A stiff, sore Achilles first thing in the morning that eases as you move, then aches again after a run, is the classic presentation of Achilles tendinopathy. It is one of the most common running injuries, it responds well to the right kind of work, and almost everything you will read about how to treat it is stated with more confidence than the evidence supports.
What it usually is
Pain and stiffness in the tendon itself, most often in the mid-portion two to six centimetres above the heel, sometimes with a thickened section you can feel. It is typically worst on the first steps of the day and after sitting, warms up during activity, and returns afterwards. It builds gradually.
Two things that are not this: pain right at the heel bone where the tendon inserts is insertional tendinopathy, which behaves differently and does not tolerate the same stretching; and a sudden sharp pain with a snap or the feeling of being kicked in the calf needs urgent medical assessment, because that is how a rupture presents.
Loading works. Now the awkward part.
The standard treatment is heavy, slow loading of the calf — and the study everybody cites for it is not what it is usually described as.
Alfredson’s 1998 heavy-load eccentric protocol is routinely called a landmark randomised controlled trial. It was 15 recreational athletes in a prospective case series. There was no randomisation. The comparison group were 15 patients who had already failed conventional treatment and all went on to surgery — not an equivalent-prognosis control. All 15 in the treated group returned to running at 12 weeks, which is a genuinely encouraging result, and the authors themselves described it as a “short-term effect”.
That does not mean the protocol does not work. It means the evidence for it is far thinner than its reputation, and you should be wary of anyone who tells you there is one proven protocol.
Heavy slow resistance: not better, but much shorter
A proper randomised trial did compare the two. 58 people with chronic mid-portion Achilles tendinopathy were randomised to eccentric training or heavy slow resistance, then followed for a year.
On the outcome that matters — the VISA-A score — there was no significant difference between the groups at any point (P = 0.62). Both improved substantially and similarly, from around 55 to the high 80s over 52 weeks.
What did differ was the burden. Eccentric training took 308 minutes a week; heavy slow resistance took 107. Compliance was 78% versus 92% (P < 0.005). So the honest summary is not that one protocol is superior — it is that one takes a third of the time and people actually do it.
No loading protocol has beaten any other
A network meta-analysis pooled 29 randomised trials across 42 treatments. Its conclusions are worth reading carefully:
- Doing nothing is the worst option. “Wait-and-see is not recommended as all active treatments seemed superior at 3-month follow-up.”
- But nothing beats anything else. “There seems to be no clinically relevant difference in effectiveness between different active treatments at either 3-month or 12-month follow-up.”
- The reason they recommend starting with calf exercise is explicitly pragmatic: it “is easy to prescribe, can be of low cost and has few harms” — not that it outperformed the alternatives.
The quality caveat is significant: 22 of the 29 trials were at high risk of bias, none were at low risk, and the authors note “large uncertainty in the comparative estimates”.
Does waiting make it worse?
Less than you might fear, but do not read that as permission to ignore it.
A study of 127 people with Achilles tendinopathy grouped them by how long they had had symptoms — from two weeks to over 22 years — and found no significant differences between the groups at baseline or after 16 weeks of treatment. The authors concluded symptom duration “may not be clinically relevant for determining prognosis”. Note this was an observational cohort, mean age 47.8, not a runner-specific group.
The other half of the picture: a review of untreated control arms found that for Achilles, patellar and elbow tendinopathies, people who received no treatment did not fully resolve within 12 to 16 weeks. It does not reliably fix itself.
What to actually do
- Keep loading it, at a level it tolerates. Complete rest is the one approach the evidence positively argues against.
- Do heavy, slow calf work. Both straight-leg and bent-knee raises — bent-knee biases the soleus, which takes enormous running load and is under-prepared in most amateurs. Slow, controlled, progressively loaded.
- Pick the protocol you will actually finish. Since none has been shown superior, adherence is the deciding factor, and that argues for the shorter one.
- Expect months. The trials above ran 12 weeks to a year. This is not a two-week problem.
- Get it assessed if it is insertional, if there was a sudden onset, or if it is not responding — the loading approach differs for insertional pain.
References: Alfredson H, et al. Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. Am J Sports Med, 1998. doi:10.1177/03635465980260030301 · Beyer R, et al. Heavy Slow Resistance Versus Eccentric Training as Treatment for Achilles Tendinopathy: A Randomized Controlled Trial. Am J Sports Med, 2015. doi:10.1177/0363546515584760 · van der Vlist AC, et al. Which treatment is most effective for patients with Achilles tendinopathy? A living systematic review with network meta-analysis of 29 randomised controlled trials. Br J Sports Med, 2021. doi:10.1136/bjsports-2019-101872 · Hanlon SL, et al. Effect of Symptom Duration on Injury Severity and Recovery in Patients With Achilles Tendinopathy. Orthop J Sports Med, 2023. doi:10.1177/23259671231164956