When I started coaching, I took a certification class, and they teach periodized heat training for only a couple of weeks heading into a hot event, but I think this science and strategy is outdated. Heat training year-round is what all the best in the sport are doing, and I wanted to figure out why.
In recent podcast interviews, David Roche praised heat training, and then so did David Sinclair and Jeff Mogavero, so I thought I would piece together why it is so valuable for unlocking better performances.
I have been heat training for almost two years (3+/- times a week in the sauna), and I have noticed anecdotal evidence that it works, but I had wanted to dive into exactly why and what the science behind it is. So here is what I have come up with, and if you find this helpful, valuable, etc, please consider joining my Patreon so I can continue to dive into science like this!
Ultrarunning isn’t just about grinding through miles—it's about surviving the wildest conditions the trail can throw at you. Whether roasting under a sun so hot it could fry an egg, shivering through a surprise mountain snowstorm, or just wondering why you signed up for 100 miles of voluntary pain, your body needs to handle it all. Enter heat training: the sweaty secret weapon that doesn’t just prep you for desert ultras—it makes you better at everything—and literally everyone is doing it!
This isn’t just about running faster in hot weather. Heat training literally transforms your body, turning you into a more efficient, heat-resistant, endurance-crushing machine. We’re talking increased blood plasma and red cell volumes, better cooling systems, and the kind of mental toughness that laughs in the face of misery. Want to feel unstoppable? Heat training is your golden ticket.
And if you’re thinking, “Isn’t this just bro-science?” Nope. Real scientists are backing this up, including a 2022 study showing that heat training supercharges your cardiovascular system. So whether you’re chasing a PR, gearing up for a desert showdown, or just looking to be a more resilient trail beast, heat training is your answer.
Let’s get into why you should embrace the heat, sweat like it’s a sport, and reap the benefits all year long. Spoiler: It’s way more fun than it sounds.
The Science Behind Heat Training
Heat training involves exercising in elevated temperatures or incorporating heat exposure, like sauna sessions. When exposed to heat stress, the body adapts by enhancing several physiological functions, including blood volume expansion and improved thermoregulation.
Increased Blood Plasma and Hemoglobin Volume
A pivotal 2022 study published in the Scandinavian Journal of Medicine & Science in Sports examined the impact of heat training on elite cross-country skiers over five weeks. Athletes participated in five weekly heat training sessions, leading to measurable hemoglobin mass and red blood cell volume increases.
Increased hemoglobin mass and red blood cell volume are the secret sauce for endurance athletes. These components are like the delivery trucks for oxygen in your bloodstream, shuttling it to your muscles where it’s needed most during a run. The more hemoglobin and red blood cells you have, the more efficiently your body can transport oxygen, which means less fatigue, more sustained energy, and better overall performance. In ultrarunning, where every breath and step counts over hours (or days), these physiological boosts can be the difference between feeling like a machine or hitting the wall.
The findings align with earlier research showing that heat acclimation increases plasma volume. A study in the Journal of Applied Physiology (2010) found a 7% increase in plasma volume within 10 days of heat exposure.
A 7% increase in plasma volume within just 10 days of heat exposure is like hitting the jackpot for your cardiovascular system. Plasma is the liquid part of your blood that keeps everything flowing—literally. When plasma volume increases, your heart works more efficiently, pumping more blood with less effort. This means better oxygen delivery to your muscles, improved hydration management, and reduced strain on your cardiovascular system during long runs. This adaptation helps ultrarunners sustain higher intensities, recover faster, and endure longer.
Improved Thermoregulation
Heat training optimizes the body’s cooling mechanisms. Athletes experience an increased sweat rate and better retention of electrolytes, enabling effective temperature regulation even during grueling efforts in extreme conditions.
Why Ultrarunners Should Train in the Heat Year-Round
1. Increases Blood Plasma Volume
Heat training causes your body to adapt by increasing blood plasma volume, the liquid component of your blood. This boost allows your heart to pump blood more efficiently, delivering oxygen and nutrients to muscles while reducing cardiovascular strain. A 7% plasma volume increase within just 10 days of heat exposure has been observed in studies, giving your endurance an immediate edge, whether you're racing in heat or cold.
2. Boosts Hemoglobin and Red Blood Cell Volume
Exposure to heat doesn’t just expand plasma volume; it also stimulates an increase in hemoglobin and red blood cell mass. These components are responsible for transporting oxygen to your muscles. The more you have, the better your aerobic performance.
3. Enhances Thermoregulation
Your body gets better at cooling itself during heat training. This makes your body more efficient at staying cool in hot weather.
4. Mimics Altitude Training Benefits
Heat training mimics some of the effects of altitude training by improving your blood's oxygen-carrying capacity.
5. Improves Recovery and Adaptability
Heat training isn’t just about performance; it also boosts recovery. Better blood flow and cardiovascular efficiency mean your body delivers nutrients and oxygen more effectively to fatigued muscles.
6. Accessible and Affordable
Heat training can be done anywhere. Whether it’s running in layered clothing, soaking in a hot bath, or using a sauna, heat training is a practical, low-cost way to optimize your performance year-round.
Practical Ways to Incorporate Heat Training
Hot Weather Runs Schedule runs during the warmest part of the day or in heated indoor environments. Start with shorter sessions and gradually increase intensity.
Sauna or Hot Tub Sessions Passive heat exposure, such as post-run sauna sessions, accelerates heat acclimation. The 2022 study highlighted that combining workouts with heat exposure enhances hemoglobin and plasma volume adaptations. This can be as simple as taking a hot bath after running too.
Layered Clothing Wearing extra layers during training in cooler weather can simulate heat stress, ensuring consistent acclimation throughout the year.
Safety Considerations
Heat training has all these magical benefits, but I also think you can overdo it. I keep an eye on my heart rate and get out, or cool down once it gets to about 125. Passive heat can take a toll on the body, so even using wrist-based heart rate readings can give a good idea of when it is time to get out.
Conclusion
The 2022 study on heat training’s effects on hemoglobin and red blood cell volume reinforces its transformative potential for ultrarunners. By enhancing cardiovascular efficiency and thermoregulation, heat training is a year-round tool for improved endurance and performance.
Incorporate heat training into your routine and experience the benefits that science—and countless elite athletes—support. Remember, every bead of sweat is a step toward becoming a stronger, more resilient ultrarunner.
References
Périard, J. D., Caillaud, C., & Thompson, M. W. (2016). Frontiers in Physiology: Cardiovascular adaptations from heat acclimation.
Sawka, M. N., & Wenger, C. B. (2010). Journal of Applied Physiology: Influence of heat acclimation on exercise performance.
Stanley, J., Peake, J. M., & Buchheit, M. (2015). International Journal of Sports Medicine: Heat acclimation and post-exercise sauna exposure.
Scandinavian Journal of Medicine & Science in Sports (2022): Heat training adaptations in endurance athletes.