7.3 Major Muscle Groups and Their Functions

5 min read•august 28, 2024

The muscular system is a complex network of tissues that enables movement and supports bodily functions. Major muscle groups, from head to toe, work together to perform various actions, each with specific origins, insertions, and roles in movement.

Understanding muscle attachments and actions is crucial for grasping how our bodies move. This knowledge not only helps in anatomy studies but also in practical applications like exercise and physical therapy, showing how muscles work together in everyday activities.

Major Muscle Groups and Locations

Head, Neck, and Trunk Muscles

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  • Facial muscles control facial expressions and movements
  • Mastication muscles (masseter, temporalis) are responsible for chewing
  • Neck muscles (sternocleidomastoid, scalenes) control head and neck movement
  • Anterior trunk muscles include the pectoralis major (chest), rectus abdominis (abs), and obliques (side abs)
  • Posterior trunk muscles include the trapezius (upper back), latissimus dorsi (mid-back), and erector spinae (along the spine)

Upper Extremity Muscles

  • Shoulder muscles include the deltoid (shoulder cap) and rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis)
  • Arm muscles are the biceps brachii (front of upper arm) and triceps brachii (back of upper arm)
  • Forearm muscles are grouped into wrist flexors (anterior) and extensors (posterior)
  • Hand muscles include intrinsic muscles (within the hand) and extrinsic muscles (originating in the forearm)

Lower Extremity Muscles

  • Hip muscles include the gluteal muscles (buttocks) and iliopsoas (hip flexor)
  • Thigh muscles are divided into the quadriceps femoris (front of thigh) and hamstrings (back of thigh)
  • Leg muscles are primarily the gastrocnemius and soleus (calf muscles)
  • Foot muscles include intrinsic muscles (within the foot) and extrinsic muscles (originating in the leg)

Muscle Origin, Insertion, and Action

Attachment Points and Movement

  • Muscles attach to bones via tendons at their origin (stationary attachment) and insertion (moving attachment) points
  • The origin remains fixed during contraction, while the insertion moves towards the origin
  • Muscle contraction generates force, which is transmitted through the tendons to produce movement

Key Upper Body Muscle Attachments and Actions

  • Pectoralis major originates on the clavicle, sternum, and ribs, inserts on the humerus, and performs arm adduction and medial rotation
  • Deltoid originates on the clavicle and scapula, inserts on the humerus, and is responsible for arm abduction, flexion, and extension
  • Biceps brachii originates on the scapula, inserts on the radius, and flexes and supinates the forearm
  • Triceps brachii originates on the scapula and humerus, inserts on the ulna, and extends the forearm

Key Lower Body Muscle Attachments and Actions

  • Quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) originates on the ilium and femur, inserts on the tibia via the patellar tendon, and extends the knee joint
  • Hamstrings (biceps femoris, semitendinosus, semimembranosus) originate on the ischial tuberosity, insert on the tibia and fibula, and flex the knee and extend the hip
  • Gluteus maximus originates on the ilium and sacrum, inserts on the femur and iliotibial tract, and extends and externally rotates the hip
  • Gastrocnemius originates on the femur, inserts on the calcaneus via the Achilles tendon, and plantar flexes the ankle

Muscle Roles in Movement

Agonist-Antagonist Relationship

  • Agonists, or prime movers, directly produce a desired movement through concentric contraction
  • Antagonists oppose or reverse the action of the agonists by relaxing or undergoing eccentric contraction
  • This reciprocal innervation allows for smooth, coordinated movements and prevents undesired actions

Synergistic Muscle Interaction

  • Synergists assist the agonists in producing a movement by stabilizing the joint or reducing unnecessary movements
  • They help refine the movement and make it more efficient
  • Examples include the brachialis and brachioradialis assisting the biceps brachii in elbow flexion, and the tensor fasciae latae and sartorius assisting the quadriceps in knee extension

Movement Examples

  • Elbow flexion: biceps brachii (agonist), triceps brachii (antagonist), brachialis and brachioradialis (synergists)
  • Knee extension: quadriceps femoris (agonists), hamstrings (antagonists), tensor fasciae latae and sartorius (synergists)
  • Shoulder abduction: middle deltoid (agonist), latissimus dorsi and pectoralis major (antagonists), supraspinatus and serratus anterior (synergists)

Applying Muscle Knowledge to Exercise

Upper Body Exercises

  • Push-ups target the pectoralis major, triceps brachii, and anterior deltoid
    • Pectoralis major and triceps brachii concentrically contract during the upward phase and eccentrically contract during the downward phase
  • Pull-ups primarily work the latissimus dorsi, biceps brachii, and posterior deltoid
    • Latissimus dorsi and biceps brachii concentrically contract during the upward pulling motion and eccentrically contract during the lowering phase
  • Bench press engages the pectoralis major, triceps brachii, and anterior deltoid
    • Similar muscle actions to push-ups, with the added resistance of weights

Lower Body Exercises

  • Squats mainly work the quadriceps femoris, gluteal muscles, and hamstrings
    • Quadriceps concentrically contract during the ascending phase and eccentrically contract during the descending phase
    • Gluteal muscles and hamstrings assist in hip extension
  • Lunges target the quadriceps, hamstrings, and gluteal muscles
    • The forward leg's quadriceps concentrically contract during the upward phase, while the trailing leg's hamstrings and gluteal muscles work to extend the hip
  • Calf raises primarily engage the gastrocnemius and soleus muscles
    • These muscles concentrically contract to plantar flex the ankle and raise the heel, then eccentrically contract to control the lowering phase

Functional Movements

  • Walking and running involve the coordinated action of various lower extremity muscles
    • Quadriceps and hamstrings alternately extend and flex the knee
    • Gluteal muscles and hip flexors control hip movement
    • Gastrocnemius and soleus plantar flex the ankle for propulsion
  • Throwing a ball requires the integrated action of shoulder, arm, and trunk muscles
    • Deltoid and rotator cuff muscles stabilize the shoulder
    • Pectoralis major and latissimus dorsi generate power
    • Triceps brachii extends the elbow for ball release
    • Trunk rotation, involving the obliques and rectus abdominis, enhances throwing force
  • Lifting and carrying objects engage multiple muscle groups
    • Back muscles (erector spinae, latissimus dorsi) maintain posture
    • Leg muscles (quadriceps, hamstrings, gluteals) provide a stable base and allow for lifting
    • Arm muscles (biceps, triceps) control the load
    • Core muscles (rectus abdominis, obliques) stabilize the trunk
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