Changes

This is a stylised view of the lateral aspect of the proximal left forelimb of the sheep.  The skeleton is made of bones and cartilages.  A combination of ligaments, muscles & tendons, and sheets of fascia, examples of which are shown, hold these together. Without these soft tissues around them, the jointed bones will not support the weight of the sheep.]]

This is a stylised view of the lateral aspect of the proximal left forelimb of the sheep.  The skeleton is made of bones and cartilages.  A combination of ligaments, muscles & tendons, and sheets of fascia, examples of which are shown, hold these together. Without these soft tissues around them, the jointed bones will not support the weight of the sheep.]]

'''Stress, strain & elasticity'''

'''The elasticity of tissues'''

An appreciation of the concept of elasticity is essential to understanding the mechanics of animals.  

An appreciation of the concept of elasticity is essential to understanding the mechanics of animals.  

Elasticity is measured by determining the effect of stress, defined as force per unit area, on the shape of the material.  When this stress acts in only one direction, this shape change is measured as strain, the distortion per original unit distance, expressed as a percentage.  

Elasticity is measured by determining the effect of stress, defined as force per unit area, on the shape of the material.  When this stress acts in only one direction, this shape change is measured as strain, the distortion per original unit distance, expressed as a percentage.  

At a particular percentage of strain, r, a stiffer material will store more elastic energy than a more elastic tissue.  Suppose that at this strain percentage, the material can no longer be deformed without damage.  Fracture will occur, and because the stiffer material releases more energy it will shatter rather that suffering a simple break.  Bone fractures are discussed later in Chapter 3.  

At a particular percentage of strain, ''p'', a stiffer material will store more elastic energy than a more elastic tissue.  Suppose that at this strain percentage, the material can no longer be deformed without damage.  Fracture will occur, and because the stiffer material releases more energy it will shatter rather that suffering a simple break.  Bone fractures are discussed later in Chapter 3.

 

The passive musculoskeletal tissues are elastic.  After being deformed by an external force, they return to their original shape.  Elasticity is measured by determining the effect of stress, defined as force per unit area, on the shape of the material.  When this stress acts in only one direction, this shape change is measured as strain, the distortion per original unit distance (Fig.  2.2), expressed as a percentage.

[[File:Fig 2.2.png|thumb|'''2.2'''  Two linearly elastic tissues A and B have stress - strain curves as shown.  The energy absorbed by A and B is represented here by the area beneath the curve,  At any given value of stress, a,  the strain r is less for A than for B.  A has absorbed less energy than  B.  A is stiffer than B.  If A and B were bones, A would be the more mineralised.]]

[[File:Fig 2.2.png|thumb|'''2.2'''  Two linearly elastic tissues A and B have stress - strain curves as shown.  The energy absorbed by A and B is represented here by the area beneath the curve,  At any given value of stress, a,  the strain r is less for A than for B.  A has absorbed less energy than  B.  A is stiffer than B.  If A and B were bones, A would be the more mineralised.]]