Sports science researcher helps Denmark’s fastest man break records

“It was a no-brainer to say yes to a collaboration with Andreas Breenfeldt Andersen.”

This is how Jacob Simonsen responds when asked why, as an elite athlete, he is working with a sports science researcher at Health.

Jacob Simonsen, who is also a medical student at Aarhus University, is the fastest Dane in history to run both a marathon and a half marathon. He is also the Danish champion in the 10-kilometre distance and holds the Danish record for the 10-kilometre road race.

The record-breaking doctor-in-training has been working with Andreas Breenfeldt Andersen, who conducts research on human physiology, for about a year.

“The contact came about through Team Denmark because Andreas was one of the few people who could measure haemoglobin mass using the CO-rebreathing method, which is considered the golden standard,” explains Jacob Simonsen.

Unlikely couple or perfect match?
The main focus of the sports science collaboration is to ensure that Jacob Simonsen can optimise his performance without burning out along the way. And the division of labour is clear: Andreas Breenfeldt Andersen advises and investigates research hypotheses. Jacob Simonsen runs, tests and breaks records.

So far, the collaboration, which also involves Professor Lars Nybo from the University of Copenhagen, has mostly investigated the effect of ketones and whether Jacob Simonsen benefits from performance-enhancing training strategies such as heat training and altitude training.

“I think we’re a good match. We have succeeded in developing a training strategy that provides sufficient stimulus without overestimating Jacob's training volume and intensity. Our collaboration has also made a significance difference to my research in a number of ways,” explains Andreas Breenfeldt Andersen.

Ideal opportunity to test research hypotheses
Andreas Breenfeldt Andersen has had many opportunities to put his theoretical knowledge into practice.

“I’ve drawn on my expertise in my previous roles, including as a doping control officer during the Olympics, and I think it’s natural and rewarding to collaborate with elite athletes like Jacob Simonsen, with elite federations and with Team Denmark,” says Andreas Breenfeldt Andersen and continues:

“In fact, I believe that collaborations like these are absolutely essential for me as a researcher because they help to communicate and apply my research in a broader and highly relevant context,” says Andreas Breenfeldt Andersen.

Through his work with Jacob Simonsen, Andreas Breenfeldt Andersen is able to test new research hypotheses and benefit from the practical knowledge and experience that exists outside the university walls, and according to the sports science researcher, these two worlds can often be combined to provide greater insights:

“It's incredibly exciting for a human physiologist like me with an interest in optimising human performance to work with highly trained individuals and see if together we can push the boundaries a little further – both in research and in training,” he says.

We want to optimise performance without risking injury
For elite runners at Jacob Simonsen’s level, who have such a large training volume, the risk of overload and injury is high. That’s why Jacob Simonsen has done some of his heat training on a bike, as it puts less strain on his joints, tendons and muscles than running.

“Heat and endurance training increases the volume of blood plasma and, more importantly, the amount of haemoglobin in your blood. This means that it increases your maximum oxygen uptake. But if you already run close to 150-200 kilometres a week, you can't 'just' add more kilometres to your training programme without risking injury,” says Andreas Breenfeldt Andersen.

He goes on to say that the great thing about heat training is that it helps the body improve its cooling mechanisms and increases blood volume. This can prevent Jacob Simonsen from overheating during runs and improve his endurance.

Collaboration is an important part of my sporting development
Jacob Simonsen knocked a full four minutes off his personal best when he broke the Danish marathon distance record in September 2024.

“This is definitely down to Jacob’s talent, training discipline and drive combined with the fact that we may have been able to fine tune a few optimisation factors,” says Andreas Breenfeldt Andersen.

The sports science researcher is not Jacob Simonsen’s only adviser, but he quickly became one of the most important. Because of Andreas Breenfeldt Andersen’s extensive knowledge within sports physiology and performance optimisation, Jacob Simonsen discusses many things with him, and they are in regular contact.

“Collaborating with researchers has been an important part of my sporting development. It has taken me to the next level. I have a lot of experience and knowledge within my own sport, of course, but not within the latest research on how to optimise my training. So why not seek out this knowledge from those who spend their daily professional lives working in this field?” Jacob Simonsen asks rhetorically and continues:

“For me it’s a no-brainer, and I would definitely recommend other elite athletes to do the same. I’m convinced that it could lead to significantly better international results for Danish elite athletes.”