Now I Know Why my Left Leg Burns

At the beginning of July I was finally diagnosed with Iliac Arterial Endofibrosis (IAE) [edit: actually it’s more appropriate to call what I have Iliac artery flow limitation]. This is a chronic condition where the main artery delivering blood to one leg becomes constricted or kinked near the hip, limiting blood supply to the lower working muscles… which are kind of important in cycling.

There are some fantastic articles explaining the condition in detail and its relevance in cycling, so I won’t repeat much of what’s already written. I want to focus more on my own experience with the condition and how it’s changed my perception of training and racing. But for more details about the condition and possible risk factors, check the links below.

Velonews Feature: Arterial disease and cycling
Cycling Weekly – Iliac artery furring: Is surgery the cure?
Veraldi et al, 2015. Arterial endofibrosis in professional cyclists.

For me the major symptom is severe burning pain in my Left lateral quad during high intensity efforts. My Left leg also loses significant power at higher intensities. Once symptoms begin they won’t resolve until I can fully rest for 5-10 minutes to allow blood flow to normalize. So once I start to feel it during a race, there’s no coming back.

I remember this breakaway in 2017 was horribly painful, but my average power was barely Sweet Spot. Could never figure it out at the time.

My whole racing career (which only goes back to 2014) I’ve been confounded by a significant L/R power imbalance. I’ve investigated, analysed, experimented, and tried everything possible to address the imbalance and find a cause, but I’ve never made any real progress. I’ve always been stuck at around 45/55% at higher intensities.

I always figured my L leg fatigued quicker than my R due to some biomechanical or musculoskeletal issue. I thought my L leg was somehow less well-trained than my R, and that I just needed to train better to bring it up to target.

I can’t recall when I started to feel the burning pain that really told me I had a problem, but the pain was certainly notable last season in 2017. I think as my fitness improved, the vascular deficiency became more of the limiting factor.


Gastown Grand Prix 2017 – Utter, inexplicable, burning failure

For example, I had a terrible race at Gastown Grand Prix in July 2017. I was coming off an amazing (for me) 21st-place finish at the Tour de Delta UCI 1.2 road race, which proved I had the fitness to survive the week of high level racing. However after maybe 3 laps of sprinting out of the hairpin corner and grinding at 50+ km/hr up the cobbled street, I remember telling myself “I can’t hurt this bad for another 60 minutes…” 

I pulled the plug early and limped back to the team tent with my leg burning and throbbing like I had never experienced.

The hairpin corner of Gastown Grand Prix (photo Scott Robarts)

I thought it was a mental failure on my part, and it really got me down for a while. I felt like I had surrendered to the pain, but that everyone was suffering the same as I was. The numbers were hardly different from what I had done in training, so why was it so bloody painful?

My L leg was particularly bad that race, but that’s just how it was: my limitation on the bike has always been about how much pain and burning I can tolerate, and how much extra power my right leg can compensate for.

Gastown2017 LRbalance_INKED
L/R Power Balance chart from Gastown GP 2017 (Strava)

It seems obvious now that something was wrong, but at the time I figured this was just the suffering of our sport, and getting more fit would improve everything.

It didn’t…


Effect on Training Philosophy

This limitation has had ramifications for how I think about training and racing. Sustained efforts are horrible for me, and I’m often unable to complete VO2max or Sweet Spot (SST) efforts that, on paper I should be able to crush easily.

So I found myself leaning toward intermittent protocol that allowed me to maintain elevated HR for longer without pain, and to hit higher power numbers and accumulate greater workload, than when I tried suffering through continuous intervals.

Those of you who read my post on Decreasing-Power 30/15 VO2max intervals, that workout protocol was inspired at least partially from my own failures to sustain continuous VO2max intervals. I was clearly biased toward thinking intermittent intervals worked better than continuous. My UPDATE post (written when I suspected the vascular issue, but before it was confirmed) corrects some of my prior assumptions, and I’m now leaning back toward continuous intervals as more effective for most well-trained athletes.


Racing Conservatively

If there’s one way I’ve benefited from having this condition, it’s that I’ve learned how to race ultra-conservatively in order to delay symptoms onset and actually survive to the end of the race. I’ve always said I’m a smarter racer more than a powerful racer. Turns out, out of necessity!

Once the burning pain begins, there’s really no relief. So I joke with my teammates that I have one match to burn and I gotta use it wisely! My teammates say I look like I’m nose breathing half the time, until all of a sudden I’ll be in full pain-face mode (see the pics above).

I’ve been able to contribute to the team leadout only by hiding and keeping myself safe during races. I can’t contribute to chasing down breaks or working on the front much until the end, because that will put me over the pain threshold which I just can’t recover from.


Why was I so fucked this race? Well, now I know!

So I’ve more or less stopped racing for this season to give the L leg a break. I’ll do the occasional Tuesday Nighter, but mostly just to sit in the pack. I shouldn’t cause my artery to get dramatically worse by continuing to race, but I just want to minimize symptoms. I just don’t want to keep smashing my face into that wall of burning pain, now that I know what it is.

I will race this coming weekend at the BC Provincial Crit Champs in Vancouver, in the brand new Awesome Grand Prix. I’m super excited for it! I only have #onematch to burn, but I’ve been training it up to be one hell of a match!

I’ve basically called my shot: all the local frenemy teams know that if I make it to the finish I’ll be ready to unleash a devastating 30 seconds in the leadout. 

I’ll hopefully have a video of that up next week. Then I’m gonna basically shut down and keep things long, slow, and symptom-free for the rest of the summer.

Until hopefully surgery this winter…

13 thoughts on “Now I Know Why my Left Leg Burns

  1. Damn! Sorry to hear about the diagnosis, but there must be some relief to finally know what was wrong. Thanks again for another post, and hope you are able to enjoy the rest of the season, rest easy, and take of care of this thing.

    Liked by 1 person

  2. Make sure to do tons of research to resolve it and don’t rely on doctors. I had a hip issue for years and after $5,000 in Dr. and PT expenses I fixed it via wearing a special belt I saw browsing the net. Had I not done that I was probably going to have my back fused in a few years. Sometimes surgery is the only option, just make sure and don’t rely on others!

    Liked by 1 person

  3. hey Cory. after a long internet search I think maybe we share the same issue, the thing is that I haven’t diagnosed… yet. after seeing physiotherapist, doctors, running an emg and ultrasound all of them said there’s nothing wrong with my leg, but still I see 45-55% and when I hit over my vo2max after 5 minutes I just want to burn my leg. the following efforts hurts too but maybe 10% below the first one. do you have any suggestions for me to treat this issue ? thanks mate


    1. I think you mean ‘hey Jem’ 😉

      Can’t diagnose anything over the internet of course, but you could bring up the possibility of blood flow limitation or iliac artery endofibrosis to your doctor. The screening & diagnostic stress test process is fairly easy, but the clinician must be familiar with the condition, the techniques, and what they are looking for. A referral to a sports doc or vascular surgeon might be appropriate.

      I can’t recommend specific treatments, but there are some positional changes that you could try. I train in a fully upright position on my home trainer to avoid excessive hip flexion which aggravates the issue. It seems to have helped a bit, but certainly hasn’t solved the issue. I’ve also adapted my racing position to bring me more forward and upright, likewise to limit hip flexion. Definitely not aero anymore! But if it helps get blood flow into my leg, it’s worth the trade off.


  4. Hi Jem! I had iliac artery endofibrosis in 2014, starting to feel it 5 months after the triathlon season. I went from doing IM 70.3 in june to not able to do a normal 5km run without a pause, 6 month later. I had surgery a year later. They install me an “GORE-TEX® Vascular Grafts ” to fix it. Long story short, It worked but now I’m back at about half the capacity that I used to have. The problem is that this artificial graft doesn’t expand like normal artery. So when pushing hard running or biking, the blood limitation is still affecting the leg. I was wondering if you could recommend interval training specific to this condition to try to develop and enlarge collateral vascular vessel? Thanks!


    1. Hi there. Thanks for sharing your story.

      Can I ask you, was it better immediately post-surgery then gradually declined down to half capacity? Or did it never fully recover after surgery?
      Do you still experience pain in the leg with exertion (assuming you did before surgery) or is it limited by general weakness and no power coming out from the leg, so to speak?

      For training recommendations, I can speculate based on my own experiences and my understanding of the condition, but please understand I really don’t know if it’s possible to change the ultimate limiter, which is the volume of blood flow through a narrow pipe. That might be a fixed limit. And what has worked for me might not work for you.

      My first priority is to minimize symptoms and protect against further tissue injury. If I’m feeling symptoms, or I’m seeing a L/R power imbalance, that probably means I’m putting more mechanical and blood flow sheer stress on the artery which is part of what led to endofibrosis in the first place. So I spend the vast majority of my training time at low intensity.

      When I do perform high intensity intervals I still try to minimize symptoms and protect against further injury. For me this means I try to minimize significant biomechanical asymmetries, for example feeling like I’m pedaling squares, dragging my leg, or compensating too much with hips, low back, etc. Or if I see a significant L/R power imbalance (for me that’s anything more than ~45/55%). These are signs that I need to shut the workout down and rest the leg. This means my high intensity workouts are typically lower volume and lower intensity than I would otherwise be capable of. Although I have as much trouble as anyone else holding back, sometimes 🙂

      In general I have found shorter work intervals work better for me, like Ronnestad’s 30/15s. The intermittent recoveries gives the leg a chance to catch up on O2 supply and avoids too severe ischemia and symptoms building up in the tissue. I also stand a lot during high intensity cycling, as the less acute hip angle allows greater blood flow. But that might not be the case if the artery patch itself cannot dilate. Over/Under workouts don’t work at all for me, because my bad leg is never ‘under’.. so I just get more and more asymmetrical through the interval. I’ve recently blown myself up a few times trying these.

      In terms of building collateral vascularization, I don’t know if the typical findings for intramuscular capillarization apply to building collateral arterial pathways alongside the larger (eg. iliac) arteries. In any case, the literature is equivocal on what kind of training is best (moderate continuous or high intensity intervals), but the stimuli that are most important to capillarization are hypoxia – which we have covered 🙂 – and sheer stress on existing vasculature. This second one is interesting. My guess is my iliac artery experiences extreme local sheer stress, but the vasculature down stream of the ‘kinked hose’ might actually experience reduced sheer stress, since blood flow and pressure are reduced.

      This was useful for me to quickly review the literature in order to answer your question. I think I’ve convinced myself that continuous moderate intensity training below the “symptom threshold” or “50/50 threshold” is probably the simplest, safest, and most effective training for long-term adaptations imposed by an iliac artery flow limitation. Not exclusively, of course. There’s a time and place for higher intensity training. But essentially, base training should remain the most important part of our training plans! 🙂


  5. First of all, I wasn’t expecting that kind of feed back! Thanks for your time and your answer! Secondly, Please excuse if my sentences are a bit odd, I’m not from a medical background and English isn’t my first language :).
    To answer your question, the symptom I still have is a general weakness on the leg. If you keep pushing, the calf and the exterior side of the thigh start to cramp. Theses symptoms came back gradually 6-9 months after surgery. (first 3 months was off, and than gradually I came back into training). So it’s fair to say that the surgery improved the situation but didn’t solved it. But the condition is stable 4 years post surgery, so it’s kind of a good news.
    My main problem with the artificial graft (beside that it doesn’t expand like normal artery), is that the seams where the artificial and natural artery meet, swell up while exercising. I experienced that I need to give 1-2 days of rest between training, to give enough time for the seems to come back to normal. If not, the symptoms appears in no time while running. So, come my idea to try to build collateral vascularization to compensate and improve my blood flow downstream.
    Since I’m having difficulties finding text about training with endofibrosis problem, Is it too much to ask to share your literature that you are talking about?

    Thanks again for your answer, it’s really appreciated!
    Bromont, Canada


    1. Thanks PY, sorry I get excited and start using more technical jargon! 🙂

      Very interesting to hear about your recovery after surgery. I’ll share that I don’t get the same burning pain as I did before surgery, so that’s a major success. But I still feel limited by the same general weakness in my thigh that you mention. I’m just coming up to 1 year post-surgery, so we will see how things change over the longer term.

      This is a question for your doctor, and please don’t take medical advice from random people on the internet 🙂 But I generally prioritize training consistency for health and performance. So I personally would rather train lower intensity and more often, than have to take 1-2 days off between harder training sessions. If that’s possible. If any riding, no matter how easy, results in swelling of the graft and needing 1-2 days off… That should definitely be a conversation with your doctor on the risks of continuing the activity. I hope you are able to continue the activities you enjoy.

      Here are some review articles that touch on the training stimuli for building vascularization with full papers available.

      MacInnis MJ, Gibala MJ. Physiological adaptations to interval training and the role of exercise intensity. J Physiol. 2017 May 1;595(9):2915-2930. doi: 10.1113/JP273196. Epub 2016 Dec 7. PMID: 27748956; PMCID: PMC5407969.

      Hellsten Y, Nyberg M. Cardiovascular Adaptations to Exercise Training. Compr Physiol. 2015 Dec 15;6(1):1-32. doi: 10.1002/cphy.c140080. PMID: 26756625.

      Gohil, R. , Lane, T. and Coughlin, P. (2013) Review of the adaptation of skeletal muscle in intermittent claudication. World Journal of Cardiovascular Diseases, 3, 347-360. doi: 10.4236/wjcd.2013.34055.

      Hope that helps


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