Since my achilles tendinopathy has recently flaired up again, I’ve been doing some more research on this condition and thought I’d share some of my findings in case they can be of benefit to others.
For the last decade, daily progressive eccentric loading has been the gold standard therapy for achilles tendinopathy: 3x15 eccentric heel drops with straight knee plus 3x15 reps with bent knee done twice daily for every day over a 12 week period. That’s 180 reps per day or 1260 reps per week!
Similar results were achieved in one study with a high volume of static stretching twice a day. However, I believe this can have deleterious effects on the functioning of the muscle tendon complex, as static stretching reduces muscle strength and makes tendons more compliant (stretchy), while a sprinter needs them to be stiff.
A recent paper, however, has shown that “heavy slow resistance” (HSR) training provides the same or even better results. The study used three different soleus and gastroc exercises (standing and seated calf raise and calf raise in a leg press machine) with weights increasing and reps decreasing (from 3x15 in the beginning to 4x8 towards the end) every couple of weeks or so. Each rep takes 6s, whith 3s used for the eccentric and 3s for the concentric phase. They only trained 3x per week (instead of 14x), which resulted in better compliance of the participants to the training protocol. After twelve weeks, the HSR group had equal or better results than the eccentric group, despite a significantly lower total training volume (405 reps per week). Both groups resumed their normal exercise routines 3 weeks into the study, so the last 9 weeks of the program took place while the subjects were engaged in sports. Anything that didn’t cause more than mild pain right after or the day following exercise was allowed.
Training only three times per week makes sense to me, as intense eccentric loading of tendons results in net collagen loss for the first 36-48 hours, after which there is net collagen synthesis until about 72h post exercise. This also suggests to me that people who are prone to achilles problems should ideally only subject their achilles tendons to intense loading once every 72h.
Others have researched optimal training protocols to strengthen/stiffen/thicken the achilles tendon. A protocol involving 5x4 near-maximal 3s isometric contractions of the calf muscles 4x per week (i.e. 80 reps per week) was found to be most effective. Longer or shorter (including plyometric) loading was less effective. Only the duration, type (isometric and plyometric) and intensity (moderate or high) of the contractions were modified to find the optimal protocol, so whether the frequency and volume of training they used is ideal remains to be seen. I would have gone for fewer sessions per week, due to the reasons described above.
Another paper looked at how long it takes for structural changes to occur in the achilles tendon in response to training. Significant changes were seen after two months. It only took one month to lose all the gains made in 3 months of achilles tendon strengthening, which suggests to me that athletes with achilles issues should train them all year round.
Interestingly, a study conducted on soccer players showed that eccentric exercise resulted in increased collagen synthesis in diseased but not in healthy tendons. This suggests to me that the tendon strengthening effect of purely eccentric contractions may plateau once the tendon is healed. Isometric loading, on the other hand, results in strengthening and thickening of healthy tendons, which may make it more useful as an ongoing preventative exercise.
To ensure I get the best of all worlds, I am thus now using a combination of eccentric, HSR and isometric exercises 3x a week, with a total volume of about 300 reps per week (120 eccentric reps, 120 HSR reps and 60 isometric reps). I do these exercises immediately after sprint training or at least 48h after and 48h before sprint training to avoid a state of continuing net collagen loss.
On a positive note, my plantar fasciitis has improved to a point were it is not affecting my training anymore. I get some pressure discomfort in my heel which starts a few hours after a sprint session, but am perfectly fine again the next day.
Some references:
Heavy Slow Resistance Versus Eccentric Training as Treatment for Achilles Tendinopathy: A Randomized Controlled Trial.
Beyer R, Kongsgaard M, Hougs Kjær B, Øhlenschlæger T, Kjær M, Magnusson SP.
Am J Sports Med. 2015 Jul;43(7):1704-11. doi: 10.1177/0363546515584760. Epub 2015 May 27.
Human Achilles tendon plasticity in response to cyclic strain: effect of rate and duration.
Bohm S1, Mersmann F1, Tettke M2, Kraft M2, Arampatzis A3.
Eccentric rehabilitation exercise increases peritendinous type I collagen synthesis in humans with Achilles tendinosis.
Langberg H1, Ellingsgaard H, Madsen T, Jansson J, Magnusson SP, Aagaard P, Kjaer M.