Kinesiology
Kinesiology is the study of human movement. This chapter covers muscle roles, joint actions, and the anatomical terms therapists use to describe and locate movement.
Muscle Roles in Movement
During a movement, the agonist (prime mover) produces the primary action, while the antagonist opposes and lengthens to allow it. Synergists assist the prime mover, and fixators stabilize a bone so the movement is efficient. For example, the biceps brachii flexes the elbow while the triceps brachii, the antagonist, relaxes and lengthens.
Joint Movements and Terminology
Common movements include flexion and extension, abduction (away from midline) and adduction (toward midline), and internal and external rotation. Anatomical direction terms such as superior, inferior, medial, lateral, proximal, and distal allow precise communication about the location of muscles and joints.
Muscle Structure and Contraction
Skeletal muscle attaches to bone via tendons, with an origin (typically more stationary) and an insertion (typically more mobile). Muscles can contract concentrically (shortening), eccentrically (lengthening under load), or isometrically (no length change). Understanding these actions helps therapists identify which tissues to address for a client's goals.