What is Biomechanics?

What is Biomechanics?

Biomechanics is the application of mechanics to biology.

Mechanics is a branch of applied mathematics that deals with movement and tendency to movement. 

In practice there is no difference between biomechanics and mechanics except what is studied. 

Certainly in terms of underlying theory there is no difference whatsoever. 

However common usage of the term varies slightly from this rigid definition. 

A biomechanist is often interested in the physiology underlying movement (muscle physiology, nervous control, for example) and also the biological role of the movement (foraging, ranging, predator avoidance). 

1)Brief History

Formal mechanics in the modern sense dates back to Sir Isaac Newton in the 17th century but studying objects in motion dates back to the Ancient Greeks.

2) Fundamental concepts:

a) Dimensions: Length (or distance), Time, Mass.

b) Newton’s Laws: Motion, Universal Gravitation

3)Forces: internal, external, Friction, Adding Forces, Colinear, Concurrent, General Case, Static Equilibrium, Free Body Diagram, Static Analysis The unit of force is the Newton which is equivalent to 1kgms-2. You will sometimes see forces measured as kg weight (or even lb weight) which is the force needed to lift that weight in kg. It is often easier for non-scientists to understand: people have a feel for how much force it takes to lift a 1kg bag of sugar but do not know how big 10N is. You convert from kg weight to Newtons by multiplying by g.

Internal forces are the forces that act within the body: muscle forces, joint reaction forces, loads that act on the various body tissues. These forces cause the body shape to change by moving the various segments (limbs, torso, head) relative to each other.

4) Linear Kinematics:

Kinematics is the subsection of mechanics that describe how an object moves: position, velocity and acceleration. Linear kinematics describe objects that move in straight lines.

5) Linear Kinetics

Kinematics allows us to describe how an object is moving. If we then add the forces that are causing it to move we use the subsection of mechanics called kinetics. This is really where we start to use Newton’s Laws of Motion since they involve forces. 

6) Work, Power and Energy

Newton’s equations are not the only way of calculating forces and movements. We can also use the principle of conservation of energy. In some situations we know the energy transformation that happens during an event and can use this to calculate the outcome.

7) Torques and Moments

Much of the movement in the human body is rotational. Limb segments rotate at joints and muscles apply torques and the skeleton acts as a system of levers. This means that we need to know about rotational movement. As you will see rotational movement is very similar to linear movements with rotational analogues for the quantities we measured for linear motion.

8) Angular Kinematics

Now we are interested in rotational movement we need to be able to describe orientation as well as position. By choosing the right units we can create angular analogues of the equations we have previously covered.

9) Angular Kinetics

Now we have the tools to describe rotation we can investigate the relationships between torques and rotational movements. As we might expect these are directly analogous to the linear relationships.