Excerpted from his book, Injury-Free Running, Second Edition

Despite its broad width and significant length, runners injure their Achilles tendons with surprising regularity. In a recent study of 69 military cadets participating in a six-week basic training program (which included distance running), 10 of the 69 trainees suffered an Achilles tendon overuse injury (1). The prevalence of this injury is easy to understand when you consider the tremendous strain runners place on this tendon; e.g., during the push off phase of running, the Achilles tendon is exposed to a force of up to eight times body weight. This is close to the maximum strain the tendon can tolerate without rupturing. Also, when you couple the high strain forces with the fact that the Achilles tendon significantly weakens as we get older, it is easy to see why this tendon is injured so frequently.

Anatomically, the Achilles tendon represents the conjoined tendons of the gastrocnemius and soleus muscles. Approximately 5 inches above the Achilles attachment to the back of the heel, the tendons from gastrocnemius and soleus unite to form a single thick Achilles tendon (Fig. 6.1). These conjoined tendons are wrapped by a single layer of cells called the paratenon. This sheath-like envelope is rich in blood vessels necessary to nourish the tendon. The tendon itself is made primarily from two types of connective tissue known as type 1 and type 3 collagen. In a healthy Achilles tendon, 95 percent of the collagen is made from type 1 collagen, which is stronger and more flexible than type 3. It is the strong cross-links and parallel arrangement of the type 1 collagen fibers that gives the Achilles tendon its strength.

Unlike the vast majority of tendons in the body, the Achilles tendon is unique in that at about the point where the gastrocnemius and soleus muscles unite, the tendon suddenly begins to twist, rotating a full 90 degrees before it attaches to the back of the heel. As mentioned in Chapter 3, this extreme twisting significantly improves efficiency while running because it allows the tendon to function like a spring, absorbing energy during the early phases of the gait cycle and returning it in the form of elastic recoil during the propulsive period.

Despite its clever design and significant strength, the extreme forces it is exposed to cause the Achilles tendon to break down all too frequently. Depending on the location of the damage, Achilles tendon overuse injuries are divided into several categories: insertional tendinitis, paratenonitis, and non-insertional tendinosis.

As the name implies, insertional tendinitis refers to inflammation at the attachment point of the Achilles on the heel. This type of Achilles injury typically occurs in high arched, inflexible individuals, particularly if they possess what is known as a Haglund’s deformity, a bony prominence near the Achilles attachment on the heel. Because a bursa is present near the Achilles attachment (bursae are small sacs that contain lubricants that lessen shearing of the tendon against the bone), it is very common to have an insertional tendinitis with a bursitis (Fig. 6.2).

Until recently, the perceived mechanism for the development of insertional tendinitis was pretty straightforward: excessive running causes the Achilles tendon to break down on the back portion of the Achilles attachment, where pulling forces are the greatest. While this makes perfect sense, research has shown that just the opposite is true: the Achilles tendon almost always breaks down in the forward section of the tendon, where pulling forces are the lowest (2) (Fig. 6.3).

By placing strain gauges inside different sections of the Achilles tendons and then loading the tendons with the ankle positioned in a variety of angles, researchers from the University of North Carolina discovered that the back portion of the Achilles tendon is exposed to far greater amounts of strain (particularly when the ankle was moved upward) while the forward section of the tendon, which is the section most frequently damaged with insertional tendinitis, was exposed to very low loads. The authors suggest that the lack of stress on the forward aspect of the Achilles tendon (which they referred to as a tension shielding effect) may cause that section to weaken and eventually fail. As a result, the treatment of an Achilles insertional tendinitis should be to strengthen the forward- most aspect of the tendon. This can be accomplished by performing a series of eccentric load exercises through a partial range of motion (Fig. 6.4). It is particularly important to exercise the Achilles tendon with the ankle maximally plantarflexed (i.e., standing way up on tiptoes), because this position places greater amounts of strain on the more frequently damaged forward portion of the tendon.

Runners with high arches are especially prone to insertional Achilles injuries and they often respond very well to lateral heel wedges. These wedges, which are pasted to the outer portion of an insole, are used to distribute pressure away from the outer aspect of the tendon. Conventional heel lifts are always a consideration, but be careful, they may feel good at first but the calf muscles quickly adapt to their shortened positions and the beneficial effect of the heel lift is lost. Heel lifts also increase stress on the sesamoid bones and the plantar fascia, and should therefore be used for no more than a few weeks.

Rather than accommodating tight calves with heel lifts, a better approach is to lengthen the calves with gentle stretches. As mentioned, the most effective calf stretch is the neutral position stretch, which can be done with the knee straight and bent to target the gastrocnemius and soleus muscles, respectively (see below). Because aggressive stretching can damage the insertion, the stretches should be performed with mild tension. You should perform this stretch routine for about a minute, and repeat this process every 3 or 4 hours daily.

If calf inflexibility is extreme and does not respond to stretching, a night brace should be considered. These braces, which are typically used to treat plantar fasciitis, are a very effective way to lengthen the gastrocnemius and soleus muscles. My favorite night brace is called The Cub, which tends to be more comfortable than any of the other commercially available night braces (Fig. 6.5).

The next type of Achilles tendon overuse injury is paratenonitis. This injury, which is very common in runners, represents an inflammatory reaction in the outer sheath of cells surrounding the tendon. Over-pronators are particularly prone to this injury because rapid pronation creates a whip-like action that can damage the tendon sheath (particularly the inner side). The first sign of the injury is a palpable lump that forms about two inches above the Achilles attachment. This mass represents localized thickening in response to microtrauma. If running is continued, the size of the lump increases and it eventually becomes so painful that running is no longer possible. Treatment for Achilles paratenonitis

is to immediately reduce the swelling with frequent ice packs. If you’re flat-footed, you might want to consider trying orthotics (start with over-the-counter models) as excessive foot pronation has recently been proven to twist the Achilles tendon (3), depriving it of blood in a way comparable to wringing a wet towel. The impaired circulation associated with this twisting action increases the risk of chronicity. Night braces are also effective with paratenonitis because tendons immobilized in lengthened positions heal more quickly (4).

If caught in time and the problem is corrected, Achilles paratenonitis is no big deal. However, if untreated, this injury can turn into a classic Achilles non-insertional tendinosis. This injury involves degeneration of the tendon approximately 1-2 inches above the attachment on the heel. Because this section of the tendon has such a poor blood supply, it is prone to injury and tends to heal very slowly.

Unlike insertional tendinitis and paratenonitis, non-insertional tendinosis represents a degenerative noninflammatory condition (i.e., the suffix osis refers to wear and tear, while itis refers to inflammation). In response to the repeated trauma associated with running through the injury, specialized repair cells called fibroblasts infiltrate the tendon, where, in an attempt to heal the injured regions, they begin to synthesize collagen. In the early stages of tendon healing, the fibroblasts manufacture almost exclusively type 3 collagen, which is relatively weak and inflexible compared to the type 1 collagen found in healthy tendons. If everything goes right, as healing progresses, greater numbers of fibroblasts appear and collagen production shifts from type 3 to type 1. Unfortunately, many runners don’t give the tendon adequate time to remodel (which can take up to 6 months) and a series of small partial ruptures begin to occur that can paradoxically act to lengthen the tendon, resulting in an increased range of upward motion at the ankle. At this point, pain is significant and the runner is usually forced to stop running altogether.

Various factors may predispose to the development of non-insertional tendinosis. In the previously mentioned study of military recruits, the recruits developing Achilles injuries were overly flexible and had weak calves (1). It is likely that these two factors create a whipping action that strains the Achilles tendons. More recently, researchers from the United Kingdom (5) prove that weakness of the soleus muscle plays an important role in the development of Achilles injuries. These authors compared gastroc and soleus strength in 38 runners with Achilles injuries, and 39 asymptomatic control runners, and determined the injured runners had isolated strength deficits in the soleus muscle. Importantly, the authors state “the soleus weakness more than likely predated the injury.” This research is consistent with prior studies showing the tendon fibers originating from the soleus are exposed to more stress and undergo greater elongation than tendon fibers originating from the gastrocnemius muscle (6,7). As a result, in order to successfully manage any type of Achilles injury, strength and endurance deficits in the soleus should always be addressed.

The good news about non-insertional tendinosis is that there is an exercise intervention you can do at home that’s been proven to be effective. Referred to as heavy load eccentric exercises (8), this treatment involves wearing a weighted backpack while standing on the edge of a stair with your heels hanging off the stair (Fig. 6.6). Using both legs, you raise your heels as high as possible and then remove the uninjured leg from the stair. The injured leg is then gradually lowered through a full range of motion. The uninjured leg is then placed back on the stairway and both legs are again used to raise the heels as high as possible. This process is repeated with the knee straight and flexed and runners should perform 3 sets of 15 repetitions daily for 12 weeks. The orthopedic surgeon who first published the eccentric protocols, Hakan Alfredson, recommends the eccentric protocol be continued unless your Achilles pain becomes “disabling.” I find Alfredson’s approach a little extreme, so I tell athletes to reduce the weight while exercising if the pain exceeds more than 4 on a scale from 0 to 10 (0 being no pain, 10 being unbearable pain).

While the 3 sets of 15 protocol works well for recreational athletes, competitive runners have to work harder to heal a non-insertional Achilles injury. In a recent study evaluating tendon resiliency with different strengthening protocols, researchers from Taiwan discovered that high-level athletes have no change in tendon resiliency unless they perform 4 sets of 80 repetitions (9). This research explains why elite athletes do not do as well with conventional eccentric protocols as recreational athletes. (Almost all studies on eccentric exercise use the 3 sets of 15 protocol.) I recommend the 4 sets of 80 repetitions protocol for runners averaging more than 50 miles per week.

Non-insertional Achilles injuries also respond very well to the tibialis posterior strengthening exercise illustrated in figure 6.7. In a recent study comparing three-dimensional motion between runners with and without Achilles tendinopathy, researchers from East Carolina University determined that compared to controls, runners with Achilles tendinopathy failed to rotate their legs outward during the pushoff phase (10). The authors theorized that tibialis posterior weakness forced the leg to twist in excessively, which in turn increased strain on the Achilles tendon. After reading this article, I began adding tibialis posterior exercises to the standard protocols for managing Achilles tendinitis and noticed reduced recovery times and better long-term outcomes.

In addition to strengthening exercises, an alternate method for improving Achilles function is deep tissue massage. The theory is that aggressive massage breaks down the weaker type 3 collagen fibers and increases circulation so healing can occur. To test this theory, researchers from the Biomechanics Lab at Ball State University (10) surgically damaged the Achilles tendons in a group of rats. In one group, an aggressive deep tissue massage was performed for three minutes on the 21st, 25th, 29th and 33rd day post injury. Another group served as a control. One week later, both groups of rats had their tendons evaluated with electron microscopy. Not surprisingly, the tendons receiving deep tissue massage showed increased fibroblast proliferation, which would create an environment favoring tendon repair.

A more high-tech method of breaking down scar tissue involves extracorporeal shock wave therapy. This technique involves use of costly machinery that blasts the Achilles with high frequency sonic vibrations. Recent research has shown comparable outcomes between shock wave therapy and heavy load eccentric exercises in the treatment of non- insertional Achilles tendinosis. As a result, shock wave therapy is typically used only after conventional methods have failed.

Regardless of whether the Achilles injury is insertional or non-insertional, a great method for lessening stress on the Achilles tendon is to strengthen the toe muscles, especially flexor digitorum brevis and flexor hallucis longus. These muscles, which originate along the back of the leg and attach to the toes, lie deep to the Achilles and work synergistically with the soleus muscle to raise the heel during propulsion.

Contraction of the flexor hallucis and digitorum longus muscles while running significantly lessens strain on the Achilles tendon because they decelerate elongation of the tendon. The easiest way to strengthen the long toe muscles is with the ToePro exercise platform (see below). An alternate way to strengthen these muscles is to get on an AirEx balance pad and lean forward into a wall while pushing down with your toes. I typically recommend 3 sets of 25 repetitions performed daily.

To make sure the toe muscles are working properly, an injured runner should forcefully curl the toes downward into the insole during the pushoff phase of the running cycle. This naturally strengthens the toe muscles and reduces strain on the Achilles tendon. It’s easy to see if you have weakness in these muscles by looking at the insole of your running shoe. Normally, when the flexor digitorum muscles are strong, you will see well-defined indents beneath the tips of the toes, whereas runners with weak digital flexors have no marks beneath the toes and shows signs of excessive wear in the center of the forefoot only.

It’s important to emphasize that runners with Achilles injuries should almost always avoid cortisone injections because they weaken the tendon by shifting the production of collagen from type 1 to type 3. In a study published in The Journal of Bone and Joint Surgery (11), cortisone was shown to lower the stress necessary to rupture the Achilles tendon and was particularly dangerous when done on both sides, because it produced a systemic effect that further weakened the tendon.

An overview of the management of Achilles tendon disorders can be summarized as follows: warm up slowly by running at least one minute per mile slower than your usual pace for the first mile and try to remain on flat surfaces. If you are a mid or a forefoot striker, consider switching to a rearfoot strike since this reduces strain in the Achilles tendon during initial contact.

Because excessive pronation has been shown to decrease blood flow to the Achilles tendon (3), runners who are excessive pronators should consider wearing stability running shoes, specifically ones with duodensity midsoles and toe springs (figure 6.8).

Overpronators should also consider wearing orthotics. Because they encourage a forward contact point, minimalist shoes and racing flats should be avoided. Lastly, if you have a tendency to be stiff, spend extra time performing the calf stretch illustrated on page 3, and if you’re overly flexible, you should consider performing eccentric load exercises preventively. To evaluate strength, try doing 25 heel raises on each leg to see if you fatigue quicker on one side. If one leg is weaker, fix the strength asymmetry with the exercise illustrated in figure 6.6.

References:

Overpronators should also consider wearing orthotics. Because they encourage a forward contact point, minimalist shoes and racing flats should be avoided. Lastly, if you have a tendency to be stiff, spend extra time performing the calf stretch illustrated on page 3, and if you’re overly flexible, you should consider performing eccentric load exercises preventively. To evaluate strength, try doing 25 heel raises on each leg to see if you fatigue quicker on one side. If one leg is weaker, fix the strength asymmetry with the exercise illustrated in figure 6.6.

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