The Skeletal System

What is the skeleton?

The human skeleton is quite simply a collection of about 206 different shaped bones that align with each other to create a protective framework for the body that muscles can connect to and provide movement from.

An example of the skeleton in the anatomical position can be seen in the adjacent image.

What does the skeleton do?

The skeleton provides four major functions, which are;

1. Support :  It provides a framework to support the organs and tissues of the body.  

2. Protection:  It protects our internal organs.  The skull protects the brain; the thorax (sternum, ribs and spine) protects the heart, lungs and other viscera (organs within the thorax).

3. Movement:  It provides a framework for muscles to attach.  Then when the muscles contract they pull on the bones of the skeleton, which act like levers to create movement. 

4. Supply & Storage:  The bones that make up the skeleton are a source of both red blood cells (which transport oxygen) and white blood cells (which fight infection), which are formed within the bone marrow.

Why is the skeleton important?

When considering the four major functions of the skeleton it is easy to see why it is so important.  Without it we would simply be a pile of 'jelly' lying on the floor, unable to move and with no blood or immunity.  So maintaining a healthy functioning skeleton is part and parcel of being able to do all our daily activities and participate in all physical activities effectively.

The skeletal system and fitness

Understanding the skeletal system and its functions is very important for you as a personal trainer.  This is because it can help you complete everyday aspects of your job such as assessing someone’s movement, identifying dangerous movements and correcting exercise technique. 

For example when working as a personal trainer it’s the posture (position of the bones) of the skeleton that indicates whether someone’s technique is correct or if their movement patterns need refining. 

This can be seen in the below images of good and bad technique of a squat.

What is bone?

Bone is the rigid organ that makes up the skeleton and it has its own nerves and blood vessels in order to help sustain it.  Bones also have a clever construction that allows them to remain lightweight yet strong.  This is because they are formed out of multiple layers of three different types of tissue, these are;

1. Compact bone; this is heavy, dense, strong and thickest at the bones weakest point, usually the centre of the shaft.

2. Cancellous bone; this has a honeycombed appearance and is strong and hard without the weight of compact bone.  It is found mainly in the ends of bones.

3. Periosteum; this is the membrane of connective tissue that lines the outer surface of all bones.  It houses the nerves and blood vessels that innervate and nourish the underlying bone and acts as an attachment for tendons and ligaments.

Bones and the skeleton

As previously mentioned the bones within our bodies come in various shapes and align with each other in order to create the skeleton. 

The major bones of the human skeleton are shown on the following image with their common names and anatomical names (in brackets). 

Knowing anatomical names certainly helps when working with other health professionals (doctors, physiotherapists) but most clients appreciate you using common names and terms that they understand.  You gain no ‘kudos’ for confusing your personal training clients so ensure you always talk with them in a language they understand. 

  Major bones of the human skeleton

Image 1: The human skeleton

Although we often look at the skeleton as a whole structure, it can also be divided into two groups, the axial and appendicular skeleton.

Axial skeleton: 

The axial skeleton consists of the following three parts and can be seen as the non-shaded area in the following diagram.

1. skull
2. vertebral column
3. bony thorax (ribs and sternum)

The main purpose of the axial skeleton is to provide protection for the central nervous system (brain and spinal cord) and vital organs, such as the heart and lungs.

It is also the structure that provides the support and attachment for your arms and legs.  This allows us to do everyday movements such as walking, running, jumping and carrying.

Appendicular skeleton: 

The appendicular skeleton consists of the following six parts and can be seen as the shaded area in the adjacent diagram.

1. arms
2. legs
3. hands
4. feet
5. pelvic girdle
6. shoulder girdle

The main purpose of the appendicular skeleton is to allow movement to occur through the joints of our arms and legs.  Without the appendicular skeleton we would be unable to move around and do the activities we do on a daily basis.

Vertabral column

The vertebral column (spine) is a key part of the axial skeleton.  It is important to have a good understanding of the spine as it is a common area that people injure and have postural issues with. 

For this reason, as a trainer understanding the spine and its natural curves will help you cue clients when exercising in order to keep them safe, as well as communicate with other professionals such as physiotherapists.

Key points of the vertebral column

The vertebral column is made up of lots of individual vertebrae which are grouped together into five different sections.  These sections are listed below and can also be seen on the adjacent diagram.

1. cervical - seven vertebrae
2. thoracic - twelve vertebrae
3. lumbar - five vertebrae
4. sacrum - five vertebrae
5. coccyx - four vertebrae

When analysing the spine or talking to another professional, such as a physiotherapist, it helps to reference each vertebra as a number.  For this reason vertebrae are numbered in descending order in their corresponding sections i.e. the top (superior) cervical vertebra is known as C1 and the bottom (inferior) cervical vertebra is known as C7. 

Below is a table showing how the vertebrae are numbered from top to bottom.