At the Quad Rock Trail Races in Fort Collins, Colorado on Saturday, I was finishing my run at 9 AM, waiting to cheer and coach athletes on the course. As I jogged uphill to see the first racers, I glanced down at my heart rate. It was 165, not that far away from my lactate threshold, at an effort that would usually be in the 140s.
Part of that might have been race-day nerves. My coaching psyche is like a duck–I look calm, but beneath the surface, my nervous system is gesticulating wildly and trying to sell you Aflac insurance. But most of that heart rate crapstorm was the sun and heat.
I haven’t done my heat training this year due to concerns that the hairy guys who grunt in pleasure at the local sauna have been replaced by hairy guys who grunt from COVID. And I run in the morning before it gets hot. So the heat crushed me, turning a slow jog into a hard effort.
When I got back to the car, I was excited to see the temperature. My guess was 85 degrees F, enough to fry this innocent winter child.
It was still 68.
Later in the day, it got into the 80s, and the Quad Rock racers were fried. Even the athletes that had amazing races talked about suffering a bit at the end. Early season heat is–and this is a technical term–a motherf’er.
But heat doesn’t have to be that hard, whether it’s a pleasant, sunny day in Colorado or stanky, armpit day in Florida. Strategic heat training can fundamentally alter how the body responds in tough conditions, starting in just a few days. Longer-term heat training may even lead to major fitness gains that apply in all conditions!
Here’s How To Heat Train For Ultras Like Western States: Heat Science Overview
I’ve dug into the science before, but the basic physiology of heat adaptation is so freaking fun that it’s worth a quick review (maybe those dudes who are grunting in the sauna just really, really like science). With heat exposure, the body circulates more blood to the surface of the skin for cooling. As a response, blood plasma volume rapidly expands, increasing the water content of the blood to improve this cooling mechanism (see this 2015 review article for more on the intermediary mechanisms).
The changes can be striking. For example, a 2015 study in the European Journal of Applied Physiology found a 17.8% increase in peak plasma volume after 4 sauna exposures consisting of 30 minutes in 188 degrees immediately after training. Other studies show a less pronounced jump, but all demonstrate a significant change with the onset of heat training.
In addition, the body becomes more efficient with sweating, decreasing the body temperature at which sweating is initiated, reducing the content of electrolytes to produce more dilute sweat, and actually changing the size and function of sweat glands. Vascular function improves, allowing the increased plasma volume to better cool the skin. And metabolic rate decreases from the heat strain and there is increased thermal tolerance at the cellular level (a phenomenon at least partially explained by genetic expression from repeated environmental exposure and proteins that respond to heat stress, as outlined in this 2016 article in the Journal of Applied Physiology). Many of these adaptations start immediately and progress over a few weeks to months.
But the next step is my absolute favorite, and it’s still being hashed out in the literature. Think back to that 17.8% number–that’s A LOT, right? That seems like a big deviation from homeostasis! The offset plays out in hematocrit levels, or the percentage of red blood cells. As the plasma volume rises, the denominator goes up as the red blood cell numerator stays steady, so hematocrit goes down.
Emerging studies are finding that this offset may spur the production of natural EPO from the kidneys to increase red blood cells, returning hematocrit levels closer to baseline and increasing hemoglobin mass. Added red blood cells are the athletic holy grail due to their importance in getting oxygen to working muscles, so heat training could be a type of doping (Alberto Salazaar smiles) that is natural (he frowns) and legal (he closes the article). A 2020 study in Experimental Physiology did a 5 week protocol with 5 weekly 1-hour rides in 100 degree heat to produce a hemoglobin mass increase, and based on the mechanisms, it probably takes 3-6 weeks to see any major change. That change could improve performance in all conditions, and it may mimic some of the adaptations from altitude.
Important Heat Training Considerations
Before getting to the specifics of the heat plans, there are two important considerations. First, genetic predispositions and individual physiology likely play a massive role at every step of heat acclimation and performance. Those include: how blood volume changes with heat exposure, responses to stress more generally, and iron levels and propensity to create new red blood cells. Make sure you listen to your doctor and your body, since what leads to breakthroughs for one person may cause another person to get tired and slow.
Second, real-world heat training incorporates tons of variables that can’t be accounted for in a lab or a closed physiological model. It starts with where you grew up. Anecdotally, I see athletes from warm climates excel in the heat for the rest of their lives, like Ashley Brasovan, a Florida native living in Colorado who set a 9-minute course record at the Quad Rock 25 Miler on a day when times were slower across the board.
It applies to how you are exposed to heat. While the studies often use a dry sauna or a heat chamber, most of the same principles should apply in any setting where core and/or skin surface temperature are significantly elevated. High dew points can likely accomplish similar goals at lower temperatures. My best athletic year was after a summer training in the stankiest swamp armpit of all, Washington D.C.
It also incorporates your current life realities. Some people don’t have sauna access, some live in colder climates, some just have limited time. The plans will try to accommodate everyone.
Biggest disclaimer: heat training is risky for the heart and body, so please, please be careful and promise me that you will get doctor approval before trying any of this. It is absolutely not worth risking your health. And when you do try heat training, remember the goal is not to fry yourself to the max like you’re a KFC chicken tender. The goal is to get the stimulus without overstressing your body, and nothing should ever be too uncomfortable. If your sauna trip is a test of your willpower, you are staying in too long.
Heat Plan Elements
Over years of coaching athletes, Megan and I have refined the recommendations from the research into elements that we think balance the excess stress of heat training with individual variability. We’ve had a real-world experiment going where we get to see athletes excel in hot races like Western States, ask them what they did, then feed it back into our research-backed model of what we think works. It’s constantly evolving, but here are the 5 elements we start with to inform the plan:
- Sauna: 20 to 30 minutes, or until it starts to get uncomfortable, ideally right after training, but it can also be later in the day. To optimize the blood volume response, don’t hydrate while inside the sauna, don’t cool off right after (a hot shower is great), and delay rehydration for 30 minutes after exiting. Most of the research is on dry saunas, but steam rooms and infrared saunas should have benefits as well.
- Hot tub or hot bath: 15 to 20 minutes, ideally submerged, with the same rules. The temperature is hard to regulate in these and core temperature can rise dangerously fast, so practice extra caution and never let yourself get uncomfortable.
- Heat exposure during run: 30 to 45 minutes easy. If it’s above 90 degrees, you can run in what you normally would (i.e. listen to legendary heat scientist Nelly). If above 80, one dark layer is ideal. If below 80, dress with two layers. A 2018 study in the Medicine & Science in Sports & Exercise journal found that overdressing for easy runs led to many of the same adaptations as training in extreme heat, but at a lower magnitude. And I can’t emphasize this enough: be safe, especially as you get used to it. Wait to rehydrate until you finish the run on these shorter ones.
- Longer run in heat: 2+ hours with the same rules, except make sure you are hydrating the whole time.
- Harder run in the heat: anything that brings your heart rate around lactate threshold for ~20 to 40 minutes during the run, with the remainder easy, and full hydration.
NOTE: stop all intentional heat interventions at least 3 days before race day to prevent overstress, and ideally dial things back to pure maintenance about 1 week pre-race in the advanced plans.
The 3 Heat Plans
The Beginner Heat Plan
- 3 consecutive daily sessions in sauna/bath or during run,
- Followed by 1-2 exposures a week in sauna/bath or during run
- Starting at least 1 week before race
The Beginner Heat Plan is what I use, since I try not to do my big races in high heat conditions. I was worried that when I got my 23&Me results, I’d learn that my mom mated with a penguin. We have had several athletes finish in the top-10 of Western States using this approach, so even though it’s called “Beginner,” it’s the place to begin the process.
The 3 sessions to start can be sauna, bath, or with an easy run, to spur the initial blood volume response. Those adaptations are relatively sticky (according to a 2018 review in Sports Medicine, there is only a 2.5% decay in HR response to heat per day), so 1-2 similar sessions per week can maintain adaptations thereafter for time-crunched athletes. For many athletes in hot climates, that can mean just running like normal, or moving those runs to midday. Since blood volume responds fast, you can push this relatively close to your race, but you’ll likely miss out on the other adaptations, like metabolic efficiency. If you stick with this plan, aim to do some higher effort runs in the hotter part of the day to supercharge adaptations.
The Intermediate/Advanced Heat Plan
- 4 consecutive daily sessions in sauna/bath or during run,
- Followed by 3-5 exposures a week in sauna/bath or during run,
- With at least 1-2 runs per week in heat,
- Plus 1 harder run in heat,
- Starting at least 3 weeks before race
The Intermediate/Advanced Plan is our go-to option for athletes competing in major events that we suspect will be hot, and it has coincided with podiums at some of the world’s more blistering races. In its simplest form, it’s 5 sauna sessions per week, with some heat running too.
After an initial heat introduction, the maintenance and development period includes a heavier focus on running in the heat, rather than passive heat exposure like the sauna. In particular, we have seen that athletes often have a tough experience on their first harder, hotter run even with adequate sauna use. On the harder run, something like a 20 to 40 minute tempo is ideal.
While it varies a ton by the athlete, a typical week might look like this:
Monday: Rest and sauna
Tuesday: easy run and strides
Wednesday: workout in AM and double in heat and/or sauna
Thursday: easy run and optional hot double and/or sauna
Friday: easy jog or cross train plus sauna
Saturday: Quality long run
Sunday: easy run and strides. Optional hike in the heat and/or sauna.
Start the plan at 3 weeks for heat acclimation, but ideally 4-6 weeks to optimize potential hemoglobin mass increases.
The Western States Heat Plan
- 4 consecutive daily sessions in sauna/bath or during run,
- Followed by at least 5 exposures a week in sauna/bath or during run,
- With at least 3 runs per week in heat,
- Plus 2 longer runs and 2 harder runs in heat
- Starting 4-6 weeks before race
The Western States Heat Plan is INTENSE, and 90% of our athletes racing Western States don’t even mess with it, including top finishers. The problem with this plan is that it may work, or it may lead to a stress bomb that makes training less efficient. Since the goal is always to keep getting faster and stronger, heat acclimation needs to support that growth. In practice, that means athletes shouldn’t try this plan unless they have lots of stress to spare in life, are feeling good in a long-term training process, do not have any issues with iron levels (with normal to high hemoglobin), and sign a waiver that’s at least 47 pages long.
The biggest addition here is the long and hard running in heat. While I don’t think that’s necessary, it can lead to a major confidence boost for race day.
After cheering at Quad Rock, I glanced at the weather forecast for my next race. I saw that it’s going to be 88 and sunny, and it’s just 6 days away. Oh crap.
So cut yourself slack if you try to get by on the bare minimum. I am currently in day 2 of the beginner plan, perching myself over our inefficient home sauna like I’m trying to lay eggs on the heater. I’ll do that for four days, with tomorrow also including a 30-minute double outside in 70 degrees in my winter running outfit.
Will I excel in the heat? No, almost certainly not. But based on the research on blood volume, along with my past experience, those 4 days will make the race exponentially better than it would have been otherwise.
To me, that fast-acting opportunity is one of the coolest things in running training. Almost everything else takes months or years. But heat training can be as simple as incubating on a sauna heater for a few days, or as complicated as a 6+-week protocol, with possible benefits the whole time.
You may never be one of those beasts that crushes heat, like Ashley Brasovan or Katie Asmuth. But I promise that you can be like me, a half-penguin who melts on a pleasant Spring day. With just a small focus on heat training strategy, I can usually do pretty well even on the hottest days.
Fellow penguins, rejoice.
David Roche partners with runners of all abilities through his coaching service, Some Work, All Play. With Megan Roche, M.D., he hosts the Some Work, All Play podcast on running (and other things), and they wrote a book called The Happy Runner.