Nearly half the runners who do their heel drops every single day for 12 weeks still hurt at the end of it. That’s not a compliance problem. It’s a known limit of the protocol itself, and studies have measured this for over a decade.
If you’ve been grinding through three sets of fifteen, twice a day, with no change in your Achilles or knee tendon pain, you’re not broken and you’re not doing it wrong. You may just be using the wrong loading plan for your tendon.
The Eccentric Heel Drops Protocol: Where “Do Your Reps” Advice Came From
Nearly every physio handout traces back to one small study. In 1998, a doctor named Alfredson tested a heavy eccentric calf program on 15 fit patients with long-term Achilles pain. The plan: straight-knee and bent-knee heel drops, 3 sets of 15, twice a day, 7 days a week, for 12 weeks.
The results looked amazing. Every patient was satisfied, and all of them got back to full activity. That one small trial became the go-to plan for every Achilles or knee tendon injury handed out since.
Here’s the catch. Fifteen people. All fit. All eager volunteers. That’s not who walks into a clinic today.
The 45% Problem: How Many Runners Actually Fail on Eccentric-Only Loading
A 2013 review in the journal Sports Medicine pooled the research on eccentric loading. It found the real failure rate could run as high as 45%. Translation: almost one in two patients who do the protocol exactly right still won’t get better.
It gets worse outside the lab. A 2007 study gave the same 12-week eccentric plan to 34 regular patients, not trained athletes, all with Achilles tendon pain. 44% saw no change at all.
The long-term picture doesn’t look better either. A 5-year study followed 58 tendons that had finished the Alfredson plan. Pain and function scores did improve. But only 39.7% of patients were fully pain-free five years later. Nearly half, 48.3%, had tried some other treatment along the way.
Eccentric loading works. It just doesn’t work for everyone. Pretending otherwise wastes months.
Knee (Patellar) Tendon Pain Is a Different Fight
Blog posts often lump Achilles and knee tendon pain together. The evidence says they don’t deserve the same fix.
A 2024 study combined data from seven separate trials, screened from over 1,400 records. Translation: it’s a big pooled comparison of past research, not just one study. Among the loading methods compared, eccentric-only training came out worst for long-term knee function. Heavy slow resistance (HSR) training gave the more lasting gains.
An earlier 2009 trial backs this up. It compared a steroid shot, eccentric decline squats, and HSR for knee tendon pain. All three groups got better. But the eccentric squat group felt a lot more pain during training than the HSR group did.
| Protocol | Target tendon | Sets x reps | Frequency | Duration | Load progression |
|---|---|---|---|---|---|
| Alfredson (eccentric-only) | Achilles | 3x15 | 2x/day, 7 days/wk | 12 weeks | Fixed bodyweight, add weight when pain-free |
| Silbernagel (combined) | Achilles | 3x15 | 1x/day | 12 weeks | Eccentric + concentric, progresses to plyometrics |
| Heavy Slow Resistance (HSR) | Patellar / Achilles | 3-4 sets | 3x/week | 12 weeks | 15RM down to 6RM over the block |
The knee doesn’t heal like the ankle does. Same load, different tendon, different result.
Combined Loading and HSR: What to Try Next
For Achilles tendon pain, a 2021 trial tested two plans head-to-head. One was Alfredson’s eccentric-only program. The other was Silbernagel’s combined plan, mixing eccentric (lengthening) and concentric (shortening) moves. Both groups improved by almost the same amount: +28.7 points for Alfredson, +23.4 for Silbernagel, on a 0-100 pain-and-function scale. That gap is too small to matter (p=.656).
Neither plan wins outright. The real choice comes down to what your tendon can handle and what you’ll actually stick with. Even how well patients stuck with each plan came out almost the same, 74.1% versus 77.3%.
For knee tendon pain, HSR has clear, repeatable numbers. Leg press, squat, or hack squat. Both directions of the lift, not just the lowering. 3 to 4 sets, 3 times a week, for 12 weeks. The weight starts moderate and climbs heavier as reps drop. A 2026 review across athlete studies found HSR gave pain relief similar to eccentric training, plus better gains in tendon stiffness and size.
A 2024 clinical guideline for Achilles tendon pain now ranks eccentric loading and HSR as equal first choices. Eccentrics no longer come first by default. That’s a real shift after a decade of “just do your heel drops.”
Fitting three heavy squat sessions into a running week takes real planning. That’s the same puzzle covered in how to combine strength and endurance training without one wrecking the other.
Insertional vs Mid-Tendon Achilles Pain: Why the Same Heel Drop Can Backfire
One detail rarely makes it into articles for runners: where your pain sits on the tendon changes which technique is correct.
Insertional pain sits right where the tendon meets the heel bone. That kind of pain responds badly to the classic heel drop off the edge of a step. Bending the ankle all the way down squeezes the tendon against the bone, right at the sore spot.
Studies using the full-range, off-a-step version reported only 28-33% good results for insertional pain. Studies that kept the drop on flat ground, with the ankle level, not bent past neutral, saw 67% good results.
Same exercise name. Same intention. Opposite result depending on where the pain actually is.
The Week 6-8 Decision Point: When to Switch Instead of Repeat
Think of a stalled tendon plan like a training block that isn’t building fitness. You wouldn’t repeat the same week four times, hoping week nine looks different.
Picture a guitar string gone flat. Plucking it harder, and more often, doesn’t fix the tune. Turning the peg, adding real tension with a heavier, slower load, does. That’s the gap between doing more eccentric reps and switching to HSR.
Take a runner I’ll call Marco. He’s 34, training for his second marathon, with pain in the middle of his Achilles. He started the standard Alfredson plan, heel drops twice a day, and logged his morning pain every day. At week 6, his pain score was stuck at a 5 or 6 out of 10. He kept going out of habit, not evidence.
At week 8, still stuck, his physio switched him to a combined plan: eccentric and concentric calf raises, done heavy, three times a week. By week 14 his pain sat at a 1. He ran his marathon six weeks later.
Switching got him there, not more of the same.
This is the same logic already built into returning to run after a bone stress injury: don’t just push volume and hope, check the trend against a clear checkpoint. It’s also why runners who track ACWR ramp caps to avoid reinjury already think in limits, not just effort.
Tracking a Tendon Plan So a Stall Doesn’t Slip By
Most rehab exercises get handed out as a one-time PDF and never looked at again. Nobody’s checking whether week 6 looks better than week 1.
AthleteOS logs heel-drop, HSR, and Silbernagel-style sessions as their own tendon-loading type, apart from your running miles. That way rehab work doesn’t get buried in your training log, or counted twice against running load. It also tracks your pain trend against the week you started the plan. That’s the same trend-over-noise idea AthleteOS already uses for reading HRV signal instead of daily noise.
When 6 to 8 weeks pass with no real movement in that trend, AthleteOS flags it. It then shows the next evidence-backed step: HSR for knee tendon pain, combined loading for the Achilles. You can log your tendon-loading sessions and start tracking the trend instead of guessing at week 12 whether it worked.
Eccentric heel drops helped a lot of people. They just weren’t built to help everyone, and the data has known that for over a decade.