{"id":452910,"date":"2026-02-04T08:26:15","date_gmt":"2026-02-04T08:26:15","guid":{"rendered":"https:\/\/www.newsbeep.com\/ca\/452910\/"},"modified":"2026-02-04T08:26:15","modified_gmt":"2026-02-04T08:26:15","slug":"iliac-artery-endofibrosis-and-flow-limitation-explained","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/ca\/452910\/","title":{"rendered":"Iliac Artery Endofibrosis and Flow Limitation Explained"},"content":{"rendered":"

Updated February 4, 2026 01:21AM<\/p>\n

Iliac artery endofibrosis<\/a>\u00a0was recently deemed by top medics as an \u201coccupational hazard\u201d of pro cycling.<\/a><\/p>\n

But despite being considered one of the inescapable risks of the sport, it remains one of the most mysterious and misdiagnosed conditions in the peloton.<\/p>\n

Indeed, iliac artery endofibrosis can be so problematic that cyclocross prodigy Eli Iserbyt<\/a> spent months struggling for a diagnosis before he suffered four unsuccessful surgeries in 12 months.<\/p>\n

Iserbyt was ultimately forced to retire aged 28<\/a>\u00a0after he was advised \u201cthe medical trajectory was exhausted\u201d in his battle with the condition.<\/p>\n

Other notable or recent victims of this vicious \u201coccupational hazard\u201d include multi-discipline GOATs Pauline Ferrand-Pr\u00e9vot and Marianne Vos, former Tour de France sprint king Fabio Jakobsen, and climbing sensation Sarah Gigante.<\/p>\n

And iliac artery endofibrosis isn\u2019t only for the pros.<\/p>\n

It could come for you too.<\/p>\n

Here\u2019s what you need to know about iliac artery flow limitations and endofibrosis.<\/p>\n

Flow limitation in the iliac artery: Shutting a lane in the oxygen superhighway
\n\"IserbytIliac artery conditions shot to the cycling world\u2019s conscience this winter when Iserbyt was forced to retire. (Photo: DAVID PINTENS\/BELGA MAG\/AFP via Getty Images)<\/p>\n

The iliac artery is a large blood vessel deep in the abdomen that shuttles blood from the heart down into the legs.<\/p>\n

For cyclists, it\u2019s a superhighway of watt-producing oxygen.<\/p>\n

Extreme and repeated hip flexion can effectively block the road in this energy expressway. An acute angle at the hip flexor compresses the area around the iliac artery and can create a \u201ckink\u201d in the vessel that inhibits blood flow to the legs.<\/p>\n

Over time and thousands of pedal revs, the wall of a kink-prone vessel thickens to withstand the pressure of the gallons of blood that batter at the point of compression.<\/p>\n

This thickening of the artery wall protects, but also narrows the blood vessel\u2019s passage.<\/p>\n

The superhighway slows even further.<\/p>\n

This is when the issue becomes an \u201cendofibrosis.\u201d<\/p>\n

In the medical world, the umbrella term for the condition \u2013 endofibrosis or not \u2013 is FLIA, or \u201cFlow Limitations in the Iliac Artery.\u201d<\/p>\n

Iliac artery conditions are mostly, but not only, for the pros
\n\"\"Amateurs with high training volume and an aggressive position can be at increased risk of IAE. (Photo: Gruber Images)<\/p>\n

Pro cyclists are prime candidates for FLIA.<\/p>\n

The low aero tuck that gives them free speed requires extreme hip flexion and all the potential downstream issues that come with it. That risk is amplified by the 30-hour weeks and 500-watt intervals of a pro training schedule.<\/p>\n

Jem Arnold is a lead researcher in FLIA<\/a>. He explained to Velo that the risk factors that make pros easy prey for the condition apply only to the strongest and most devout weekend warrior.<\/p>\n

\u201cThis condition is essentially a supply-demand mismatch,\u201d Arnold told Velo. \u201cA less fit rider will never reach the point of limitation in the iliac artery. They won\u2019t have the muscle power to create the necessary metabolic demand that promotes the blood flow increase.<\/p>\n

\u201cLikewise, it doesn\u2019t affect people at rest, when the demand for oxygen and blood flow is very low,\u201d Arnold continued. \u201cIt\u2019s only when we increase the demand and blood supply that we see restriction at this section of the artery.\u201d<\/p>\n

But Arnold cautioned that while there\u2019s a relatively low incidence of FLIA in amateur riders, we\u2019re not off the hook entirely.<\/p>\n

\u201cThis could come up for an amateur with a high training volume or intensity, but there\u2019s less risk,\u201d he said.<\/p>\n

\u201cIt\u2019s more prevalent in pros precisely because of the amount of time they spend in those provocative positions and the accumulation of training volume and intensity.\u201d<\/p>\n

Well, that\u2019s one good excuse to only ever do coffee rides.<\/p>\n

The difficulties of diagnosis
\n\"Dombrowski'sDombrowski\u2019s early years as a pro before he joined Team Cannondale were hampered by his iliac artery endofibrosis. (Photo: Gruber Images)<\/p>\n

Iserbyt\u2019s failed battle with FLIA stood out not only because of his heart-wrenching retirement message.<\/p>\n

That he struggled with the condition for months before diagnosis and underwent four procedures in 12 months made his tale all the more harrowing.<\/p>\n

Iserbyt\u2019s story exemplifies exactly why FLIA is a scourge of pro cycling. \u00a0Unlike a broken bone, tendinopathy, or muscle tear, it\u2019s incredibly hard to diagnose, and can be the product of multiple problems.<\/p>\n

Retired U.S. climber Joe Dombrowski<\/a> suffered with symptoms for 18 months before he was properly diagnosed in 2014 during his sophomore season with Team Sky.<\/p>\n

\u201cThere was a numbness and lack of power in the affected leg,\u201d Dombrowski told Velo.<\/p>\n

\u201cI spoke at length to the doctors at Team Sky, and they didn\u2019t have a lot of experience with it. That led to it being a long time before we arrived at what the problem actually was.\u201d<\/p>\n

Dombrowski\u2019s early years in the WorldTour were derailed by blood flow limitations<\/a>\u00a0and the difficulty of its diagnosis.<\/p>\n

Fast-forward through more than a decade of medical progress, and FLIA is still a painstaking puzzle.<\/p>\n

It\u2019s rare to see a rider in the headlines only once if they\u2019re suffering a flow limitation. A victim might suffer a long period of piecing together symptoms, clues, and misdiagnoses.<\/p>\n

Flow limitation in the iliac artery? Or just a bad day on the bike?
\n\"\"Symptoms of iliac artery conditions can be similar to the pain of a top-end effort. (Photo: Gruber Images)<\/p>\n

In the early stages, an athlete who\u2019s experiencing a flow limitation might not even realise there\u2019s a deeper issue.<\/p>\n

\u201cEarlier in the condition when there\u2019s not so much endofibrosis and it\u2019s just an acute kink, the symptoms might only appear at maximal intensity,\u201d Arnold said. \u201cSo it\u2019s hard to differentiate from normal exercise discomfort.\u201d<\/p>\n

Who doesn\u2019t feel burning, heaviness, or weakness in their legs when they\u2019re red-lining their final set of VO2 Max intervals?<\/p>\n

Athletes might at first suspect simple training fatigue or underlying sickness.<\/p>\n

\u201cIf you have a flow limitation, you can\u2019t deliver enough oxygen through blood flow to meet the demand of the effort,\u201d Arnold told Velo. \u201cSo it\u2019s like an exaggeration of how you might feel at intensity.\u201d<\/p>\n

But symptoms worsen over time.<\/p>\n

Lidl-Trek\u2019s rising star Shirin Van Anrooij<\/a> said she \u201cfelt an enormous burning sensation\u201d and suffered unexpected drops in form during the early stages of her struggle with FLIA.<\/p>\n

Van Anrooij and Dombrowski both described how things became more alarming \u2013 and in need of deeper explanation \u2013 when the lack of oxygen and strength in the affected leg made itself brutally clear in their power files.<\/p>\n

\u201cI had some atrophy in the leg that was affected. It wasn\u2019t an issue at aerobic power, but I could see the difference,\u201d Dombrowski said. \u201cI also developed a significant asymmetry between my left and right power.<\/p>\n

\u201cI noticed that the difference got bigger over long rides, or even during efforts. It was like a cumulative effect,\u201d Dombrowski said.<\/p>\n

Van Anrooij\u2019s power tilted to a dizzying 70\/30 left-right imbalance before she realized something was seriously wrong.<\/p>\n

An aggressive position, high training volume \u2026 and bad genes
\n\"ExpertsExperts are still struggling to understand all the risk factors of iliac artery flow limitations and endofibrosis. (Photo: Gruber Images)<\/p>\n

But how is it possible that FLIA can develop so far before it\u2019s diagnosed?<\/p>\n

Just like the symptoms are hard to detect, the medical world still doesn\u2019t fully understand the cause.<\/p>\n

If extreme hip flexion and 30-hour training weeks were the sole factors, the entire WorldTour would have jammed up arteries.<\/p>\n

\u201cWe know that it takes more than just an aggressive position to cause FLIA,\u201d Arnold said. \u201cBut we don\u2019t actually know what the other risk factors are.\u201d<\/p>\n

Arnold theorized that those unexplained additional risk factors could be the product of \u201cbiological variability or anatomical variability.\u201d<\/p>\n

Rolling a 1 on the genetic dice might cause the iliac artery to take a kink-prone pathway through the hip or be restricted by its interplay with ligaments in the groin.<\/p>\n

And none of those things are simple to detect.<\/p>\n

\u201cDiagnosing FLIA typically comes down to a combination of clinical interpretation of a number of different tests and measurements,\u201d Arnold said.<\/p>\n

\u201cThe big problem is there\u2019s no single gold standard test for the condition and no binary yes\/no answer,\u201d he continued. \u201cWe can\u2019t just put an X-Ray up on screen or have a blood test that raises a red flag.\u201d<\/p>\n

But fear not \u2013 it\u2019s not like FLIA is at the center of a diagnostic black hole.<\/p>\n

We see more and more pros undergoing surgery to fix arterial problems not because it\u2019s become more prevalent, but because there\u2019s a better awareness and understanding of the condition than in Dombrowski\u2019s day.<\/p>\n

A dozen years ago, an athlete may have suffered massive endofibrosis and never been diagnosed.<\/p>\n

Iliac artery endofibrosis is not the end
\n\"\"Ferrand-Pr\u00e9vot and Vos both proved that it\u2019s possible to have wildly successful cycling careers after undergoing surgeries to fix iliac artery issues. (Photo: Gruber Images)<\/p>\n

And while surgery didn\u2019t solve Iserbyt\u2019s iliac artery issues, corrective procedures are largely successful.<\/p>\n

Surgery might involve a loosening of tissue around the blood vessel to reduce the chance of compression, or a shortening of the artery to prevent it looping into a kink. Angioplasty \u2013 the widening of the artery with a patch harvested from another blood vessel \u2013 is the last resort.<\/p>\n

Whatever the required procedure, recovery will require several months of inactivity and a slow rehab. It can write half a year off of a pro\u2019s already short career.<\/p>\n

But it might not always be so dramatic.<\/p>\n

\u201cIf there are symptoms, treatment can start with looking at bike fit,\u201d Arnold said.<\/p>\n

\u201cWe advise athletes with symptoms that make us suspect FLIA to trial a less aggressive position, especially during high-intensity sessions. And then for competition, they could maybe switch back to the more aggressive fit,\u201d Arnold said.<\/p>\n

\u201cThat will allow them to get the full physiological benefits from training and then the faster position in racing.\u201d<\/p>\n

Opening the hip angle by tweaking saddle height, handlebar reach, or switching to oh-so-trendy short cranks<\/a> can help riders manage symptoms.<\/p>\n

And let\u2019s face it, if you\u2019re an amateur, a more relaxed position will be way more comfortable, too.<\/p>\n

And if you are one of the few weekend warriors to be diagnosed with a flow limitation or endofibrosis that requires surgery, don\u2019t worry. Your Zwift racing and town sprinting days aren\u2019t over.<\/p>\n

Just look at what Ferrand-Pr\u00e9vot and Vos went on to do after they had their arteries fixed.<\/p>\n","protected":false},"excerpt":{"rendered":"Updated February 4, 2026 01:21AM Iliac artery endofibrosis\u00a0was recently deemed by top medics as an \u201coccupational hazard\u201d of…\n","protected":false},"author":2,"featured_media":452911,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[445],"tags":[168574,49,48,635,54263,82,168571,62576,186201,186202,168572,54267],"class_list":{"0":"post-452910","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-cycling","8":"tag-audio-true","9":"tag-ca","10":"tag-canada","11":"tag-cycling","12":"tag-parent_category-road","13":"tag-sports","14":"tag-tag-eli-iserbyt","15":"tag-tag-evergreen","16":"tag-tag-explainer","17":"tag-tag-fabio-jakobsen","18":"tag-tag-iliac-artery-endofibrosis","19":"tag-type-article"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/452910","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/comments?post=452910"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/452910\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media\/452911"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media?parent=452910"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/categories?post=452910"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/tags?post=452910"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}