Sport-Related Vascular Conditions in Endurance Athletes
Sport-related vascular conditions are uncommon but problematic conditions which can affect the arteries of the legs in otherwise healthy, highly trained endurance athletes.
In recent years a rising number of professional cyclists and triathletes have been diagnosed with a debilitating sport-related vascular condition called blood flow limitations in the iliac arteries, or FLIA. Marianna Vos (NED), Tayler Wiles (USA), Amanda Spratt (AUS), Zdeněk Štybar (CZE), and Bob Jungels (LUX) are just a few of the household names in the men’s and women’s World Tour Cycling peloton who have publicly struggled with this frustrating vascular condition.
Although uncommon, amateur cyclists can also develop FLIA. However, with less clinical knowledge available about vascular conditions in amateur athletes, it can often be a difficult and lengthy process to detect and diagnose.
Jem Arnold is a PhD researcher at the University of British Columbia and a physiotherapist working with Allan McGavin Sports Medicine Clinic Physiotherapy. He has worked internationally with cyclists, triathletes, and runners with sport-related vascular conditions, and has helped to develop screening tests for cyclists with FLIA. We are pleased to be able to offer clinical assessment for vascular conditions at our Plaza of Nations clinic location in downtown Vancouver.
More information about FLIA and sport-related vascular conditions can be found below. If you are an athlete or a clinician suspecting a blood flow limitation and want to arrange an appointment, please contact plaza@allanmcgavinphysio.com or jem.arnold@ubc.ca.
Presentation
Flow limitations in the iliac arteries (FLIA) is an uncommon vascular condition where blood flow through the arteries in one or both legs is impaired during exercise.
The iliac artery is a large blood vessel in the lower abdomen that carries blood from the heart to the legs. If blood flow is limited through the iliac artery, the muscles of the legs will not get enough oxygen to meet the demands of exercise. Thus, causing symptoms (listed below), pain, and limiting exercise performance.
During exercise the muscles in the affected leg(s) may feel symptoms including pain, burning, weakness, powerlessness, heaviness, cramping, tingling, and other sensations. These symptoms are usually at their worst during higher intensity or longer exercise bouts and go away relatively quickly after stopping exercise. Usually there are no symptoms at rest, although some patients experience symptoms during non-exercise activities such as climbing stairs.
Causes
The exact causes and risk factors for FLIA are not yet fully understood. The condition is thought to be related to the crouched forward racing position used in sports such as cycling, speed skating, and rowing; and the repeated hip flexions in running and other endurance sports1.
However, it is important to point out that not every cyclist or endurance athlete is at risk of developing FLIA. Suspected additional risk factors include previous injury around the hip, natural anatomic differences in the arteries, or changes in muscle activity with certain cycling pedaling styles (see Treatment section below for more information on pedaling styles).
Athletes may perform millions of repeated hip flexions over years of training and competition. The iliac artery can be compressed by surrounding tissues as the hip flexes up toward the chest. In particular, the iliopsoas (hip flexor) muscle can put pressure on the iliac artery when it is repetitively contracted. The artery can become kinked, like squeezing a garden hose to stop the flow of water.
Elite athletes can deliver 10-15+ litres of blood per minute through the arteries to the legs during exercise. This high volume of blood flow trying to push through a kinked or compressed artery causes stress to the artery walls. The artery walls can abnormally thicken over time in response to this stress, a process called endofibrosis.
The inside of the vessel can become narrower because of this stress over time (months or years of exposure), which further limits blood flow during exercise and causes symptoms to gradually worsen. FLIA and endofibrosis are like a chronic overuse injury, which gradually gets worse over many months and years. This process is different from more common age-related cardiovascular diseases such as atherosclerosis or diabetes, and typically affects much younger and fitter individuals.
Prevalence
FLIA typically appears in relatively young, healthy endurance athletes under 50 years of any gender. It may be associated with longer training histories and higher lifetime training volumes. It is suspected that as many as 20% of professional cyclists may develop FLIA during their careers2. The prevalence in other sports and in amateur athletes is unknown.
Overall, FLIA is an uncommon condition and should not be the first suspected diagnosis for unexplained leg pain during exercise.
Other common causes for symptoms include orthopaedic injuries of the muscles and soft tissues around the hips and lower back, problems with managing training load, nutrition & energy imbalance, and training + non-training stress i.e. overtraining. Other sport-related vascular complaints to consider include popliteal artery entrapment syndrome and chronic exertional compartment syndrome, both common in runners.
Common orthopaedic conditions should be investigated and treated by a qualified clinician as part of the investigation process for FLIA. Treating these conditions may help to improve the athlete’s symptoms whether or not they have a blood flow limitation. If the athlete is not responding to treatment as expected, then FLIA or another vascular complaint may be suspected and investigated further. It is very possible for multiple conditions to be present together.
Screening and Diagnosis
If FLIA is suspected, the first step of diagnosis is to review medical and training history to understand the presentation and history of complaints. A specialised questionnaire for detection of sport-related vascular problems can be provided to the athlete.
The next step is a clinical assessment to evaluate the athlete’s movement and function, particularly of the lower back and hips.
This is followed by a provocative exercise test in which the athlete must exercise hard enough to reproduce their symptoms. This may be at a much higher workload than is typically performed with vascular patients in a hospital setting. The exercise protocol must be adapted to the higher fitness level of these athletes3.
Provocative exercise should be performed as cycling on a stationary bike or treadmill running, in the same body position in which the patient experiences symptoms. An incremental ramp or multi-stage exercise test can be performed with resistance increasing over 15-30 minutes until the athlete reaches their maximal effort or maximal tolerance of symptoms.
During and after the exercise test, the clinical investigator will take various measurements to help detect a blood flow limitation. This includes recording the workload at which the athlete first reports feeling limited by symptoms.
Near-infrared spectroscopy (NIRS) devices are non-invasive light sensors that can be used to monitor oxygen saturation in muscle during exercise. These are small wearable devices placed on the thigh muscles. This technology is similar to common sport watches which use a light sensor to measure heart rate. Interpretation of these data can help to differentiate a blood flow limitation from a muscle recruitment issue4.
Immediately after the athlete reaches maximal exercise tolerance, blood pressure cuffs are placed around one arm and both ankles to measure the ankle-brachial blood pressure index (ABI) while the athlete remains in the provocative cycling position, or lays on their back with their hips flexed toward their chest and their knees supported on a stool3.
If these tests suggest the presence of FLIA, the athlete will be referred to a sports physician or vascular specialist for the next step of diagnostic evaluation. Echo-Doppler ultrasound will be used to take images the arteries at rest and after a brief exercise task such as fifty standing squats. Images will be taken of the left and right iliac arteries with the athlete laying on their back with straight legs, with their knees flexed to their chest, and while pushing against their own knee to contract the hip flexor muscles. This may visually reveal the presence of a kink, narrowing, or other abnormality in the artery5.
Further diagnostic imaging may include peak systolic velocity with Echo-Doppler ultrasound, magnetic resonance angiography (MRA), computed tomography (CT) scan, and/or intravascular ultrasound6. These methods provide more detail on the artery structure and can help guide treatment options, such as surgical reconstruction.
Treatment
Unfortunately, there are limited options for conservatively treating FLIA. The first step should be to modify body position and bike fit, such as raising the handlebar height, moving the handlebars closer to the body, and moving the saddle forward to reduce the amount of hip flexion. Using shorter-length pedal cranks can help to further open the hip angle. Trying to focus pedaling technique more on pushing the pedals down and pulling up less can help reduce hip flexor muscle contraction. These modifications can be used during training to reduce symptom burden. Alterations to bike fit should be performed with an experienced clinician or bike fitter. View more general tips about bike fitting in a past webinar by our physiotherapists Midori Lam here (bike fitting at minute 9:30 to 16:30) or email plaza@allanmcgavinphysio.com for further details on booking a bike fit.
High intensity training can be reduced or modified to manage symptoms. Repeated short interval training with frequent brief rests can be effective to reduce symptoms and preserve fitness. For non-professional athletes, reducing their provocative training and adding alternative activities can be helpful. Rehabilitation and strengthening exercises guided by a clinician can help to further reduce symptoms and maintain fitness.
In some cases, conservative management will not be sufficient. Athletes understandably may not want to give up their sport, and professional athletes rely on their performance for their livelihood. For these individuals, surgical reconstruction can be considered.
Diagnostic imaging mentioned above will help to guide the most appropriate surgery. Surgery will involve making an incision through the lower abdomen to reach the iliac artery. Surgical repair may include releasing tissues around the artery, cutting and shortening the artery, or cutting and patching the artery with a vein graft harvested from the patient’s leg 9.
Surgery has very good outcomes and high satisfaction by patients. However, surgery is an invasive option that requires sufficient time and rehabilitation to return to sport. Surgery is not a ‘quick fix’. Depending on the individual condition, some athletes are able to return to training and competition within 5-10 weeks. Others may take 6-9 months or longer to regain full performance. Unfortunately, some athletes do not manage to return to the same level of performance at all.
Surgical details and prognosis must be discussed on an individual basis between the patient and medical experts.
Patient & Clinician Considerations
FLIA is a condition which develops gradually and is difficult to detect and diagnose. For this reason, it is still not fully understood. Athletes, coaches, and clinicians should be aware of vascular conditions as a possible cause for unexplained performance impairment and painful symptoms when other common causes have been excluded or treatment response is insufficient. Increasing awareness about sport-related vascular conditions will help to improve patient management.
Performance may decline gradually over months or years and symptoms can be subtle. When an injury/disease is not visible, it can be difficult to identify what the problem is, or if there is even a problem at all. This painful, unexplainable loss of fitness can be very distressing to the athlete, and the process of finding a diagnosis can feel frustratingly slow. Providing the athlete with trust, education, and support will help to reduce feelings of fear and uncertainty, and empower the athlete with greater autonomy during their diagnosis and management process, which will improve their outcomes.
To arrange a vascular assessment with Jem Arnold at Allan McGavin Sports Medicine Clinic Physiotherapy, please contact plaza@allanmcgavinphysio.com or jem.arnold@ubc.ca for more information.
References
1. Peach G, Schep G, Palfreeman R, et al. (2012) Endofibrosis and Kinking of the Iliac Arteries in Athletes: A Systematic Review. Eur J Vasc Endovasc Surg. https://doi.org/10.1016/j.ejvs.2011.11.019
2. Bender MH, Schep G, de Vries WR, et al. (2004) Sports-Related Flow Limitations in the Iliac Arteries in Endurance Athletes: Aetiology, Diagnosis, Treatment and Future Developments. Sports Med. https://doi.org/10.2165/00007256-200434070-00002
3. Schep G, Bender MH, Schmikli SL, et al. (2002) Recognising Vascular Causes of Leg Complaints in Endurance Athletes. Part 2: The Value of Patient History, Physical Examination, Cycling Exercise Test and Echo-Doppler Examination. Int J Sports Med. https://doi.org/10.1055/s-2002-33142
4. Van Hooff M, Arnold J, Meijer E, et al. (2022) Diagnosing Sport-Related Flow Limitations in the Iliac Arteries Using near-Infrared Spectroscopy. Journal of Clinical Medicine. https://dx.doi.org/10.3390/jcm11247462
5. D’Abate F, Paraskevas KI, Oates C, et al. (2017) Color Doppler Ultrasound Imaging in the Assessment of Iliac Endofibrosis. Angiology. https://doi.org/10.1177/0003319716649113
6. Sharifi M, Snyder R, Sharifi I, White E. (2024) Long-Term Outcome of Percutaneous Endovascular Stenting in External Iliac Artery Endofibrosis. Vasc Med. https://doi.org/10.1177/1358863×241227476
7. Zugail AS, Shaabi HI, Idir S, Becquemin J-P. (2020) Cyclist Endofibrosis (Exercise-Induced Arterial Endofibrosis) Treated by Drug-Coated Balloon Angioplasty. Case reports in vascular medicine. https://doi.org/10.1155/2020/4290271
8. Arnold J, Yogev A, Koehle MS. (2021) Evaluating Arterial Blood Flow Limitation Using Muscle Oxygenation and Cycling Power. Clin J Sport Med. https://doi.org/10.1097/jsm.0000000000000942
9. Van Hooff M, Colenbrander FFC, Bender MHM, et al. (2023) Short- and Long-Term Outcome after Endarterectomy with Autologous Patching in Endurance Athletes with Iliac Artery Endofibrosis. J Vasc Surg. https://dx.doi.org/10.1016/j.jvs.2023.03.501
