Every autumn I get the same message. A runner adds mileage for a spring goal, feels a "grumble" at the back of the heel, ignores it for two weeks, and then can't push off the ground without wincing. By the time they write to me, the tendon is stiff first thing in the morning, warm during the run, and sore again by evening.
That pattern is Achilles tendinopathy (what most people still call tendinitis). And the frustrating truth is that resting it does very little. Tendons need load to remodel. The trick is giving them the right kind of load, in the right order, for long enough.
This is the 12-week Achilles tendinitis rehab plan I actually walk my runners through. I've used a version of this on myself between ultra blocks, on my callanetics students, and on friends who kept trying to stretch their way out of it. The plan draws heavily on what the research calls heavy slow resistance and eccentric loading, but the real work is patience and consistency.
Before you start: the two things you need to accept
1. Tendons are slow. Muscle recovers in weeks; a tendon recovers in months. The 12 weeks below is a floor, not a ceiling. If you've had symptoms for six months, expect closer to four or five months of structured loading.
2. Some pain during exercise is allowed. This is the part that surprises people. Loading a cranky tendon at pain level zero is often not enough stimulus to change it. We use a simple monitoring rule.
The 0–4 pain-monitoring rule
On a 0–10 scale:
- 0–2 during the exercise: green light, continue as planned.
- 3–4 during the exercise: still acceptable, do not push higher.
- 5 or above: back off, reduce load or reps.
- Morning after check: stiffness should settle within 30 minutes of moving. If it's worse than the previous morning for two days running, you've done too much.
I write this on a sticky note for every runner. It's the single most useful tool in the whole plan.
Which Achilles problem do you actually have?
Two locations, two slightly different plans:
- Mid-portion tendinopathy: pain 2–6 cm above the heel bone. Responds well to full-range calf work.
- Insertional tendinopathy: pain right at the heel bone attachment. Does not like being stretched into deep dorsiflexion in the early phases. We keep the heel level with the toes or slightly above — no dropping off a step.
If you're not sure which one you have, work from a flat surface for the first four weeks. It's the safer default.
For the broader picture on how tendon rehab differs from muscle rehab, I've written about it in my patellar tendinopathy protocol — the phase structure is very similar.
Phase 1 (Weeks 1–2): Isometrics to calm the tendon
Isometrics are pushes and holds without movement. They reduce tendon pain quickly and let you start loading even when the tendon is grumpy.
The exercise: Double-leg calf raise hold on flat ground. Rise up onto the balls of your feet, hold at the top.
- Sets/reps: 5 holds × 45 seconds
- Rest: 2 minutes between holds
- Frequency: daily, or twice daily if you have time
- Load: bodyweight is usually enough; add a backpack if 45 seconds feels easy
If double-leg is pain-free, progress to single-leg holds by day 4 or 5. Keep the tempo boring — no bouncing, no cheating with the other foot.
What else to do during these two weeks:
- Reduce running volume by 60–70%. I rarely tell people to stop completely unless the pain is above 5/10 during a normal walk.
- Walk daily.
- If you sit at a desk, get up every 45 minutes and do 10 slow calf raises.
Phase 2 (Weeks 3–6): Heavy slow resistance
This is where the tendon starts to remodel. Heavy slow resistance (HSR) means genuinely heavy loads moved slowly through range. Research on Achilles tendinopathy shows HSR performs as well as classic eccentric-only protocols, and most runners tolerate it better because it's only three sessions a week instead of twice-daily eccentrics.
The exercise: Single-leg calf raise, either standing (targets gastrocnemius) or seated (targets soleus). I ask most runners to do both — one variation each session, alternating.
- Tempo: 3 seconds up, 1 second pause at top, 3 seconds down. Six seconds per rep.
- Sets/reps: Week 3 — 4 sets × 15 reps. Week 4 — 4 × 12. Week 5 — 4 × 10. Week 6 — 4 × 8.
- Load: heavy enough that the last two reps are genuinely hard. Add a dumbbell in hand, a loaded backpack, or use a Smith machine.
- Frequency: 3 sessions per week, at least 48 hours between sessions.
- Pain rule: 0–4 during, settling within 30 minutes after.
Range of motion:
- Mid-portion Achilles: full range, dropping the heel below the step.
- Insertional Achilles: flat ground only until week 6, then gradually add depth.
You can keep running through this phase. Easy pace only, flat routes, every other day. If the tendon is warm and stiff for more than an hour after a run, that run was too long.
Phase 3 (Weeks 7–9): Adding energy storage
Now the tendon needs to learn how to store and release elastic energy again. Running is basically hundreds of little bounces — we build up to that gradually.
Session A (2× per week): keep the heavy work
- Single-leg calf raise, 4 × 6–8, heavy, same 3-1-3 tempo.
Session B (2× per week): add faster loading
- Week 7: Sub-maximal hops in place, both feet. 4 × 20 hops, easy height.
- Week 8: Single-leg hops in place. 4 × 15 per leg.
- Week 9: Single-leg hops forward and back over a line. 4 × 15.
Space these sessions out. If a hop session leaves the tendon sore for more than a day, drop back to the previous week's version.
Running during Phase 3: Slowly increase easy mileage. Add one session with short strides — 6 × 20 seconds at 5K pace on a flat surface, with full recovery. This is where I lost patience myself once between race blocks and paid for it with another six weeks of rehab. Don't sprint before your tendon is ready.
Phase 4 (Weeks 10–12): Return to running properly
By now the tendon should tolerate:
- 15 single-leg calf raises with heavy load, 3–1–3 tempo, no pain above 3/10
- Single-leg hopping for 30 seconds without symptom flare
- Easy running most days without next-morning stiffness beyond 20 minutes
Return-to-run progression:
- Reintroduce hills gradually. Uphill first (loads the tendon less aggressively than downhill).
- Add one session per week at moderate intensity. Keep the others easy.
- Any speedwork on a track: alternate weeks, not consecutive.
- Long runs: build by no more than 10% per week.
The strength work does not stop. I ask my runners to keep two heavy calf sessions per week for another 3–6 months after finishing the protocol. This is non-negotiable — the moment they drop it, symptoms often creep back within a season.
I wrote more about how this looks for calf muscle injuries (which are cousins of Achilles issues) in my calf strain return-to-running piece — the transition phase is very similar.
Daily support during rehab
A few practical things I ask runners to do outside of the loading sessions.
Warm up before every strength session. Five minutes of easy walking or an easy stationary bike. Cold tendons don't like heavy loads.
Mind what you wear during the day. For insertional cases especially, a small heel lift (5–10 mm) in your regular shoes for the first 4–6 weeks reduces load on the attachment. Remove it once symptoms have settled.
Support the calf on long days. Runners doing this rehab often also work long shifts, travel, or teach classes on their feet (I do all three). A snug 20–30 mmHg graduated compression around the calf reduces the muscle fatigue that otherwise feeds back into the tendon. I'll wear HYKLE Compression Socks on long teaching days, on flights to races, and on the drive home from trail runs — not as a treatment for the tendon itself, but to keep the calf less thrashed so the loading sessions land on fresh tissue rather than junk-tired tissue.
Sleep and protein. Tendons remodel with collagen synthesis, and collagen synthesis needs raw materials. Don't undereat during a rehab block.
What derails Achilles rehab (from watching a lot of runners)
- Stretching hard on a sore tendon. Aggressive calf stretches compress the tendon at the heel bone. It feels productive; it isn't. Skip it, especially for insertional cases.
- Adding hills too early. Uphill running loads the Achilles more than flats. Save it for Phase 4.
- Skipping the heavy phase. Bands and bodyweight are not enough for a chronic tendon. It needs weight.
- Stopping when it feels better. Symptoms improve well before the tendon has fully remodelled. Finish the 12 weeks even if you feel great by week 6.
- Chasing every new modality. Shockwave, PRP, massage guns, ice baths — none of these replace loading. Some can complement it, none can substitute for it.
A quick note on when to see someone in person
Most Achilles tendinopathy is manageable at home with the plan above. But get a proper assessment if you have:
- Sudden sharp pain with a "kick in the back of the leg" sensation (possible partial tear).
- A palpable gap in the tendon or inability to push off the foot at all.
- Pain that isn't improving after 6 weeks of consistent loading.
- Any numbness, tingling, or pain that radiates up the leg.
For guidance on the more serious end of the spectrum, I've covered that in Achilles rupture rehab and return to sport.
The summary
Achilles tendinopathy responds to load, not rest. Two weeks of isometric holds to settle the tendon. Four weeks of heavy, slow single-leg calf work to remodel it. Three weeks to reintroduce bouncing and elastic loading. Three weeks to rebuild running properly. Twelve weeks minimum, followed by maintenance strength that never really stops.
The runners who get better and stay better are the ones who accept that timeline, respect the 0–4 pain rule, and don't skip the heavy phase because bodyweight felt "good enough." Boring, patient work beats every clever protocol I've ever seen.