While body fluid loss through heavy sweating per se is not as detrimental for performance itself as common belief is telling, some other mechanism is. It’s called hyperthermia.

Hyperthermia is just a fancy scientific word for simple condition when our body core temperature is elevated. Humans are just like any other mammal, and our basal core temperature is around 37°C no matter if we are asleep or we are awake. If our core temperature drops, say 1-2°C or more, we are speaking of hypothermia and if our core T rises, say 1-2°C or even more, we are experiencing hyperthermia.

But before we dig into the physiology behind hyperthermia and its effect on athletic performance, we should stop and see one practical example from our Bolgarian league friend, Boris Syarov. In the past weekend, we were racing in Innsbruck and Boris is always recording his rides and making nice short 15min race recap’s later. Here you can watch his Innsbruck recap. If you watch and listen carefully to his video you can easily see why his experience during the stage was school case of hyperthermia, one for the books. Just look at this short clip he sent us.

As it’s clearly visible, Boris was sweating profoundly during his effort, with sweat dripping off his face almost in steam. Next, the red radiating skin color of his face indicates he was also overheating at the same time. Boris is very enthusiastic but relatively new to indoor cycling. He is currently riding his Zwift set up outside but without any additional cooling. On this particular ride, it was just 3-4°C outside, that’s why Boris was dressed that much at the beginning of his ride. But despite a very cold environment, what happened merely 20min later into a stage was nothing else than a severe hyperthermia. He was fighting strong uphill for the first 10+min, surviving initial selection, following wheels of the front group, and then all a sudden he breaks down completely. His legs simply turned off, his heart rate was at the high end and he struggled like an animal just to merely turn his legs and slowly climb up the mountain. Even much, much slower riders were catching him back and passing without being able to stick to their wheels. And this has nothing to do with his aerobic capacity or fuel (glycogen) utilization. It has one and only reason, he was severely overheated. His brains, his central governor, shut him down to preserve core temperature from rising over biologically dangerous limits. And brains can do this regardless of your will, you simply can’t push beyond limits. At least a healthy human can’t. Luckily, Boris is healthy, as most of us are. Thus, before continuing on the solution for overheating, we need to dig just a little into physiology to understand what happened.

Humans are fairly inefficient machines when speaking of mechanical efficiency. Only 20 – 25% of all energy released during physical (muscular) activity turns into mechanical work, everything else is released as a (metabolic) heat. So when a cyclist turns his cranks with 200w power, approximately 800 – 1000 W of energy is released as heat. Once this same cyclist starts climbing or time trialing at 350 W, his working muscles will release 1450-1750w of heat. Now imagine working out in an air standstill condition regardless of outside 3-4°C or inside 18 – 22°C. How fast will your basal core T of 37°C rise above the critical level of 39.5 – 40.5°C if your internal stove is releasing extra heat with ~1.5 kiloWatts? The answer is, very fast. Within a few minutes. As we could learn from Boris’s case, this happened roughly after 12min into hard climbing.

What happens during strenuous muscular work? When our muscles contract hard, our heart starts pumping blood into those muscles to provide the oxygen needed to continuously perform work. Once our core temperature starts rising, say over 38.5 – 39.0°C, our internal receptors reports this to our brains, which in turn starts releasing specific hormone with the ability to open thin blood vessels under our skin. This blood vessel opening is called peripheral vasodilation. Our heart is suddenly not pumping blood into working muscles only, but also into our skin area. Once more blood is under the skin, we start sweating, which means losing water from our blood plasma. When sweat is exposed to airflow, water evaporation occurs, which means our skin gets cooler. This same mechanism cools our peripheral blood under the skin and this same blood once circulating back to the internal parts of the body, lowers our core temperature. This essentially means, your heart rate is artificially elevated since the heart needs to pump blood simultaneously to working muscles and to the periphery to cool our body. What happens if heat dissipation despite rigorous sweating isn’t enough? Your core temperature keeps rising and rising. Once our T passes critical point our brains will simply stop contracting muscles. Less and less neuron motor units will be recruited, and brains will continue to do this as long as needed. If we would still try to continue, the final state would be complete paralyzes. OK, this one is the extreme, impossible scenario on a turbo trainer, but in mother nature its not that uncommon thing to happen. Just for your knowledge, humans evolved in hot African climate as one of very few sweating organisms overall and could slowly catch an antelope during hottest mid-day time simply by forcing an animal to stop running due to thermal paralyzes. OK, we are a bit off into evolutionary biology, let us go back to 4K Zwifting in the 21st century.

And above described was precisely what Boris had experienced during Stage 4. Sudden performance breakdown, complete collapse with elevated HR even after severely reduced intensity. That was the school case for the books.

To keep our core temperature within the normal range we need some sort of effective cooling aid. Airflow around our body has to be strong enough for sweat to evaporate at a high enough rate. And it’s far better to workout indoor at normal temperatures between 18-22°C and has some strong ventilator (or more of them), than working out at cooler temps with little or no wind at all. In a warm room with enough wind around our body, the chance of catching a cold is much lower than in a cool garage or basement with temps lower than 15°C. What’s really important is the amount of air that flow’s around our whole body, but most importantly around our upper body. We can achieve this in many different ways. Most will use 2 or more stand-alone ventilators turned into different parts of the body (legs, chest, head). But since this article is an Add at the same time, we will present one of the most effective and cool looking solutions, called Wahoo Kickr HeadWind

While HeadWind ventilator certainly is not the cheapest solution for cooling, it is for sure, the most specific indoor cycling developed, cool-looking fan on market. It is relatively compact in size, measuring 30 cm in width and a bit less than 50cm in height, but with a strong 175 W motor being able to generate wind speed output at 48kmh, which is enough to keep you cool even during hardest efforts. And the most exciting feature of Headwind is his sensor-based fan speed control. When connected to a speed sensor or heart rate monitor fan will increase its speed with higher speed or heart rate. Just imagine, during warm-up when your heart rate is fairly low you are getting just a gentle breeze. But during hard climbing when your heart wants to explode, you get full air force into your upper body. Badass feature, isn’t it?

You wanna cool looking fan? You actually wanna be cool?

Well, Kickr HeadWind is now available at our sponsor’s VS Bike shop for 230 €.

Ride on!