Achilles Tendinitis in Runners: Causes, Treatment and Prevention
The injury runners fear the most. Learn to identify Achilles tendinopathy, treat it with eccentric exercises and return to running pain-free.
If you feel a sharp pain at the back of your ankle when you take your first steps in the morning, or your Achilles tendon flares up every time you run uphill, you are likely dealing with Achilles tendinopathy. It is the second most common injury in runners —behind only plantar fasciitis— and one of the most deceptive: ignore it and it can become chronic, sidelining you for months.
The good news is that sports science has come a long way. We now know that complete rest is not the answer: the tendon needs controlled load to repair itself. This guide covers everything you need as a runner: from understanding what type of tendinopathy you have to the eccentric exercise protocol, the shoes that help and when it is time to see a professional.
What is Achilles tendinopathy
The Achilles tendon is the largest and strongest tendon in the human body. It connects the calf muscles —the gastrocnemius and the soleus— to the heel bone (calcaneus). Its role is essential for running: it stores and releases elastic energy with every stride, handling forces up to 8 times your body weight during the running gait.
When the load placed on the tendon repeatedly exceeds its capacity to recover, the collagen fibers become disorganized and the tissue begins to degenerate. This is Achilles tendinopathy. The more accurate term is no longer "tendinitis" (which implies inflammation) but tendinosis in most chronic cases, as biopsies show tissue degeneration without active inflammatory cells.
Tendinitis vs. tendinosis: why it matters
This distinction completely changes the treatment approach:
- Tendinitis (acute phase): true inflammation of the tendon, common in the first 2-4 weeks. Responds to ice, relative rest and anti-inflammatories
- Tendinosis (chronic phase): collagen degeneration without inflammation, typical when the problem has been present for months. Does not respond to anti-inflammatories; it requires progressive mechanical loading (eccentric exercises) to stimulate tissue remodeling
Most runners who seek treatment already have tendinosis, because they ignored the symptoms for weeks or months. The sooner you act, the faster the recovery.
Insertional vs. midportion: two different problems
Where the pain is located determines the type of tendinopathy and shapes the treatment plan:
- Midportion tendinopathy: pain located in the central part of the tendon, 2-6 cm above the heel. It is the most common in runners (55-65% of cases). Responds well to classic eccentric exercises
- Insertional tendinopathy: pain right where the tendon attaches to the heel bone. More common in older runners or those carrying extra weight. Classic eccentric exercises can make it worse; it requires a different approach that avoids excessive dorsiflexion
Key facts about Achilles tendinopathy in runners
- Prevalence: affects 5-12% of runners, more common in men than women
- Typical age: peak incidence between ages 35 and 55, though it can appear at any age
- Recovery: 70-80% of cases resolve with conservative treatment (eccentric exercises and load management)
- Recurrence: up to 27% of runners experience a recurrence within 5 years if they do not maintain a strengthening program
Symptoms: how to recognize it
Achilles tendinopathy has a characteristic pain pattern that worsens if left untreated. Knowing the early warning signs is key to acting before it becomes chronic.
Morning stiffness: the first sign
The earliest symptom is stiffness and pain in the tendon when you take your first steps in the morning. During the night the tendon shortens and loses lubrication. When you get up, the ankle feels stiff and sore. This discomfort typically improves within 10-30 minutes once you start moving, which leads many runners to dismiss it.
Pain pattern during running
The pain follows a typical pattern in the early stages:
- At the start: discomfort during the first 5-10 minutes of the run
- Warm-up effect: the pain eases or disappears as the tendon warms up
- After running: the pain returns with greater intensity 1-2 hours after finishing
- Advanced stage: if it progresses, pain is present throughout the run and worsens with hills and speed
Tendon thickening
In tendinopathies that have been present for weeks or months, it is common to notice that the affected tendon is thicker than the healthy one. If you compare both ankles, you may feel a palpable nodule or bump in the painful area. This thickening indicates disorganized tissue and signals that the tendinopathy has been developing for some time.
Crepitus
Some runners notice a creaking or grinding sensation when moving the ankle up and down. This may indicate inflammation of the paratenon (the sheath surrounding the tendon) or adhesions between the tendon and the surrounding tissues.
Pain during specific activities
- Climbing stairs: the tendon works harder when pushing upward
- Rising onto tiptoes: pain when trying to rise onto one foot
- Running uphill: forced dorsiflexion stretches the tendon under load
- Changes of pace: accelerations demand rapid contractions from the tendon
Causes in runners
Achilles tendinopathy develops when the load on the tendon exceeds its capacity to adapt. There is rarely a single cause: it is the combination of several factors that ultimately overwhelms the tendon.
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Calf weakness (gastrocnemius and soleus)
This is the most important and most underrated factor. The calf muscles are the engine that drives the tendon. If they are weak, the tendon absorbs a disproportionate share of the mechanical load. Many runners log 40-50 km per week but never do specific calf strengthening exercises. The result is a tendon that works above its threshold with every stride.
Sudden increase in training load
The classic cause in runners. Bumping up weekly mileage by more than 10%, adding speed work or hill sessions without gradual progression, or doubling volume to prepare for a race at the last minute. The tendon adapts, but it needs time: tendon tissue remodels more slowly than muscle or the cardiovascular system.
Hills and speed work
Uphill running increases ankle dorsiflexion and demands a more powerful calf contraction. Intervals and tempo changes generate high peak loads on the tendon. Adding too much hill or speed volume at once is one of the fastest ways to trigger a tendinopathy.
Low-drop or zero-drop shoes
Minimalist or low-drop shoes (0-4 mm) place the Achilles tendon in a more stretched position, increasing the demand on it. If you are used to shoes with a 10-12 mm drop and switch to a 4 mm drop without a transition period of several weeks, you are inviting the tendon to complain. Check our running shoe guide for help choosing the right pair.
Calf tightness
Tight gastrocnemius and soleus muscles limit ankle dorsiflexion, forcing the tendon to work through ranges of motion that overload it. This is a common cause in runners who spend many hours sitting during the day and do not stretch after training. Check our stretching guide for runners to work on flexibility.
Other risk factors
- Age: the tendon loses elasticity and regenerative capacity from around age 35-40. Veteran runners need more recovery time between demanding sessions
- Excess weight: every extra kilogram increases the load on the tendon during running, where forces are multiplied
- Hard surfaces: always running on asphalt without varying generates constant repetitive stress on the same structures
- Biomechanics: excessive overpronation creates a whip-like effect on the tendon, especially in its midportion
- Medications: certain antibiotics (fluoroquinolones such as ciprofloxacin) weaken tendons and increase the risk of rupture
- Training after a break: returning to previous volume after a holiday or injury without gradual re-adaptation
Treatment: load management
The current approach to treating Achilles tendinopathy has changed radically: complete rest is contraindicated. The tendon needs controlled mechanical stimulation to remodel. The key concept is load management: reduce what irritates the tendon while maintaining what stimulates repair.
Phase 1: Isometrics and pain relief (weeks 1-2)
Isometric exercises (holding a position without movement) are the first step. They have an immediate analgesic effect on the tendon and begin to stimulate collagen synthesis without the stress of movement.
- Calf isometric holds: hold the tiptoe position for 30-45 seconds, 4-5 reps, 2-3 times a day
- Reduce running load: cut weekly volume by 30-50%. Temporarily eliminate hills, intervals and tempo changes
- Ice after activity: 10-15 minutes with ice wrapped in a cloth over the tendon, only during the acute phase with visible inflammation
- Avoid aggressive stretching: in the acute phase, stretching the tendon can worsen irritation. Isometrics are safer
Phase 2: Eccentric exercises — the Alfredson protocol (weeks 2-12)
Eccentric exercises are the cornerstone of treatment. In an eccentric contraction, the muscle lengthens while generating force (the lowering phase of a heel raise). This type of loading stimulates remodeling of the disorganized collagen.
The Alfredson protocol, developed in 1998, remains the gold standard:
- 2 exercises: eccentric heel drops with the knee straight (gastrocnemius) and with the knee bent (soleus)
- 3 sets of 15 reps of each exercise, twice a day, 7 days a week
- Minimum duration: 12 weeks
- Moderate pain during execution is acceptable (up to 4-5 out of 10)
- Progression: add weight gradually (backpack with books, weighted vest) once you can complete 3x15 without pain
Phase 3: Progressive functional loading (weeks 8-16)
- Combined concentric-eccentric exercises: full heel raises with added weight
- Light plyometrics: single-leg hops, jump rope, low-intensity bounding
- Gradual return to running: following the return-to-running protocol (see below)
- Gradual reintroduction of hills and speed: only after 4-6 weeks of pain-free running
Complementary treatments (if no improvement after 3 months)
- Extracorporeal shockwave therapy (ESWT): the strongest evidence after eccentrics. Stimulates vascularization and tendon remodeling
- PRP injection: platelet-rich plasma. Promising results but evidence is still limited
- Manual therapy: deep transverse friction massage, myofascial release of the triceps surae and trigger point work
- Corticosteroid injection: last resort due to the risk of weakening and rupturing the tendon. Only indicated for insertional tendinopathy with associated bursitis
Specific exercises
These are the exercises with the strongest scientific evidence for Achilles tendinopathy in runners. Perform exercises 1-3 daily; exercises 4-6 should be done 3-4 times per week as supplementary strength work.
Stand on a step or curb, supported only on the balls of your feet. Rise to the tiptoe position using both legs. Then lift the healthy leg and slowly lower using only the affected leg over 3-5 seconds until the heel drops below the edge of the step. Rise back up using both legs. 3 sets of 15 reps, twice a day. Add weight with a backpack once you can do them pain-free.
Same exercise as above but with the knee of the affected leg slightly bent (about 20-30 degrees). This shifts the load from the gastrocnemius to the soleus, which is the muscle that works hardest during easy-paced running. 3 sets of 15 reps, twice a day. The soleus is key for distance runners.
Standing in front of a wall, rise onto one foot to the tiptoe position and hold for 30-45 seconds. The muscle works without movement, which reduces pain and starts loading the tendon safely. 4-5 reps per leg, 2-3 times a day. Ideal as a warm-up before running or as a pain-relief exercise when the tendon is very irritated.
Sitting on a chair with your feet flat on the floor, place weight on your knees (weight plate, heavy backpack). Raise your heels slowly (3 seconds up, 3 seconds down). 3 sets of 10-12 reps, 3 times per week. This exercise isolates the soleus and allows you to add heavy load safely and in a controlled manner.
Standing on a step, raise the heel to the maximum tiptoe position on one leg, holding for 2 seconds at the top and lowering with control over 3-4 seconds. 3 sets of 8-12 reps, 3 times per week. This exercise combines the concentric and eccentric phases and is the natural progression before returning to running. Goal: be able to do 20 reps on one leg without pain.
Weak glutes and hip stabilizers alter lower-limb biomechanics and overload the tendon. Include single-leg squats (3x10), single-leg glute bridges (3x12) and lateral band walks (3x15). 3 times per week. This is an essential complement that many runners overlook. Also check our guide on preventing running injuries.
Shoes during recovery
Footwear plays an important therapeutic role in Achilles tendinopathy. The right shoe reduces load on the tendon and supports recovery, while the wrong one can perpetuate the problem.
What to look for in a recovery shoe
- 10-12 mm drop: a high drop elevates the heel relative to the forefoot, which reduces tension on the Achilles tendon by shortening the distance it has to stretch. This is the most important feature during recovery
- Good heel cushioning: reduces the impact forces transmitted to the tendon with every stride
- Soft heel collar: a rigid heel counter that presses directly on the tendon can irritate the insertional area. Look for shoes with a padded, flexible collar
- Rocker sole geometry: a curved sole facilitates the foot's transition and reduces the work the calf has to do during toe-off
What to avoid
- Zero-drop or minimalist shoes: they place the tendon in a position of maximum tension. Not suitable during recovery
- Racing flats or competition shoes: typically have low drop and minimal cushioning
- Shoes with more than 700-800 km: worn-out cushioning increases load on the tendon
- Abrupt shoe changes: any change in footwear should be gradual
Check our complete running shoe guide to choose the right model. The Hoka Clifton (5 mm drop but with rocker geometry that compensates), Brooks Ghost 16 (12 mm drop) and ASICS Gel-Nimbus 26 (8 mm drop) are popular choices among runners recovering from Achilles tendinopathy.
Temporary heel lifts
A useful strategy during the first few weeks is to place a 6-10 mm heel lift inside the shoe (both running and everyday footwear). This elevates the heel, reduces tension on the tendon and provides immediate relief. It is a temporary measure: remove it gradually over 4-6 weeks as the tendon improves.
How to prevent Achilles tendinitis
Preventing Achilles tendinopathy is built on three pillars: strengthening the calf, progressing load intelligently and taking care of recovery. If you have already had an episode, these strategies are even more important to prevent recurrence.
Progressive calf strengthening
The best prevention is a strong tendon. Incorporate heel raises into your weekly routine permanently, not just when it hurts:
- Bilateral heel raises: 3 sets of 15 reps, 3 times per week for maintenance
- Single-leg heel raises: 3 sets of 10-12 reps, 2-3 times per week
- Progress by adding weight: the long-term goal is to be able to do a single-leg heel raise with 25-30% of your body weight added
- Include variation: straight knee (gastrocnemius) and bent knee (soleus)
Smart training progression
- The 10% rule: do not increase weekly mileage by more than 10% per week
- Gradual hill introduction: add hills progressively, starting with gentle slopes
- Speed with a base: do not add speed sessions until you have a solid volume base
- Recovery weeks: every 3-4 weeks, reduce volume by 20-30% so the tissues can adapt
- Gradual shoe transition: if you change models, alternate with the old pair for 2-3 weeks
Proper warm-up
Never start running flat out from the first step. A warm-up of 5-10 minutes of brisk walking or very easy jogging allows the tendon to increase its temperature, improve its blood supply and gain elasticity before handling heavy loads. Isometric calf holds (30 seconds on one leg) are an excellent tendon-specific warm-up.
Cross-training
Complementing running with lower-impact activities —cycling, swimming, elliptical— lets you maintain cardiovascular fitness without constantly overloading the same structures. This is especially useful during high-volume weeks or when you notice the tendon starting to complain.
Monitor the warning signs
Pay attention to morning stiffness. If it appears consistently for more than 2-3 days in a row, it is a signal that the tendon is accumulating load. Reduce your training volume and ramp up isometric exercises before the problem escalates.
When to see a doctor
Most Achilles tendinopathies respond to treatment with eccentric exercises and load management. However, there are situations where you need a professional assessment:
- Pain does not improve after 3-4 weeks of eccentric exercises and load reduction
- Pain worsens progressively despite following the protocol
- Sudden snap during running: if you feel a crack or a sensation like being struck at the back of the ankle followed by intense pain, it could be a partial or complete tendon rupture. Stop running immediately and go to the emergency room
- Significant lump or thickening: a large palpable nodule may indicate advanced tendinosis or partial rupture
- Bilateral pain: tendinopathy in both tendons at the same time can be a sign of a systemic cause (medications, metabolic disease)
- Difficulty rising onto tiptoes: indicates significant weakness that needs evaluation
- Diffuse swelling or redness: may indicate paratenon inflammation or infection
Diagnostic tests
- Ultrasound: first-line option. Detects thickening, partial tears, neovascularization (new blood vessels associated with pain) and calcifications. It is dynamic: it can be done with the ankle in motion
- MRI: more detailed than ultrasound, useful when a partial tear is suspected or to plan a surgical procedure
- X-ray: does not show the tendon, but can reveal calcifications at the insertion or bony deformities (Haglund's disease)
Which specialist to see
- Sports physiotherapist: first port of call for active rehabilitation. They can supervise the exercise protocol, provide manual therapy and adjust progression
- Sports medicine doctor or orthopedist: needed if a rupture is suspected, if conservative treatment fails or if advanced imaging is required
- Sports podiatrist: useful if there is a biomechanical component (overpronation, malalignment) contributing to the problem
Returning to running: criteria and protocol
The return to running after Achilles tendinopathy must be progressive and based on functional criteria, not arbitrary dates. Coming back too soon is the number-one cause of relapse.
Criteria to start running
- You can walk briskly for 30 minutes without pain during or after
- Morning stiffness has disappeared or lasts less than 5 minutes
- You can do 20 single-leg heel raises without significant pain
- You can do 3 single-leg hops without pain
- Tendon thickening has reduced (compare with the other side)
Gradual return-to-running protocol (6-8 weeks)
- Week 1: Walk 25 min + easy jog 5 min (3 sessions, alternate days). Keep pace below zone 2
- Week 2: Walk 15 min + jog 10 min. Monitor pain and morning stiffness the following day
- Week 3: Walk 10 min + jog 15 min. If the tendon is fine, add a fourth session
- Week 4: Jog 20-25 min continuously at an easy pace. Flat terrain, no hills
- Week 5: Increase to 25-30 min. Allow slight pace variations, but no structured intervals
- Week 6: 30-35 min. Introduce gentle hills gradually
- Weeks 7-8: 35-40 min. Add easy tempo progressions. Consider reintroducing short intervals
Common mistakes when returning
- Dropping the eccentrics: continue the strengthening exercises for at least 6 months after returning to running. Do not stop just because it no longer hurts
- Returning to previous volume too fast: the tendon has lost capacity during the injury. You need 3-4 months to regain your previous level
- Adding hills and speed too soon: wait at least 4-6 weeks of pain-free flat running before introducing hill or speed work
- Ignoring the signals: if the tendon starts complaining again, step back one week in the protocol immediately. Also check our articles on runner's knee and shin splints to understand other common injuries during the return to training
Frequently asked questions
How long does it take for Achilles tendinitis to heal?
Midportion tendinopathy usually improves significantly within 6 to 12 weeks with eccentric exercises and load management. Insertional cases tend to be slower and may require 3 to 6 months. Chronic cases lasting over a year may need additional treatments such as shockwave therapy or PRP injections.
Can I keep running with Achilles tendinitis?
In many cases yes, but with adjustments. The key is to manage the load, not eliminate it. If pain during the run stays below 3 out of 10, does not worsen the following day and does not increase morning stiffness, you can maintain a reduced volume. Temporarily avoid hills, speed sessions and uneven surfaces.
What is the difference between Achilles tendinitis and tendinosis?
Tendinitis involves acute inflammation of the tendon, common in the first few weeks. Tendinosis is chronic degeneration of the tissue without active inflammation, typical when the problem has been present for months. Treatment differs: tendinitis responds to anti-inflammatories and relative rest, while tendinosis needs progressive loading with eccentric exercises to stimulate collagen remodeling.
What shoes should I wear with Achilles tendinitis?
During recovery, choose shoes with a 10-12 mm drop to reduce tension on the tendon. Avoid minimalist or zero-drop shoes. Models with good cushioning such as the Hoka Clifton, Brooks Ghost or ASICS Gel-Nimbus are solid options. Temporary heel lifts inside the shoe can also help.
Do eccentric exercises hurt when you do them?
It is normal to feel mild discomfort during eccentrics, especially in the first few weeks. The Alfredson protocol accepts moderate pain (up to 4-5 out of 10) during execution. However, the pain should not be severe and should decrease gradually over the weeks. If it increases session after session, reduce the load or consult a professional.
Does ice help with Achilles tendinitis?
Ice can relieve pain in the acute phase (first 2-3 weeks), applied for 10-15 minutes after activity. However, in chronic tendinopathies there is no active inflammation, so ice only masks symptoms. In those cases, progressive loading exercises are far more effective than cryotherapy.
When should I see a doctor for Achilles tendon pain?
Consult a professional if the pain does not improve after 3-4 weeks of exercises and load management, if you notice a visible lump or thickening, if you feel a sudden snap followed by intense pain, if the pain is bilateral, or if you have difficulty rising onto your tiptoes.
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