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Agonist Muscle: Definition and Examples

What is An Agonist Muscle?

An agonist is the primary muscle involved in an action, also known as the prime mover. For example, when doing a neutral-grip bicep curl (a hammer curl), the bicep brachii would do most of the work and be the agonist. The brachialis and brachioradialis assist the bicep in this movement, making them synergist muscles.

Agonist vs. Antagonist vs. Synergist Muscle (+ Examples)

As mentioned, an agonist is the primary muscle that contracts to produce force and create a specific movement. 

Synergist muscles assist the agonist muscle in some way, be it by producing additional force to create movement or stabilizing the prime mover so it can do its job better.

An antagonist is a muscle with an opposite function to the agonist. When the agonist shortens, the antagonist lengthens

For example, the bicep is the agonist during a bicep curl because it is the prime mover. In contrast, the tricep is the antagonist since it functions opposite to the bicep and lengthens during arm flexion.

The roles reverse during a tricep exercise, such as a rope extension. In this scenario, the tricep becomes the agonist because it serves as the prime mover, and the bicep is the antagonist.

Agonist Muscle Examples

  • Bench press – agonist: pectoralis major
  • Squat – agonist: quadriceps
  • Shoulder press – agonist: deltoids
  • Bicep curl – agonist: bicep
  • Tricep extension – agonist: tricep


1. How is an agonist muscle different from an antagonist muscle?

An agonist muscle is the prime mover during an activity, whereas an antagonist is the muscle with the opposite function. For example, the tricep would be an antagonist to the bicep during a bicep curl.

2. What is the difference between an agonist and a synergist muscle?

The agonist is the prime mover during an activity, whereas a synergist muscle assists by generating additional force or promoting stability.

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