When the temperature drops, it’s tempting to stick to cooler, drier training conditions. But what if embracing the heat, even in the depths of winter, could give you a serious performance boost? That’s where heat training comes in; an approach that could prepare you for the unpredictable spikes in temperature we may see in races for 2025.
Heat training isn’t just about surviving hot conditions; it’s about thriving in them. By enhancing blood flow, improving oxygen delivery to muscles, and teaching your body to regulate heat more efficiently, this method can elevate your performance in both warm and cool weather.
With advice from experts in heat training and the help of Core wearable tech, I explored how this strategy could take my fitness to the next level.
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Why start heat training?
The mantra is simple: train hot, race cool.
Incorporating heat training into your routine can be a game-changer, especially while preparing for endurance events. As global temperatures climb and heatwaves become more frequent for major sporting events, athletes of all disciplines, from runners to cyclists and beyond, can benefit from heat adaptation, even in mild conditions.
The key advantage? Increased blood flow. Heat training raises your sweat rate and lowers the temperature threshold at which you start sweating, making it easier for your body to cool itself under pressure. Over time, this also boosts haemoglobin levels and lactate thresholds, improving oxygen delivery to your muscles and acclimating your body to handle higher temperatures.
On race day, your body generates heat far beyond what’s typical in training. Without preparation, these elevated core temperatures can derail your performance. Heat training ensures you’re ready to handle the intensity, giving you an edge when it counts most.
Why heat train in the winter?
Terrence Mahon, a Core running coach who has integrated the sensor into his training with elite athletes, explains: “Running in the winter typically means exercising in cold and dry conditions. While these conditions can be great for chasing a personal best, they rarely mimic what we experience during major races. If you only ever train in cool weather, you’ll find yourself underprepared when spring races roll around.
“By incorporating heat training during the winter months, you can maintain the heat adaptations developed over the summer. This not only prepares you for that first unexpectedly warm day in March or April but also boosts your overall performance. Research shows that heat training doesn’t just prepare you for hot and humid conditions; it also enhances performance in cooler weather. Heat training stimulates an increase in blood plasma and raises haemoglobin and hematocrit levels. These are technical terms, but essentially, heat training enables your body to deliver more oxygen to your working muscles. And more oxygen means you can maintain faster paces for longer; regardless of whether it’s a hot or cool day.”
How to heat train in cold UK weather
If you're looking to heat train outdoors in the cooler UK climate, the trick is to create your own warm microclimate. The idea is to overdress and trap the heat your body generates during exercise, replicating the conditions you might face in hotter climates. Here’s how to do it effectively:
Torso
Start with a long-sleeved nylon shirt directly against your skin to wick away sweat. Layer up with a waterproof jacket to prevent sweat evaporation, which can cool your skin down. On top of the rain jacket, add a thick thermal layer to keep the warmth in and prevent sweat from soaking through.
Legs
Go for nylon or spandex tights. These materials allow for warmth and moisture-wicking properties, which help maintain a comfortable body temperature during exercise.
Accessories
In colder air temperatures, a warm hat and gloves can help keep your extremities protected.
Experiment with different combinations to see what works best for you. Remember, the goal is to create a warm and humid environment around your body, which helps simulate the heat training conditions necessary for improving your body’s heat adaptation.
Who can try heat adaptation training?
According to Puck Alkemade, a Core physiologist and study coordinator, fitness levels do play a part in our ability to handle the heat, which is why it’s good to track.
By maintaining good levels of fitness (for instance, being well-trained in endurance sports or sports with considerable duration and intensity), your core temperature increases, and your body needs to lose heat.
This way, your body starts to adapt (although specific heat training would result in better heat adaptation). Generally speaking, if you are more fit (which doesn’t just mean strength), you’re more likely to be able to handle the heat.
How do women respond differently to heat training?
There is currently no evidence to suggest that women have a clear disadvantage compared to men when exercising in the heat based on sex alone.
However, Core did find that smaller individuals (with low body mass, typically females) experienced a large heart rate adaptation, whereas larger individuals (with high body mass, typically males) had a larger sweat adaptation. Both groups adapted, but in different ways.
The menstrual cycle and oral contraceptive use may influence the thermoregulatory system, though the effects on heat susceptibility and performance in the heat require further exploration. Core’s technology can also be used for fertility or ovulation tracking as an alternative to other thermometers, although this feature is not yet integrated into the app.
Some female athletes and teams are experimenting with training optimisation based on the menstrual cycle. For instance, if you feel energetic during a particular phase, you can schedule heavier training blocks. Conversely, if you’re less energetic, struggling with sleep, or dealing with menstrual pain, you can ease off. Tracking the menstrual cycle allows you to align your training with how you’re feeling.
How long should I heat train?
Heat training is incredibly accessible and can deliver impressive results if you stick with it.
The body can adapt to withstand hotter and colder temperatures, but these changes happen gradually over the course of a few weeks.
Using a device like the Core sensor lets you gather personalised data about your heat strain in different conditions (exercise, daily activities, or throughout your menstrual cycle). This can help you predict and adapt your training to match environmental conditions.
According to Core running coach Terrence Mahon, heat training is unique because you don’t need to dedicate hours each day.
Just 40 to 90-minute heat sessions a few times a week can make a difference. Unlike altitude training, which typically requires travelling to the mountains for weeks, heat training is more convenient and cost-effective. Once you’re heat-adapted, you can maintain your gains with occasional top-up sessions.
Another bonus? Heat training can also be achieved passively by hopping into a sauna or steam room, which has the added benefit of supporting recovery.
Core sensor
The Core sensor is the first and only real-time core body temperature wearable monitor built with advanced, Swiss-made Calera thermal energy transfer technology which provides medical-grade accuracy.
It is the only non-invasive wearable solution that allows both elite and amateur athletes to continually monitor for accurate core body temperature data without the need for an ingested or inserted thermometer.
The thermal energy transfer sensor embedded in the Core sensor utilises the power of an AI algorithm to provide the most accurate data backed by clinical, lab, and field tests.
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How the Core device works for heat training
How the Core sensor works for me
When I started using the Core sensor, I quickly noticed how much more advanced it is compared to typical wearable thermometers. This clever bit of tech tracks heat as it moves into or out of my body, giving me an accurate reading no matter where I am; whether I’m training in the sun abroad, pushing through a tough indoor workout, or dealing with extreme humidity.
Simplified real-time tracking
Once I charge it and shake it to activate, I know it’s ready to go when I see the flashing green light. During training, it sends real-time data straight to my paired Apple Watch. The Core app makes it even better by showing my Heat Strain Index live, so I can see exactly how hard my body is working to stay cool.
This is where the Heat Zones feature comes in handy. By comparing my Heat Strain Index against these zones, I get a clearer picture of how heat is impacting my performance and what adjustments I might need to make.
Why heat adaptation matters
One of the most valuable insights for me has been Core’s Heat Adaptation Score. It combines the Heat Strain Index and Heat Zones to show how well my body is adapting to thermal stress, whether I’m preparing for a hotter race season or just trying to improve my overall endurance.
Core has helped me understand that the body’s core temperature needs to stay within a very tight range. But during intense workouts or in hot environments, my body’s heat loss mechanisms have to work overtime to balance the heat I’m producing.
When that balance tips, heat strain kicks in. I’ve learned that managing this strain is key, as it directly impacts performance. The more I expose my body to controlled heat stress using the Core sensor, the better I adapt over time, and the less heat strain I feel in challenging conditions.
With Core, I’ve turned heat training from an abstract idea into something measurable, trackable, and effective. It’s not just about coping with heat; it’s about building resilience that makes every workout more efficient, no matter the conditions.
Verdict
The combination of advanced thermal technology, real-time data tracking, and AI-powered insights allows me to optimise my performance in ways I never thought about before. It’s not just about surviving the heat; it’s about adapting to it, and Core gives me the tools to do just that.
Whether you’re preparing for a hot race, looking to enhance your endurance, or simply want to understand how heat impacts your body, Core offers invaluable data that makes a real difference.
A learning curve
While the Core sensor offers impressive technology, there is a slight learning curve for those new to heat training or wearable tech. Setting up the device and getting accustomed to tracking data in the app can take some time, especially if you're not already familiar with metrics like the Heat Strain Index or Heat Adaptation Score.
Additionally, for athletes who are used to more straightforward performance trackers, the depth of data may initially feel overwhelming. However, once you get the hang of it, the insights are invaluable for optimising your heat training.
