Tendinitis can be classified into three different stages. It starts with acute hamstring tendon pain and if the right steps are not taken to get the tendon back to a healthy state, it progresses. The structure of the tendon weakens over time and can start degenerating and disintegrating.
1. Reactive tendinitis (First stage)
The acute phase of hamstring tendinopathy (reactive tendinitis) is caused by a change in the amount of work that your hamstring tendon needs to do. Straining, overload and overburdening the hamstring tendons are the main factors causing this condition. Usually, in this phase there will be some inflammation and possibly swelling around the tendon or tendon sheath (synovium).
Let’s say you felt your hamstring ‘pulling’ during an uphill run, but it goes away after a while. Now you continue running every day for the rest of the week. At the start of each run you feel discomfort and stiffness in the lower part of your buttock (proximal hamstring tendinitis) or behind your knee (distal hamstring tendinitis), but it improves when you run. It can’t be that bad then, can it? When you push through this pain every time, you are repeatedly causing micro-trauma to your hamstring tendon. If you do not get the right treatment during this phase, the structure of the tendon starts to change and it gets weaker. At this stage the tendon has the potential to recover and revert back to its normal structure.
2. Tendon dysrepair (Second stage)
Reactive tendinitis (first stage) can progress to tendon dysrepair (second stage) if the tendon is not allowed to recover. During this phase there is continuous breakdown and disorganisation of the collagen network as your body tries to heal the tendon. This means that the collagen fibers are not neatly arranged in bundles, but tear away from each other, like a cable or rope where the individual strands break and separate. Applying more force will cause more damage.
In this phase, you will feel a dull pain in the lower part of your buttock or behind your knee at the start of your run, but it will linger a little bit longer, and bother you more and more. Now you start to feel the pain not just during your run, but also throughout the day with simple activities like sitting down or climbing stairs. As the tendon structure changes, it is not capable of doing the work it should and this causes you more pain. If you do not decrease the burden on your hamstring tendon injury and allow it to rest, further damage will occur and it can now lead to problems elsewhere, like your knee, hip and lower back.
3. Degenerative tendinitis (Final Stage)
Degenerative tendinitis is the final stage and at this stage the tendon damage is permanent because the degeneration of the tendon is irreversible. The structure of the hamstring tendon weakens further and adhesions form between the tendon and the sheath around it. Adhesions are patches of wound tissue attempting to heal the torn fibers. These adhesions, together with the fact that the tendon thickens, makes your hamstring tendon less flexible and the normal gliding movement of the tendon inside its sheath becomes impossible.
Now, the tendon cannot withstand even the stress and load of normal everyday activities like getting out of bed, climbing stairs and walking.