十二经筋是十二经脉之气结聚于筋肉关节的体系，是十二经脉的外周连属部分。

The Twelve Muscle Regions are the conduits which distribute the Qi of the Twelve Regular Meridians to the muscles, tendons and joints, They are external connecting regions of the Twelve Regular Meridians.

十二经筋的分布与十二经脉的体表通路基本一致，其循行走向从四肢末端走向头身，行于体表，不入内脏，结聚于关节，骨骼部。足三阳经筋起于足趾，循股外上行结于鸠(面部)；足三阴经筋起于足趾，循股内上行结于阴器(腹部)；手三阳经筋起于手指，循蠕外上行结于角(头部)；手三阴经筋起于手指，循孺内上行结于贲(胸部)。各经筋在循行途中还在踝、胴、膝、髀、腕、肘、腋、肩、颈等关节处结聚，特别是足厥阴经筋，除结于阴器，并能总络诸筋。

The distribution of the muscle regions is parallel to the body superficies course of the Regular Meridians. All the muscle regions start from the terminals of the limbs and run on to the head and trunk. Instead of entering Zang-Fu organs, they travel along the body surface and connect with the joints and bones. Three Yang Muscle Regions of Foot start from toes and ascend along the lateral aspect of the leg and end at the face. Three Yin Muscle Regions of Foot originate from the Toes, and ascend along the medial aspect of the leg and to the genital region. Three Yang Muscle Regions of Hand start from the fingers and proceed up along the lateral side of arm and end at the angle of forehead. Three Yin Muscle Regions of Hand start from the finger, run along the medial side of the arm and end in the thoracic cavity. In their circulations, the Twelve Muscle Regions connect with ankle, popliteal fossa, knee, thigh, wrist, elbow,axilla, shoulder and neck. Especially the Liver Muscle Region knots with the genital region and connects with all the other muscle regions.

The main functions of the muscle regions are to connect with all the bones and control them to ease flexing and extending of the joints and normal motion of the body. This refers to in the Chapter "Discussion on Flaccidity-Syndrome" (Chapter 44)in Plain Questions"The tendons control and connect with bone to ensure proper joint."