Peroneal Tendinopathy in Runners

If you're feeling a nagging ache on the outside of your ankle — behind or just below that bony bump — you might be dealing with peroneal tendinopathy. It's the kind of injury that starts as a mild annoyance and gradually gets louder if you ignore it. The good news is that it responds well to the right approach, and most runners can work through it without a major break from training.

What's Going On

Your peroneal tendons are two thin tendons (peroneus longus and brevis) that run behind the bony bump on the outside of your ankle — the lateral malleolus. Think of them as your ankle's stabilizer cables: their main job is to prevent your foot from rolling inward, and they work constantly during running to keep you balanced on uneven ground. Every time your foot lands, these tendons fire to fine-tune your stability.

Peroneal tendinopathy develops when these tendons are asked to do more than they're conditioned for. Trail running, cambered roads, and sloped surfaces all increase the demand on the peroneals, and they can also become overworked after an ankle sprain — when the damaged ligaments can't do their share of stabilization, the peroneal tendons pick up the slack. Like other tendinopathies, this is a gradual-onset condition. It builds over days to weeks rather than striking suddenly.

The encouraging part is that tendons respond well to progressive loading. Rest alone won't fix this — it actually weakens the tendon. The path forward is targeted strengthening combined with smart training modifications, and most runners see steady improvement over a few weeks.

Why This Happens

• Uneven terrain — trails and sloped surfaces demand constant lateral stabilization from the peroneals, and high mileage on these surfaces can tip them past their tolerance
• Post-ankle sprain compensation — after a sprain, loosened ligaments mean the peroneal tendons have to work overtime to stabilize the ankle. This is one of the most common triggers.
• Lateral instability — if your ankle stability is poor (from previous injuries or lack of balance training), the peroneals are perpetually overloaded
• Running on slopes — consistently running on a cambered road or sloped shoulder means one ankle is constantly tilted, loading the peroneals unevenly
• Sudden training change — switching from flat roads to trails (or adding significantly more trail mileage) without a gradual transition period
• Tight footwear — shoes that press or rub against the outside of the ankle can compress and irritate the peroneal tendons directly

How to Recognize It

• Pain behind or just below the bony bump on the outside of your ankle
• You'll notice it's worse with lateral movements or when running on uneven ground
• An aching feeling after running, particularly after trail runs or routes with cambered surfaces
• Tenderness when you press the area just behind the outer ankle bone
• You might feel a sense of instability on uneven surfaces, like your ankle isn't quite trustworthy
• The onset is gradual — it builds over days to weeks rather than appearing after a single incident

When to Get Help

If you've been modifying your training and doing consistent peroneal strengthening exercises for 3 to 4 weeks without meaningful improvement, it's time to see a professional. This is especially true if you have a history of ankle sprains, since imaging may be needed to rule out a tendon tear or subluxation (where the tendon slips out of its groove behind the ankle bone).

Watch for these signs that need earlier evaluation:

• Pain that's getting worse despite rest and modification
• A snapping or popping sensation behind the outer ankle bone
• Significant swelling on the outside of the ankle
• Pain that's now present during walking, not just running

How to Adjust Your Training

Mild

You can keep running, but move to flat, predictable surfaces and avoid lateral movements for now. Start peroneal strengthening exercises: resistance band eversion (pulling your foot outward against the band) and single-leg balance holds on a firm surface. These directly address the root cause by building tendon capacity. Most runners at this stage can maintain nearly all their training volume with these simple adjustments.

Moderate

Stick to flat, even surfaces and easy effort. Your tendon needs a structured loading progression to heal — start with isometric holds (pressing your foot outward against an immovable surface for 30 to 45 seconds), then progress to slow eccentric eversion exercises. It can be frustrating to dial things back when you have a training plan calling for more, but this phase of targeted loading is what builds a tendon that can handle everything you'll ask of it later. Pool running or cycling can help maintain fitness during this period.

Severe

If you've been managing this for several weeks without improvement, it's time for a professional evaluation. Imaging can determine whether there's a tear or structural issue that self-management won't resolve. In rare cases, chronic peroneal tendon problems may need more involved intervention, but catching it at this stage and getting the right treatment plan means you're still on a path back to full running. The worst thing you can do is keep pushing and hoping — that's how a manageable issue becomes a long-term one.

Staying Ahead of It

• Peroneal strengthening — resistance band eversion exercises are quick, easy, and highly effective. Two to three sets a few times per week keeps these tendons conditioned for the demands of running.
• Ankle stability work — single-leg balance drills and proprioception training build the neuromuscular control that takes load off the peroneal tendons, because your whole system works together to stabilize the ankle
• Gradual terrain progression — if you're adding trail running or hillier routes, ramp up gradually over a few weeks. Your peroneals need time to adapt to the increased stabilization demands.
• Post-sprain rehabilitation — if you've sprained your ankle in the past, don't skip the balance and stability rehab. Unrehabilitated sprains are one of the most common precursors to peroneal tendinopathy.
• Appropriate footwear — make sure your shoes provide adequate lateral stability without compressing the outside of the ankle. If you can feel pressure on the peroneal area when your shoes are laced up, try a different lacing pattern or a wider shoe.

The Bottom Line

Peroneal tendinopathy is a manageable injury that rewards a proactive approach. The combination of targeted strengthening, smart surface choices, and gradual progression back to demanding terrain is what gets you past this. Don't ignore outer ankle pain that's been building — address it early with the right exercises, and you'll resolve it faster and reduce the chance of it coming back.