Synergists (Muscle)

Synergists: Synergists are muscles that assist the prime mover in performing a joint action. By definition, all agonists that are not the prime mover are synergists.

For example, the rectus abdominis is the prime mover of spinal flexion (e.g. during a crunch ). All of the other agonists for spinal flexion are synergists, including the external obliques , internal obliques , and the psoas .

• Synonym: By definition, the synergists are all agonists that are not the prime mover.
• Opposite: The antagonists are all of the muscles that perform the opposite joint action.

For additional information, including a video lecture:

• Lesson 21: Functional Roles of Muscles

Functional Roles of Muscles Glossary Terms:

• Prime Mover
• Agonist
• Synergist
• Antagonist
• Neutralizer
• Fixator
• Stabilizer

Articles listing all of the muscles by functional role for each joint action:

• Kinesiology of the Shoulder and Scapula
• Kinesiology of the Elbow
• Kinesiology of the Trunk
• Kinesiology of the Hip
• Kinesiology of the Knee
• Kinesiology of the Ankle

Examples of Joint Actions, Prime Movers, and Synergists

Shoulder Adduction

• Prime Movers:
  • Latissimus dorsi
• Synergists
  • Pectoralis major (sternal portion)
  • Teres major
  • Subscapularis (assists in stabilizing)

Spine Extension

• Prime Movers:
  • Erector spinae group (iliocostalis, longissimus, spinalis)
• Synergists:
  • Multifidus
  • Semispinalis (thoracic and cervical regions)
  • Interspinales
  • Rotatores

Hip Extension

• Prime Movers:
  • Gluteus maximus
• Synergists:
  • Hamstrings (biceps femoris, semitendinosus, semimembranosus)
  • Adductor magnus (posterior fibers)

Plantar Flexion

• Prime Movers:
  • Gastrocnemius
  • Soleus
• Synergists:
  • Tibialis posterior
  • Peroneus (fibularis) longus and brevis
  • Flexor hallucis longus
  • Flexor digitorum longus
  • Plantaris (weak assistance)