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

There are over 600 muscles in the body, but fortunately it is only necessary to know about 40 of the main ones for a level 3 gym instructor qualification. This includes a brief description, the origin and insertion, the joint crossed and its action. Not only will this be a part of a level 3 gym instructor exam, it is essential for training yourself and others in order to choose an exercise that works the intended muscle in the correct way. It is also helpful for identifying the exact location of any muscle pain or injury so the cause (muscle imbalance, poor technique, other exercise) can be dealt with.

Muscle Mechanics

Bones and muscles work together as lever systems, which involves a rigid rod, a fulcrum (pivot point) and a force to move the rod over the fulcrum. In the body, bones are the levers, joints are the fulcrum and contracting muscles provide the force. Levers are classified regarding the relationship between the components.

Muscle Mechanics - Level 3 Gym InstructorA First Class Lever is load – fulcrum – effort. Using a crowbar, scissors and lifting your head off your chest are examples of this. It is known as a power lever as it operates at a mechanical advantage, in other words the effort required is small compared to the weight being lifted. Not all first class levers have a mechanical advantage but they are better at controlled power moves.

A Second Class Lever is fulcrum – load – effort. A good example of this is a wheelbarrow, with the effort at one end of the lever and the load at the other, or raising yourself up onto your toes. This is another power lever as the load is nearer to the fulcrum than the effort (the muscle).

A Third Class Lever is load – effort – fulcrum. They are always at a mechanical disadvantage, meaning great effort to lift a small load. Tweezers are a good example, as is flexion at the elbow such as during a bicep curl. Although not a powerful movement it can be done quickly and through a large range of movement.

Muscle Roles

The role a muscle plays during a movement is either as an agonist antagonist, synergist or fixator.

Agonist, or Prime Mover, is the muscle most responsible for the movement.

Antagonist, is the opposing muscle which relaxes to allow the agonist to bring about movement, such as the triceps during a bicep curl.

Synergist, is a muscle which assists the agonist, often at the beginning or end of a movement when the force is greatest.

Fixator, is any muscle that prevents movement at joints other than those intended. These are often postural muscles, such as during a bicep curl, which would keep the posture upright instead of leaning or even falling forward with the weight.

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

Neck Muscles

Name: Sternocleidomastoid
Description: Elongated muscle with 2 heads
Origin: Sternum and Clavicle
Insertion: Mastoid (jaw bone)
Joint Crossed: Cervical vertebrae
Joint Action: Lateral flexion and head rotation

Name: Scalenus
Description: Elongated muscle with 3 parts (tripartite)
Origin: Cervical vertebrae
Insertion: Upper 2 ribs
Joint Crossed: Cervical vertebrae
Joint Action: Elevate ribcage to assist breathing

Name: Splenius
Description: Broad, elongated, bipartite (2 parts)
Origin: Cervical and thoracic vertebrae (C7-T6)
Insertion: Mastoid
Joint Crossed: Upper cervical vertebrae
Joint Action: Extension and hyperextension of head

Shoulder Girdle

Man Showing Trapezius - Level 3 Gym InstructorName: Trapezius
Description: Large, flat, triangular, covering most of upper back. Fibres travel in 3 directions
Origin: Back of skull, C7 and all thoracic vertebrae
Insertion: Spine of scapula and lateral edge of clavicle
Joint Crossed: Acromioclavicle (AC joint)
Joint Action: Upper fibres elevate shoulder girdle, middle fibres retract shoulder girdle, lower fibres depress shoulder girdle and downwardly rotate scapula

Name: Rhomboids
Description: Short, rectangular, major and minor divisions
Origin: C7 and T1-T5
Insertion: Medial border of scapula
Joint Crossed: Scapula stabilisers
Joint Action: Assist in retraction and rotation of scapula

Name: Serratus Anterior
Description: Originates at several points, broad at insertion
Origin: Front of ribs 1-8
Insertion: Anterior surface of scapula
Joint Crossed: AC joint
Joint Action: Protraction of scapula

Name: Pectoralis Minor
Description: Flat, thin muscle with 3 origins
Origin: Front of ribs 3-5
Insertion: Top of scapula (coracoid process)
Joint Crossed: shoulder joint
Joint Action: Assists in protraction of scapula and elevates ribs during breathing

Shoulder Joint

Name: Deltoid
Description: Thick, short muscle forming “shoulder pad”. Anterior, medial and posterior sections
Origin: Spine of scapula, acromion process and clavicle
Insertion: Laterally on top of humerus
Joint Crossed: Glenohumeral (shoulder) joint
Joint Action: Abduction (raising) of arm. Anterior fibres assist in flexion, horizontal flexion and medial rotation of the humerus. Posterior fibres extend (hyperextend) and laterally rotate humerus.

Man Showing Pecs - Level 3 Gym InstructorName: Pectoralis Major
Description: Large fan-shaped muscle covering chest and forms anterior wall of the axilla (armpit)
Origin: Clavicle, sternum and cartilage of ribs 1-6
Insertion: Lateral part of humerus
Joint Crossed: Shoulder joint
Joint Action: Flexion and medial rotation

Name: Latissimus Dorsi
Description: Broad, flat, triangular, covering most of lower back
Origin: Thoraco-lumbar fascia (TLF) from C7-C12, lumbar vertebrae and iliac crest (pelvis). Also lower 3 ribs and bottom (inferior) edge of scapula
Insertion: Top lateral part of humerus
Joint Crossed: Shoulder joint
Joint Action: Prime mover in arm adduction, extension and hyperextension. Assist in medial rotation of the arm and depression of shoulder girdle

For part two of level 3 Gym Instructor muscle anatomy click here.

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

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