Exercise boosts your immune system — but how does that actually work, and does exercise intensity matter?
In this episode of MS-Perspektive International, I spoke with David Walzik, PhD student in exercise science at TU Dortmund University and medical student at the University of Cologne, about exercise immunology, immune-cell adaptation, and what his latest research could mean for people living with multiple sclerosis (MS).
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Who are you and what is your professional background?
David Walzik (PhD student in exercise science at TU Dortmund University; medical student at the University of Cologne, Germany): My name is David Walzik. I’m a PhD student in exercise science at TU Dortmund University, where I focus on exercise immunology, and at the same time I’m studying medicine at the University of Cologne and close to finishing my degree.
I’ve been working in Professor Philipp Zimmer’s group at TU Dortmund University for several years. I actually started there as a student assistant, and over time this developed into my PhD project. We recently published a paper presenting our newest findings.
What role does immune health play in your work or research?
David Walzik: Immune health plays a central role in my work because it is involved in so many diseases. This includes infections, chronic inflammatory conditions, autoimmune diseases, and even cancer. Especially in oncology, immune therapies rely on the body’s immune system to identify and eliminate cancer cells.
What fascinates me about exercise immunology is that exercise is a modifiable lifestyle factor. Through physical activity — and lifestyle in general — we can actively influence the immune system. That gives this field a lot of potential across very different diseases.
Why is exercise especially relevant for people with MS?
David Walzik: Exercise has many positive effects, but it’s important to differentiate between different types of evidence. On the one hand, we have epidemiological studies — large population-based studies that show associations, for example with disease risk, disease progression, or mortality.
On the other hand, we need to understand the mechanisms behind these associations. That means asking why exercise is beneficial and which type of exercise might be particularly helpful for specific groups, such as people with MS.
In exercise immunology, a lot of research has focused on immune-cell mobilization — how immune cells move through the body during exercise due to increased blood flow. What has been studied much less is whether the immune cells themselves actually change through exercise. That’s especially important if we want to understand long-term training effects.
For MS specifically, most immune-related exercise studies have focused on redistribution of immune cells. To my knowledge, there are still very few studies that truly examine cellular or molecular changes within immune cells in people with MS.
What exactly did you investigate in your recent study?
David Walzik: In our study, we compared two different exercise modalities: high-intensity interval exercise and moderate-intensity continuous exercise. We used a randomized crossover design, which means that every participant completed both exercise sessions. This allowed us to compare the effects within the same individuals.
We isolated immune cells before exercise, immediately after exercise, and again one hour later. Then we analyzed two main aspects. First, we looked at immune-cell mobilization — which immune cells were mobilized by each exercise session. Second, we performed proteomic analyses, meaning we examined the proteins inside the immune cells.
Proteins are important because they define what a cell can do. By analyzing the proteome, we can gain very deep insights into immune-cell function.
What were the key findings of your research?
David Walzik: One of the most interesting findings was that immune-cell mobilization was actually quite similar between high-intensity and moderate-intensity exercise. So both exercise types moved immune cells through the body in a comparable way.
The big difference appeared when we looked inside the immune cells. After high-intensity exercise, we saw a much stronger reorganization of the immune-cell proteome. In simple terms, the internal machinery of the immune cells changed much more after HIIT than after moderate exercise.
This suggests that higher exercise intensity may trigger a deeper level of immune adaptation.
Why does exercise intensity seem to matter so much?
David Walzik: The key point is not that moderate exercise doesn’t do anything — it clearly does. But high-intensity exercise seems to induce a much stronger internal response within immune cells.
If proteins determine immune-cell function, then a stronger reorganization of the proteome could mean that these cells adapt more profoundly. That’s why intensity appears to matter when we look at immune-cell biology, not just at cell numbers.
Can the immune system be trained like a muscle?
David Walzik: I think it can, yes. I like to explain this using a very basic biological principle: “use it or lose it.” We know this very well from muscles. If you don’t use them, they shrink. If you train them, they adapt and become stronger.
But this principle doesn’t apply only to muscles. During exercise, many tissues and organs are stressed, including the immune system. We already know that immune cells are mobilized during every acute exercise bout. With our study, we now also see that immune cells reorganize their protein structure after just one exercise session.
If this happens repeatedly over time, it’s very likely that this leads to long-term changes in immune-cell phenotype and function. That’s why I’m careful when people say very generally, “exercise is good for the immune system.” We need to understand why this is the case. Only then can we make solid, evidence-based recommendations.
What does it mean that more than 1,000 proteins changed after exercise?
David Walzik: In the high-intensity condition, we measured more than 6,000 proteins inside immune cells, and over 1,000 of them changed after a single exercise session. That’s roughly one sixth of all measured proteins, which shows how dynamic the immune system really is.
We didn’t just look at individual proteins. We also used gene ontology analyses, which allow us to link protein changes to biological functions. We saw changes related to immune effector functions, such as increased cytotoxic capacity, improved migration ability, and higher activation patterns of immune cells.
This suggests that the immune system responds to exercise in a very adaptive and functional way, especially after high-intensity exercise.
Is high-intensity training always better than moderate exercise?
David Walzik: I try to avoid absolute statements here. The biggest problem we currently face is not that people don’t train intensely enough — it’s that many people don’t move at all.
From a public health perspective, getting people to move regularly is far more important than optimizing exercise intensity. That’s why I often refer to the WHO physical activity guidelines: 150 to 300 minutes of moderate-intensity exercise per week, or 75 to 150 minutes of higher-intensity exercise.
If someone doesn’t like high-intensity training, moderate-intensity exercise is absolutely fine. Evidence for HIIT is growing, but flexibility is key — especially for people with MS, where symptoms can fluctuate from week to week.
What do we still need to learn specifically for people with MS?
David Walzik: Our published results are based on healthy participants, and we still need to see how these findings translate to people with MS. Researchers often start with healthy individuals to better understand basic physiological mechanisms.
The good news is that we’ve already completed a randomized controlled trial with people with MS in Dortmund. We used similar methods and analyses, so we’ll soon be able to see whether immune-cell proteome rewiring also occurs in people with MS.
One limitation we encountered is that our MS participants trained on a bicycle. Not everyone with MS can do that, so in the future we’ll also need to explore different exercise settings and modalities.
Could these immune changes explain reduced inflammation over time?
David Walzik: Our work connects two important aspects. First, we know that immune cells are redistributed during exercise. Second, we now see that immune cells also undergo functional changes after exercise.
This opens up many hypotheses across different diseases. Immune cells might migrate into tumors, inflamed tissue, adipose tissue, or mucosal areas relevant for infections, such as the respiratory tract, and influence the local immune environment there.
In humans, it’s very difficult to directly observe where immune cells go. In animal models, especially in mice, imaging studies can sometimes show this more clearly.
What advice do you have for people who want to start exercising but feel hesitant?
David Walzik: My strongest advice is to look for support and community. Exercise doesn’t have to be super exhausting or fancy, especially at the beginning. What really matters is regularity and building a habit.
Social connection helps a lot. That can mean meeting friends for a walk every week, joining a course, or exercising in a group — including groups specifically for people with MS. Having other people involved makes it much easier to stick with it.
What is the biggest barrier to regular exercise – and the biggest reward?
David Walzik: The biggest barrier, in my opinion, is making time. I deliberately avoid saying “finding time,” because it’s really about making time. I catch myself saying the same thing sometimes — that I don’t have time for exercise — and then I realize it’s not that I don’t have time, it’s that I haven’t made it a priority.
The biggest reward is that you start feeling better. If you exercise regularly, you’ll notice after a few weeks that your physical capacity increases. And with that, you simply feel better — both physically and mentally.
Why do you think it’s worth making the effort to stay active – even when it’s tough?
David Walzik: I think it’s worth it because, even though exercise can feel difficult at the beginning, the return on that effort is very real. If you manage to stay active regularly, you will notice after a few weeks that your physical capacity increases. Things that felt hard before suddenly become easier.
And with that, you simply start to feel better — physically and mentally. That positive feedback is extremely powerful. You invest some effort now, but your body gives something back to you later. From my perspective, that makes it absolutely worth it, even on the days when motivation is low.
Looking ahead, what kind of progress or change would you like to see in how we use exercise to support people with chronic conditions like MS?
David Walzik: Looking ahead, I would really like to see lifestyle interventions — especially exercise — become more accessible and better supported for people with chronic conditions like MS.
Right now, many patients are told to eat healthier and move more, but they’re often left alone with that advice. And changing behavior is hard, even without a chronic disease. I think we need more structured support, for example trainers or exercise professionals who help people find realistic, sustainable movement routines, and nutrition experts who give practical guidance.
If we want people to stay active over one or two years — not just for a few weeks — we need systems that support them in everyday life. That would not only help individuals feel better, but it could also reduce long-term strain on the healthcare system.
Farewell
David Walzik: I think what’s most important to me is that people don’t feel left alone with the idea of exercise. If you’re curious about how physical activity can support health — whether you live with MS or not — I would really encourage you to ask questions, seek support, and take small, realistic steps.
If people are interested in our research or would like to participate in future studies, they’re very welcome to get in touch with us at TU Dortmund University. We’re always happy when people are interested in what we do and want to learn more about how exercise can influence the immune system.
See you soon and try to make the best out of your life,
Nele
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