Iliac Artery Endofibrosis: The Condition Behind Laidlow’s Kona Withdrawal

Sam Laidlow, the 2023 world champion, came off the bike in second place at the IRONMAN World Championship in Kona on 10 October and stopped about 5 km into the marathon. According to tri247, he told the IRONMAN film crew he has been struggling with iliac artery endofibrosis, a narrowing of the iliac artery that reduces blood flow to the leg and is best known in cyclists.

What Laidlow Said

In tri247’s report (Matthew Reeder, 11 October), Laidlow told the IRONMAN film crew that from the start of the bike he had a lack of blood flow in his left leg and used his right leg a lot more. After the first ten minutes he realised blood wasn’t reaching the leg: “I was probably 40-50 watts off where I wanted to be.” (Triathlete’s live coverage reports the same remark as 30-40 watts.) He nearly pulled out up at Hāwī.

He still reached T2 in second, as Triathlete’s race coverage also reports. Then: “As soon as I got on the run, my whole leg was numb.” He said he had known about the condition for a while and would fly back to France for the operation. The reports we read do not say which part of the artery is affected or which operation is planned, and we found no public update on the surgery by 26 October. Nothing below is a statement about his case.

What the Condition Is

Kung and colleagues’ 2025 scoping review in Vascular Specialist International (43 studies, 443 athletes, published 1997–2023) describes thickening of the inner layer of the iliac artery wall, often with fibrosis, which narrows the vessel and limits blood flow to the leg during exercise. It is not atherosclerosis: the lesions lack the lipid deposits and calcium of arterial plaque and rarely show inflammation.

Lindner and colleagues’ 2014 review in Sports Health gives the external iliac artery as the site in more than 90% of cases and dates the first description to 1985, in two competitive cyclists. The leading explanation is repeated mechanical stress: hip hyperflexion in an aerodynamic position, iliac arteries long enough to kink as the hip flexes, an artery tethered by surrounding tissue or by branches to the iliopsoas muscle, and a hypertrophied psoas. Lindner et al. also note that both the distance and the intensity of cycling correlate with developing it.

Who Gets It

The true prevalence is unknown; Kung et al. put it at possibly below 0.01%. Cyclists were 70% of athletes in the case reports they reviewed, and they cite earlier work linking a greater risk to elite or professional cyclists under 40 riding roughly 14,500 to 20,000 km a year. The left leg is affected more often: in a Lyon series of 180 surgical patients, 136 of 195 symptomatic limbs were left-sided (Rouvière et al., 2014). Laidlow described his left leg.

It is not confined to young professionals: the case reports span ages 18 to 52, as does a UK series of 46 patients (median 36; Peake et al., 2018). More on training hard past 40: masters cycling training.

Symptoms: What Riders Notice

Lindner et al. describe athletes who usually feel nothing at rest or at submaximal effort. At or near maximal effort come cramping, pins and needles, weakness, numbness, a swollen thigh and an unexplained drop in performance, usually in the thigh but sometimes spreading to the calf and buttock. Symptoms go when the effort stops, though as the disease progresses they can appear at submaximal effort. Peake et al.’s patients typically had thigh pain, foot numbness and limb weakness on exercise.

For cyclists, power is often the signal. Kleinloog et al. (2019) note that cyclists with iliac flow limitation complain of pain and loss of power. In van Hooff et al.’s 2023 surgical cohort, symptoms began at a reported 226 W in a maximal cycling test before surgery and at 333 W after it.

It is easy to miss. Kung et al. note that the symptoms are often mistaken for sports injuries and fade at rest, which is when examinations are done. Peake et al. found a median delay to diagnosis of three years (range 0–14), and Lindner et al. observe that athletes usually see an orthopaedic sports physician first.

Is It the Artery or Something Else?

Bonasia and colleagues’ 2015 review of exercise-induced leg pain lists causes in bone, muscle, blood vessels, nerves and tendons. The table sets endofibrosis beside three of them. Use the table to describe your symptoms to a clinician, not to sort them out yourself.

How It Is Diagnosed

History and examination go a long way: Peach et al.’s 2012 systematic review found they identify nearly 80% of patients with iliac flow limitation, though exercise tests and imaging are still needed to decide on treatment. Lindner et al. report a bruit (an abnormal flow sound) over the femoral artery in 44% of patients.

The central test is the ankle-brachial index (ABI), which compares blood pressure at the ankle and in the arm; it was used in about 84% of the studies Kung et al. reviewed. Timing matters. Lindner et al. note that the ABI can be normal at rest or with standard protocols, while cycling-specific protocols identify up to 85% of patients. A 2016 Delphi panel of vascular surgeons, sports physicians and other specialists (Hinchliffe and the INSITE collaborators) agreed that an exercise test is needed and that duplex ultrasound is useful.

Cut-offs differ between sources. The pathway uses a post-exercise ABI drop of more than 0.3; Bonasia et al. cite an ABI of 0.66 or less one minute after exercise, or a post-exercise gap of more than 0.18 between the legs when one side is affected. The Delphi panel did not agree on specific criteria.

Kung et al. also describe two newer tests. One times how long the ABI takes to recover after cycling: under 2 minutes is normal, still below 0.9 after 6 minutes is abnormal. The other compares power between the legs. In Kleinloog et al.’s study of 45 patients with an iliac flow limitation in one leg and 25 healthy participants, the left-right difference at 95% of maximal power had a sensitivity of 0.76 and a specificity of 0.88, and a sensitivity of 0.91 combined with the ABI. That was a lab ergometer test alongside ultrasound; none of the studies we read tested riders’ own left-right power data.

Treatment and Outcomes

For mild or no symptoms, Kung et al. describe conservative care: bike-fit changes such as saddle position to reduce hip flexion, adjusted training intensity, regular position changes on long rides and yearly checks. Lindner et al. suggest raising the handlebar and moving the saddle forward, noting this may not be feasible for professionals. The Delphi panel agreed the disease is likely to progress with continued exercise and that stopping may prevent that. If a specialist recommends a position change, our guide to bike fit tools and services explains what each type of fit measures.

With high-grade narrowing and disabling symptoms, especially in athletes who want to keep competing, Kung et al.’s pathway points to surgery. The Delphi panel agreed on endarterectomy with a vein patch: removing the thickened lining and closing the artery with a patch of the patient’s own vein. The panel judged endovascular treatment inadvisable. In the case reports Kung et al. reviewed, bypass grafts were used mostly for long or extensive disease, balloon angioplasty (tried in five cases) was generally less effective, and stents risk fracture under the mechanical stress of exercise.

In that cohort, 91.2% of patients reported fewer symptoms in the short term; after a median of 11.1 years, 94.5% still did and overall satisfaction was 91.7%. The 30-day major complication rate was 5.1%: two haematomas, one bleed from a deep infection and one blocked artery. Peake et al. report that symptoms resolved in 23 of 27 repaired limbs (85%), with superficial wound infections in 11%. Across the cohort studies Kung et al. reviewed, 90–100% of patients returned to their previous exercise.

There is no agreed return schedule; the Delphi panel disagreed on post-operative care and resuming exercise. Lindner et al.’s rider rested for six weeks, rebuilt over six more and was back to his pre-surgery level at six months. Mazurová et al. (2023) summarise a 491-patient series in which one patient died of an iliac artery rupture three weeks after surgery, put down to returning to sport too early. The surgical team sets the timeline.

When to See a Specialist

Kung et al. write that symptoms during activity should prompt non-invasive testing and that untreated endofibrosis can lead to arterial dissection and thrombosis. Mazurová et al. call the vascular surgeon the most relevant physician, noting that even top athletes’ own doctors may have little experience of the condition.

So if one leg repeatedly loses power, goes numb, cramps or feels swollen at hard efforts and recovers within minutes of easing off, see a sports physician and ask whether a vascular cause has been considered. Expect an exercise test, since a resting test can be normal, and a referral to a vascular surgeon experienced with endofibrosis if the results point that way. The pathway starts with your history, so note which leg, at what effort and how long it takes to settle. In the literature, bike-fit changes are part of care after a diagnosis, not a substitute for one.

Sources

• Laidlow and the race: Matthew Reeder, “Sam Laidlow plans surgery after Kona withdrawal” (tri247, 11 Oct 2026); tri247, “IRONMAN World Championship 2026: Men’s finishing order and Pro Series standings” (11 Oct 2026); Jonathan Turner, “IRONMAN Kona 2026 men’s race: Start time, how to watch and World Championship preview” (tri247, page dated 11 Oct 2026), for the race date; Susan Lacke and Chris Foster, “Vincent Luis, Taylor Knibb Win 2026 Ironman World Championship” (Triathlete, race report and live coverage, updated 12 Oct 2026).
• Reviews and consensus: Kung C, et al. “Diagnostic Approach and Management of Iliac Artery Endofibrosis in Athletes: A Scoping Review.” Vasc Specialist Int 2025;41:24. INSITE Collaborators (Hinchliffe RJ, et al.). “Diagnosis and Management of Iliac Artery Endofibrosis: Results of a Delphi Consensus Study.” Eur J Vasc Endovasc Surg 2016;52:90–98. Peach G, et al. “Endofibrosis and kinking of the iliac arteries in athletes: a systematic review.” Eur J Vasc Endovasc Surg2012;43:208–217. Mazurová T, et al. “Endofibrosis as a cause of peripheral artery disease: a comprehensive review and proposal of two novel algorithms for diagnosis and treatment.” Rev Assoc Med Bras 2023;69:352–356. Lindner D, et al. “An Unusual Case of Leg Pain in a Competitive Cyclist: A Case Report and Review of the Literature.” Sports Health 2014;6:492–496. Bonasia DE, et al. “Exercise-induced leg pain.” Asia Pac J Sports Med Arthrosc Rehabil Technol2015;2:73–84.
• Clinical studies: van Hooff M, et al. “Short- and long-term outcomes after endarterectomy with autologous patching in endurance athletes with iliac artery endofibrosis.” J Vasc Surg 2023;78:514–524. Peake LK, et al. “The Investigation and Management of Iliac Artery Endofibrosis: Lessons Learned from a Case Series.” Eur J Vasc Endovasc Surg 2018;55:577–583. Kleinloog JPD, et al. “Pedal power measurement as a diagnostic tool for functional vascular problems.” Clin Biomech2019;61:211–216. Rouvière O, et al. “Arterial endofibrosis in endurance athletes: angiographic features and classification.” Radiology 2014;273:294–303.

We read the full text of Kung et al., Mazurová et al. and Lindner et al., the relevant sections of Bonasia et al., and the published abstracts of the Delphi study and the Peach, van Hooff, Peake, Kleinloog and Rouvière papers. The ABI recovery-time test and the 491-patient series are reported as summarised in Kung et al. and Mazurová et al. This article is general information, not medical advice.

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