Research suggests that a large percentage of degenerative changes are observed on the underside of tendons and ligaments that are attached to protruding bones. This is called 'enthesis' (See the images above). Put simply, degenerative change can be seen as a scratch caused by the rough side of the bone, which results in a scar through the recovery process.

As you can see in the table below, the Achilles tendon is prone to get compressed by its protruding attachment which is the top part of the heel bone, called 'Superior calcaneus', and that pressure/friction gets intensified in the ankle dorsiflexion (Pulling the toes up towards the shin <- this should be avoided not to irritate the affected area).

Similar studies have shown that tendons are vulnerable when they are exposed to the combination of increased tension and compression against bones. This can be interpreted that if a muscle becomes tight due to overloading or postural imbalance, its tendon (the muscle's attachment) gets pulled by the tight muscle itself. As a result, there will be increased friction in the enthesis area, which can cause tendon problems.

Another study (See the image below) suggests that pathological tendons due to Achilles tendinitis and patellar tendinitis have more good structures compared to healthy tendons. Surprisingly, this 'Regeneration' process naturally occurs without any treatment! 

In fact, pathological tendons also have more poor structures (degenerative changes). Therefore, it can be concluded that

1. Degenerative changes (scar tissues) are irreversible/irreparable

2. The remaining tendon gets bigger to function better

This can be easier to comprehend if you imagine a donut with a hole in the middle. The hole is the degenerative change (the irreparable scar tissue). The donut around the hole is the remaining tendon. Because of the hole, the initial tendon cannot function 100%. Then, the tendon tries to rectify this itself by creating more tissues around the initial tendon thus enlarging the tendon as a whole (bigger donut!). It is important to note that the 'Regeneration' is NOT repairing the scar tissue/degenerative change itself (NOT filling the hole) but rather making new tissues on the outer ring of the tendon!

However, if these new tissues fail to adapt to the load required in daily tasks, they will start to degenerate again. Since the renewability of our body is not infinite, the self-repairing process will become less effective as it has to be repeated over time. At some point, the tendon will no longer be able to produce healthy tissues.

In conclusion, there is strong evidence that your painful tendons have already regenerated sufficient healthy tissues for you to load properly. Thus, the real question is 'are you willing persistently do something to help these new tissues load properly?'. If yes, follow the instructions in this program thoroughly so that the new tissues can adapt to the loading in whatever activities you do in your everyday life. Even painful tendons change and adapt on their own to survive. It is time for you to do the same.

References

Cook, J. L & Purdam, C. (2012). Is compressive load a factor in the development of tendinopathy? British Journal of Sports Medicine, 46(3), 163-168.

Cook, J. L., Rio, E., Purdam, C. R., & Docking, S. I. (2016). Revisiting the continuum model of tendon pathology: what is its merit in clinical practice and research?. Br J Sports Med, 50(19), 1187-1191.

Docking, S. I., and J. Cook. "Pathological tendons maintain sufficient aligned fibrillar structure on ultrasound tissue characterization (UTC)." Scandinavian journal of medicine & science in sports 26, no. 6 (2016): 675-683.

Tsehaie, J., Poot, D. H. J., Oei, E. H. G., Verhaar, J. A. N., & de Vos, R. J. (2017). Value of quantitative MRI parameters in predicting and evaluating clinical outcome in conservatively treated patients with chronic midportion Achilles tendinopathy: a prospective study. Journal of science and medicine in sport, 20(7), 633-637