Paul Warloski (00:46)
Hello and welcome to the Athletes Compass Podcast, where we navigate training, fitness, and health for everyday athletes. We're honored today to welcome Dr. Julia Casadio a sports physiologist and applied researcher with over 15 years of experience in high performance sport. She worked with multiple medal-winning Olympians at High Performance Sport New Zealand, and she's the founder of Her Strength, which we'll hear about.
A digital platform designed to educate, equip, and empower coaches, parents, and athletes involved with youth female sports, specifically athletes aged twelve to eighteen. Her mission stems from a deeply personal experience. As a competitive cross-country skier in her teens, she received misguided advice to quote lean up, unquote, which led to an eating disorder and an early exit from the sports she loved. Today she's dedicated to changing the narrative around female physiology and
Ensuring f young female athletes get the support they need to thrive in their sport and stay in sport for the long haul. Welcome, Julia.
Julia (01:51)
Thank you, Paul. Thank you for having me. It's great to be here.
Paul Warloski (01:54)
We're talking specifically today about heat adaptation. What is the most important thing you've learned about female physiology and training in the heat?
Julia (02:05)
yeah, the the most important thing I guess is that females we know in the literature they take a little bit longer to adapt to heat acclimation or acclimatization than their male counterparts. and that's that's actually a really big one because the reason why you do heat acclimation is so you have the adaptations you need to be able to compete and perform in the heat well, right? So if you're
Doing what you would do with a male athlete, say males adapt in four to seven days, and you do that with a female and they actually still struggle in the heat, well that's that's kind of a big deal, right? So that that's that's the big the biggest one. So females take a little bit more time to adapt. They might take more like 10, 10 to 14 days, or
a more concentrated amount of heat exposure in a short term period and I can get into what I mean by that. But I'll just leave it at that so people can think
Paul Laursen (03:08)
Yeah. So what why don't we
s why don't I start in with a little bit more background? so Julie and I listeners, she we go way back to lots of different lots of different stuff in the area of of of science and physiology. And Julia was you know one of my key workers in New Zealand Olympic when when we were back there. And her whole PhD was really in this area and it was, you know, revolutionary kind of stuff where she was looking at
the impact of heat training across all the new all of New Zealand's Olympic athletes and actually doing research at the coal face to to do to to optimize their preparation specifically for the hot games of of Rio and Tokyo. Immense, immense immense heat in both of those places. So where do we sort of start with that, Julia? Like where when we kind of even go back into there.
Julia (04:04)
Yeah, I guess it was very coach and sport driven the questions that we came up with. Like at the time when I was doing my PhD it w heat
Training studies were predominantly done in endurance sports and were kind of more predictable the questions that were being asked. And when we came to the New Zealand Olympic program, they had questions in a across a variety of sports. And some of them even included like, can we use heat as a training tool for our sprint track cyc cyclists? You know? And how do we add heat training to the non-traditional endurance athlete when where they have lots of different types of training going on?
Paul Laursen (04:39)
Yeah. Yeah.
Julia (04:48)
on concurrently. So that was quite fun because everything that we did had to be easily applied in the field and something that they would do in real in real practice at an elite level. So
Paul Laursen (05:02)
Yeah.
What what I what I most remember and loved about your research, Julia, was how applied it became. And w the biggest thing that that I learned from it was that just like we program training sessions in Athletica, you can kind of do the same thing with heat. You can you can periodize it. You can do you don't have to do kind of like what you let off with, Julia, just talking about, you know, your classic ten to f se to fourteen days, which is what everyone thinks you have to do. You could do
You could do two days in a row or three days in a row at as a little bit of a block here. and and then bring it back. And so to me that was that was kind of the the coolest thing is really and then also looking at the individual and then you know, looking at the female athlete. And it was just like it was all of a sudden this new t tool in your tool belt that you could leverage to to optimize. so that's that was yeah, that's what I loved about it.
Julia (06:01)
Yeah, and I think like for your l for your listeners, that that's probably one of the biggest ones is
For people preparing to do an Iron Man or a long distance event in hot conditions, you you really don't wanna be doing introducing heat right before the event because that's when you're tapering and and heat stress is of actually a c considerable added load to anyone's training. So it it like the traditional recommendations were you do this right before you leave, but we don't actually do that in any
Paul Warloski (06:29)
Mm-hmm.
Julia (06:38)
anymore. we we know from studies done with military that we can if if we like a month out, two to two to four weeks out of an of when they need to be ready for the heat, we can do the heat intervention there, do a proper heat block, get all the adaptations, and then we the body has thermal memory.
Which is crazy. And and you you reintroduce like in in your taper week leading up to the event, you know, two to four exposures of the heat and you can re add reacclimate rapidly. And that's how
Paul Laursen (07:01)
Yeah. Yeah.
Julia (07:15)
that's how we use heat with at an elite level. We never do it right before because and especially if you've never done heat before, you don't know how you're gonna handle it. And and often people underestimate how fatiguing it is. so that that was so we took those military studies and we actually did that kind of thing with the Olympic sailing team that were preparing for world championships in Oman.
Marjaana Rakai (07:27)
Mm-hmm.
Paul Laursen (07:28)
Yeah.
Julia (07:39)
And it worked brilliantly. Their responses just, you know, showed that, yeah, they can reacclimate really quickly and it's become like a beautiful periodization tool.
Paul Laursen (07:51)
and now I I reflect on my partner MJ's experiences with heat. And it this is hilarious. We've talked about this on on podcasts before, but she was dead set that she could not adapt to the heat when she was preparing for well were you for Nice, maybe it was MJ, or it was it was a hot event. I can't remember. Tell us a story about that.
Marjaana Rakai (08:09)
Yeah.
yeah, so I've never really enjoyed heat. And even after like living five years in Dubai, I just like struggled. I think it was mostly mental. Like I'm from North Finland, I love winter. So I did Ironman Texas twenty twenty four, which was in April, and then I qualified for Nice, which was in September, and I was dead set to, you know.
Be better in the heat. So I changed my mindset and I'm like, I'm gonna learn how to love heat. And Texas is very humid and very hot, and I would run in the middle of the day, and it was it took a few weeks to really get used to the heat, but I did eventually I did adapt, but I think
I did not respect how much stress and load it is to my body. and I kind of want to go in there. Like, how do you how do you kind of quantify that extra load from from heat? Like how do you know or evaluate when the training is enough, especially when you're you're training for Iron Man? Like I'm thinking, you know.
Paul Warloski (09:25)
Mm-hmm.
Marjaana Rakai (09:38)
Kona is humid can be hot. How do people combine the heat training and the normal load that comes into you know the summer training, August, September, the top top qu you know, quality months and top volume months? How how can like do you have any advice to people how to evaluate the total load?
Julia (10:03)
Yeah.
You well we we we don't I haven't really seen any metrics that say like, this much heat equates to this much T S S A or or whatever training training load score that you have. but we we do know that we would not add we do we do look at the volume and and the RPE and
Marjaana Rakai (10:17)
Yeah.
Julia (10:29)
of each of each session and the RPE will often be a bit higher. and so we we look can look at that. we also don't add heat to anything but like an easy to moderate week of training. So you're not like a moderate hard or hard week. No, you do not add heat. You would just topple over. So and and we don't add heat when a athlete's super tired already, fatigued. You want to be while rest
Marjaana Rakai (10:34)
Yes.
Julia (10:58)
w well rested and healthy coming into a heat block. If an athlete ever is like starting to get symptoms of illness or feeling like, I've got a scratchy throat, like we immediately stop heat because heat will exacerbate any symptoms and probably tip someone over the edge to get sick. So we we do handle it carefully, but you don't have to be scared of it. So it's just like treat it as, you know, this is this is something that is gonna add stress.
To my body, which is good stress that I need, and add it to an easy to moderate week. And you make sure your your recovery and your fueling and hydration in and around that week are really good. You know, you you make sure sleep quality is better. Maybe you have a nap if you're feeling really puffed, like really tired, and you because it's kind of the the load of heat kind of almost accumulates more as the days go on of consecutive heat.
exposure and the literature ha like you can play around with how much heat you do but the the most the most rapid adaptations come from consecutive days of heat so if you're doing a hate heat block say Monday to Friday by Friday you're gonna feel you're gonna really feel it so over the weekend you just let your body recover and it makes a big difference if you can if you can have that mindset rather than just
doing everything as normal and chucking something else on top of it.
Marjaana Rakai (12:29)
Mm-hmm.
Yeah. So so what
Paul Laursen (12:31)
Yeah. And I I would say
I would say athletica athletes, you've got access to your HR V as well and it'd be a good one to to monitor and kind of keep keep track of. And the other the other rule for me personally with the athletes I coach, I don't often if there's a thirty thirty VO two session, that's not a session I'm gonna do in the heat because you're at now at you're confounding sort of two heat variables and it's gonna affect the recovery between the boats. and it and it's like it's like a different
I don't want hit those two nails with one hammer at at one at one session, personally. So I would like to kind of to Julia's point, I would do those, do your four you know, zone two, zone one, two, three, even fine with with heat. But when you're kind of moving four and five, where, the intensity's going off in the high domain, then it's probably time just focus on that.
Paul Warloski (13:05)
Mm.
Paul Laursen (13:27)
on getting the higher recruitments and leave the leave the cardiovascular cooling system at at play at that at that day. And yeah, and then of course you gotta be careful about how the heat is affecting that that key key session as well. There's there's a few things to consider, but but yeah be c I I'd just be careful about balancing those those those two stresses.
Marjaana Rakai (13:49)
Yeah, so I I would do low intensity sessions outside and then high intensity sessions indoors. But w what I am curious about learning more is the thermal memory. you said that you would do a heat block. So some for someone who is training for Kona.
Where would you actually place the heat blocks if you don't want to do it like continuously over the the summer? Like how far away and would you just like do repeated heat blocks up to when you travel to Kona? Or how how would you do that?
Julia (14:31)
yeah, so I guess w one thing that is easy for people to get wrong is what is a heat exposure. And they might think, you know, it's a sunny, warm day today. I'm gonna go out and ride my bike and that's gonna be a heat stimulus. But
like there's a breeze and they're riding and they're drinking a cold drink with ice in it and and actually if we look at their core temperature and their sweat response it's actually not hitting the thresholds that we need to see heat adaptation.
So the key things that and I'll just start with this because this is like you need to know this before you can actually say, okay, I'm gonna do a heat block. so you need to have your core body temperature go up by one 1.5 degrees roughly. So like let's say you're targeting like 38.5 is what you you need to hit at that and above. and you need to start sweating heavily.
So if your core temperature isn't quite getting there and you're not sweating heavily, you're not gonna be able to drive the physiological adaptations that you're after. So it's just, you know, with being outside on a bike and stuff
Paul Warloski (15:45)
Mm.
Julia (15:50)
you've got, you know, you might be better off doing running outside. And what you said, MJ, is going out at the heat of the day. and then and then what about the people who don't live in a hot place but they're competing in a hot environment and they don't have access to a heat chamber or they don't have hundreds of dollars to use a heat chamber that is in their city or whatever. Well, passive passive means of heating, so post training,
hot water immersion, so being in a hot tub or post-exercise sauna are though those things if they're done immediately after exercise for around half an hour will drive those responses as well. So there's there are affordable ways of doing it. But to so I just wanted to start with that because that's like you need to do that r properly.
Marjaana Rakai (16:45)
Right.
Julia (16:45)
And then in terms of the planning, if you've if you have paid all this money and invested all this time to to compete in the event in hot conditions, you really wanna kinda test out a heat block. Well, this is what I would do. You wanna ideally test out what it how do you go in the heat before
you actually do a heat block that's leading up to your event if you can. So say say like three months out and you you know that you're doing this event, I would just do a heat block then. And that would look like something like for for males, four to seven days of heat. Maybe you can take a couple days, like a weekend break in the middle of it. But consec mostly consecutive days is the best.
Women would would be going more for up to ten days, like ten to fourteen days, which is kind of a annoying that you have to do that much more, but it does it does make a difference. One I I c I'll tell you what it r
a a quick trick that you can do to p potentially shorten that number of days from ten to fourteen more down towards seven and that is if you you preheat before a heat training session for a female because the reason why females
Marjaana Rakai (18:08)
Yeah.
Julia (18:14)
This is what we think, anyways. The reason why we take longer to adapt to the heat is because we have a higher threshold for onset of sweating, and we don't sweat as much as males. So males start sweating faster and they sweat more. And I I just said that that's one of the drivers of the adaptations.
Right. So if females come into a session already hot and what this could look like, and this is what I've done with athletes, is preheating them in a sauna for 15 minutes before they go in the heat chamber on their bike. Because the response has already started.
Paul Laursen (18:55)
Cruel.
Marjaana Rakai (18:55)
That sounds
terrible.
Julia (18:59)
Right. An another thing, like I've discussed this with Stacy Sims before is about targeting doing a heat block in the luteal phase when you're already hotter. Core temperature.
Paul Laursen (19:00)
Yeah, totally.
Marjaana Rakai (19:00)
Yeah.
Julia (19:18)
in the luteal phase, the second half of your cycle after ovulation, your body temperature is higher by point two to point five degree and that alone could start your onset of sweating out of f faster. So just just little things like that. but anyway, so females do need longer and then you would maybe like a month out from your event you do your actual that that's when you don't want to miss out. A month out do a pro
proper heat block, this is what's gonna be your your foundation of getting you through your event. And then in the in the two weeks leading up, you do a couple top-up sessions. And those can look like passive heat sessions.
Paul Laursen (19:55)
Yeah.
Marjaana Rakai (19:59)
Mm, yeah.
Okay, so
Paul Laursen (20:03)
Yeah. And don't don't leave
it, don't leave it too late, right? Like you gotta yeah. and the other I mean the other key thing, if we want to just want to take like a simple message home, you gotta get hot. That's what MJ learned, right? And that she she didn't like it. She was kind of she was resisting psychologically about this whole thing, but sh then she she broke through and she's like, Okay, let's let's let's see if these guys are right and maybe I can adapt. And she she made herself very hot and then she was I I just remember the comments.
Julia (20:06)
Yeah.
Paul Laursen (20:33)
The coaching comments coming out, she was just like it was like hallelujah. I can actually I can finally see a reduction in my heart rate on on these submaximal, you know, rides and runs. Like there was actually evidence that something was changing in her body. But yeah, it's it takes it takes time on time on heat, right? Time being hot for these physiological adaptations to manifest.
Marjaana Rakai (20:37)
Yeah.
Yeah. Yeah.
Julia (21:01)
Yeah, and
MJ MJ, I'll just say to you, like you were talking about how you lived in Dubai and you hated the heat. But like, if people are from a hot place, simply living in a hot place does not adapt you to the heat. You have to again, you have to get hot, like like Prop said, you have to, you know, increase your core temperature significantly and be sweating profusely. So
Marjaana Rakai (21:17)
Mm-hmm.
Mm-hmm.
Julia (21:29)
walking around in Texas, even though you're uncomfortable, it's not gonna do it. Walking around in Dubai it's not gonna it's not gonna do it. And and so that's, you know, something that people really need to to be aware of. And the other cool thing that you said, you know, like genetically based a bit about where you're from, you do have you're from Northern Finland. Like you might have less heat shock protein than someone who is born in Hawaii.
Right. And so you feel the heat more and you don't like it. But the cool thing about the heat is it doesn't matter who you are or how how many episodes of of heat illness you potentially could have had in the heat, you can't your body will adapt with repeated exposure. You if it's done properly. It will adapt.
Marjaana Rakai (21:58)
Mm-hmm.
Now how long can I hold on to that thermal memory?
Julia (22:23)
the thermal memory. Yeah, I think like we know less about that. Like if you haven't done any heat for a couple of years, I don't I've never seen a study looking at at that far back. But I I I think it's kind of like, you know, base endurance training.
You know, if you were a young athlete and you were you had a really good base and you haven't done anything for ten years and you start getting back into it, you're gonna be yes, yes, you're gonna feel it the first few days and the first few weeks, whatever, but eventually you're gonna be better off from someone who's coming into the sport very late and has never done any bass training. Right? So our body our body does remember things.
Marjaana Rakai (23:03)
Mm-hmm.
Julia (23:12)
It's not all lost.
Marjaana Rakai (23:14)
S so what I'm hearing is that somebody who is going to Kona, for example, in October, try a heat block way out, then go back to your training, have maybe a few those passive heat training
shots every once in a while and then one month before Kona, you start kind of tapering a little early, have that 10 days, 14 days of proper heat block, and then ta taper into the race day. And and if you're going with the happy or a boyfriend, you have to book the flights early because you might need a little bit more time to adjust to the heat and humidity. Is that somewhere there?
Julia (24:04)
Yeah, that that's spot on. And again, like being able to play. So yeah, guys wouldn't need that ten to fourteen days. They're probably needing, you know, four to seven days. and and women, yeah, needing a little bit longer. So but but definitely like it is an in it is a highly individual thing, again. So we're we've been talking about male and female differences, but again, the individual like you can have
Marjaana Rakai (24:20)
Mm-hmm.
Paul Laursen (24:21)
Yeah.
Julia (24:33)
Two people that have like I and I've had this. I've had two sailors that have the same like performance performances, the same VO2 max, and one one really struggles in the heat and the other with others like on fire in the heat. So again, that's that's kind of probably more linked to the the genetic side and the the heat shock protein. So you you have to learn
Marjaana Rakai (24:51)
Yeah.
Julia (25:02)
like what your body does itself. And and most people will know. Most people will know because we're we're creatures of comfort. they'll know if like, I don't like the heat. Right? So you might need, if you don't like the heat, that's okay. You might just need to pay a little bit more attention and and give yourself a little bit more time to adapt and really kind of like hit it on the head.
Marjaana Rakai (25:12)
Uh-huh.
Paul Laursen (25:14)
Yeah.
I would agree. And I would I would think if if you don't like heat, that's possibly a signal that you probably need a bit more heat training in your in your diet. so you get to the level that MJ finally finally found for herself. so I think y you need to develop a bit of a thirst for it. that's a hard line from a coach, but you know, but I I think it's yeah, that's that's my belief, kind of that's w with my experience in coaching coaching hat on, right? That you got MJ. You you're look you know.
Paul Warloski (25:50)
Okay.
Paul Laursen (25:55)
You know what you know I'm talking about. Hard not.
Marjaana Rakai (25:57)
I
know I know what you're talking about. Too bad that Nice was actually a cool day. I didn't need the heat training after all, but
Paul Laursen (26:00)
Yeah, yeah.
No. But
but on that, that's a really good point too. I I don't think there's ever anything wasted by training in the heat, even with respect to to like cool cool performances. and Julia, I'm not sure if you remember any of the studies where but I think there's there's even some evidence that heat training can benefit your performance in in cool conditions, is there not?
Julia (26:25)
Yeah, definitely for endurance sports. like the the literature is a little bit like there's kind of two sides of it, but there it there is you know, physiologically we get an increase in plasma volume, hemoglobin goes up, cardiovascular strain is reduced, and all those things can potentially elicit better performance in temperate or cool conditions as well. Exactly.
Paul Laursen (26:51)
Yeah, so you kinda can't go wrong, really. You're not wasting
your you're not wasting your time. Yeah.
Julia (26:56)
Yeah, and that's
how I that's how I I always sell it to athletes, is like, you know, this is a win-win. If we do this properly, this is a win-win for you. And, you know, often athletes like say someone's got an injury and they have to do a little less volume. We might just add heat. They don't have a competition in hot conditions, but we're adding volume in a different way. And so it it's a it's a tool that's really useful.
Paul Laursen (27:22)
Yeah, couldn't agree more.
Marjaana Rakai (27:23)
So what about age differences? I have a daughter who is 14 and and doing a strength and conditioning camp in the Texas heat. They take the kids out and they do sprints outside. what what can happen with the youth sport youth athletes in the heat and obviously like they're doing sprints there.
And not endurance sessions. do you have any advice?
Julia (27:56)
Yeah, so I guess the the the what we know about teens or children competing outside in the heat is I guess they they are a little bit more at risk of heat illness and and so
we we use a little bit more caution around them making sure you know they're having enough breaks for drinking, that they're in the shade when they can be and things like that. So and and and really having coaches aware of like what are the signs of heat illness of when, you know, when's enough for an athlete to be pulled out. and and part of that is again like their their pseudomotor function or their ability to sweat.
is not as developed as a mature adult. So they're cooling the h when we sweat, we cool. Or that's how their body cools itself. So that they can get hotter.
Paul Warloski (28:47)
Yeah.
Julia (28:56)
than than an adult without have like the their ability to cool is not as good. So that's that's kind of the main thing. and then also their body size is is smaller too. So their their their body surface area to body mass ratio is different than a growing adult and and they're more likely to just get hotter because of that. So that's kind of the background. So I guess then you then you've got the
Marjaana Rakai (29:03)
Mm-hmm.
Julia (29:23)
the teen who maybe has a little bit less awareness of how much they should be you know, are they drinking enough? are they and if and if they are feeling a bit funny, are they gonna be afraid to speak up and say something because of their peers and they don't want to appr appear like they're weak. So those those are kind of the biggest challenges, I guess, with with teens. They can still adapt to the heat. there's nothing to show that they they
Paul Warloski (29:47)
Yeah.
Julia (29:51)
they can't be outside and when it's hot. And but it's just, yeah, adults having a little bit more awareness and watching over them, I think is a big one. and then, you know, so you as you said to your daughter, like she's not doing an an endurance activity. She's doing sprints, which might she might actually feel better running in the heat.
Marjaana Rakai (29:58)
Mm-hmm. Yeah.
Julia (30:15)
doing sprints in heat. Like we know that that performance for that type of exercise goes up in hot conditions. But it's just having talking it like for anyone out there that has kids that train outside and it's really hot, having some really good strategies for them. So giving them slashy in their water bottle or just putting ice, having having their their their hydration drink and then some crushed ice that they can chew on in between and just doing things that that will promote cooling.
Marjaana Rakai (30:15)
Mm-hmm.
Mm-hmm.
Mm. And what are what are the signs of heat illness?
Paul Laursen (30:47)
Yeah.
Julia (30:52)
Yeah, so dizziness, just yeah, perf yeah, dizziness, lightheadedness, getting like cool and clammy. suddenly not really being able to to perform. Like the body just starts is protecting itself and it just starts kinda like shutting down. fainting could be something.
Marjaana Rakai (31:15)
Mm-hmm.
Julia (31:19)
And and that's kind those are kind of the things like body feeling cool and clammy is is more heat exhaustion. When you get to the point where the skin is red and and hot to touch, then that's actually even more dangerous. That's looking at at heat stroke and and that's the kind of situation where you kind of need immediate
attention, first aid attention to that person. So it's removing them from the environment, getting them into some cool water where actually it would be more like cooler than air temperature, and potentially calling medical medical support. So those are the key things, but the body is really good at telling us it's it's in danger.
Paul Laursen (31:59)
Mm-hmm.
Marjaana Rakai (32:06)
Mm-hmm.
Julia (32:06)
So, you know, checking
in with your athletes, you know, anyone feel everyone feeling okay, anyone feeling a bit funny, anyone feeling dizzy, if you see someone that looks pale and it's a hot day, that's not a good sign, right?
Marjaana Rakai (32:20)
Yeah. Sometimes
Paul Laursen (32:20)
Yeah. Yeah.
Marjaana Rakai (32:21)
you can see like in the ski like a like the upper lip gets all white and they're red. S sometimes like you can see signs if you know your kid really well, you can see, something is up right now. Like yeah. Yeah.
Julia (32:33)
Yeah, watching, yeah,
yeah.
Paul Laursen (32:37)
Yeah, and if you have access to cold water in any of these conditions, so whether you're you know, w whether you're youth or adult and you're having some of these symptoms, usually cold immersing immersing yours yourself in cold water is through the conduction process is a f is the fastest way to rid that heat from the bee from the body and potentially save save a life. So just keep that in mind.
Paul Warloski (33:02)
Well thanks, Julia. We appreciate your time today.
Julia (33:04)
thank you for having me. It's a pleasure to get to to chat with the three of you.
Paul Laursen (33:08)
Yeah, it was awesome. It's awesome. You're amazing.
Paul Warloski (33:08)
Good.
Julia (33:10)
Thanks guys. Keep up the great work. Really appreciate the work that you guys are doing and and the different lenses and perspectives you bring.
Paul Warloski (33:18)
Thanks for listening today to the Athletes Compass Podcast. Take a moment now, subscribe, share, and let's keep navigating this endurance adventure together. Improve your training with the science-based training platform Atletica and join the conversation at the Athletica Forum. For Dr. Julia Casadio Marjaana Rakai, and Dr. Paul Laursen I'm Paul Warloski and this has been the Athletes Compass Podcast. Thank you so much for listening.