There is a heat wave sweeping the Midwest these last few weeks as athletes are preparing for tough races like Lumberjack 100 and Tour of Americas Dairyland. I have had multiple athletes ask about how to best prepare for each race considering this heat.
I have always done well racing in the heat, for as long as I can remember. I thought I was just naturally good at it or maybe I just could suffer in it more than everyone else. After moving to the desert, I found a few strategies to get the most out of my training when the temps rise past 100 degrees by 10 AM. Looking back now, I realize that in those hot races I did well at, I was simply better prepared.
I have analyzed my training and racing preparation in the last 10 or so years and here are the strategies I found that work well for myself and the athletes I work with.
Heat Acclimation
Heat acclimation is simply training your body to perform better in the heat. This is the number one most effective way to increase your performance in every hot race, but it requires a lot of time and work to do it.
How does your body cool itself?
As you exercise, your body produces heat from every muscle contraction that occurs. The harder you exercise and the longer you exercise, the higher your body temperature will rise. However, your body also has methods to cool itself down.
There are two main methods your body uses to cool itself off, vasodilation and evaporative cooling.
Vasodilation is a fancy word that describes the process of expanding the blood vessels so you push more blood through them. Your blood gets hot while it is deep inside your body, typically your core is the warmest part. This hot blood then moves to the skin where it is cooler than inside your core. The blood vessels that vasodilate near your skin allow more blood to be exposed to this cooler air so it has a better chance to cool off before returning to the core and repeating the cycle.
If you are familiar with cars or computers, this works very similar to a radiator or a liquid cooling circuit. The engine block or CPU gets very hot, and some sort of liquid touches or gets near the hot element and "steals" some of its heat. This liquid then moves to a radiator or heat sink with lots of folds to increase the surface area to increase the effectiveness of the cooling action. These are both closed loops so the liquid then moves back to the hot element to repeat the cycle.
Evaporative cooling is simply the cooling effect from some sort of liquid, in this case, sweat, evaporating from a surface. If you have ever used a product like Icy-Hot spray or other alcohol-based cooling liquids, this is exactly how they work. They sit on your skin, absorb some heat, then evaporate and displace that heat into the surrounding air.
The effectiveness of evaporative cooling is increased when paired with the vasodilation of the blood vessels. More blood is exposed to the sweaty skin, meaning more heat is pulled from the blood as the sweat evaporates.
What can be trained to increase performance in the heat?
Knowing that the two main methods of cooling are vasodilation and evaporative cooling, the two main adaptations your body makes are in those areas.
Changes to the blood
As you acclimate to the heat, your body undergoes what is called angiogenesis (angio- meaning "blood vessels" and -genesis meaning creation; the creation of blood vessels). This means the amount of blood vessels in your body increases allowing more surface area to absorb heat from your core as well as release it on your skin. Not only does the quantity increase, the ability of these blood vessels to vasodilate also increases, further increasing the surface area available for heat exchange.
Secondary to angiogenesis is an increase in blood volume. You now have more space to store blood within your veins, so your body creates more. There are two benefits of this.
First, the main part of the blood that increases is the plasma, or the watery part. Water is great at absorbing and storing heat, so the battery you have to store heat is now bigger.
Second, you now have more space to store and carry red blood cells. Red blood cells are responsible for transporting oxygen from your lungs to your muscles and it is one of the most important limiters in athletic performance. Increasing your red blood cell volume will increase your performance across all temperatures.
Changes to sweat
The last main adaptation is related to your sweat rate. Initially, as you begin riding more in hot temperatures, your sweat rate increases. If it's been a while since you rode in hot weather, you may find yourself "sweating bullets". Big sweat drops form on your skin and drip off constantly.
This is not efficient. First, every drop of sweat that falls off your skin does not evaporate, so you miss out on half of the cooling effect of that sweat. Second, large drops of sweat take a lot more energy before they evaporate.
If you remember from earlier, I said water does a great job at storing heat before it evaporates, but the evaporation is what cools your body off. If these big sweat drops absorb the heat but never get a chance to evaporate from your skin, they still won't cool you off as much as they could.
After weeks of heat training, your sweat rate will decrease. This seems counterintuitive seeing that sweat is a major part of your body's cooling, but your body gets more efficient at using that sweat.
Instead of "sweating bullets" and dripping sweat all day long, your body adapts to have a constant, thin layer of sweat across your skin. This maximizes the evaporative cooling effect and prevents you from losing water important for your hydration.
How should I train to acclimate to the heat?
Heat training should be done slowly, progressively, and with caution. I often recommend starting heat training with an indoor trainer so that if things go wrong you can immediately get off and start cooling yourself off before you get sick.
As with all aspects of training, the goal is to slowly increase the amount, intensity, or both over time to build resistance. With heat training, the main thing you need to focus on is your core body temperature. If this increases, the adaptations will occur; if you ride in the heat but you don't raise your core temp, adaptations will be small or zero.
There are two types of heat training you should be aware of: passive and active.
Passive Heat Training
Passively training for heat adaptations is simply exposing your body to the heat without performing exercise simultaneously. This is good to start safely, as well as extend your heat training if you only have limited time to train.
By being constantly exposed to warmer temps (just being in a hot climate, wearing warm clothes more often, etc) you will increase your general resistance to the heat.
A common, effective method to do passive heat training is through hot water immersion. If you are familiar with higher-end cooking tools, this is exactly what a sous vide does. You sit in hot water until your core temperature rises, essentially cooking yourself. Your core temperature only needs to rise by 0.5-1 degree Fahrenheit to make this method effective, but you want to extend the amount of time you spend with your core temp in that range.
Research shows a significant increase in hot weather athletic performance when athletes are immersed in hot water (104 degrees Fahrenheit) for 40 minutes immediately after completing their normal aerobic exercise. They did this for 6 consecutive days and measured almost 1 degree Fahrenheit lower core temps at rest and exercise in the hot water immersion group. These athletes also saw, on average, 14 BPM lower heart rate for the same intensity (based on % of VO2 max) vs their pre-acclimation test.
Active Heat Training
Getting more sport-specific, by progressively training your heat resistance during exercise will further increase your performance in the heat.
As your core temp rises during exercise, your heart rate will climb, your power/ performance will decline, and you will feel weak and possibly ill. I recommend doing these heat training workouts on the trainer and keeping them relatively short to reduce the risk. You can ride your trainer with the fan and air conditioning off, and wear progressively warmer clothes as you build your resistance.
For example, your first few days of heat training workouts would be in your regular summer kit, the next few days in a long-sleeved jersey, then move to tights and a winter jersey, and so on. You should begin to feel a little more comfortable before you move to the next warmer kit. You will also want to slowly increase the time you spend on the trainer from around 20 minutes if you're a complete beginner to an hour.
If you wish to extend these rides, I would recommend only doing the heat training for an hour max at the beginning, then ride outside in your regular clothes and let your body auto-regulate. You won't be directly training your heat resistance, but you will be training how well your body can recover from the heat stress.
The next step to extend these heat training days further would be to incorporate passive, hot water immersion after you finish the ride.
You should still work on your hydration through these workouts, you will lose a lot of water and we don't want you to become too dehydrated and get sick. If it is not already clear, this should be done slowly, progressively with continued hydration and a quick way to remove yourself from the heat if you begin to feel ill.
Body Cooling
All of the methods described in heat acclimation are ways to cause adaptations in your body to be better prepared for the heat. These next methods can be used at any time with immediate performance increases.
We understand that our performance drops when our core temperature rises above a certain level. So to minimize our performance decline during a race, we want to ensure our core never reaches those temps or extend the time before it reaches that point.
The key is to keep your core body temperature low before the race starts. By cooling your body down before you start racing or training, you can extend the amount of time you go before your core temperature reaches that critical point and your performance drops.
Electrolyte Slushie
Research suggests that eating slushie-type products is an effective way to reduce your core body temperature. This is because it has the coldness of ice (or sometimes even colder) but the surface area of water. This has the additional benefit of being in your body so it can directly cool your core.
Adding electrolytes to the slushie will help keep you hydrated, but it will also decrease the freezing point of water. This means there is a chance your slushie could be colder than 32 degrees!
Making these slushies is simple. Mix the ice to a blender with the corresponding amount of electrolyte mix. You should eat this for an hour or so leading up to the race start. This means before your warmup even starts and throughout the warmup.
Ice Packs and Socks
If you are forced to warm up on the turbo trainer and aren't able to use a fan, this is especially important. Air rushing over your skin causes your sweat to evaporate and it is very important for cooling. If you don't have this, you need to cool your skin with something else.
I suggested completely packing your jersey full of ice packs or ice socks. This will keep the skin cool and allow the blood on the surface to cool off before heading back to your core, cooling your full body off. Your stomach is one of the most effective places to put the ice, but the lack of your neck, wrists, and back of the hands are great places too.
It is a good idea to race with the ice socks in the front of your jersey if the race is long and hot. The ice keeps you cool, but the melting ice helps increase the cooling effect when it evaporates.
Water Yourself
Sweat is effective at cooling because as it evaporates, it pulls heat energy away from your skin, cooling you off. Water can store a lot of heat energy before it evaporates, so by completely covering yourself in water, you can essentially create a battery to store that heat.
Completely soaking your jersey in water before the race starts will give you that heat battery to work with throughout the race. All of the water in your jersey can pull and store the heat away from her body AND when it evaporates it will cool you off even more.
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