In this instructional video, Floris Gierman (with occasional input from a co‑speaker) addresses the challenges runners face in hot and humid environments and offers a comprehensive set of evidence‑based strategies for training and racing under heat stress. He begins by illustrating how temperature and humidity directly affect pace, heart rate, and perceived effort using personal Strava data from runs at 23 °C/63 % humidity versus 30–39 °C/85 % humidity, showing clear performance degradation as heat rises. He then explains the body’s thermoregulatory physiology: core temperature must stay within a narrow range, most metabolic energy during exercise is spent on heat management, and sweat evaporation—not sweating itself—is the primary cooling mechanism, which is compromised by high humidity. The video outlines the signs, symptoms, and severity spectrum of heat‑related illnesses (heat exhaustion to heat stroke) and stresses immediate treatment and medical attention. Practical training adaptations are presented, including timing workouts for cooler parts of the day, indoor treadmill sessions, splitting long runs, seeking shade, avoiding concrete, and adjusting effort rather than heart‑rate zones. Gierman details heat‑acclimation techniques such as layered‑clothing runs and sauna sessions, describing physiological benefits (lower core temperature, reduced heart rate, increased sweat rate, improved plasma volume, enhanced VO₂max, and better electrolyte retention). Race‑day cooling tactics are covered: gradual warm‑up, ice‑filled water bottles, head/neck cooling, drinking to thirst (400‑800 ml/h), electrolyte supplementation, minimal sunscreen, and avoiding overdressing. Sun‑protection advice includes strategic sunscreen use, hats, bandanas, sunglasses, and nutritional support (omega‑3s, antioxidants, vitamin D). Finally, he emphasizes a mindset of pacing by perceived effort, patience, and positivity, warning against artificially raising training zones in heat. The video concludes with a brief promotion of his marathon training program and an invitation for viewer feedback.
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I often hear from runners living in hot and humid climates saying things like, it is so hard for me to run in these conditions, especially to keep my heart rate low. And then I also hear the exact opposite in the winter months from athletes saying, it is so cold out here and so snowy, it is very tricky to run in these conditions. Weather stress is real, and this can be caused by a variety of different elements, from very hot temperatures with very high humidity all the way to very cold conditions with very low temperatures. Then there's a variety of other weather elements as well, such as wind, high dew points, extreme rain, hail, snow, ice on the ground, you name it. All these weather conditions can impact your perceived effort, your heart rate, and your running pace. And in this video, we're going to go through a few different strategies specifically for the hot and humid conditions and seeing how we can adjust our training and our racing accordingly to still maximize our performance. I want to show an example of how a difference in temperature can really change your overall performance. Let's take a look at this data. So here's an example of a recent run that I did, and here you see it was 73°F, so 23°C, with 63% humidity. I first did a mellow walking warm-up, and then after that I ran mile 1 in 7:17, so 4:32 per kilometer. So the first 2 miles are really still focused on warming up. Then mile 3, you see 7:08 minute mile. Mile 4, 7:09 minute mile. And this was at a heart rate of 143 and 145. Then let's take a look at another run that I did the following day, but the temperature, this was inland towards the desert, the temperature was significantly higher. It was 96 Fahrenheit, so 30 degrees Celsius. 36°C. So what we see over here at mile 3, so 5K into the run, I was still running about the same as the previous day. Like, I ran a 7:07 minute mile and a 7:08 minute mile at around the same heart rate, 143 versus 146. But then I noticed that the heat was starting to get to me, and then look at mile 4 over here. I slowed down 36 seconds per mile versus the previous day. So I ran it in 7:45 minute miles or 4:49 minute per kilometer at a heart rate of 149 versus 7:09 minute mile, 4:27 minute per kilometer at 145 heart rate. So here we see an example of 6 miles, so about 10K on July 8th. This was a few years ago actually. 102 Fahrenheit, so 39 Celsius. At mile 3 here, I was running a 7:45 54-minute mile, so 4:55 per kilometer at 149 heart rate. As I progressed at mile 6, so about 10K in, I ran an 8:38-minute mile, so 5:22 per kilometer at 150 heart rate. If we go the next day, it was significantly cooler. I ran in the evening at 8:36. It was 85 Fahrenheit, so it was significantly cooler here, 29 Celsius. If we look at mile 3 here, I was running 147 heart rate, 6:55 minute mile, so 4:18 minute per kilometer. Mile 6, so 10K in, I ran a 7:13 minute mile. So the drop-off per mile was significantly lower here. And what you see when you compare mile 6 on both of these days, it's almost a minute and a half difference. So I'm almost a minute and a half slower when the temperature became higher over here. So keep in mind, I've trained myself very well to be able to handle the heat. I've slowly, gradually introduced myself to heat. I absolutely do not recommend doing these tests, especially if you're not used to running in the heat. What I will do is I'll add some links to Strava in case you want to see some closer-up details of, of these different runs. So what is happening in our bodies during heat stress? For humans to live, we must maintain a body temperature in a very narrow range between 95°F and 107.6°F. So that's 35°C to 42°C. There are many differences of outside temperatures and physical activity levels. During exercise, the majority of your energy is actually used for heat management, and only a smaller percentage is actually used for muscle contractions to move you forward. As your running effort level increases,, the heat production increases as well. The main cooling mechanism from your body is actual sweat evaporation. Some people are more affected by different weather conditions than others, and the biggest difference is into the main body's thermoregulation, so your water and electrolyte regulation. Tim Noakes, he wrote about this in much detail in the book The Lore of Running. One important point that he made here Sweating does not cause heat loss. It is the evaporation of the sweat into the atmosphere that causes heat to be lost. So this phase change from liquid sweat to vapor is what extracts heat from your skin. Humidity is a measure of the amount of water content in the air, and if the humidity is really high, your sweat cannot vaporize. It can only drip off, so it does not have the cooling factor on the skin. A frequent question that I hear is, shall I adjust my aerobic training heart rate by 5 or 10 beats because of the heat and the humidity. No, you don't want to adjust your training heart rate. Your body is under additional stress and tells your brain what's going on. We want to run at the same or even lower effort levels, which often means having to slow down our running pace. For some athletes, this might mean having to slow down further or even take walk breaks to stay aerobic. Some athletes get very frustrated about hot and humid weather conditions, and I almost hear it daily in these summer months. People almost getting angry. But there truly are several things that you can do to keep the frustrations under control and actually make these workout cycles very enjoyable as well. Before we do that, I want to talk for a minute about the dangers of actual heat illness. Heat exhaustion and heat strokes are very serious illnesses for athletes. And this can happen on race day, but this can happen on training days as well, especially in hot conditions. And so what happens is an athlete is unable to regulate their actual body temperature and dehydrates. Signs and symptoms here may include a fast heartbeat, fast breathing or hyperventilation, fatigue more than usual, dizziness, feeling hot, heavy sweating, headache, nausea and vomiting, diarrhea, muscle cramps, pale skin, problems coordinating movement, so not being able to run or even walk, or fainting. Then there are additional heat stroke symptoms as well. These are even more severe, and this is a dehydration of both the body and the brain. These are confusion and disorientation, you can't see clearly, seizure, or even a coma. Do not underestimate the severity of heat illness during races and even during training runs. Treatment could require medical attention to get your body temperature down as soon as possible. At most races that are warm, there's a medical facility with an ice bath around the finish line. This is an effective cooling method to bring the body temperature down. Otherwise, ice packs are another good way to lower your body temperature. The risk of heat illness is determined by a variety of different factors, such as the athlete's size— a larger athlete will have a higher risk of heat illness than a smaller athlete— running speed and intensity, temperatures and humidity, and drinking the right amount of fluids, to name a few. Adults over the age of 65 and young kids have a higher risk of heat exhaustion and heat stroke. Because their bodies simply have a harder time thermoregulating and cooling down. If you recognize any of these signs or symptoms, don't be tough, especially when you're alone. Stop running immediately to make sure that the symptoms don't become worse. So how do you train on hot and humid days? There are several different strategies here. You can run early in the morning or late at night. Don't run during the heat of the day. You can run indoors on a treadmill. You might wanna consider joining a local gym for a few summer months or buying a treadmill. Adjust your pace according to your effort level and slow down your pace if needed. The brain constantly receives information about the temperature of your skin, brain, and core temperature. When the temperatures become too high in most runners, the brain subconsciously tells your muscles that you're tired, so you either slow down or you stop running altogether. With less effort, the body produces less heat. Standing in the shade and in the wind can also help speed up this cool-down process, preventing heat stroke. So when training, keep your effort levels under control. Even at a slower pace, you're still getting a great workout in. Split long runs into shorter runs. Instead of going for a 90-minute run, just split it up. 45 minutes in the morning and 45 minutes later in the day. Run in shaded areas as much as possible. Running in the sun can increase your skin temperature much more than the outside air temperature. Limit concrete runs. This heat from the concrete gets right back at you. Running on flat trails, grass, or sandy areas can be a better option here. Don't run in the heat if you're not very fit or if you're not very much used to the heat yet, especially when you have previously experienced heat issues. Some medication and supplements can also impact your heat regulation, so be extra careful there. When running in higher temperatures and humid conditions, hydrate well but don't overdo it. Acclimate yourself with heat training. Let's talk about heat acclimation and training for race day. There's several different ways that you can engage your sweat mechanisms by actually training it. 2:21 marathoner Jason Cheriman on our recent Extramileless podcast talked about this in much detail. He goes on several different runs with a lot of layers of clothing on just to activate his sweat mechanisms.
Another option for heat acclimation is sauna training. I have my own sauna here at home, and it really helps me get used to running at higher temperatures.
It's pretty similar to running with multiple layers of clothing on.
If you don't have access to a sauna at home or with one of your friends, you might want to consider joining a gym. So you can get some sauna training in, and on the hot days you can get some treadmill running in as well.
Let's talk about the benefits of heat acclimation training. So it lowers your core body temperature, which helps with cooling. You will lower your heart rate during exercise. You will increase your sweating rate, so you will run at a higher intensity like marathon pace, and your body has the ability to cool itself more easily. You will develop your sweat glands. What that means is that you will retain more electrolytes and you can decrease sodium concentration in your sweat. You don't want to sweat out all your sodium. You don't have to drink as much as non-adapted runners would, especially within a marathon. It has demonstrated to improve your VO2 max. It increases your blood plasma volume, so there's more blood to go around, which can only be good to get oxygen to the muscles. And it enhances your blood delivery to the skin.
In just a short period of time, like 7 to 14 days, heat acclimation can already happen. So I would sit in a sauna 2 to 3 times a week for probably about 2 weeks and really get accustomed to the heat. And you can do this either a few weeks prior to an actual race, or you can do this at the beginning of a training cycle and then repeat it again closer to race day. I absolutely do want to caution you both with sauna training and with heat training wearing multiple layers of clothing to take it slow and to build things up gradually. Overheating can happen even on these short periods of time. Your body will have to adjust, so make sure you listen to the signals of your body. And when it's very hot outside already and humid, for example, if you live in Texas or you live in certain parts of India, you're gonna experience a lot of heat already even when you're not wearing multiple layers of clothing. You might not even need multiple layers of clothing over there to get the heat acclimation effect. So, um, yeah, take it easy and make sure to listen to your body there.
There are several different marathon cooling strategies that you can use as well. You can use the early race miles to warm up, so you start at a slower pace and you don't really do a long pre-race warm-up. You can run with a water bottle filled with ice. You can drink throughout the race, and you can keep your head and your neck cool as well. Make sure you stay hydrated well before, during, and after your workouts, but do not overdrink either. There's a condition called hyponatremia where you drink too much water and your sodium levels are diluted. At the Boston Marathon and the London Marathon, runners have died from drinking too much water and having extremely low sodium levels. Hyponatremia is more common in runners who have slow times and mass body indexes that are extreme. There's no one-size-fits-all for the amount you should drink. The drinking guidelines for most marathons have changed to drink to thirst. Tim Noakes, a South African scientist and professor, also mentions that a more reasonable approach is to urge runners not to drink as much as possible but to drink to thirst, no more than 400 to 800 milliliters per hour. Manage your electrolytes and salt. You can either drink sport drinks with electrolytes or take tablets, gels, or mixed powders. During a race, I take some gels, and depending on the temperatures, I also take a salt and electrolyte pill about once an hour. Do not overdress. I see many athletes running in several layers of clothes. It's okay to feel cool the first few miles of a race. Keep your head and neck cool. Pour water over your head at aid stations or use an ice bandana or a towel to cool your neck. Cooling the blood in the large arteries in the neck which carry blood to the brain can be an effective cooling strategy. Sponging the body, focusing on lowering the skin temperature. Using minimal sunscreen in key areas If you have a thick layer of sunscreen all over your skin, the sweat can't evaporate from your skin, which is what keeps you cool. Whenever you can, try to run in the shade and use some cooling from the wind. So try not to run in a big pack of runners. I've noticed this can make a really big difference in temperature feel as well. Dr. Phil Maffetone shares several great insights about sun protection and exposure in his The Big Yellow Book of Endurance Training and Racing. I can highly recommend that book. One thing that he mentions, that healthy athletes are much better protected from sun exposure than unhealthy athletes. He mentions that by maintaining a good balance of fat, especially that in fish oil, you can control your inflammation and you can protect yourself well to a long day of exposure in the sun. Antioxidants. Vitamin E complex and vitamin C can also help protect the skin. Eating enough vegetables and fruit will help with this as well. Many people have a deficit in vitamin D, and this may cause you to burn faster as well. And some people are just more sensitive to, to sun than others. People who have very light skin or people who have freckles or red hair. So keep that in mind too. Some skin areas burn much faster than others, and I've noticed this myself as well. For example, your nose, your ears, your lips, your neck, and your head. Therefore, it's very good to actually wear a hat or a bandana on your neck to protect yourself from it. Another important thing here is to actually wear sunglasses to protect your eyes. There are many different viewpoints about tanning, about cancer risk, and about using sunscreen products. I'm not gonna go in much detail here. Dr. Phil Maffetone does mention that moderate tanning is a great way to actually protect your skin protect your skin from the sun. When running in sunny conditions, use a sunscreen to protect the skin that is exposed. In particular, your face, your shoulders, your arms, and your legs. Be careful with the sunscreen type that you actually use. Several of the sunscreens have a ton of chemicals in it, so you want to make sure that you use the right one. And there are several consumer reports that tell a lot more about this in detail. That was a lot of information over here. In closing, I want to say there are several things that you can control when you're dealing with hot and humid conditions for your training and for your racing. So don't blindly follow a specific pace. Actually follow your effort level and let that indicate what your pace is going to be when you're dealing with hot and humid conditions. If you want to develop an aerobic base and use low heart rate training for this, It is best not to increase your training zones by 5 or 10 beats during hot and humid conditions. And I totally understand it can be frustrating at times, but try to focus on the things that you can control. Having a positive mindset will absolutely help lower the overall stress levels during your training cycle, and this is an important part of this holistic approach to training. When you slow down your running pace in training, you're still getting a great workout in. And this is great training for your mind as well. You have to learn how to enjoy this process. Patience is absolutely key here. If you enjoyed this video, you might also enjoy my new marathon training program. This course includes 25 new videos with more than 5 hours of video footage about low heart rate training, nutrition, race strategies, and mindsets to improve your running. There are also flexible and editable training schedules with different goals. More info can be found at extramileist.com/marathon. I would love to hear from you what has worked well for you dealing with hot and humid conditions in both training and in racing. Please let me know in the comments. Have fun out there on your run and stay cool, my friends.
