In my clinic, I have seen many cases of the above come into the clinic. Generally, Tendonitis is irritation of the tendon, Bursitis is inflammation of a kind of pad that sits on a bone that a muscle runs over and inflammation can also occur where the tendon attaches to the bone. Each condition will be treated differently in terms of reducing the inflammation but the cause has been fairly consistent and that is the property of the muscles themselves.
Essentially, in my opinion, the issue with all three conditions is that the muscles have lost their elasticity due to inflammation and adhesions within the muscle belly itself and creating too much tension where the muscle becomes a tendon, where it travels over the bursa (fat pad) or where it attaches to the bones. This will cause inflammation at these 3 points causing the tendonitis/bursitis/bone inflammation.
A muscle the becomes adhered also loses it’s ability to properly lengthen and shorten making it a weaker muscle not able to contract properly. An adhere muscle will traditionally not receive as much blood with oxygen and as a consequence may have increased levels of metabolic waste creating an acidic environment in the tissue causing pain and further tightness.
Part of my treatment is focused on releasing the adhesions within the muscle belly, and any adhesions between that muscle belly and any other tissues surrounding that muscle belly, to return circulation to the muscle and some light stretching with some home care to maintain a flexible strong muscle.