many days in a row do i need to do this for what are the different time courses of adaptations and there's this really cool i was just trying to find it there's just ah there we go there's a really cool figure in the paper it's figure 21 which i have a rendition of this in my book by the way um this is this is one of your uh papers correct your paper specifically brilliant uh brilliant graph i've probably seen this 50 times in the last two years in different lay articles and scientific journals and things like that that describe the time course of adaptations for all of these very specific physiological

phenomenons that are going on plasma volume heart rate core temperature skin temperature and things like that i'll put a link obviously in the show notes to the entire paper so somebody can like check this out but why why is that time course for adaptation so important to understand well i think you nailed on you you hit the nail on the head there it's important to understand that just because you want to know you know what adaptations develop and how quickly in terms of your preparation right so and i think if you look at the figure you'll see that you know most of the adaptation is developed to a pretty solid percentage within the first week so that's why you know optimally you want 10 to 14 days to get as much adaptation as you can but people have i've kind of tried to tailor more short-term heat acclimation protocols now you know five to seven days for athletes who are traveling and need kind of a quick fix acclimation protocol because yes maybe it's not optimal but you get a lot of adaptation within the first week um so i think one thing to remember as well however is that you know this is kind of a rough estimate right so everybody has an individualized response depending on the dose and so forth so even the same person doing the same protocol might see that the adaptations for the reduction in heart rate at rest or the reduction in core temperature during exercise might be slightly different from one one year to the other depending on you know how well they're coming in to the acclimation protocol with their training and so forth but generally speaking we see that one of the first adaptations is an expansion of plasma volume um so your blood volume plasma volume start to increase

and that obviously supports the cardiovascular response and supports that increase in sweat rate which kind of develops a bit more progressively and then you'll see a reduction in resting core temperature um and resting resting heart rate like now those those reductions as well it's important to note that obviously the less fit you are and you acclimatize you probably see a greater reduction in your core temperature and your heart rate right so if you're very very fit that's one of the things to remember as well and i touched upon earlier if you're very fit and you're running all the time you know you're getting to a high core temp well not a high core temperature but you're increasing your core temperature you're sweating you're increasing your skin blood flow so you're already partly or partially acclimatized because you're you're fit in exercising on a regular basis so the level and the magnitude of adaptation for someone who's got a resting heart rate of 45 is not isn't you know the scope's not much right so if you're resting heart rate 75 well then you have a bit of room to work with so um and the same thing with resting core temperature so if you're very lean and you have a resting core temperature in the morning of um well in degrees celsius you know 36.5 or something like that there's less scope for that to change so you know the change that that the changes that can occur vary between between individuals um anyways i digress but yeah so these things kind of kind of develop so the reduction in core temperature obviously affects the reduction in heart rate so if you start off your exercise at a lower core temperature and then if you're running at the same speed and after an hour you have a lower core temperature then obviously that will affect your heart rates because you're less hot so your heart

rate is going to be a bit lower and your cardiovascular response is going to be better supported by a greater blood volume so therefore your cardiovascular response can be lower so your rpe so perceived exertion is probably going to be a bit lower you'll feel more comfortable in the heat after um after you've done you know some some training so after four or five six days some of these things kind of develop um plasma volume tends to kind of increase quite quickly after and after a week or so it starts progressing not back down the baseline but going down now there is some suggestion that you know if you maintain a thermal stimulus you can maintain your adaptation uh but those projects haven't had like a control condition where people um don't and that was dehydration so i won't get into that but typically it goes up and goes back down a little bit um all of that obviously increases um performance because you know your core temperature your heart rate your thermal and cardiovascular responses are lower you feel better so obviously performance is going to be improved but here's like the this is why this this this graph in particular is so practical is it sets the boundaries for how many days you actually need and when the point of diminishing returns starts to starts to kind of rear its head and are in the coaching community and you've seen this at the australian institute for sport we see it over here at the olympic training center the acclimation protocols are pretty standard within you know just five or six days it's anywhere between six and fifteen days or something like that right if you want to put

kind of the widest bookends on it we don't see people doing it or at least we shouldn't see people doing it for a month right because then you're getting all the stress and very little adaptation which then starts to impact the workouts and things like that that's why i wanted to bring this out is is that it it really does very very nicely and in a little bit complicated way because you're trying to track down all the different physiological mechanisms it kind of puts the bookends on the process of how how much time you need to reap the benefits which is always what we're concerned about with endurance sports it's like how much time do you need for the adaptation is it a day is a week is it a month is it a year and in this case it's between six and 14 or 12 days or something like that like it's not that much time i guess is what i'm trying to point out yeah i guess the only caveat with that is if those days should be in a row right yeah or if anything you know you can take one day on one day off and so forth which extends that to 30 total days but 15 days of acclimation so you know so if we go back to the scenario before you know doing it twice a week for example for five six weeks you know if you do it twice a week for 10 weeks it is 10 sessions but it's not the same as doing 10 sessions in a row so that's one of the things i guess you need to to consider but if you are doing you know as you said before a block six week before and then kind of a top up afterwards then yes those five six days would be all right and in another paper that we've done we looked at the decay of heat acclimation and there's not a ton of papers there yeah on so what we what we did is we focused on heart rate

core temperature during exercise and sweat rate a little bit so essentially what we determined was that you know if you do a good 10 14 day block of heat acclimation and you get you know what we term optimal optimally acclimatized which is another thing i'll chat about in a second so if you do that you know then if you spend two weeks without being exposed to the heat you'll lose about 35 of your adaptations for each of those you know that that reduction in heart rate core temperature and sweat rate so for every day outside of the heat you lose about 2.5 of the adaptation you know but again that's that's a ballpark figure you know individuals will respond will respond differently not of the performance of the adaptation yeah i wanted i wanted to make that clear because a lot of people will say oh if i don't get in the sauna the day before the race i'm going to lose 2.5 of my performance is of the adaptation the adaptation yeah so for example if core temperature decreases by um i don't know half a degree for example so it'll be 22.5 of that 0.5 degree exactly so it's it's different um and i guess the other thing too is that um there's um there's one mikhail horowitz has done lots of work in the animal model and she's done what you talked about before like a month of acclimation two months of acclimation and this is putting rats and i think dogs as well in like 34 degrees which is not super

hot but in there all the time for a month or two months and she's also looked at dehydrating them and keeping them dehydrated by 10 percent for a while so obviously things that we can't necessarily do in humans and and what that has shown is that there's changes that occur at the kind of epigenetic level um so what we're looking at is more physiological changes and kind of that phenotype so those those are changes in physiology that occur in 10 14 days but there's obviously more changes that it can occur um i'm not suggesting that someone lives in 34 degrees you know and gets dehydrated for you know for for a month that's not what i'm saying at all there's no difference but the thing with the dehydration as well is that it blunted some of the adaptations because um because the dehydration was so severe so in terms of physiological adaptations now yes you know 10 to 14 days is probably what the recommendations are um and then if you tailor that to different times of the week or prolong it then obviously you need to take into consideration that it's not going to be optimal but you still will get adaptations yeah and once again i encourage athletes that are not familiar with this just to go and look at that chart even if you don't you know understand physiology all that well you get a really good sense of the time course for adaptations when you're looking at that and when you're trying to diy it or yourself or you know coaches trying to design it for you and they're not used to these protocols that it just gives a good what's the word i'm looking for like operating parameters for how to set up the protocol and even if you're copy pasting the australian institute for sports

protocol which a lot of people do or the usoc's protocol which a lot of people tend to do or whoever they heard on whatever podcast is protocol at least then now you kind of understand the physiology behind why those protocols have been developed the length of time that they're recommending for the dual thing that i mentioned earlier that i just stumbled upon and now it's got some sort of you know scientific efficacy behind it that i can that i can kind of pin on there's there's reasons for it i guess is what i'm saying yeah i think another thing that people can do as well is you know if they're doing this by trial and error and they want to see if it's working you know if it's efficacious is just have yourself plan yourself a session like a standard session where you know you do at the same time of day um you weigh yourself pre-post whether you drink or not just make sure you drink the same thing um look at your heart rate and your speed so just go on there at a given speed and then just track your heart rate for example you know um you don't have to track your core temperature if you can track core temperature perfect but just look for example you know whether it's running an hour at i don't know eight miles an hour just jump on do that track your heart rate throughout track your your body mass pre and post and then when you're acclimatized you should find that your heart rate is going to be lower you'll feel better and then your sweat rate is higher so you'll lose more body mass during that so those are two very simple things you know your heart rate and your body mass to see if your acclimation protocol is is working that is a brilliant place to leave it the two simple things the things that probably matter the most you're sweating more in your exertion level your

heart rate is lower for heat any any heat acclimation protocol that we just talked about yeah and i think the important thing with um with with weighing yourself and i'm sure you do this with your athletes is you know obviously ideally you weigh yourself you know nude before and nude afterwards and if you drink you need to know you know how much you had in your bottle before and how much you have in your bottle afterwards so you can subtract that so you know not real scenario you wear yourself nude before and after and don't drink but um you know if if you are drinking just make sure that you um you know how much you drank to kind of take that off your body mass because obviously that's how much you sweated during that that one hour it's amazing how it comes down to such simple stuff yeah why are we doing you have to simplify it right all right well especially for most of our listeners are going to be lay audience you know they don't have access to all these tools and things like that we really got to boil it down to some simple stuff but everybody's curious about it because as i mentioned uh offline ultra marathon is one of those things where either part or a small part or a long or a big part of a lot of ultra marathons are contested and hot environments and it really behooves athletes to prepare for those environments because that can make that can literally be a make or break uh part part of the race and it's good when we have olympics come around and hot weather environments like tokyo because everybody ups their game i mean you guys did it australian institute for sport did it the olympic training center here did it everybody canadians did a really good job with it as well everybody ups their game because they want their athletes to perform and if one of the determinants

of performance is how well they handle the heat you know you got to know what you're doing there absolutely absolutely well thanks for coming on i appreciate it where can people learn a little bit more about your lab and the work that you do um so i'm at uc rye so the university of canberra research institute for um exercise so you can have a look at that also if you're interested in some of this stuff you can follow me on twitter and i post a lot of the um all the papers obviously that i publish and so forth so i think that's at um dr j perryard so d-r-j-p-e-r-i-a-r-d um so feel free to obviously have a look at that and i think this paper i think that you'll send a link to is is um um the biggest works i've ever done so it's a good starting point anyways um we also have a book on exercising in the heat um and within that um so it's a springer book so um a colleague of mine edited that a colleague of mine and myself edited that and there's chapters in there about um for different sports as well about thermoregulation heat exchange hydration all those things so if you're interested in that it's um exercise under heat stress the thermophysiology of exercise i think i will put links to that in the in the show notes uh but once again congratulations on the paper it's something that i'll use as a resource and our coaches will use it as a resource and i'm sure other people out there will find it fascinating well thank you very much and thank you for having me on i love to talk about this stuff as you can see it's awesome it's awesome we'll have you back on how's that when summer rolls around and everybody's really interested in it

well our summer's coming up in a few months that's true very good all right we're gonna let you go thank you very much all right folks there you have it there you go much thanks to julian for coming on the podcast today i guarantee you we will have him back at some point in time because he has such an incredible body of work and there's definitely more to come from him and his colleagues out there i appreciate the heck out of all the listeners out there remember this podcast is always and will always come to you add and sponsor free it's a commitment that i made to the audience at the very beginning of starting this podcast you can help the podcast out by sharing it with your friends and your training partners on social media you can hit me up on instagram i always appreciate those comments and those feedbacks coming from the audience and it honestly it helps me generate a lot of ideas for future podcasts i appreciate the heck out of all the ears out there listening and as always we will see you out on the trails