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Muscular System. Back muscles Abdominal muscles Proprioceptors Lever system Fast / slow twitch muscles. Trapezius : Origin: occipital bone and vertebrae. Insertion: scapula Action: moves scapula -- adduction, elevation & rotation. Also rotates head of humerus

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Back muscles
  • Abdominal muscles
  • Proprioceptors
  • Lever system
  • Fast / slow twitch muscles

Trapezius: Origin: occipital bone and vertebrae. Insertion: scapula

Action: moves scapula -- adduction, elevation & rotation. Also rotates head of humerus

Latissimus dorsi: Origin: vertebrae

Insertion: humerus

Action: adducts and medially rotates arm


Levator Scapulae

Origin: transverse process of C1 – 4

Insertion: scapula – superior medial border

Action: elevate scapula

Rhomboids: minor / major

Origin: spinous process of cervical & thoracic vertebrae

Insertion: medial border of scapula

Action: adduct & downward rotation of scapula


Deltoids – anterior/ middle/posterior Origin: clavicle & scapula Insertion: Humerus

Action: abducts the arm

Errector Spinae

Origin: transverse & spinous processes of thoracic & lumbar

Insertion: spinous & thoracic process of thoracic & cervical, ribs

Action: extends & lateral flexion of neck & vertebral column

Obliques: Internal & External

Action – compress abdomen

Internal – origin: Iliac crest & fascia

insertion: lower ribs & fascia

External – origin: rib cage

insertion: iliac crest & fascia

Transversus abdominis: action – compress abdomen

origin: lower ribs & fascia

insertion: linea alba & pubis

Rectus Abdominis: flex vertebral column & compress abdomen

origin: pubic bone

insertion: ribs & sternum

  • Proprioceptors are sensory nerve endings found in all joints, muscles, and tendons. that sense (-ception) a change in body position (proprio-).
  • detect any changes in physical displacement (movement or position) and any changes in tension, or force, within the body
  • can cause an immediate reaction or its memory can be stored in the brain for minutes or years and then used to determine a bodily reaction at a future date.
  • The proprioceptors related to stretching are located in the tendons and in the muscle fibers
There are two kinds of muscle fibers: "intrafusal muscle fibers" and "extrafusal muscle fibers". Extrafusil fibers -contain myofibrils and are what is usually meant when we talk about muscle fibers.
  • Intrafusal fibers -called "muscle spindles" and lie parallel to the extrafusal fibers. Muscle spindles, or "stretch receptors", are the primary proprioceptors in the muscle.
  • Another proprioceptor, called the "golgi tendon organ” is located in the tendon near the end of the muscle fiber, is associated with stretching
  • A third type of proprioceptor, called a "pacinian corpuscle", is located close to the golgi tendon organ and is responsible for detecting changes in movement and pressure within the body.
When the extrafusal fibers of a muscle lengthen, so do the intrafusal fibers (muscle spindles). The muscle spindle contains two different types of fibers (or stretch receptors) which are sensitive to the change in muscle length and the rate of change in muscle length. When muscles contract it places tension on the tendons where the golgi tendon organ is located. The golgi tendon organ is sensitive to the change in tension and the rate of change of the tension.
  • Each muscle is attached to at least 2 bones & cross at the joint [ exception – sphincters]
  • Each lever has components:

Rod = bone

Pivot = joint

Weight that is moved = muscle +

Force = energy for movement

lever types
Lever Types
  • 1st class : weight ----pivot---force
  • 2nd class: pivot—weight---force
  • 3rd class: pivot—force—weight

This is the most common type in the body

** not every muscle will operate within a lever system

fast twitch slow twitch fibers
Fast Twitch/Slow Twitch Fibers

Skeletal muscle consists of three types of fiber.

Type I fibers (also called slow-twitch) cope better

with repeated muscle contractions, partly because

they have higher numbers of mitochondria than

type II (fast-twitch) fibers. Slow muscle fibers

contract slower and are used mostly in endurance

exercises.  Fast muscle fibers contract quickly and

are involved in quick movements. Most top sprinters

are 80% fast twitch while top marathoners are 80%


  The average person has a ratio of fast:slow twitch fibers that falls between 60:40 and 40:60.

Type I cells = Slow Oxidative. Have alot of mitochondria (containing oxidative enzymes) and capillaries.
  • Type II cells = Fast fibers are divided into two sub-categories: Fast Glycolytic (FG) or Fast Oxidative Glycolytic (FOG).
  • The FG fibers store lots of glycogen and have high levels of enzymes necessary for producing energy without oxygen, but contained few mitochondria. The FOG fibers have the best of both worlds, high speed and glycolytic capacity, plus high levels of oxidative enzymes.

These INTERMEDIATE fibers [FOG] were termed type IIA fibers by Brooke & Kaiser, 1970.

The pure fast fibers (FG) were termed Type IIb.

It does appear that pure fast (Type IIb) fibers can transition to "hybrid" (Type IIa) fibers with chronic endurance training. Biopsies of elite endurance athletes reveal that after years of training, they have almost no IIb fibers, but often have a significant percentage of the intermediate, IIa fibers. BUT, the majority of the available research suggests that Type IIa fibers do not transition to Type I.


Type I is darkest

Type IIb is lightest Type IIa is medium color

energy use muscular activity
Energy Use & Muscular Activity
  • Resting Muscle tissue – low energy need. Tissue reserves of ATP and CP [creatine phosophate ] are made [ fatty acids]
  • Moderate levels of activity – energy needs increase, mitochondria able to meet demands with available oxygen and body fuel [glucose/ fatty acids]
  • High Intensity level of activity – mitochondrial ATP production at maximum said to be about 1/3 of needed amount [glucose]
muscle fatigue
Muscle Fatigue

When you can no longer sustain a certain level of activity –it is said to be fatigued

Depletion of ATP / CP reserves, calcium levels

Damage to the tissue

Effects of energy, pain