Castelli athlete Kirstine Frida Rysbjerg shares the personal story behind her diagnosis of flow limitation of the iliac arteries, the long road that led her to surgery, and how the experience changed her understanding of performance, recovery, and trust in her own body.

At 60 kilometers into Unbound 2025, I was exactly where I wanted to be.

Second group in the race. Elite women’s race. Through Little Egypt. One rider ahead.

After crashes, surgeries, rehab, and months away from feeling like myself as a cyclist, I was finally racing again.

Although a mechanical took me out of the race shortly after the first feed zone, it was still one of the biggest moments of relief I had felt in a long time. I was back in a race situation again. Back doing what I loved.

What I did not fully understand yet was that both of my legs were struggling to get enough blood flow during high intensity efforts.

And that the thing cycling had taught me to become exceptionally good at — ignoring pain and pushing through — had also become one of the biggest barriers to understanding what was happening to my body.

One of the greatest strengths in endurance sport is the ability to tolerate discomfort. Cyclists learn early that progress often requires suffering, and that the athletes who succeed are usually the ones capable of enduring more than others.

But sometimes that mentality becomes dangerous.

“It is often assumed that surgery for flow limitations is a quick fix. In reality, surgery is only one part of the overall treatment process. The multidisciplinary team surrounding a professional athlete plays a crucial role in optimizing every aspect of care, including prehabilitation and rehabilitation.” - Dr. Posthuma, surgeon from Flevoziekenhuis in Almere.

And perhaps no quote explained the mindset of endurance athletes better than this:

“Athletes, especially endurance athletes, are often successful because they are able to ignore alarming signals from their bodies for prolonged periods of time. Professional racing is frequently compared to “putting your finger between a door with ten others, and the person who holds on the longest wins.” It is therefore not surprising that elite athletes become highly skilled at ignoring physical warning signs.” - Dr. Posthuma

For a long time, I genuinely believed that was simply part of being a cyclist.

In February 2024, I suffered two disc herniations following a crash during a Belgian road race racing for a Belgian road team, most likely combined with months of overtraining. Towards the end of the year, I started working with physiotherapists in Girona at Forca13, where Kat Stene helped identify some of the reasons I continued struggling with pain and power loss in one of my legs — particularly poor core and glute engagement.

Around the same period, I was also hit by a car while training in Girona and needed surgery for a double fracture in my left elbow. Rehab became my life.

Like many cyclists, I kept trying to return before my body was truly ready.

I would show up to races because that is what cyclists do. If you start a race, you finish it too. Looking back, there were probably multiple races I should never have started in the first place, but I pushed through because that mentality had always been part of my identity as a rider. Something I was quite proud of actually.

The first time I heard someone describe flow limitation of the iliac arteries, something immediately resonated.

I had listened to a Danish cycling podcast where a former professional rider explained the symptoms he experienced before being diagnosed: loss of power, numbness, asymmetry, and the feeling of simply not being able to push through efforts anymore. He later underwent surgery in the Netherlands and returned successfully to cycling.

At the time, I was unsure whether my own symptoms came from the disc herniations, poor muscle activation patterns, or something else entirely. After Unbound, I actually had a period where I raced symptom-free and genuinely believed I was finally healthy again.

But the symptoms returned.

Around the same time, I came across an article about Canadian professional rider Maggie Colelyster from Human Powered Health Cycling women’s team having surgery for the same condition. I reached out to her directly on Instagram, as her boyfriend Joe Laverick was a part of SOG Castelli too, and she was incredibly generous in sharing her experience and the contact details of hospitals in the Netherlands that specialized in the condition.

Shortly afterwards, I got in contact with Dr. Jelle Posthuma - a surgeon at Flevoziekenhuis in Almere in the Netherlands and doctor for the Dutch National Cycling team too.

Although I was invited to come directly to the Netherlands for a screening, I initially wanted to explore whether the Danish healthcare system could help me first.

In September, I underwent a cycling-specific exercise test in Copenhagen, where blood pressure measurements are taken in the legs before, during and after maximal exercise. The results showed a significant drop in blood pressure in my right leg. I was then referred for CT and ultrasound scans.

Unfortunately, the scans were not considered clear enough for the Danish vascular surgeons to recommend surgery.

I was advised to stop my cycling career.

That sentence stayed with me for a long time.

But somehow, I wasn’t ready to accept it.

I asked Dr. Posthuma to help me uncover what exactly flow limitation of the iliac arteries (FLIA) actually is, as he is one of the progressive surgeries in the field. Moreover, he used to be a professional cyclist himself, and had to stop his career because of FLIA.

“The condition is difficult to diagnose because symptoms occur only during exercise. At rest, the artery may appear normal on ultrasound or imaging scans. During high-intensity exercise, maximal blood flow to a single leg can reach approximately 19–20 liters per minute, which is when the problems arise. The artery normally dilates to accommodate increased blood flow, but the current understanding is that the affected segment does not dilate as effectively as the healthy portion of the vessel, resulting in a relative flow restriction. Since we are currently unable to perform imaging during maximal exercise, the abnormality can be difficult to visualize at rest.

Symptoms such as unilateral or bilateral ischemic pain that consistently occur at a specific exercise intensity, recur repeatedly, and do not improve after periods of rest should not be ignored, particularly when they occur in a time-trial position. Although these symptoms are not always caused by iliac artery flow limitations, they do warrant further evaluation.

It is still unclear exactly what happens when athletes continue to push through these symptoms. However, we often observe that athletes with flow limitations of the iliac artery develop musculoskeletal asymmetries. Many athletes report unilateral hip stiffness, and approximately 80% of patients with FLIA complain of back pain. This is likely related to asymmetrical use of the legs. Over time, this may lead to a “software problem,” where muscle activation patterns and core stability become increasingly asymmetric. After surgery, we frequently observe that restoring symmetrical muscle activation and core stability requires time and professional guidance.” - Dr. Posthuma

What made the difference for me in the Netherlands was that the scans and testing were performed in provoked positions designed to replicate an aggressive cycling posture. A resting scan often will not show the problem.

Following additional testing, MRI imaging, and consultations with Dr. Posthuma and his team, it became clear that I had flow limitation in both legs.

On Tuesday January 20th, I underwent surgery in Almere.

Posthuma also mentions how surgery is not the finish line to overcome the flow limitation of the iliac arteries.

“One of the biggest misconceptions around flow limitation surgery is that the operation itself solves everything immediately.

In reality, surgery is only one part of the process.

Recovery typically takes an entire season. Following surgery in our hospital, and depending on the surgical technique used, patients begin stretching and early mobilization from day one, including walking for at least two weeks. Because we do not cut through the abdominal muscles, we believe early mobilization is safe and important to help reset core stability, muscle activation, and muscle stiffness in the early phase of recovery.

After two weeks, athletes begin a gradual build-up program that allows them to return to cycling relatively early. However, progression must remain slow and should primarily be guided by the symptoms experienced by the athlete. Throughout the year, riders often experience ups and downs, but on average, most athletes become symptom-free or nearly symptom-free within 6–9 months and are able to return to their previous level of performance.

I wish more cyclists understood earlier that the team surrounding them is one of the most important factors in recovery. Overactivation of the iliopsoas muscle appears to be a significant issue during rehabilitation after FLIA surgery and should be addressed early in the recovery process.

More broadly, I wish this condition were recognized sooner. I believe that many athletes stop competitive cycling because of FLIA without ever receiving the correct diagnosis.

Awareness is therefore essential. Teams and team doctors play an important role in referring athletes to specialized centers with expertise in diagnosing and treating FLIA. In my opinion, only centers with specific experience and knowledge in this condition can provide optimal treatment and rehabilitation.” - Dr. Posthuma

Four and a half months later, I am back in structured training again, and I have been for about a month now.

But my understanding of performance and recovery has changed completely.

Core stability, mobility work, movement quality, and recovery are no longer “extra” work around cycling. They are now part of my daily life as an athlete.

One of the hardest parts of recovery is not always physical.

It is rebuilding trust in your body again after months — or years — of feeling that something was wrong.

That process became a huge part of my rehabilitation with physiotherapist Kat Stene.Kat Stene and Dr. Posthuma have a unique collaboration regarding FLIA and makes it possible for athletes not to be left alone at any point in their FLIA journey. Kat Stene has also observed Dr. Posthuma perform a surgery on a rider with FLIA, and together they have elaborated a week-by-week comeback protocol post the surgery.

I asked Kat the following - How do you get back trust and confidence in your body post the surgery of FLIA?

“I think the first thing is understanding that it is completely normal not to trust your body straight away.

Most cyclists who have had FLIA have spent a long time feeling that something is wrong, but also doubting themselves. They may have been told they are unfit, overtrained, anxious, lacking strength, or simply not trying hard enough. So by the time they get a diagnosis and surgery, the physical problem may be addressed, but the relationship with their body has often taken a hit.

Rehab is not just about getting the leg strong again. It is about rebuilding evidence that the body can respond normally.

That happens gradually. You start with small, controlled sessions where the athlete can finish feeling okay. Then you build load, intensity, position, and duration in stages. Confidence comes from repeated experiences of: “I did that, my leg responded well, and I recovered normally.”

For cyclists, trust is rebuilt through data, sensations, and time. I want them to learn what normal training discomfort feels like again, versus the warning signs they lived with before surgery.” - Kat Stene

That idea — rebuilding evidence — became one of the most important parts of the process for me, and still is today.

Not chasing one perfect ride or one perfect performance, but slowly building trust through consistency again.

One of the reasons I wanted to share this story is because awareness matters.

This is what Kat recommends you to do if you have a suspicion of FLIA.

“The first thing is to take the symptoms seriously, especially if they are repeatable.

Flow limitation often shows up at high intensity. Riders may describe one leg “shutting down,” loss of power, heaviness, cramping, weakness, numbness, or a feeling that the leg will not respond. It is often very effort-dependent and may ease when they stop or reduce intensity.

The tricky part is that cyclists normalize suffering. They are used to pain. They are used to pushing through. But this is different. If the same symptom keeps appearing at the same intensity or position, particularly on one side, it is worth investigating.”

Kat Stene also recommends athletes document clear patterns:

1. Which leg?
2. What intensity?
3. What position?
4. What heart rate or power?
5. How long before symptoms disappear?
6. Is there numbness, weakness, or loss of power?

She also emphasizes the importance of first ruling out lumbar spine issues, as they can create very similar symptoms.

Kat stresses that most importantly, athletes should seek professionals familiar with vascular issues in cyclists, because general testing at rest can often miss the condition entirely.

“If someone isn’t a professional cyclist but more an elite level rider, they might be able to help the symptoms with a conservative approach - fixing pelvic and hip stability and control issues through exercises and adaptive training techniques, rather than needing to immediately go for surgery. Everyone is different and going through a program to initially work on these issues will give a better outcome in the long run, even if surgery is needed.” - Kat Stene

Watch my conversation with Maaike Boogaard about undergoing the same surgery with Dr. Posthuma: