May-Thurner syndrome occurs when the right common iliac artery presses against the left common iliac vein, and exercise can both unmask the condition and complicate life after treatment. For many people the compression exists silently from birth; the anatomy is present in roughly one in five people, most of whom never develop symptoms. But physical activity, especially vigorous lower-body effort like running, raises venous pressure and blood flow demand in the legs in ways that can expose a narrowed iliac vein that was previously getting by. Understanding how exercise interacts with May-Thurner syndrome matters whether you are an active person wondering why your left leg swells after a run, or a patient navigating life after stenting or a blood clot.
What Happens Inside the Vein
The left common iliac vein carries blood from your left leg and pelvis back toward the heart. In May-Thurner syndrome, the right common iliac artery, which crosses over the vein, physically compresses it against the spine. Over time, the repetitive pulsation of the artery can cause changes inside the vein wall, thickening and scarring the inner lining and eventually promoting clot formation.1PubMed. Iliac vein compression syndrome, the “May Thurner Syndrome” The result is a vein that does not drain as efficiently as it should. At rest, this bottleneck may cause no trouble at all. During exercise, when the muscles of the leg demand far more blood flow and the venous system has to handle a dramatically higher return volume, that partially blocked vein can become the weak link.
Importantly, mild compression alone may not be dangerous. Imaging studies of people with no venous complaints have found that significant left iliac vein compression is a common anatomic variant, not an automatic disease.2PubMed. Iliac vein compression in an asymptomatic patient population Given how frequently the compression appears in the general population relative to how rarely people develop deep vein thrombosis, mild compression on its own may not raise your risk much.3Journal of Thrombosis and Haemostasis. May‐Thurner syndrome: History of understanding and need for defining population prevalence The trouble tends to start when other factors pile on: dehydration, prolonged immobility before or after an event, an inherited clotting tendency, oral contraceptive use, or the sheer volume of blood the legs need to push back uphill during sustained hard effort. Some researchers have proposed that May-Thurner syndrome may intersect with inherited thrombophilia, meaning that a person who has both the anatomic compression and a genetic tendency toward clotting faces a compounded risk.4PubMed. May-Thurner syndrome will be completed?
How Exercise Can Unmask a Silent Condition
Most people with May-Thurner anatomy go their entire lives without knowing about it. The compression only becomes medically relevant when it starts producing symptoms, and exercise is one of the most common triggers that brings those symptoms to the surface. Several published case reports describe runners, in particular female distance runners, presenting with burning pain, swelling, or heaviness in the left groin and thigh during or after long runs. One review identified multiple cases of May-Thurner syndrome in female runners and noted that the anatomy is present in roughly 20% of the population, yet only a fraction develop clinical problems.5PubMed Central. May Thurner syndrome revealed by left calf venous claudication during running, a case report
In one well-documented case, a 39-year-old male runner developed left calf pain specifically during running that was severe enough to impair his athletic performance and eventually force a career change. The pain was caused by venous claudication, a cramping sensation that occurs when blood cannot drain fast enough from the working muscles. After imaging confirmed the iliac vein compression, endovascular treatment provided lasting improvement and allowed a return to activity.6PubMed Central. May Thurner syndrome revealed by left calf venous claudication during running, a case report The pattern is consistent across cases: the person is active, the left leg develops exercise-triggered pain or swelling that seems out of proportion to the effort, and the diagnosis often takes months or years because clinicians are looking for musculoskeletal problems first.
Recognizing Exercise-Related Symptoms
The symptoms May-Thurner syndrome causes during exercise can be tricky because they mimic other conditions. Runners and cyclists often chalk up leg heaviness or calf cramps to overtraining, compartment syndrome, or a muscular strain. A few clues point toward a venous origin rather than a musculoskeletal one:
- One-sided swelling: May-Thurner syndrome almost always affects the left leg. If your left calf or thigh swells during or after exercise and the right does not, that asymmetry is worth investigating.
- Positional worsening: Symptoms that improve when you elevate the leg and worsen when you stand or sit suggest a drainage problem rather than a muscle injury.
- Burning or aching at a consistent effort level: Venous claudication tends to appear at a predictable workload, unlike muscle strains that fluctuate with recovery status.
- Skin changes over time: Chronic venous insufficiency from an untreated compressed vein can eventually lead to discoloration, visible veins, or skin thickening around the ankle or lower calf.
Venous claudication itself is the hallmark. Unlike arterial claudication, where the muscles are not getting enough oxygen-rich blood in, venous claudication happens because blood is not getting out fast enough. The muscles fill with deoxygenated blood and metabolic waste, producing a sensation that many patients describe as tightness, heaviness, or a deep ache that builds during effort and resolves with rest and elevation. If you have been told you have a clean arterial system but still get left-leg cramping during sustained exercise, a duplex ultrasound looking specifically at the iliac veins is a reasonable next step.
What Happens Inside the Veins During Walking and Running
Research using treadmill tests with direct venous pressure measurements illustrates why exercise feels different when the iliac vein is obstructed. In patients with postthrombotic deep venous obstruction (the kind of chronic damage that can follow a May-Thurner-related clot), walking caused the pressure in the common femoral vein to jump by an average of about 28 mmHg, compared with just 2 mmHg in healthy control limbs.7PubMed. Intravenous pressure changes in patients with postthrombotic deep venous obstruction: results using a treadmill stress test That is a massive difference. In a normal leg, the calf muscle pump squeezes blood upward and the veins empty efficiently, so pressure stays low. When there is a blockage upstream at the iliac level, the pump keeps squeezing but the blood has nowhere to go efficiently, so pressure builds. The result is congestion, swelling, and the heavy, crampy sensation that disrupts exercise.
This pressure dynamic explains why low-impact activity like walking might feel manageable while higher-intensity work like running or cycling at race pace becomes intolerable. The faster the muscles work, the greater the volume of blood being pushed through the system, and the bigger the backup behind a compressed or scarred vein. It also explains why compression stockings help some people: external pressure supports the calf pump and helps prevent fluid from pooling in the tissues, partly compensating for the poor drainage upstream.
Exercise After a May-Thurner-Related Blood Clot
One of the biggest fears after developing a deep vein thrombosis from May-Thurner syndrome is whether exercise will trigger another clot or make things worse. The evidence is reassuring. A systematic review examining the effect of exercise after DVT found that early mobilization improved quality of life and reduced pain. Over two years of follow-up, it led to a significant reduction in the severity of post-thrombotic syndrome, the chronic condition of pain, swelling, and skin changes that can develop after a clot. None of the studies in the review reported an increased risk of recurrent clotting or worsening symptoms from physical activity.8PubMed. Effect of exercise after a deep venous thrombosis: A systematic review
A separate systematic review focusing on exercise therapy specifically for post-thrombotic syndrome found similar results: exercise appeared safe and showed improvements in quality of life scores, though the research base remains small.9PubMed Central. Systematic review of exercise therapy in the management of post-thrombotic syndrome The general direction of the evidence is that staying active after a clot is not just safe but actively beneficial for the affected leg, provided the acute clot has been treated and you are on appropriate anticoagulation. The old advice to stay in bed after a DVT has been largely abandoned.
That said, the transition back to exercise should be gradual, especially if you had extensive clotting or if the vein is still partially blocked. Walking is usually the starting point. Graduated compression stockings worn during activity can help manage swelling. The intensity and type of exercise should be discussed with the treating physician, because the specifics depend on whether you received a stent, whether you are on blood thinners, and how well the vein is draining now.
Stent Placement and Staying Physically Active
Many patients with symptomatic May-Thurner syndrome end up with a venous stent, a small mesh tube placed inside the iliac vein to hold it open. Stenting has become a mainstay of treatment, and long-term patency rates are encouraging, with studies of non-thrombotic iliac vein stents reporting that roughly three-quarters to nearly all stents remain open over follow-up periods of several years.10PubMed Central. Outcomes Following Iliac Vein Stenting for Non-Thrombotic Iliac Vein Lesions—A Narrative Review Based on Large Sample Studies The case report of the runner with venous claudication, mentioned earlier, described rapid and sustained clinical improvement after endovascular care.11PubMed Central. May Thurner syndrome revealed by left calf venous claudication during running, a case report
But a stent in the pelvis lives in a mechanically demanding environment, and research has highlighted a concern that active people should know about. A study examining stent deformation in the common iliac and iliofemoral veins found that hip flexion and extension cause measurable bending and compression of the stent. The deformation was greatest during high hip flexion (think deep squats, lunging, or bringing your knee close to your chest) and during hyperextension (as in the push-off phase of sprinting or doing a yoga backbend). Iliofemoral stents, which extend further down past the inguinal ligament, interacted with the pubic bone during hip hyperextension.12PubMed. Stent deformations in the common iliac and iliofemoral veins as a result of hip flexion and extension
The researchers suggested that device fatigue could be influenced by a patient’s activity level and that some people might benefit from modifying the types of movement they do regularly. This does not mean you cannot exercise after a stent. It means the biomechanical stress on the stent varies by activity type. Low-impact, moderate-range-of-motion exercises like walking, swimming, and cycling at a comfortable position likely place less strain on the stent than activities involving extreme hip angles. If you have a stent and want to return to high-intensity training, it is worth discussing your specific stent placement and the activities you plan to do with your vascular specialist.
Blood Thinners and the Contact-Sport Problem
Many May-Thurner syndrome patients who have had a DVT end up on anticoagulant therapy for months or longer. Anticoagulants reduce the risk of another clot but increase the risk of bleeding, and that creates a real dilemma for anyone who wants to participate in contact sports or activities with a significant fall risk. Official guidance from major medical bodies generally advises against sports that increase the risk of trauma in patients on anticoagulants.13PubMed Central. Thromboembolic prevention in athletes: management of anticoagulation in sports players affected by atrial fibrillation
For athletes unwilling to give up contact sports entirely, some hematologists have explored intermittent dosing strategies with direct oral anticoagulants. The idea is to use personalized pharmacokinetic testing to find the window when the drug’s blood-thinning effect is at its lowest, time athletic participation for that window, and then resume the medication afterward. This approach has been described in the literature as a potential strategy that could allow return to full athletic activity for selected patients, though it requires careful medical supervision and is far from standard practice.14PubMed Central. Elite athletes and anticoagulant therapy: an intermittent dosing strategy For most recreational exercisers, the practical takeaway is simpler: low-contact activities such as running, cycling, swimming, rowing, and strength training are generally fine on anticoagulants. Activities with a high likelihood of taking a hard hit to the body or head are the ones that warrant a frank conversation with your doctor about whether the risk is acceptable.
Practical Guidance for Staying Active
If you have been diagnosed with May-Thurner syndrome, whether you are pre-treatment, post-stent, or managing chronic post-thrombotic changes, a few practical principles can help you stay as active as possible without running into trouble:
- Start with walking: Walking is the safest and most studied form of exercise after DVT and venous stenting. It activates the calf muscle pump, promotes venous return, and has been shown to improve post-thrombotic symptoms over time.
- Wear compression: Graduated compression stockings during exercise can reduce swelling and improve comfort. They are especially useful for upright activities like running or hiking where gravity works against venous drainage.
- Stay hydrated: Dehydration thickens the blood and raises clotting risk. This matters more when you already have an anatomic bottleneck in the venous system.
- Avoid prolonged immobility before and after exercise: Sitting in a car for two hours to reach a trailhead and then sitting for two hours on the drive home bookends your activity with exactly the kind of stasis that promotes clotting in a compromised vein. Break up long travel with movement.
- Watch for asymmetric symptoms: If your left leg swells more than your right during exercise, or if you develop new calf pain that does not match your training load, get it evaluated.
- Know your stent’s location: If you have an iliofemoral stent that extends past the inguinal ligament, be mindful of activities involving extreme hip flexion or extension. You do not have to avoid all hip movement, but repetitive deep squats, heavy deadlifts from the floor, or aggressive stretching at the end range may place more mechanical stress on the device.
Swimming deserves a special mention as an exercise that works well for many May-Thurner patients. The horizontal position reduces the hydrostatic pressure column from the leg to the heart, which partly offsets the drainage problem caused by the compressed vein. The water pressure itself acts as a form of gentle external compression. And the movement patterns in most swim strokes involve a relatively neutral hip position compared with running or cycling.
Why the Diagnosis Gets Missed in Active People
One of the frustrating aspects of May-Thurner syndrome is how long it can take to diagnose in physically active patients. The average time from symptom onset to diagnosis in many case reports spans months to years, in part because exercise-related leg pain has a long list of more common causes. Clinicians understandably think of shin splints, stress fractures, compartment syndrome, or nerve entrapment before they consider a venous compression problem in the pelvis. Standard venous ultrasound of the calf and thigh often looks normal, because the compression is happening higher up at the iliac level, where ultrasound has more difficulty imaging through the pelvis.
Dedicated hemodynamic assessment of the iliac veins using duplex ultrasound, sometimes performed before and after exercise to provoke the obstruction, has been described as a useful diagnostic step in case reports.15PubMed Central. May Thurner syndrome revealed by left calf venous claudication during running, a case report CT venography and MR venography can also visualize the compression directly. If you are an active person with persistent, exercise-triggered left leg symptoms that have not responded to the usual treatments, bringing up May-Thurner syndrome by name with your physician is entirely reasonable. It is not a rare anatomy. It is a commonly overlooked one.
When Inherited Clotting Risks Overlap
Some researchers have noted that May-Thurner syndrome does not always act alone. The anatomic compression sets the stage, but an inherited tendency to form clots can be the factor that tips a person from asymptomatic compression into an actual DVT. Conditions like Factor V Leiden, the prothrombin gene mutation, or deficiencies in natural anticoagulant proteins such as protein C or protein S can coexist with the iliac vein compression. The suggestion from molecular research is that the syndrome may be “completed” by an inherited thrombophilia, meaning that the anatomic and genetic factors together create a higher risk than either would alone.16PubMed. May-Thurner syndrome will be completed?
For active people, this overlap matters because exercise often comes with additional transient clotting risks: dehydration during long events, immobility during travel to competitions, and the inflammatory response after very hard efforts. If you have May-Thurner anatomy and also carry a genetic clotting variant, the cumulative risk profile during endurance events could be meaningfully elevated. Thrombophilia screening is not routinely performed, but it is worth considering if you have had a clot attributed to May-Thurner syndrome and especially if you have a family history of venous thromboembolism. Knowing whether you carry an additional genetic risk factor can influence decisions about how long to stay on anticoagulation and how cautious to be around high-risk situations like ultramarathons or multi-day stage races.