Eccentric loading for Achilles tendinopathy: what the evidence says

The Achilles tendon responds to mechanical load through collagen synthesis. Eccentric load, where the muscle produces force while lengthening, applies the highest tensile stress to the tendon. This stress is the stimulus that drives collagen remodelling: disorganised, degenerated collagen is replaced by better-organised, stronger fibres.

The rate of collagen synthesis after eccentric loading peaks at 24–72 hours post-exercise. This is why twice-daily loading, rather than once, produces faster adaptation, you are applying the stimulus more frequently.

The Alfredson protocol (published 1998) is three sets of 15 eccentric calf raises, twice daily, performed to the point of pain. The key elements: straight-leg (gastrocnemius focus) and bent-leg (soleus focus) variants, performed with bodyweight initially and progressed to loaded (rucksack with added weight) as strength improves.

The evidence for the Alfredson protocol in mid-portion Achilles tendinopathy is strong. Multiple randomised controlled trials show significant pain reduction and return to activity at 12 weeks. The limitation is compliance, the protocol is painful to perform, particularly in the first 2–3 weeks, and many patients stop early.

Heavy slow resistance (HSR) uses a slow tempo, 3 seconds concentric, 3 seconds hold, 3 seconds eccentric, with progressive load, performed without the same pain demand as the Alfredson protocol. Research by Beyer et al. (2015) showed HSR produced equivalent outcomes to the Alfredson protocol at 12 months with significantly better patient satisfaction and compliance.

The practical protocol: seated calf raise and standing calf raise, 3 sets of 15, twice daily, with load progression every 2 weeks. Start with a load that challenges but does not produce pain above 3/10 during the exercise.

The Alfredson protocol is specifically for mid-portion tendinopathy. For insertional cases, the eccentric drop (heel below the step surface) compresses the tendon against the calcaneus, which is the primary aggravating mechanism for insertional presentation. The protocol for insertional cases uses a flat surface (no drop), a higher heel throughout, and avoids dorsiflexion end range.

Getting this distinction wrong and applying the mid-portion protocol to an insertional case typically flares the condition significantly.

The benchmark before return to running is a single-leg heel raise of 25 repetitions, pain-free, symmetric to the unaffected side. This is a strength test, not a time test. If this criterion is not met, the tendon is not ready to absorb the eccentric load of running.

Return is then graduated: walk-run intervals with next-morning monitoring. If pain the morning after a run is above 2/10, reduce the run volume for the next session.