Very simply, manual handling is all about mechanics! Just think back to those physics lessons at school when we learned about forces and levers etc.
Go on – you remember Newton’s Laws of Motion!
Biomechanics is the name given to the study of mechanics as applied to human movement. It looks at the mechanisms involved when we move and the forces that act upon our bodies during specific actions. By having an understanding of these forces it is possible to identify:
1 Those factors that increase loading on the spine and other structures and
2 What is involved in ‘good’ posture when handling
Lifting and handling tasks involve three kinds of risks:
Risk 1 – The risk of accidental injury for example the loss of footing, the load falling on the handler, the load trapping the handler.
Risk 2 -The risk of overexertion
Risk 3 – The risk of repetitive or cumulative damage
The risk involved in the handling of a load will increase as a direct result of:
1 The weight of the load – if it’s heavy there is more risk of injury!
2 The distance of the load from the persons body (either forward or to the sides) – the further away from the body the load is handled e.g. when having to work with the arms outstretched the risk of injury increases with the distance from the body.
Over exertion and therefore injury is more likely when:
1 The strength of the lifting action is less
2 The body is out of balance
3 The back might be bent (flexed)
In order to understand the biomechanics of human movement we need to understand:
The principles of mechanics – gravity, force, friction, stability, stress and strain and levers
Efficient movement of the human body involves the application of biomechanical principles. The better the control of movement and balance we have the less strain is put on muscles and the less static muscle work is required.
Although some ways of moving and handling feel ‘normal’ that does not necessarily mean they are correct or safe. We develop habits that may be potentially harmful. These have to be unlearned and the new, safer ways must replace them.
Centre of Gravity (COG)
The centre of gravity is roughly the centre of the space that a load occupies i.e. the centre of the box.
Unfortunately the human body is not a uniform or regular shape so that the centre of gravity moves as the body changes position and so for a person standing with their arms at the side, the centre of gravity coincides with the middle of the pelvis but if the person raises their hands above their head then the centre of gravity rises into the tummy area.
The further the centre of gravity is from the centre of the body the more effort is needed to keep the body stable so that raising the arms as in reaching and stretching causes the centre of gravity to rise making the body less stable and at more risk of injury.