Achilles Tendinopathy: Returning to Running Without Restarting the Flare

The first steps out of bed are the worst. The back of the heel is stiff and sore, it loosens as you move, and a run can feel almost normal by the second kilometre. Then the next morning tells you what the run really cost. If you have been cleared to run again after Achilles tendinopathy, this guide covers what the research says about loading the tendon while it hurts, why where it hurts matters, what calf strengthening does and does not do, and a staged walk/run progression gated by one reading: how the tendon feels the morning after.

The short version: the Achilles tolerates, and needs, progressive load. The pain-monitoring model that lets you keep running with mild pain, as long as it settles by the next morning, was tested on this tendon first. Heavy, slow calf strengthening is the engine of adaptation and continues alongside the running. Pain at the heel bone (insertional) is handled more conservatively than pain in the tendon itself (midportion), because the evidence for training through it is thinner. Hills, speed and a quicker cadence come back last. And a surgically repaired rupture is a different situation with a different, slower path.

Who this is for

• You have been told you have Achilles tendinopathy (midportion or insertional), and a physical therapist, physician or other qualified professional has cleared you to return to running.
• You are 18 or older and past the acute phase: you can walk briskly for 30 minutes, and the tendon is sore rather than sharply painful.
• You want to run again without the cycle of rest, return, flare, rest.

If you ruptured the tendon and had it repaired, read the section near the end: the timelines and the rules are different. If the rupture was treated without surgery, or you have had other surgery on the tendon, your care team's timeline governs, and this guide (and Rebound's program) is not written for you yet.

What the evidence says

• Continuing to run under a pain-monitoring model did no harm. In a randomized trial of people with midportion Achilles tendinopathy, one group kept running and jumping under fixed pain rules (pain up to 5 out of 10 acceptable if it settled by the next morning, nothing above 5, no week-over-week rise) while the other rested from those activities for six weeks. Both groups did the same calf exercise program. Continuing to train showed no negative effect on recovery at any follow-up (Silbernagel et al. 2007). This is the trial the pain rules in this guide come from, and it is why they are stated for the Achilles with more confidence than for any other site.
• The trial excluded insertional cases. Participants had pain in the tendon itself, 2 to 6 cm above the heel bone. People with pain at the attachment to the heel were not studied, so the "keep running with mild pain" evidence does not extend to them directly. Clinical reviews treat insertional tendinopathy as its own case, more sensitive to the position where the heel drops below the toes (Silbernagel, Hanlon and Sprague 2020).
• Heavy slow resistance matched the classic eccentric protocol, with far less time. For decades the standard was Alfredson's program: 3 sets of 15 heel drops off a step, straight-knee and bent-knee, twice a day, every day (Alfredson et al. 1998). A randomized trial then compared it with heavy slow resistance (three sessions a week of slow, heavy calf work, building toward 6 to 8 hard repetitions) and found the same improvement in pain and function at 12 weeks and one year, with higher satisfaction in the heavy slow group (Beyer et al. 2015). The shared ingredient is progressive load on the calf, not the specific exercise.
• Isometric holds relieve pain in some tendons, but the evidence is mixed. A single session of heavy isometric holds reduced patellar tendon pain for about 45 minutes in one study (Rio et al. 2015); results in the Achilles have been less consistent. Relief after a hold is analgesia, not adaptation, and should not be read as readiness for more running.
• Keep insertional work in a limited range. A 2025 expert consensus on exercise for Achilles tendinopathy recommends keeping calf exercises within a limited range of ankle bend for insertional cases, at least early on, because the stretched position compresses the tendon against the heel bone (BJSM 2025 exercise consensus). In practice: calf raises from the floor, not from the edge of a step.
• The soleus does the heavy lifting in running. Peak Achilles forces in running reach several times body weight, and the soleus, the deeper calf muscle that works best with the knee bent, contributes most of it. A calf program that only trains straight-knee raises misses the muscle that running leans on hardest. Bent-knee raises belong in every Achilles program.
• The usual cadence advice cuts the other way here. Shortening your stride and quickening your cadence by 5 to 10 percent lowers load on the knee, which is why it is standard advice after a knee injury. It shifts that load onto the calf and Achilles. In a one-year trial of gait retraining in novice runners, the retrained group had fewer injuries overall but more calf and Achilles complaints (Chan et al. 2018). With a sore Achilles, run with your natural stride.

The pain rules

Ask one question first after every session and every morning: is there joint, bone or tendon pain, as opposed to tired, sore calf muscles? Muscle soreness the day after calf work is normal and does not count. Then rate the tendon pain 0 to 10, and note where: the injured Achilles, the other one, or somewhere else entirely.

The rules, judged at the Achilles you named and against how it felt before the run:

• 0 to 2: nothing to do. Two clean runs at a stage, with the mornings after answered, and you move up. One step up a week at most.
• 3 to 5 at the injured Achilles: acceptable as a dose, provided the next morning is back at or below where that run started. Settled, you continue. Raised the next morning, you hold the stage or step back one.
• 3 to 5 anywhere else, at the other Achilles, the knee, the shin or the foot: that is a new symptom with no known pattern behind it. Step back right away, and settle at 2 or less.
• Above 5: step back at once, whatever the morning says.
• A 6 or more before a run or the next morning, or pain that comes back raised on the run after a step back: stop the plan and talk to a professional.

One rule is narrower than the rest, on purpose. For midportion pain that has stayed mild (3 to 5) and settled by morning, the run can still count toward earning the next stage, because that is the population Silbernagel studied. For insertional pain, or if you are not sure which you have, the same reading holds the stage rather than earning it, and you step up on clean runs only. It is a small difference in a single rule, and it is the honest reading of where the evidence stops.

On morning stiffness: stiff first steps that loosen within a few minutes are typical of this tendon and are not a pain reading on their own. Rate the pain, not the stiffness. Pain that is higher the morning after than before the run is the signal that yesterday's dose was too much.

The walk/run progression

Every session begins and ends with a 5-minute brisk walk. Easy pace, flat ground, never on consecutive days. Repeat a stage until the morning-after response is boring, and never skip one because a run felt good.

Sequence the hazards last. Uphill running, speed work, plyometrics and a deliberately quicker cadence are the highest Achilles loads and return only after the progression is complete and the morning readings have been quiet for weeks.

Between runs: calf strengthening

Two or three times a week, on non-running days:

• Straight-knee calf raises, for the gastrocnemius. Midportion pain: from the edge of a step, letting the heel drop below the toes. Insertional pain, or unsure: from the floor, heel never below the toes.
• Bent-knee calf raises, for the soleus. Same range rule.
• Single-leg balance and hip work (glute bridges), because the whole chain decides how the tendon lands.

Start with both legs if a single-leg raise is too much, progress to single leg, then add load (a backpack, a dumbbell) and slow the tempo. The research protocols are heavy for a reason; the goal over months is more weight, moved slowly, not more repetitions.

A word on what Rebound does here. Its strength sessions schedule these exercises as fixed sets and repetitions, keep insertional and unsure cases at floor range, and bias the soleus with bent-knee work. That is honest calf strengthening. It is not the heavy slow resistance protocol from the Beyer trial, which progresses external load week by week to a hard 6 to 8 repetitions, and no fixed-set app session should claim to be. If you have a physical therapist, their loading plan outranks the app's.

After a repaired rupture

A rupture that was surgically repaired is a different tissue state, not a worse tendinopathy. The repaired tendon remodels for months, and return to running is led by the surgeon, with function rather than the calendar deciding. Published protocols place the first running at roughly 16 to 24 weeks after surgery.

A 2025 expert consensus on return to running after Achilles rupture proposed a set of functional readiness criteria: no pain in daily life or in rehabilitation, walking without a limp, walking on tiptoe, ten single-leg heel rises, single-leg balance, and the person's own confidence to run (expert consensus, 2025). The authors are clear that the items still await prospective validation. Read them as a conservative checklist to discuss with your care team, not a test that certifies readiness.

Rebound's path for a repaired rupture asks for at least 16 weeks since surgery (the earliest possible start, never a sign of readiness), your surgeon's or physical therapist's explicit clearance to begin running, and your confirmation of each readiness item, before a plan is built. Once it is, the stricter pain rules apply throughout: 3 to 5 steps back, settle at 2 or less, no earned steps on mild pain. Calf work stays at floor range.

Stop and talk to a clinician if

• A sudden sharp pain, snap or pop at the back of the heel, during a run or a calf exercise, or being unable to push off or rise onto your toes
• Swelling that is new or growing, rather than the tendon's familiar thickening
• The ankle gives way, or you cannot bear weight normally
• Pain at night or at true rest
• Pain that keeps building run after run despite stepping back
• No real improvement after 12 weeks of consistent, structured loading

How Rebound fits in

Rebound's Achilles path asks which Achilles, and whether the pain is midportion, insertional or unsure, and the rules and the strength work follow the answer. Before each run you answer whether anything hurts, how much and where; the next morning, the same. The pain rules above are fixed and deterministic: the plan holds, steps back or pauses the way a careful coach would, never advances you on a morning you did not answer, and never suggests a quicker cadence. A repaired rupture has its own door, behind the 16-week floor, the clinician's clearance and the readiness checklist.

Rebound is a fitness product, not medical care. This article is general education, not medical advice, and nothing here is a diagnosis. If your pain pattern does not match this description, or something feels wrong, talk to a physical therapist or sports medicine clinician.

Sources

Links go to the PubMed record for each paper, or the publisher's DOI where listed.

• Silbernagel KG et al. 2007, AJSM: continued sports activity, using a pain-monitoring model, during rehabilitation in patients with Achilles tendinopathy (randomized trial; midportion cases only). PubMed
• Silbernagel KG, Hanlon S, Sprague A. 2020, J Athl Train: current clinical concepts, conservative management of Achilles tendinopathy. DOI
• Beyer R et al. 2015, AJSM: heavy slow resistance versus eccentric training as treatment for Achilles tendinopathy (randomized trial). PDF
• Alfredson H et al. 1998, AJSM: heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. PubMed
• Rio E et al. 2015, BJSM: isometric exercise induces analgesia and reduces inhibition in patellar tendinopathy. PubMed
• BJSM 2025: international consensus on exercise therapy for Achilles tendinopathy. DOI
• Expert consensus 2025: return to running after Achilles tendon rupture. PubMed
• Chan ZYS et al. 2018, AJSM: gait retraining for the reduction of injury occurrence in novice distance runners, 1-year follow-up of a randomized controlled trial. ResearchGate