MUSCLE MOVEMENT FUNCTION TERMINOLOGY

Muscles causing complex human movement are typically placed in certain descriptive classifications based on their role within a particular movement. Like most definitions there are multiple names used to describe the same meaning. Do not consider the list below comprehensive.

TERMINOLOGY

Primary Mover (Prime, Major) --» A muscle that is a major actor or controller of a particular movement.

• It is common to have more than one primary mover in complex movements.
• Technically, when eccentrically contracting, prime movers are only controlling movement not causing it.

Agonist --» Muscles that cause and/or control movement.

• If possible, a body part will move toward the agonist's point of origin.
• Commonly associated with the prime movers of a particular movement.
• Can be considered the motive force if the muscle is concentrically operating.
• Can be considered the resistive force if the muscle is eccentrically operating.
• It is also appropriate to associate assisting movers with the agonist group.

Assistant Mover (Secondary) --» A muscle that aids the prime mover in its action but is not as involved in causing the movement.

• Assisting movers usually have the same or similar lines of action as the prime movers.

Antagonist --» Is a particular muscle or group of muscles that directly oppose the Agonist muscle group.

• Provide the ability to decelerate (slow down) moving body parts.
• If activated, operate as a resistive force when the agonist is concentrically contracting.
  • Technically, during concentric contraction of the agonist muscles, an antagonist muscle can never operate as a motive force. Why?
  • What about agonist eccentric contractions?

Agonist-Antagonist Relationship --» A muscle designated as an agonist muscle in one movement can be an antagonist muscle in the next.

• E.g., when straightening the knee joint the hamstring muscle group is considered an antagonist group, but when the knee is flexed to prepare for the next step the group is now considered a agonist group.

Synergist --» any muscle except for those considered prime movers.
A broad term that can include several categories of muscle function during movement. These can include assisting, guiding, stabilizing (fixator), and neutralizing functions.

• Assistant mover (see earlier in notes)
• Guiding function works to deflect, divert the moving body part from the prime movers exact line of action. (E.g., The hips adductor muscle group allows for diagonal movement of the leg such as in kicking a ball soccer style)
• Stabilizer (fixator) --» the muscle functions to lock or stabilize a particular body part(s) to allow other muscles to act from or upon it. (E.g., stabilizing neck so the shoulder can be elevated, shoulder shrugs)
• Neutralizer --» the muscle functions to eliminate unwanted actions within a particular movement. (E.g., for the neck to laterally flex (move sideways toward the shoulder, anterior and posterior muscles oppose or neutralize each other)
• Technically, there may be a case in which antagonistic muscles could be possibly considered a synergist. Ideas?