The purpose of this post is to provide an overview of the evidence in regards to Achilles Tendinopathy (AT). This is by no means an all encompassing post about every minute detail that is AT, however, it is an attempt to provide an accompanying summary to our previous podcast on the topic (Found Here)
Here are the things we will cover…
The Anatomy and Physiology of the Achilles Tendon
The Healthy Tendon
The Achilles’ tendon is the thickest and strongest tendon in the body. It is able to withstand repetitive loads up to 12x body weight with activities such as running and jumping.1
It spans 3 different joints and produces knee flexion, tibiotalar flexion, and subtalar inversion.
The tendon is unique in that it doesn’t have a synovial sheath as other tendons do. It is instead surrounded by a paratenon sheath (a flexible connective tendon that allows tendon gliding).1 It is innervated by nearby nerves that stem from the Sural N.1
As far as vascularity goes, there isn’t much within the tendon. However, the paratenon is highly vascular. Interestingly, one of the more hypovascular portions of the tendon is at the mid-portion, which makes sense based on the location of mid-portion AT.1
The Injured Tendon
Initially, when a tendon is injured, it will begin a healing process in which various inflammatory mediators will influx into the area and Type III Collagen will be laid down quickly as a “patch.” This leads to a weaker tendon initially due to the unorganized orientation of the Type III Collagen. An effective healing process will eventually lead to the Type III collagen being replaced by Type I collagen restoring the tendon’s original function.
When the tendon is in a “state of disrepair” due to various factors (one being lack of adequate recovery) you won’t see a gradual transition from type III to type I collagen. Instead, there will be an accumulation of type III collagen along with neovascularization and neoinnervation resulting in a weaker and more painful tendon.2 It is now understood that chronic tendinopathy is a result of failed healing as opposed to an inflammatory condition. This process results in degeneration of the tendon and the aforementioned neural ingrowth and neovascularization. This “failed healing process” creates a vicious cycle in regards to tendon strength, pain, and tolerance to activity.3
What Type Of Achilles Tendinopathy Are We Dealing With?
There are generally two types of AT. One being Mid-portion AT and one being Insertional AT.
Mid-portion : Occurring 2-6 cm proximal to the insertion at the calcaneus.4,5
Insertional: Occurring within 2 cm of the Calcaneus-Achilles junction. 4,5
Mid-portion AT is going to be seen in the more active population while Insertional AT is seen more in the less active, overweight population.
Mid-portion AT is a result of repetitive loading with inadequate healing or recovery. Insertional AT is more of a compression issue at the tendon insertion in which the the posterior edge of the calcaneus impinges against the AT and surrounding structures including the bursa and paratenon. (This difference in physiology of the injury leads to one of the big differences in the management of these two forms of AT.)4
How Common Is Achilles Tendinopathy and Who Is At Risk?
You will typically see AT with athletes in sports that require repetitive loading of the gastroc/soleus/achilles complex. Those whose sports require repetitive running and jumping are more at risk. In general, it has been shown that LE Tendinopathy (includes all tendinopathies) has an occurs at a rate of 10.52 per 1000 persons per year, which exceeds OA.6
There are many risk factors (RF) that may predispose someone to experiencing AT. Below are a list of extrinsic and intrinsic factors. This is by no means an exhaustive list and you will find varying lists depending on what you are reading in the literature.8
Extrinsic (factors that are external to the body that may increase load on the tendon)8
Intrinsic (internal factors that may increase loading or impair healing of the tendon)8
Evaluation (History and Exam)
I won’t get into our standard process of taking a history, but instead will focus on aspects specifically related to AT.
The main goal is to get an insight into activity level changes particularly in an athletic population. Due to training errors being a very common and modifiable risk factor, it is important to understand the patient’s activity history. Keep in mind that a change in activity/training can be a result of one factor such as increasing mileage abruptly in the case of a long distance runner OR it can be due to a combination of factors that may present in a biopsychosocial perspective (ie. Lack of sleep + stress + change in training).
Beyond that, we need to know what the patient is attempting to return to, how fast, and at what intensity. Your management may change if you are working with an in-season athlete vs. someone in their offseason vs. someone without a particular time frame for return (ie. The weekend warrior).
The earlier you can see these patients the better (as is typical with most injuries). Initial symptoms might appear as soreness/stiffness at the beginning of an activity that then undergoes a “warm-up” phenomenon in which the pain resides as the activity progresses. Eventually, you may start to see pain in the morning that worsens as the day goes on, stiffness, swelling, crepitus, pain with palpation, and possibly hypertrophy of the tendon.1
“On the table testing” includes special tests, palpation, and ROM/strength testing.
As with most pathologies, there are a ton of special tests out there. Unfortunately, these tests haven’t been proven to be very helpful. However, according to the Revision of the Clinical Practice Guidelines for Achilles Pain, Stiffness, and Muscle Deficits for Mid-portion AT, the Royal London Hospital Test and the Arc Sign can be useful.6
Having said that, we mainly rely on symptom report and location of pain. Assessing strength and ROM will help in regards to treatment strategy.
“Off the table testing” consists of functional testing including single leg calf raises, hopping (both double leg and single leg), and visualization of the painful activity if able including walking, stair descent, jumping, or running.
Because it is important to rule out, before ruling in keeping in mind possible differential diagnoses can be helpful.
Treatment: Comparing Heavy Slow Resistance vs. Eccentrics vs. Isometrics
Eccentrics have been the mainstream treatment for AT. The most widely used protocol initially described by Alfredson et al. is listed below.7 The mechanism behind improvements noted with eccentric training is not quite clear. It has been proposed that eccentrics can create structural adaptations at the tendon, improve tendon length, reduce neuro-vascular ingrowth, create neuro-chemical and neuro-muscular alterations, and alter fluid dynamics.11
Now, not all of these proposed changes have been clearly supported in the literature. For example, tendon changes related to a reversal of the degenerative process is not needed for and does not guarantee success or failure of treatment. However, knowing and learning about the possible results of eccentric exercises may help your understanding as well as your patient’s understanding of the purpose of this treatment protocol.11
Alfredson’s Potocol for Eccentric Exercises with AT3,7
Exercises: Unilateral heel raise off a step with a straight knee and a bent knee.
Frequency: 2x/day; 7 days/week
Volume: 3x15 each exercises
Tempo: 3 second eccentric
Rest: 2 min b/w sets; 5 min b/w exercises
Tendon Load Time: 63 min/week
Total Time Commitment: 308 min/week
Note: Load is increased gradually using a backpack as the patient tolerates.
Heavy Slow Resistance (HSR)3
HSR is another treatment option for AT. Essentially, you are loading up exercises that address the gastroc/soleus complex. These exercises are performed at a tempo of 3030 (3 seconds down, 3 seconds up) for a total of 6 seconds per repetition. The protocol used by Beyer et al in their article comparing HSR vs Eccentrics is listed below.
In this study, it was determined that both HSR and eccentric cohorts achieved positive results in both the short- and long-term.3 They also noted a reduction in A-P thickness and neovascularization that was associated with clinical improvements. So, HSR is not more effective than eccentrics, however, it does provide another treatment option that is of similar efficacy.
Exercises: seated heel raise, standing heel raise deficit, straight leg calf raise on leg press.
Volume: 3-4 sets; 3x15 —> 3x12 —> 4x10 —> 4x8 —> 4x6 (progressed over a period of 12 weeks)
Rest: 2-3 min b/w sets; 5 min b/w exercises
Tendon Load Time: 41 min/week
Total Time Commitment: 107 min/week
Note: The repetitions noted above are intended to be maximal. For example, 3x15 refers to 3x15 RM. Load was increased and repetitions were decreased as tolerated over a 12 week period.
Isometrics are another possible treatment for AT. Previous studies have shown isometrics to be beneficial in those with patellar tendinopathy.9 That protocol included 5 sets of 45s isometrics at 70% MVC. However, in AT, isometrics did not change pain or increase motor output of the plantarflexors. There isn’t clear indication of why it is beneficial in patellar tendinopathy and not AT, however, the difference may lie in the fact that they are two distinctly different tendons in that the patellar tendon essentially has a sesamoid bone in the middle of it.9
Despite isometrics not being the most effective treatment for AT, we believe that it could still be useful in a graded exposure sense. If a patient is unable to tolerate isotonics, isometrics could be used to initiate loading in non-painful ranges. The intent would be to improve the tolerance of the tendon to loading and then eventually progress to HSR or eccentrics.
We now know that there are multiple ways to attack achilles tendinopathy. It is clear, at this point, that eccentrics or HSR are the gold-standard and should be utilized during treatment. It is really up to the patient and therapist as to which strategy you use. They both promote similar results. However, there a couple things that you may want to think about when adding these to a patient’s program.
(Other treatment strategies include dry needling and BFR. These won’t be covered here, but you can hear our thoughts about them in Ep. 1 of the podcast.)
(The interventions above focus on mid-portion AT. To apply them to Insertional AT you would decrease the ROM in that you won’t go into a deficit with heel raises to prevent impingement of the tendon on the calcaneus.)
Return To Sport After Achilles Tendinopathy
The final stage of rehab and likely the most important when it comes to active individuals and athletes is Return to Sport.
In order to properly progress a patient back to their goal activity, it is imperative to understand the demands of the sport including cumulative loads, peak loads, and rate of loading. This will vary based on the activity, but, in general, running and jumping activities will demand the highest load tolerance.
For example, in the sense of a runner, you can control loads based off distance, steps taken recorded via a smart watch, or based off time on feet. Beginning with a tolerable activity such as level ground walking or a walk/run program. Then progressing to higher load activities including hill running and speed work.
There are multiple papers out there that provide return to sport methodology. One that we really like is a clinical commentary by Silbernagel and Crossley.10 They provide a very structured approach detailing progression based on pain, RPE, and level of activity (light, medium, hard). It also provides sample programs for inspiration.
Hopefully you were able to pick up something from this write-up, that is, if you got this far. We do not pretend to be experts in any topic, but we enjoy putting our ideas on paper for our own sanity and, possibly, for your benefit.
References are below. Feel free to reach out with any questions or comments and if you aren’t sick of achilles tendinopathy at this point check out Episode 1 of the Athletes First Performance podcast.