• Anatomy Of Fitness

How to classify SKELETAL MUSCLES?

Updated: Nov 12

What are skeletal muscles? How do we classify skeletal muscles?

The article will teach us to classify Skeletal Muscles based on critical parameters.

Typically muscles are classified as:

  1. Skeletal Muscles

  2. Smooth Muscles

  3. Cardiac Muscles

Classification of Muscles in the human body.

Google dictionary defines a Skeletal Muscle as a muscle which is connected to the skeleton to form part of the mechanical system which moves the limbs and other parts of the body.

Skeletal Muscles are referred to as striated muscles because of their striated appearance.

There can be numerous classifications based on various parameters for Skeletal Muscles. The most common types are as follows:

Based on Fibre Direction and Shape

Parallel: Fibres extend the whole length of the muscle and are parallel to each other

  1. Rectangular: Fibres parallel to each other having equal length abdomen

  2. Rhomboidal: Fibres parallel in sides, adjacent sides are unequal in length

Pennate: Fibres arranged in the form of a feather-like pattern, are short and parallel, lying obliquely to a central axial tendon

  1. Unipennate: Fibres are attached to one side of the tendon resembling half of a feather

  2. Bipennate: Fibres are attached to both sides of the tendon resembling a complete feather

  3. Multipennate: Collection of multiple bipennate structures

  4. Circumpennate: Fibres attached to all sides of the tendon

Fusiform: Arranged in the form of a spindle as a belly and two tendons

  1. One head

  2. Two heads

  3. Three heads

  4. One belly

  5. Two bellies

  6. Multiple bellies

Triangular: One side triangle or two side triangle-shaped

  1. Fan-shaped: Triangle shaped on one side

  2. Trapezoidal: Triangle shaped on two sides

Sphincter: Arranged in a circular form

Classification of Skeletal Muscles based on FIBRE DIRECTION & SHAPE.

Based on Action

Agonist muscle: Prime mover (may contain primary and secondary movers)

Antagonist muscle: Oppose the prime movers to allow agonist to move

Synergist muscle: Assistor to the agonist muscle

Stabiliser muscle: Keeps joints stable

For example, when you flex your elbow:

  1. Biceps brachii is the agonist muscle

  2. Triceps brachii is the antagonist muscle

  3. Brachioradialis and brachialis (forearms) are the synergist muscles

  4. Shoulder muscles like anterior deltoid, middle deltoid, posterior deltoid etc. are the stabiliser muscles

Classification of Skeletal Muscles based on ACTION.

Based on the Number of Joints Crossed

Uniarticulate muscle: Muscle crossing only one joint

Example – brachialis, soleus etc.

Biarticulate muscle: Muscle crossing two joints

Example – gastrocnemius, hamstrings, rectus femoris

Multiarticulate muscle: Muscle crossing more than two joints

Example – erector spinae, multifidus

Classification of Skeletal Muscles based on NUMBER OF JOINTS CROSSED.

Based on Myoglobin Content

Slow-twitch muscle: Contain more red fibre, responsible for movements requiring slow action for an extended time

Fast-twitch muscle: Contain less red fibre, responsible for movements requiring fast action for a short time

Classification of Skeletal Muscles based on MYOGLOBIN CONTENT.

Based on the Type of Muscle Contraction

Isometric contraction: Muscle contracts but does not shorten

Isotonic contraction:

  1. Concentric contraction: Helps in moving weight against the line of gravity; muscles origin and insertion come closer while contracting

  2. Eccentric contraction: Helps in moving weight in the line of gravity; muscles origin and insertion move farther while contracting

Classification of Skeletal Muscles based on type of MUSCLE CONTRACTION.

Based on the Orientation of the Line of Pull in Relation to the Joint

Flexor: Line of pull passes anterior to the joint axis

Extensor: Line of pull passes posterior to the joint axis

Adductor: Line of pull passes medial to the joint axis

Abductor: Line of pull passes lateral to the joint axis

Classification of Skeletal Muscles Based on ORIENTATION OF LINE OF PULL IN RELATION TO THE JOINT.

Key takeaways:

  1. Typically muscles in the human body are classified as: Skeletal Muscles, Smooth Muscles and Cardiac Muscles.

  2. Skeletal Muscles can be classified using various parameters.

  3. The key parameters for classification of Skeletal Muscles are based on: Fibre Direction & Shape, Action, Number of Joints Crossed, Myoglobin Content, Muscle Contraction and Line of Pull.

Now we understand how to classify Skeletal Muscles using critical parameters.

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