Muscle Functions and Actions

Muscle Groups and Actions Overview

Upper Back & Shoulders: Prime Movers of Arm

• Latissimus Dorsi
  • Action: Extends, adducts and medially rotates the humerus.
• Pectoralis Major
  • Action: Flexes, adducts & medially rotates the humerus.
• Rotator Cuff (SITS)
  • Supraspinatus: Abduction of arm.
  • Infraspinatus: Lateral rotation of arm.
  • Teres Minor: Lateral rotation of arm.
  • Subscapularis: Medial rotation of arm.

Back & Pelvis Muscles

• Quadratus Lumborum
  • Action: Extends & laterally flexes the trunk; extends the trunk when contracted bilaterally; laterally flexes the trunk when contracted unilaterally.
• Erector Spinae
  • Action: Extends trunk (maintains posture).
• Piriformis
  • Action: Laterally rotates the leg.

Buttocks & Legs Muscles

• Gluteus Maximus
  • Action: Extends & laterally rotates the femur.
• Gluteus Medius
  • Action: Abducts & medially rotates the femur.
• Tensor Fascia Latae
  • Action: Flexes, abducts & medially rotates the hip.

Major Leg Muscle Functions

• Iliopsoas
  • Action: Hip flexor, also flexes trunk.
• Adductors
  • Action: Adducts the femur.
• Hamstrings
  • Action: Flex leg at knee, assists hip extension.
• Quadriceps
  • Action: Extend knee, flex hip.
• Sartorius
  • Action: Flexes knee & hip, laterally rotates femur.
• Gastrocnemius
  • Action: Plantar flexion of ankle (knee extended).
• Soleus
  • Action: Plantar flexion of ankle (knee flexed).

Chest & Abdomen Muscles

• Rectus Abdominis
  • Action: Flexes trunk.
• External Oblique
  • Action: Flexes & twists trunk.
• Internal Oblique
  • Action: Flexes & twists trunk.
• Transverse Abdominis
  • Action: Compresses abdomen.

Additional Muscular Actions

• Serratus Anterior
  • Action: Elevates scapula, protracts scapula.
• Levator Scapula
  • Action: Elevates & retracts scapula.
• Occipito-frontalis
  • Action: Raises eyebrows, wrinkles forehead, moves scalp.
• Brachio-radialis
  • Action: Flexes arm at elbow, also supinates forearm.

Respiratory Muscles

• External Intercostals
  • Action: Lift ribs (inspiration).
• Internal Intercostals
  • Action: Lower ribs (expiration).
• Diaphragm
  • Action: Main muscle of respiration, lowers base of lungs during inhalation.

Functional Groupings

• Wrist & Finger Flexors: Flex wrist & fingers.
• Wrist & Finger Extensors: Extend wrist & fingers.

Key Terms:

• Adduction: Movement towards the midline of the body.
• Abduction: Movement away from the midline of the body.
• Medial Rotation: Rotation towards the midline of the body.
• Lateral Rotation: Rotation away from the midline of the body.
• Plantar Flexion: Movement that increases the angle between the foot and the lower leg.
• Dorsiflexion: Movement that decreases the angle between the foot and the lower leg.