Achilles Tendonitis: Overload that Tendon!

Achilles pain is one of the most common lower leg injuries and it can be very debilitating. Although it is usually associated with runners, it can affect anyone including: cyclists, walkers, new shoe wearers and basketball players. If the achilles pain is chronic (usually more than 1 month), there is one common exercise I prescribe to all of my patients. Some of them think I’m off my rocker when I tell them this portion of the program, but clinically it works. And, research supports the heck out of it!

What is the achilles tendon?

Achilles Pain

It is a thick, fibrous band of connective tissue that attaches the soleus, gastrocnemius and plantaris onto the calcaneus (heel bone). Simply, it attaches the calf to the heel bone. It is considered the strongest tendon in the body and is imperative for plantar flexion of the ankle. Without this tendon, you are unable to point your toe or push your foot off the ground with walking or running.

What is tendon primarily made of? (This becomes important in a minute)

1. Type I Collagen: This is strong stuff. It resists tension and stretch and likes to arrange itself in a nice, orderly fashion.

2. Tissue Cells: Fibroblasts make the collagen and proteoglycans and GAG’s (glycoaminoglycans) found in ground substance.

3. Ground Substance: The liquid state the collagen and cells sit in. It is mostly made of water, along with the proteoglycans and GAG’s listed above.

Together, these three create a strong, orderly, healthy tendon that can resist a lot of force. However, this arrangement changes with chronic achilles pain. Most people associate pain with swelling and so this injury continues to be called achilles tendonitis (itis= swelling). But, research continues to prove that chronic tendon pain does not have any signs of inflammation. Achilles tendinopathy (tendon “sickness”) is a more accurate name.

What causes achilles tendinopathy?

  • Increased load: over-training, repetitive use (i.e. jumping, running)
  • Poor gait mechanics with walking or running
  • Improper shoe wear
  • Weak ankle stabilizers
  • Genetics (i.e. Haglund’s deformity)
  • Short soleus or gastrocnemius muscle
  • Lengthened soleus or gastrocnemius muscle (yes, you can be too flexible!)

What happens to the tendon with chronic pain?

Above, I mentioned that the achilles tendon is primarily made of type I collagen in healthy tissue. However, with chronic pain Type III collagen becomes dominant. Yikes! Type I is very strong and resilient to stress and is excellent at forming strong bundles for optimal force production. Type III is delicate, fabric-like collagen and does not like to form strong bundles. Additionally, there is an increased amount of ground substance (water). The result is a weakened, “gooey” tendon that is not so great at force production.

Check out the pictures below. Notice the difference in the thickness and organization of these collagen types. I don’t know about you, but I would MUCH rather have type I collagen dominating my achilles tendon.

Chronic Achilles Pain

Type III Collagen

Normal Achilles Tendon

Type I Collagen

How do you heal achilles tendinopathy?

Eccentrically overload it! What does that mean?? Eccentric is a specific type of contraction (often called “a negative” to weight lifters) that lengthens and strengthens the tendon at the same time. Eccentric contractions increases the production of type I collagen to help the chronic tendon return to its healthy state. Seriously. This type of contraction will actually remodel the tendon. And, when overloaded, people return to their activity faster and without surgery. It’s like exercise gold for a chronic tendinopathy.

Blog Activity: Eccentric Calf Raise 

Stand on your bottom stair with the heels off. Raise up and slowly lower your heels 3 counts. Raise up again on 1 count. “Lower on 3 counts, up on 1 count.” Simple, huh? Yes, simple, but this sounds painful to do. It can be a little painful, but I always tell my patients that 5/10 pain or less is reasonable. In 3-4 weeks the pain will decrease as the tendon begins to remodel itself back to a normal, healthy state.

How long do I have to do this? A minimum of 12 weeks; I educate my patients to continue eccentrics 6-9 months after seeing me to ensure the tendon stays happy and healthy as they return to their activity.

Case Study

A triathlete with chronic achilles pain on both sides came to see me a few years ago. He had pain for over 6 months and was having difficulty running.  I told him to eccentrically overload the tendons with calf raises. Starting with a manageable load (25 lbs), he continued to add more weight as tolerated. Because of time constraints, I instructed him to do a set (a good quality set) to fatigue. Within 4 weeks, he reported signficant decrease in pain, especially with running. By the time his race season came around, he was running pain-free. Currently, he still reports doing these 2-3x/wk as a part of his maintenance program.


(Alfredson et al). 15 runners (unable to run because of achilles pain) participated in this study. After 12 weeks of heavy eccentric overloading (3 sets of 15 repetitions), all of them were back to running with increased strength and significantly decreased pain. The other group (control group) in the study had treatment consisting of: rest, medication, change of shoe wear and orthotics. All of these people had surgery. My summary: a painful achilles tendon does not mean surgery! Try physical therapy first.

(Lamberg et al.) This research study concluded that type I collagen was regenerated 5 TIMES MORE with eccentric loading than the group that did not do eccentric loading. Other cool side note: the eccentric loading had no effect on the healthy tendon. My summary: Healthy tendon just stays healthy with eccentric loading and regenerates the unhealthy one. That’s a win-win situation.

(Heinemeir et al.) Type I collagen regenerated 5-6x more with concentric, eccentric and isometric achilles contraction. But, the gastrocnemius (calf muscle) was more sensitive to the eccentric contraction.  My summary: If the tendon responds to any contraction and the muscle responds best to eccentric load, might as well bust out some eccentric calf raises.

Although this post concentrates on how to regenerate and treat a painful achilles tendon, it is still important to have a physical therapy evaluation. Don’t you want to know WHY you have achilles pain? Is it your gait? Your shoe wear? A tight muscle? Get to the root of the issue, perform some eccentric calf raises and return to your activity happy and healthy.

© 2014 and Beyond. ALL BLOG CONTENT at by Lori Duncan PT


Lori Duncan, DPT, MTC, CPT is a respected Physical Therapist, Manual Therapist and Pilates instructor in Lafayette, CO. Lori is passionate about preventive physical therapy and education and is a nationally recognized presenter. She can be reached at [email protected]. You can also follow Duncan Sports Therapy + Wellness on Facebook & Instagram for more free tips and information.


Alfredson H, Pietila T, Jonsson P, Lorentzon R. Heavy-load eccentric calf muscle training for the treatment of chronic achilles tendinosis. Am J Sports Med. 1998;26: 360-366

Heinemeir K, Olesen J, Haddad F, et al. Expression of collagen and related growth factors in rat tendon and skeletal muscle in response to specific contraction types. J Physiol. 2007;582:1303-1316.

Kountouris A, Cook J. Rehabilitation of achilles and patellar tendinopathies. Best practice and research of clinical rheumatology. 2007;21(2): 295-316.

Langberg H, Ellingsgaard H, Madsen T, et al. Eccentric rehabilitation exercise increases peritendinous type I collagen synthesis in humans with Achilles tendinosis. J Med Sci Sports. 2007;17(1):61-6.


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