If you’ve ever felt that deep, nagging ache in the back of your heel, the one that’s stiff and sore for the first few steps out of bed and then warms up once you get going, you’ve met tendinopathy. And if your instinct was to stop, rest it, and wait for it to heal, I understand why. It’s also the single most common mistake I see athletes make.
I have worked through tendinopathy myself and completely resting it, will do NOTHING to heal a tendon. Careful and progressive loading is what the tendon actually needs to rebuild. Here’s why, and how to think about it.
Rest Feels Right. It Also Doesn’t Work.
A muscle strain and a cranky tendon are different problems. When you rest a tendon completely, it doesn’t come back stronger. It gets less capable. The tendon loses the very capacity you need to run pain-free, so when you return to training, the same loads that irritated it before now land on a weaker structure. You feel better for two weeks off, then you’re right back where you started within days of running again. Sound familiar?
Tendons are living tissue that adapts to the demands you place on them. Take the demand away entirely and they detune. The fix for an under-capacity tendon isn’t less load. It’s the right load, applied in the right order.
How Load Actually Repairs a Tendon
Tendons respond to mechanical loading by remodeling. When you load a tendon in a controlled, progressive way, you stimulate the cells inside it to reorganize and build, gradually increasing the tendon’s stiffness and its ability to store and return energy. Over weeks and months, that’s what raises your pain threshold and your performance ceiling at the same time.
The keyword is progressive. You’re not trying to blast the tendon or push through sharp pain. You’re giving it a reason to adapt, then a slightly bigger reason, then a bigger one, staying just ahead of where it is without overwhelming it. Think of it the way you’d build mileage: you don’t jump from 20 to 50 miles a week, and you don’t fix a tendon by going from zero to plyometrics.
The Loading Ladder
Rehab research generally moves a tendon through stages, from least demanding to most. You climb the ladder as pain and capacity allow.
Rung one: isometrics. These are holds. You contract the muscle and load the tendon without any movement at the joint, like rising onto your toes and holding, or pushing against something that doesn’t move. This is the smart on-ramp when a tendon is irritable, because you can load it meaningfully without the stretch-and-shorten cycle that tends to aggravate it early on. You get to start building capacity right away instead of waiting.
Rung two: heavy slow resistance. Once you tolerate holds, you progress to slow, heavy, full-range strength work, calf raises through their full range with real load, moving slowly up and down. This is where a lot of the meaningful tendon remodeling happens, and the evidence base here is strong.
Rung three: energy storage and release. The final rungs reintroduce speed and spring, hops, bounding, and eventually the running-specific loads your sport demands. This is where the tendon relearns to act like the spring it’s supposed to be. You don’t get here first. You earn it.
A Straight Answer About Isometrics
Isometrics got popular a few years ago on the back of a widely shared finding: a 2015 study of athletes with patellar (knee) tendon pain found that isometric holds produced a large, immediate drop in pain.1 That’s a real result, and it’s why you’ll hear coaches talk about isometrics as a pain-relief tool you can use even in-season.
But here’s the honest part, and it matters because so many of you are dealing with the Achilles specifically. When researchers tested that same immediate pain-relief effect in people with mid-portion Achilles tendinopathy, they didn’t find it. In a trial of 91 patients, isometric calf holds produced no meaningful immediate pain relief compared to other approaches, or even to rest.2 The dramatic painkiller effect that made isometrics famous shows up more reliably in the patellar tendon than in the Achilles.
So don’t do your isometric holds expecting the ache to vanish on the spot. That’s not why they’re on the ladder. They’re there because they let you start loading a grumpy tendon safely and begin rebuilding capacity from day one. The pain relief, when it comes, comes from the weeks of progressive loading that follow, not from a magic hold.
That distinction is the whole point of doing this honestly. Isometrics are the on-ramp, not the destination.
Let the Tendon Tell You Where You Are
The reason I don’t hand athletes a rigid day-by-day tendon protocol is that tendons don’t read calendars. They respond to load, and the tendon itself gives you the feedback you need if you’re paying attention. Two rules I coach:
Use a pain scale, and stay in the acceptable range. Some discomfort during loading is okay for a tendon; sharp or climbing pain is not. A common guideline is to keep pain at a low, tolerable level during and right after the work, not pushing into the range where you’re wincing.
Judge by the next morning. The real test isn’t how it feels during the exercise, it’s how the tendon responds over the next 24 hours. If it’s calmer or the same the next morning, the load was appropriate. If it’s noticeably more irritated and stiff, you asked for too much, and you scale back the next session. That morning check-in is your traffic light: green to progress, yellow to hold steady, red to back off.
This is exactly how I’m managing my own Achilles. I’ve been using an AlterG anti-gravity treadmill to control the load precisely, dialing body weight up as the tendon earns it, and reading that next-morning response to decide each day’s dose rather than forcing a predetermined plan. Progressive, responsive, patient. That’s the game.
The Bottom Line
Your sore tendon isn’t asking you to stop. It’s asking you to load it intelligently: start with holds to get on the ramp, build through heavy slow strength, and earn your way back to speed, all while letting the tendon’s day-to-day response set your pace.
Rest might quiet the pain for a week. Load is what rebuilds the tendon. Respect the difference, climb the ladder in order, and you come back not just healed, but harder to break next time.
Dealing with a nagging Achilles or a cranky tendon and not sure how to load it? That’s exactly the kind of thing our coaching is built for. Reach out and let’s build you a plan that fits where your tendon actually is.
This article is educational and reflects current research on tendon rehabilitation; it isn’t a substitute for individualized assessment. If you have persistent or worsening tendon pain, get evaluated by a physical therapist or sports medicine professional.
Footnotes
-
Rio, E., Kidgell, D., Purdam, C., Gaida, J., Moseley, G. L., Pearce, A. J., & Cook, J. (2015). Isometric exercise induces analgesia and reduces inhibition in patellar tendinopathy. British Journal of Sports Medicine, 49(19), 1277–1283. ↩
-
van der Vlist, A. C., van Veldhoven, P. L. J., van Oosterom, R. F., Verhaar, J. A. N., & de Vos, R. J. (2020). Isometric exercises do not provide immediate pain relief in Achilles tendinopathy: A quasi-randomized clinical trial. Scandinavian Journal of Medicine & Science in Sports, 30(9), 1712–1721. ↩