How to Use Heat Training to Thrive in Warm Weather Ultras!

The following article is based on my personal experiences of heat training and coaching, and material I learned through UESCA‘s Ultrarunning Coaching Certification.

I live in Squamish, Canada, a mountain town that gets only 56 hours of sunshine, and an average high of 5 degrees Celsius in December.

So, how did I prepare for HURT100 in mid-January, which is a race on the Hawaiian island of Oahu that’s known for its sunny, warm climate?

It’s also probably worth noting that I’ve actually been hospitalized for heat stroke before, so this is something I’ve had to learn. I was about 13 years old, and was simply jumping on a friend’s trampoline outside when my vision started to deteriorate. I ended up vomiting all over the doctor’s office and then passing out, taking an ambulance to the hospital. I woke up the next day naked under a hospital gown, with IV fluids pulsing through my arm. (Some people would maybe even just totally refrain from doing runs in the heat if they had my experience!) In addition, I’ve had the dreaded hyponatremia, and various occasions of heat exhaustion. This was all before I knew about heat training…

Here, I’ll share my heat training protocol, which brought me from snowy Canada to the tropics of HURT, and equipped me to feel great and stay safe while handling the heat. This is what I recommend to my athletes, and I hope you can gain something from it too!

Why I recommend passive heating

There are many options for heat training, including exercising in a hot environment, over-dressing for runs, and passive heating, in which you passively heat yourself by lounging in a sauna, steam room, bath tub, hot tub, or heck, even sitting in your car with the heating on max.

Exercising in a hot environment isn’t very accessible, as it means you either have to live in a warm climate, have the race/event you’re training for happen during your city’s warm/summer season, or have access to a university or fancy lab that has a climate chamber. If you do live in a warm place, it may only be warm at a certain time (like mid-day), and that might not be accessible for everyone.

On the other hand, over-dressing for runs is something that’s accessible to everyone. You simply layer up, and get out there. The major downside of this method is that it may impact the quality of your training. You’ll be super uncomfortable, and it’s hard to imagine that you’ll be able to maintain the same intensity in your runs while being so over-heated.

This leads me to my preferred method, passive heating. This is a method that many people have access to, as many people have a bath tub at home, or may have a community center nearby that has amenities such as a sauna, hot tub, or steam room. (And if you’re in Squamish, there are even some hidden saunas in the forest! But I’m getting distracted and off topic.) By separating the heat training from your run, it’s less likely to interfere with the quality of the run, while still providing a lot of great physiological adaptations. Sauna training in particular has also been shown to produce other beneficial cardiovascular adaptions, so it feels very productive, if you’re able to find one. Even better, it’s fun! It’s basically permission to incorporate spa-like activities into your daily life and training.

How long is required for heat acclimation?

To produce the heat acclimation adaptations you seek, it’s ideal if you can heat train for 7-10 days in a row. This is why it’s so important to choose a method that is accessible to you, and something that you can find the time to do. Once those 7-10 days are checked off, you can maintain your adaptations if you continue to add one heat training session every 3 days.

For sauna training, it’s ideal if you can work your way up to 60 minute sessions if you’re entering the sauna cold, to ensure adaptations are occurring. However, there’s a technique for shortening the time required in the sauna. If you can carve out the time to have your session immediately post-run, then 30 minutes will produce meaningful benefits, because your body is already pre-warmed from the run.

For HURT100 in 2023, I used these principles to create a protocol that worked well for my schedule and availability. I didn’t have time to run and sauna during the day, so instead I completed my training runs during the day, and then I indulged in one-hour “spa nights” in the evenings. Instead of doing another run at night to pre-warm, seeking recovery, I went in the bath tub for 20-30 minutes, which effectively pre-warmed me before a 30-minute sauna session (at my sauna’s max, which is 60 degrees Celsius). At HURT, I felt extremely adapted to the heat. In fact, before I left for the event, I was the only person in my office wearing a large insulated ski jacket and toque, and still cold! When I returned back to Canada from the race, I was wearing an extra layer than normal on most runs.

What about hydrating?

To further your adaptations, it’s ideal if you can actually dehydrate yourself a little bit before your sauna sessions. I know, it feels wrong, but here’s why: when you’re dehydrated, you have low blood volume. If you enter a sauna or other passive heating method in this state, the kidney naturally increases its production of EPO and red blood cells, and your body will then respond by increasing its blood volume, to account for the additional red blood cells. Typically, most people would already be dehydrated after a run or in the evening before bed, so this is pretty easy to accomplish. Having said this, it’s a slippery slope. You don’t want to dehydrate yourself to the extent that it affects your training the following day. If possible, gradually re-hydrate from the session. (Source: Stacy Sims’ book, ROAR.)

Note: this is definitely more advanced. If the idea of using “passive dehydration” freaks you out, just don’t bother with it. You’ll still get great results without.

When should I heat training before my goal race/adventure?

Part of the appeal of the passive heating protocol is the flexibility, as you can fit those 7-10 days in anywhere in your training cycle, and then re-expose yourself to heat every 3 days to keep your adaptations. I recommend not heat training too far into the race week, as it does elevate your heart rate and add to training stress. For HURT, my last session was on a Tuesday evening before a Saturday morning race, and anything later in the week felt too risky. I’d recommend having your last heat exposure on the Sunday or Monday before your race the following weekend, to be safe. Research suggests that women may need closer to the high end (10 days) to acclimate, while men may be able to get away with only 5 days. (See other great suggestions specific to women on Dr. Stacy Sims’ blog.)

When possible, it may be ideal to consider avoiding your biggest-volume or most intense training weeks. As I mentioned above, sauna training does provide cardiovascular benefits, but it also adds to the overall training load for the week. I’d recommend considering heat training during a lighter training week, or even slightly reducing your training volume or intensity to account for the additional training stress. It’s important that you don’t over-do it. Resist all temptations to get competitive with your heat training, by spending longer than you need to. Like most training, it’s best to do the minimum effective dose, and then focus on recovery.

Happy trails!