Podcast Transcripts
Paul: I’m here with Magnus Ditlev and Dr. Peter Christensen. Gentlemen, welcome to the podcast.
Magnus & Peter: Thank you for having us.
Paul: It’s a real honor. What drove me to contact you guys was this incredible case study that you published, Peter, with Magnus as the subject – a case study on energy turnover. I know Magnus is down in the Canary Islands right now training with his national team, and Peter, you’re coming to us from Denmark.
Peter’s Background
Paul: Peter, why don’t we start with your background? Apparently, we’ve actually met briefly in a previous life when I was at Team Denmark.
Peter: The short version is I come from Copenhagen, Denmark. I had my master’s degree at the University of Copenhagen at the August Krogh Institute with Jens Bangsbo as my supervisor, and continued doing a PhD also with Jens. That was in collaboration with Team Denmark – the Olympic sport national organization. From there, I was lucky to get employed there full-time and apply physiology to real athletes like Magnus. It’s something I’m very proud of and fortunate to work with skilled athletes and coaches, applying physiology in various ways.
When you were here in Copenhagen, I think I was still a student. Science is both a small and big world, but there’s usually a “who’s who” thing going on. Jens is also still around – he hosted a conference some time ago. I try with this case study to still get involved with research when time is available and it suits everyone’s needs.
Magnus’s Origin Story
Paul: Magnus, I really want to know your “why” – where did it all start for you?
Magnus: I was never a triathlete as a kid growing up. I wasn’t even doing any of the three sports, but I was always very active – playing soccer and badminton. I remember when I was very young, I made my own goal in the garden and would practice even when it was snowing or raining, just kicking the ball and hitting the top corner or the bar. I did this so much that the grass in my parents’ garden was completely gone because I was just constantly practicing.
I think I’ve always been extremely active and had this drive to be better and see how far I can go. In high school, I got in a class with two elite runners who showed me where they were training. I started running with them and biking with my father in my spare time.
The turning point was the local Ironman Copenhagen, which goes through my hometown. We were spectating every year, and I thought the Ironman looked pretty crazy but I wanted to try it out. I signed up for a half-distance triathlon. I remember walking even more than I ran on the half marathon, but something inside me said it was fun, and things just took off from there.
I was introduced to the local triathlon club in Copenhagen where my current coach was the head coach. He’s a former professional himself who had been to Kona twice as a pro. He saw my numbers and we quickly realized I had the potential to become a professional. At the time, I was studying to become a chemical engineer, and it’s difficult for me to combine things because I don’t function well if I don’t do things 100%.
After I finished my bachelor’s degree in chemical engineering, I decided to take a break and see if I could make it as a professional triathlete. The thought was if I don’t have what it takes, I can always start on a master’s afterwards. Things went crazy really fast – my progression showed improvements very quickly.
The Science Behind Performance
Paul: What a cool combination – you’ve got that gift you discovered, but there’s also that passion seeking the next advantage. That probably brought you to Peter and Team Denmark and your willingness to experiment and research. Looking at your website, it speaks to your “why” – you’re not done yet, right?
Magnus: No, not at all. I remember very clearly when I first was introduced to Peter in 2021 going into Kona, which was my first Kona. Jens, my coach, and I were seeking advice regarding heat preparation. That’s when we first started doing a project with Peter where we did something similar to this study – we used Team Denmark’s climate tent where we were able to simulate Kona conditions.
That was when Peter and I started working together. It was very project-based initially, but now it’s a constant dialogue where we’re pushing ideas back and forth.
The Case Study Overview
Host: Peter, this case study really speaks to this new “fourth dimension” that you call durability – the fact that we all slow as we progress. Let’s talk about some science. There are so many different factors when we look at what causes fatigue in prolonged exercise – heat, substrate use, oxygen uptake, neuromuscular fatigue, brain and motivation aspects. It’s so complex. Where did you start with this problem?
Peter: When there are so many variables, you can end up in a lot of rabbit holes, but it’s also nice because you can prioritize and make progress in areas where you can gain an advantage. The paper you did with Chris Abbiss sums it up quite nicely. Back when I was a student, our research group was called “integrated physiology,” which speaks to acknowledging this as an integrated response with many components.
You need understanding of various components, how to measure them, what the limitations are, and then integrate it into an athlete-specific scenario. In this context, that’s long-distance triathlon. As a physiologist, you have a lot of things to work with in triathlon, which can be nerve-wracking but I actually enjoy it.
We had to start somewhere and address various questions: How big of a deal is fueling? How big of a deal is heat? Hydration? Sweat rates? That’s where we started, and we’re here now. It’s been a good journey so far.
The Case Study Protocol
Host: Let me summarize what I understand from the case study published in the International Journal of Sports Performance and Physiology. You’re looking at race simulation before Challenge Roth that Magnus sets the record in. You’re doing simulations of pieces of the race itself – swim, bike, run – roughly 30 days and 12 days before. Talk us through what you were thinking.
Peter: We have all these components that we believe are important for triathlon performance. We were unsure what substrate availability actually looks like in Magnus – not in a subject from a random study that maybe wasn’t designed for triathlon. We had ideas based on good science, but we know it can be very case-specific, and very few subjects are in Magnus’s caliber.
We had gray areas, especially regarding the nutrition part and metabolism. We could measure things in the lab in a fresh setting, but we realized that’s just a brief picture. Most of the time when an athlete is competing, it’s under influence from previous exercise. We wanted to see how running economy and cycling economy change, if at all, and get ideas as to whether we should change something in the race protocol.
Key Findings
Peter: Having this metabolic focus and knowing Magnus was doing his race routine with carbohydrate fueling, we saw that he starts off at 320-325 watts on the bike – pretty moderate for Magnus but still race-specific. We had Magnus do swimming first because we wanted the hormonal situation from that stress, not just start fresh on the bike.
When he started biking, he was carbohydrate-dominant based on the RER values, and we saw it slightly decreased despite good carbohydrates coming in during the activity. He looked pretty stable – the cycling economy was rock solid, and there was only a drop in RER to around 0.9 when the bike leg finished.
We did a second test day focusing on the run part. We had Magnus not eating many carbohydrates the day before, then doing two hours of solid, fatiguing biking, then close to 30 kilometers of running at close to race pace. We had treadmill tests every 45 minutes to see what the RER value and running economy looked like.
We saw a gradual decrease in RER value – having higher reliance on fat as substrate for oxidation – but Magnus was quite solid with no huge decrease in running economy. We got answers where we were uncertain.
Magnus’s Experience
Host: Magnus, what did you get from this whole experience? Did you gain confidence?
Magnus: Jens and I are very curious people, and we wanted to know what is actually limiting me in this Ironman. We had ideas but weren’t certain how much different factors limit me. For me, even though it’s a super hard protocol, it’s something I really enjoy doing. Apart from the knowledge we gain, it gives me energy and inspiration working with people like Peter.
A big part of why I do triathlon is to see what we can learn, how we can do things better, and how we can optimize things. Some people might be the opposite – they don’t like going to the laboratory and prefer normal training because it takes something out of the program and you have to restructure everything around test days.
For me, it gives knowledge, motivation, and confidence. After doing close to 40 kilometers running at Ironman pace at 3:35 or something like that, it gives me confidence. I strive on being very well prepared. When I’m well prepared, I feel much better going into the race and tend to perform better.
Heat as a Training Tool
Host: You mentioned heat strategies. How do you think about heat as a training tool?
Magnus: Heat is probably the thing that Peter, Jens, and I have spent the most time discussing and testing. It’s no secret that I’m a big athlete for triathlete standards – around 80 kilos – and producing very big power numbers. When you do that, a lot of it goes to heat, so heat is probably one of the biggest limitations for me in racing, even in climates that many people might not think are very warm.
Heat is something we pay a lot of attention to. It was the first thing Peter and I started working with because I had previously been struggling in the heat. We’ve used a lot of time refining heat protocols going into warm races and cooling strategies.
Peter: Heat is interesting because you can have athletes that in normal settings lose a lot of positions, or you can have people who usually aren’t close to top 10 but can advance a lot by having superior strategy. The really nice thing is when everything comes together – the training, pacing, equipment – but this doesn’t happen as frequently as you might wish.
There’s a huge performance reserve if you can dial in heat preparation, but it’s a delicate balance. It’s easy for me to come up with a plan, but much harder to execute because everyone who has tried being hyperthermic knows that something happens mentally too.
Nutrition Strategy
Host: One focus of your case study was substrate use – fats versus carbs. You were measuring RER, hovering around 0.89 throughout the day. What’s your whole philosophy around nutrition?
Peter: We try to evolve with our knowledge. On the bike, Magnus is pretty intense on carbohydrates, and he’s raised the game even higher compared to the Roth data you see here. In the case study, it was 140 grams per hour on the bike and around a little more than half of that in running.
We’re trying to see how much we can push those boundaries while still being able to utilize fat. It’s a spectrum – you can have people who focus entirely on carbohydrates or entirely on ketogenic diets. We acknowledge both parts and try to make use of both.
Magnus: It’s difficult to say if performance rises with more carbohydrates because you never do the race twice with different strategies. I feel that I have energy throughout the entire Ironman and the ability to push without bonking.
Where I really notice high carbohydrate intake helping is during long training camps – going into Kona or six weeks at altitude training above 30 hours every week. If you go with low carbs for such high volume, I feel like I burn out throughout the camp. Higher carbohydrates in training help me sustain quality throughout the entire camp.
Looking Forward
Host: What’s next for both of you?
Peter: I hope we can build on this knowledge. We have some ideas and a list we probably won’t tell too much about in a podcast, but we’re not finished evolving. There are still a lot of factors here, and Magnus has to stay fit, healthy, and motivated to do these kinds of things.
Magnus: I had a longer off-season than previously after a very long 2024 season. We’re trying to get back into solid training rhythm. I’ve made the decision to make the Ironman World Championships my primary goal, meaning I’m not racing anything else than the Ironman Pro Series – no T100 or Roth.
It’s been a tough decision because that would have been the safer option, but I decided to follow my heart and what’s the biggest motivation for me – winning the Ironman World Championships. It’s in Nice this year, which is different from Kona. The challenge is more the hilly bike course where you can make a lot of choices on the equipment side.
Closing Thoughts
Peter: It’s important to give and take in science. I’ve benefited from papers like your classic review with Chris Abbiss. You read other people’s work and have to give something back for science to evolve. We have a clear elite focus, and if we think we have an ace up our sleeve, we won’t reveal that to the public, but it’s still about give and take.
I hope this can encourage similar studies because I think these case studies are valuable. We need both case studies and randomized controlled trials that are more generally applicable.
Magnus: One of the motivations is to encourage everyone to keep pushing. If no one did it and we were the only ones, it wouldn’t be fun. We’re trying to show something so others can seek inspiration, learn from it, and hopefully progress from there.
