The Tendino-Muscular Meridians (TMM) or Sinew Meridians, are secondary meridians named JING JIN.

JING means: Texture of a fabric. Road drawn from north to south. Meridian, longitude.

JIN means: Tendons; muscles. Muscle strength. Physical force.

It is, therefore, the muscular strength of a body oriented according to precise and immutable directions and rules. 

They are widely described in the Ling Shu at chap.13.

They take the name from the Primary Meridian to which they are linked. The TMMs have an anatomical localization and an energy path that is the most superficial among all the meridians (Primary and Secondary); in all their pathways they never penetrate at the level of the organs and viscera (Zang Fu).

The anatomical localization of the TMM is similar to the pathway of the Primary Meridian that are connected to, but, more superficial, even if, at times, the pathway can be very different. In fact, points belonging to other Primary Meridians can also be part of a TMMs.

In queste traiettorie superficiali circola uno specifico tipo energia (Qi) denominato WEI QI o energia di difesa, con caratteristiche dinamiche molto più accentuate rispetto alla YING QI (energia nutritiva che circola nei Meridiani Principali (MP))

I MTM hanno un caratteristico decorso a fascia, e vanno ad interessare non solo i tessuti tendinomuscolari ma anche la membrana che avvolge il muscolo (aponevrosi) ed i legamenti che fungono da ancoraggio alle ossa permettendo così il movimento articolare;

The TMM are related to a specific type of Energy called WEI QI, or Defense Energy, that is a much more dynamic and less nutritive energy, then the one that flows in the Primary Meridians. 

Wei Qi warms, protects, activates upright posture, and activates movement, and mostt importantly, protects the body from External Pathogenic Factors (Cold, Humidity, Heat, Fire, Dryness, Wind).