Eli5: why are tendon injuries harder to heal than muscle injuries?

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Eli5: why are tendon injuries harder to heal than muscle injuries?

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Blood flow is needed for cellular regeneration (healing) tendons are less vascular than muscle tissue and thus will heal slower.

Muscles are made of cells. To heal, the cells need to repair/regrow, which they’re quite good at. It’s how muscles grow in size in the first place.

Tendon’s aren’t made of cells, they’re made of collagen fibers. When damaged, the body needs to create the repair machinery first (cells that can lay down new collagen fibers) and it takes a *long* time for the fibers to fully form and coalesce.

There’s more than you probably care about here: [http://www.synthasome.com/tendon-repair.php](http://www.synthasome.com/tendon-repair.php)

The relevant part is:

Tendons repair and heal through a well-described process common to most
connective tissues. It involves inflammation providing oxygen,
nutrients, and clot formation. Macrophages invade and digest the clot,
release growth factors, fibroblasts are recruited, and a vascularized
granulation tissue is formed. New collagen synthesis occurs, the
collagen is deposited and organized as new fibers primarily along the
axis of the tendon. Covalent crosslinks are formed and mature into
stable crosslinks over a period of several weeks. This comprehensive and
dynamic repair system, which occurs over weeks and months and
eventually restores function to the tendon.