In professional cycling, where performance comes down to minute details, four letters have quietly been shaping the trajectories of some of the sport’s top athletes.
FLIA, or flow limitation in the iliac artery, is a condition almost unheard of outside of elite endurance sport and has become an enigmatic nemesis of cyclists. Also referred to as iliac artery endofibrosis, it’s a condition that disproportionately affects cyclists.
It is essential to note that symptoms can present differently in each case, but in general, FLIA occurs when the iliac arteries, which branch from the abdominal aorta and supply blood to the pelvis and legs, narrow or kink against surrounding tissue. This is due in part to repetitive hip flexion, crucial to a cyclist’s pedal rhythm, but which can lead to the innermost membrane of these arteries thickening. On an MRI, this presents as a kink in the artery, and to the naked eye, fibrosis (a type of yellowy scarring) fills the artery.
FLIA doesn’t announce itself with the dramatic snap of a crash but lurks in the background, stealing power from one leg, limiting blood flow during maximal efforts, and eroding performance in ways that are frustratingly hard to diagnose.
High-profile examples of cyclists going under the knife and coming back stronger have made headlines over the past seasons, and in 2025, the condition affected Olympian and Human Powered Health athlete Maggie Coles-Lyster. But what can it feel like, and how is FLIA diagnosed? Coles-Lyster is back on her bike after surgery to combat FLIA, and we spoke to her about the stages of her journey, her recovery, and her hopes for the future.
How FLIA presented in Maggie
When Coles-Lyster began struggling to stay with the peloton earlier this year, she assumed it was the remnants of an illness. The sprinter had just come off racing in the UAE, and when the Spring Classics rolled around, her body wasn’t responding the way it usually did.
“As soon as the race would get hard, I just couldn’t keep up,” the 26-year-old recalls. “I would just go out the back and couldn’t push any more than I was doing. It was kind of like, am I still sick? Is something lingering? Is this an energy thing?”
For weeks, she searched for answers. Rest didn’t help. Training harder didn’t help. Blood tests showed nothing. The confusion only deepened when one of her legs had a sensation she had never experienced before.
“The only way I’ve been able to describe it is as if the blood down in my entire leg was aching,” she explains. “It wasn’t specific to any muscle, it was such a deep ache, and it would linger for days after races.”
Then, at the Tour of Flanders, Coles-Lyster cramped unusually early. She describes how her nutrition was optimal and that 70 km into De Ronde was an odd time to be feeling these effects. She dove into her Wahoo pedal data and saw a 45-55 imbalance when putting in effort. But this was not indicative of just FLIA.
“It’s hard to pinpoint it as FLIA, and that’s why it can sometimes take up to three years from symptom onset to actual diagnosis,” explains the 26-year-old. “I thought, let’s just do the testing to rule it out, even just for peace of mind.”
Diagnosis
After reading everything that could be read on FLIA (which is not an extensive amount), and talking to other athletes, Coles-Lyster traveled to a clinic for the first diagnosis.
“They do everything in one day,” she explains. “MRA with contrast, ultrasounds at rest and under strain, a bike test with ankle-brachial blood pressure measurements that they compare with arm blood pressure to determine if there’s a drop in your ankles.”
The verdict came quickly, and she did, in fact, have FLIA. But the diagnosis didn’t bring immediate relief. She began with physio and medication, and although the early physio would help in her recovery, it did not pinpoint the issue.
“My leg was aching all the time, nothing was fixing it,” she explains. “But I heard about a surgeon with a less invasive approach who had the surgery himself as an athlete, and it had become his project.”
Surgery
It was a quick turnaround after an initial consultation, with Coles-Lyster being put at ease thanks to a method that only cuts through one layer of connective tissue, and not multiple layers of muscle.
“My leg scar comes from where they take the part of your saphenous vein, and that’s what they patch the artery with,” she explains. “It’s common enough to have bilateral endofybrosis, but bilatrial surgery is less so. They then do the surgery on the abdomen, and for me, that was on both sides, but they were able to get to it with one incision. I did not have an obvious kink which could be seen on scans, but fibrosis in that artery.”After surgery, which consisted of cleaning the affected area, Coles-Lyster was provided with immediate relief and validation.
“When I woke up, they texted me saying, ‘I can’t believe you were training with that much fibrosis in your artery,’” she says. “That was super validating. It was proof I wasn’t imagining it. I also felt that my feet were warm for the first time in months. I hadn’t realized they weren’t before.”
Recovery
Coles-Lyster spent two nights in the hospital after the surgery before being discharged, and was advised that she could already start rehabilitating movement with lunges and figure four poses.
“I was like, hang on, I’m like a jigsaw cut open,” she jokes. “It was more like a mind game of stretching and moving, knowing your arteries are pretty cut open, but healing.”
Coles-Lyster had to be careful because so much fibrosis was removed, so time was needed to build the arteries back up. She began her rehab with walking.
“Every day post-op, something was better, and I was walking quicker and for longer,” she says. “I also recorded my lunges from day one, and pretty much every one was lower and deeper. I feel lucky that there were no roadblocks. The physio before addressed very similar things that were going on in the hips and pelvic floor, and that was a great foundation.”
For Coles-Lyster, her off-bike movement is a huge part of her routine, as highlighted in 11 gym exercises to make you a faster cyclist and 8 yoga exercises all cyclists should be doing.
“You want to balance rest, but movement felt a lot better.”
Listening to her body was key. Week one was focused on walking and light hip movements, and by week two, she began cautiously activating her core before starting to use an elliptical machine in week three.
“I got off it and I’m like, oh my God, I can’t feel my legs,” she exclaims. “The sensations were very odd. I thought I wasn’t gonna be able to walk down the stairs. But every time I got on the elliptical, it got better.”
She has also been managing the post-op scars with daily massage of the scar tissue area, as well as using skin-optimising oil and repair oil from NAQI, and by the fourth week, she was back on two wheels.
“100 watts felt like endurance for the first three weeks,” she says. “But lately, things have started to feel more normal.”
What Maggie learned
Having gone under the knife, Coles-Lyster is keen to share her journey and advice for each stage of the process.
“Listening to symptoms was important,” she says. “The more people you can talk to and the more information you can gather, the more you feel the autonomy to make your choices.”
Coles-Lyster also did an AMA through her Instagram, which shone a light on the thoughts athletes have about FLIA and surgery.
“Once I started actually sharing a bit on how the recovery was going, I was probably having one person a day reach out to me,” she says. “Saying things like, this makes so much sense, where did you get tested? What was the recovery from surgery like? What are your scars like?”
The majority of her responses were from cyclists, and she was keen to impart her experience.
“I say, either grab coffee or have a phone call or talk about it because, as I found, it’s hard to get that much information on it,” she explains. “From people’s experiences, you can find rehab protocols or find out whether you should be tested for it. When it comes to the scars, scars are stories. I don’t need a perfect bikini bod anyway.”
The road ahead
Sarah Gigante, the winner of two stages at the Giro d’Italia post-FLIA operation, is an example of how eradicating endofibrosis can get an athlete back to their best. Such turnarounds give Coles-Lyster optimism for the future, while acknowledging the need to be cautious.
“I think recovery can go up and down just in sensations,” she explains. “It’s pretty common to still have symptoms for many months after the surgery because you still have swelling in your arteries and all around the area.
Even with those challenges, she remains positive and motivated about what’s ahead.
“Most of the riders I’ve talked to were anywhere in that six to eight months post-op when they feel that it’s really worked. So I’m like, perfect, I’ll be peaking for the classics at this rate. That’s awesome.”
Her excitement for racing again is fueled by early signs of improvement and the hunger to pick up where she left off.
“I felt there was so much to build on and I was so excited to keep pushing that, so I’m really stoked to be able to push those limits at those races again, and actually see what I’m capable of.”
