The influence of mechanical forces on Fascia?
Connective tissue / fascia is an incredibly adaptable and plastic tissue. It is transformed, remodeled and strengthened or weakened according to the mechanical stimulation (load) to which it is exposed. If we don’t move, the tissue will diminish.
Different type of mechanical stress provides different stimuli to the tissue cells.
Depending on the type of load, the cells are stimulated to produce different constituents in the connective tissue, such as different types and amounts of collagen and ground substance (different glucosaminoglycans and proteoglycans, including hyaluronan).
- This means that in a tendon that is loaded (stretched and extended), the cells are stimulated to form more fibers of collagen type I, which is the most common type in tendons, ligaments and muscle fascia. It is also the strongest type of collagen, which forms strong fibers, which lie parallel in the direction of the mechanical load. This stretch also stimulates an enzyme, lysyl oxidase, which helps to create cross-links between the collagen fibers, to make the tissue stronger, a tendon for example. The more tensile stimulation, the more collagen type I and the more crosslinks.
- The collagen in a joint that is loaded, is compressed, and then the pressure lightens. This dynamic compression of the cells stimulates them to form more collagen type II. Collagen type II is the type of collagen that is mainly found in cartilage.
- In loose fascia, the superficial fascia and between layers of dense fascia in the myofascial, where a lot of sliding is needed between two surfaces, shear forces take place. This type of mechanical force stimulates production of collagen type I and III in approximately equal amounts and there is also a need for more ground substance, including hyaluronic acid, which binds water and provides the sliding function. Hyaluronic acid is produced by special cells, fasciacytes, which are located just in the boundary area between two sliding layers.
What happens if a tendon’s not being used?
When a tendon is not used, if the load ceases, the tissue will decrease in size and it will be transformed and have a more scar-like structure. The number of cells will increase and after some weeks there are five times as many cells in the tissue. The collagen fibers decrease in size and after six weeks have almost halved their size. They will also cease to lie parallel in the direction of the mechanical load because there is no force direction as the tendon is not loaded. Instead, the fibers lie more disorderly, just like a scar. When the tendon is to be used again, it must be carefully adjusted to the load again, not to split.
A recent research study (Myrick et al, 2019) has investigated how ligaments adapt to intense training and strain in female football players. With the help of MRI, the volume of the anterior cruciate ligament has been measured after the end of the competition season compared with the same measurement before the start of the season. The volume of the cruciate ligament increased during the competition season and the difference was greatest in the “kick leg”. During the more intense load period, the players probably received continuous micro-damage, which led to inflammation, proliferation of cells and increased collagen production. The tissue tries to adapt to the increased mechanical force.
- Majima et al, 2003. Stress Shielding of Patellar Tendon- Effect on Small-Diameter Collagen Fibrils in a Rabbit Model.
- Myrick et al, 2019. Effects of Season Long Participation on ACL Volume in Female Intercollegiate Soccer Athletes.
- Gillard et al, 1976. The Influence of Mechanical Forces on the Glycosaminoglycan Content of the Rabbit Flexor Digitorum Profundus Tendon.
- Stecco et al, 2011. Hyaluronan within fascia in the etiology of myofascial pain.
- Stecco et al, 2018. The Fasciacytes- A New Cell Devoted To Fascial Gliding Regulation.