Ian Griffiths Sports Podiatry
Foot, Ankle and Lower Limb Injury Specialist
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Biomechanics of Injury     Tissue Healing     Sports Injury Myths      

Biomechanics of Injury

 

When human tissues are subjected to a loading force (or stress) such as they are during activity, then they will deform (this deformation is called strain).  The relationship between stress and strain can be shown graphically and is often referred to as a load deformation curve, seen below.

 

Whether tissues will become injured when performing high impact activity will depend upon the forces (stresses) and deformations (strains) within the tissues, and may therefore also be influenced by an individuals own structure/anatomy and its ability to tolerate such loads.  

                                          

 

 

 

Deformation of tissue is initially proportional to load (1).  Using an Achilles Tendon as an example; most normal daily movements will occur within this region, the initial deformation due to the straightening out of crimped fibres.

 

As stress and strain increase the tissue moves into the linear portion of the curve known as the elastic region (2).  In this region it will return to its original shape when the force is removed.  So in our Achilles example, the tendon will deform/elongate when loaded (when running for a bus for example), but once it is unloaded (sitting on the bus) it will return to its previous state.  This is a mechanical property known as viscoelasticity.

 

At higher or repetitive forces (such as training for a marathon) a tissue may become stressed beyond its elastic range, and into the plastic region where it may enter the microfailure zone (3).  Clinically this may be seen as a tendinopathy.  If loading continues further (i.e. training through this 'niggle') the tissue may permanently deform or potentially fail (4).  Clinically this may present as a partial or complete rupture of the Achilles Tendon.  It is this mechanism of tissue damage which is responsible for the majority of chronic overuse sporting injury.

 

In order to remain injury free human tissues (bone, cartilage, tendon, ligament and skin) must function at stress levels that are within the elastic region of their load/deformation curves*.  This may well require appropriate tissue conditioning, and good training habits alongside analysis of movement patterns.

 

*N.B. This curve will be different for each type of tissue, but will usually follow a similar shape.