Level 3 Gym Instructor – Muscle: Anatomy (part two)

Level 3 Gym Instructor – Muscles Of The Body (Part Two)

 Rotator Cuff Muscles

Name: Supraspinatus, Subscapularis, Infraspinatus, Teres Minor
Description: A group of 4 short, broad muscles that work together
Origin: Scapula
Insertion: Laterally on top of the humerus
Joint Crossed: Shoulder joint

Joint Action: Subscapularis, prime mover in medial rotation. Supraspinatus, prevents downward dislocation of the humerus and assists in abduction. Infraspinatus and Teres Major rotate the humerus laterally.

Vertebral Column

Name: Erector Spinae
Description: 3 different columns of muscle on either side of the posterior spine. Thick and rectangular at lumbar becoming thinner, strap-like bundles in thoracic area.
Origin: Iliac crest and processes of vertebrae
Insertion: Vertebrae and base of skull
Joint Crossed: Vertebral column
Joint Action: Extension and hyperextension

Name: Quadratus Lumborum
Description: Short, thick muscle
Origin: Iliac crest and iliolumbar fascia
Insertion: Upper 4 lumbar vertebrae and lower margin of 12th rib
Joint Crossed: Lumbar vertebrae
Joint Action: Assists in extension of spine when working bilaterally. Unilaterally, lateral flexion and helps prevent hyperflexion

Name: Multifidus
Description: Deep muscle column of lower back spanning 1-3 vertebrae
Origin: Transverse processes of vertebrae
Insertion: Spines of superior adjacent vertebrae
Joint Crossed: Lower vertebrae
Joint Action: Rotation and lateral flexion. Spinal stability during lifting.

Anterior Abdominal Wall Muscles

Woman Showing Abs - Level 3 Gym InstructorThe anterior abdominal wall is composed of three layers of broad, flat muscles with fibres running in different angles. The upper layer is the external oblique muscle which originates from the lower ribs and runs downwards and inwards in a V shape. The middle layer is the internal oblique muscle which originates from the lumbar fascia and iliac crest, running upwards and inwards in an A shape. It is at right angles to the external obliques. The deepest later is the transverse abdominis which originates mainly at the lumbar fascia but also from the cartilage of the lower ribs and iliac crest. It runs horizontally in a band across the front of the abdomen.

The tendons of these muscles converge in a broad, fibrous sheet or Aponeurosis that extends down the front of the abdomen from the iliac crest and pubic bone up to the sternum and rib cage.

The paired column of muscle known as the rectus abdominus is embedded in the aponeurosis and causes spinal flexion, while the centre of the aponeurosis is called the Linea Alba. The two columns of the rectus abdominus are separated into 4 blocks, which when visible in trained individuals is called the 6 pack (or 8 pack if body fat is low enough).

These muscles all work with the back muscles to prevent hyperextension of the spine and maintain posture, as well as protecting the internal organs and causing changes in intra-abdominal pressure.

Name: Rectus Abdominus
Description: Superficial double column of fibres divided into 4 segments
Origin: Pubis Symphysis
Insertion: Cartilage of ribs 5-7 and base of sternum
Joint Crossed: Lumbar and lower thoracic vertebrae
Joint Function: Flexion and rotation of vertebral column and stability of pelvis during walking

Name: External Obliques
Description: Broad band of muscle on either side of the trunk
Origin: Outer surface of bottom 8 ribs
Insertion: Mainly linea alba but also iliac crest
Joint Crossed: Thoracic and lumbar vertebrae
Joint Function: Flexion of vertical column together. Rotation and lateral flexion working unilaterally

Name: Internal Obliques
Description: Broad band running beneath external oblique
Origin: Lumbar fascia and iliac crest
Insertion: Linea alba and bottom 3 ribs
Joint Crossed: Thoracic and lumbar vertebrae
Joint Function: Flexion of vertical column together. Rotation and lateral flexion working unilaterally

Name: Transverse Abdominus
Description: Broad band deep in the abdomen
Origin: Lumbar fascia and cartilage of lower 6 ribs and iliac crest
Insertion: Linea alba
Joint Crossed: Lumbar and thoracic vertebrae
Joint Function: Support and protection of abdominal contents

Upper Limb Muscles

Toned Woman - Level 3 Gym InstructorName: Biceps Brachii
Description: Two-headed muscle converging at insertion
Origin: Separate points on top of scapula
Insertion: Top of radius, medially
Joint Crossed: Shoulder and elbow
Joint Function: Flexes elbow and supinates (turns upward) forearm. Assists in flexion at shoulder when arm is straight

Name: Brachialis
Description: Short, thick muscle
Origin: Front of humerus
Insertion: Top of ulna
Joint Crossed: Elbow
Joint Function: Helps flex elbow. Prime mover in first 30 degrees of flexion

Name: Brachioradialis
Description: Long muscle in lateral forearm
Origin: Lateral at distal (away from body) end of humerus
Insertion: Laterally and distally on radius at wrist
Joint Crossed: Elbow
Joint Function: Flexion when arm is semi-pronated (drinking action) and synergist for other flexors

Name: Triceps Brachii
Description: Large, broad, tripartite muscle covering whole of upper arm posterioly (back of)
Origin: Long head on scapula, other two on humerus
Insertion: Olecranon of ulna (elbow)
Joint Crossed: Shoulder and elbow
Joint Function: Shoulder and elbow. Also assists in shoulder stabilisation and adduction

Muscles Of Pelvic Girdle And Hip Joint

Name: Iliopsoas
Description: Two muscles, iliacus and psoas major, with same insertion point
Origin: Iliacus from front of iliac crest and psoas major from lumbar and T12 vertebrae
Insertion: Top of femur anteriorly (front)
Joint Crossed: Hip
Joint Function: Hip flexion and lateral flexion of spine unilaterally

Name: Sartorius
Description: Longest muscle in body running obliquely across front of thigh
Origin: Anteriorly and laterally on iliac spine
Insertion: Medially on tibia
Joint Crossed: Hip and knee
Joint Function: Flexion and lateral (outer) rotation of thigh

Name: Gluteus Maximus
Description: Large, thick muscle forming buttocks
Origin: Base of spine (sacrum and coccyx) and back of ilium
Insertion: Top of femur (posteriorly)
Joint Crossed: Hip
Joint Function: Extension of thigh and lateral rotation

Name: Gluteus Medius And Minimus
Description: Smaller muscle beneath gluteus maximus
Origin: Ilium
Insertion: Top of femur (laterally)
Joint Crossed: Hip
Joint Function: Abducts and rotates thigh medially. Important in hip stabilisation during walking

Name: Adductor Group And Pectineus
Description: Thick, triangular muscle mass
Origin: Anteriorly from base of pelvis
Insertion: Medial (centre) length of femur
Joint Crossed: Hip
Joint Function: Adduction and medial rotation

For level 3 gym instructor you will need to know there are 3 groups of muscles in the thigh arranged anteriorly, posteriorly and medially.

Anterior muscles flex the hip and extend the knee.
Posterior muscles extend the hip and flex the knee.
Medial muscles adduct the thigh (bring to the centre).

There are also posterior-lateral muscles which abduct the thigh (move away from centre).

Lower Limb Muscles

Man With Big Quads - Level 3 Gym InstructorName: Quadriceps Group – Rectus Femoris, Vastus Medialis, Intermedius And Lateralis
Description: Large, thick, long muscle group of 4 muscles covering front and sides of thigh
Origin: Rectus femoris is iliac spine and top of acetabulum (socket of hip). Vasti muscles are anterior below neck of femur
Insertion: Front of tibia
Joint Crossed: Hip and knee
Joint Function: Rectus femoris is a hip flexor. All muscles extend knee

Name: Hamstrings – Biceps Femoris, Semimembranosus, Semitendinosus
Description: Group of 3 large, long muscles. Biceps femoris has 2 heads
Origin: Ischial tuberosity (pelvis) except for short head of bicep femoris which is posterior distal femur
Insertion: Biceps femoris tibia and head of fibula. Others tibial shaft medially.
Joint Crossed: Hip and knee
Joint Function: Extension and rotation at hip and flexion at knee

Name: Tibialis Anterior
Description: Superficial muscle running length of lower leg
Origin: Proximal head of tibia and interosseus membrane
Insertion: Medially on foot (big toe)
Joint Crossed: Ankle
Joint Function: Dorsiflexion and inversion of foot

Name: Gastrocnemius
Description: Covers posterior of lower leg with 2 heads
Origin: Medial and lateral femur just above knee
Insertion: Calcaneous via calcaneal (Achilles) tendon
Joint Crossed: Knee and ankle
Joint Function: Plantar flexion and assists in knee flexion when foot is dorsiflexed

Name: Soleus
Description: Covers posterior of lower leg
Origin: Proximal tibia and interosseus membrane
Insertion: Calcaneous via calcaneal tendon
Joint Crossed: Ankle
Joint Function: Plantar flexor of foot

For Level 3 Gym Instructor – Muscle: Anatomy (part one) click here.

As always, any questions or feedback leave a comment below.

Leave a Reply

Your email address will not be published. Required fields are marked *