Heat Training the Real World: Coach and elite mountain biker Erik Åkesson

Editor’s note: Erik Åkesson is a 25 year-old elite mountain biker representing Sweden in both the European Championships in Laissac, France and the World Champs in Glasgow. He is also a highly trained coach who focuses on cycling, working at Toppfysik and at Sweden’s largest high school coaching 16–18 year olds.

We thank Erik for his guest post explains how he does heat training throughout the season.

Value of heat training

As many of you might know, something called "heat training" is taking the endurance sport world by storm and is one of the most interesting things in sport science right now. Core Body Temp is the leading company and is working with the top triathletes and World Tour cycling teams to help them measure and understand human physiology. But it's not only the professional athletes that are benefitting from doing a heat training protocol.

Even amateur athletes are now using it to boost their performance, including me (I’m a 25 year old elite Swedish mountainbiker that focuses on cross-country marathon and olympic distances). I've used the Core Body Temp sensor and have been doing heat training continuously for the last 3–4 years. But if I'm being honest it's only for the last year or so I've gone all in and done it more strictly with a heat training protocol that I actually follow to the letter and measure core temp and Heat Strain Index more carefully.

The things I did before I still do, but now I run a more strict protocol to keep track of my core body temperature. I have also tested out different methods, timing, amount of heat stress, length of the heat training period and more. I believe I have found something that works really well for me.


Heat training protocol

How many heat training session per week?
The length of my heat training blocks have varied during the years, but now I've found that about 10 days is the perfect length for me. The basic tools I use are an indoor trainer with the CORE Heat Suit as well as a sauna. This period looks a bit like:

DAY 1: Normal training outside + 30–40 min sauna

DAY 2: Normal training outside + a 1 hour Zone 2 heat training session on the indoor trainer with the suit

DAY 3: Normal training inside + 30–40 min sauna

DAY 4: Normal training outside + 30–40 min sauna

DAY 5: Normal training inside + a 1 hour Zone 2 heat training session on the indoor trainer with the suit

DAY 6: Rest day + sauna

DAY 7: Long ride outside + sauna

DAY 8: Normal training inside + a 1 hour Zone 2 heat training session on the indoor trainer with the suit

DAY 9: Normal training outside + a 1 hour Zone 2 heat training session on the indoor trainer with the suit

DAY 10: Normal training outside + 30–40 min sauna

This is an example during the winter/spring days when I don't have a competition on the weekend.

Are these heat training sessions done as part of a workout or separated from your normal training sessions?

I land in about four Zone 2 heat training sessions on the trainer and 6 sauna sessions in this block. It could vary a bit but normally it’s like that. Most of the heat sessions on the trainer are separated from my "normal" training with a few hours between. The sauna sessions I almost always do right after my normal training, while my core body temperature is already elevated from the training.

But how does a heat training session look? You mentioned Zone 2 a lot.

Yes, if I dive into a specific heat training session it looks like this: I put my bike in the trainer and put on my heat suit and weigh myself (just to know how much fluid I lose during the session). Then I do a 10 minute warm-up before I do a 5 minute threshold effort, to stress my core temp up and to start sweating a lot. The last 45 minutes I keep my watts in the middle part of zone 2 and watch my heart rate slowly go up into zone 3.

It gets pretty uncomfortable the last 20-25 minutes. I also keep my water intake to 500ml/hour during the session, but I make sure to refill that after! Since CORE released the Heat Strain Index (HSI), I've used it in some sessions to keep the heat load in check. More on HSI a bit later.

See picture below. My typical heat training session on the smart trainer looks like this.


Grey: Heart Rate, Pink: Power Output, Green: Core temperature

As you can see the core temp starts rising about halfway through the threshold effort and slowly starts to plateau in the last 10 minutes. My heart rate is pretty stable at 120 bpm to the 25 minute mark around the point where my core temp has raised about 1°C from my "normal" state (not from the start of the session).

This is a time in the session there it starts getting a bit heavy mentally in the heat suit which feels very warm. I have debated back and fourth with myself if I should lower the watts and dress a bit warmer instead, to keep the mechanical load even lower. But I concluded this has been working well for me, so why change a winning concept? Below you can see the exact same training session, but it shows skin temperature and inside temperature as well.


Grey: Core Temperature, Grey line: Inside temperature, Blue: Skin temperature

My smart trainer is located in a big industrial premises which is quite hot in the summer but pretty nice in the winter days. In the summer normally it is between 21-23°C inside and about 20-25 % humidity. I can't really change the indoor temperature that much, and I keep the sessions low intensity with a higher intensity effort in the beginning of the training session to boost up the core temp. That basically means that I rely on clothing to raise my core temperature to the right zone.


Most of the heat sessions I do during my block are sauna sessions. Those are a bit tricky since I can't measure my core temp with the sensor inside the sauna. I've tried to have my heart rate monitor and sensor right outside, and walked out and put it on in a break. But I find it taking a bit too long and it takes time to accurately measure the core temp, so right now I take sauna sessions based on feel.

I normally sit about 30 minutes in 80-85°C. Sometimes 40 minutes if I keep the session RPE manageable. If possible I do the sauna sessions straight after a bike ride, when the core temperature is already elevated from training. Normally around 38°C when I enter the sauna which should raise up to 38.5–39.5°C in the half hour I sit there and that is in the right span according to my Heat Ramp Test.

Heat training zones and Heat Strain Index

To maximize my heat training I'm using my individual Heat Training Zones as well as keeping an eye on the Heat Strain Index. Too much and too hot is damaging more than making myself faster. Below you see the HSI for the workout. It is on the upper limit of what Core Body Temp themselves recommend (keeping it to 3-6 HSI). Normally I land between 4.8–6.0 when I'm using the CORE Heat Suit. In the second print screen you see my personalized heat training zones and how much time I spend in each. I don't want to be over 39.2°C because that stresses my body way too much. High 38s is good for me.


Maintaining the heat training throughout the season

Now you have done a big heat training block, how do you maintain this during the season?

Since I’m a mountainbiker and do both XCM and XCO races, almost every weekend between late April to late September is race week. So I plan my heat training blocks to fit my “A” competition-schedule best. That means I do this kind of heat training block continuously during race season as well. But, not to often. With my own experimentation I have concluded that I can finish a heat block pretty close to my A-races to get maximum benefit. Of course, this is very individual, but for me, that works good. I start this 10-day block 14 days before A-race. If the race is on a Sunday, I do the last heat stimuli on Wednesday.

Between these blocks I try to maintain the heat stimuli about 2 times a week, normally in the sauna, but sometimes I jump on the trainer for a heat session as well.