Tendons are made of rubbery collagen material that connects our muscles to our bones. They can be long and skinny or short and wide, and they tend to work in very close proximity with other structures like joint capsules, tendon sheaths, and bursae. There are times when these surrounding structures prevent a tendon from gliding properly with movement. If a tendon is repeatedly pinched or rubbed against, it can become irritated and develop tendinopathy. Sometimes the surrounding structures become irritated too.
Over time, the structure of an irritated tendon actually changes and the result is a thicker and weaker tendon. It’s no wonder these conditions often become chronic and repetitive, since a full recovery requires a reversal of these structural changes.
Some of the most common areas to develop tendinopathy include the knee (patellar), the ankle (achilles), the elbow (tennis elbow), or shoulder (rotator cuff or biceps). In general, these conditions develop because of overuse, and are often associated with repeated motions such as running and jumping, reaching overhead, or using the same tool at work all day.
There are many treatment approaches for tendinopathy, depending on the tendon involved. Rehab may include bracing/taping, manual therapy, strengthening & stretching exercises, injections, modalities, and so forth. In the upper body, there is sometimes a neural component that needs to be addressed (this may also be true in the lower body but research is limited). In the lower body, isolated eccentric exercise is a popular treatment approach.
An eccentric muscle contraction refers to a muscle lengthening while bearing a load, as opposed to a concentric contraction where a muscle shortens while bearing a load (imagine doing a biceps curl: when you curl your arm up with a weight and your muscle bulges, that’s concentric; when you slowly lower it back down, that’s eccentric).
Once again the research is limited. Most available studies look only at whether eccentric exercise is effective for patellar or achilles tendinopathy. In general, they show that yes, it is effective. But because very few studies have investigated whether concentric exercise is effective, we really don’t know if eccentric is actually better. What we do know is that, for a tendon to fully heal, it does need to be strengthened one way or another!
References
Couppe C, Svensson RB, Silbernagel KG, et al. Eccentric or concentric exercises for the treatment of tendinopathies? J Orthop Sports Phys Ther 2015;45(11):853-863.
Scott A, Backman LJ, Speed C. Tendinopathy: update on pathophysiology. J Orthop Sports Phys Ther 2015;45(11):833-841.