Based on the knowledge you have acquired in (Basic Anatomy and Physiology), you now have an understanding of how the body’s locomotive. Structures allow movement and the handling of loads. In this chapter, we turn that anatomical and physiological knowledge into mechanical principles of loading, allowing you to identify, analyse and evaluate the greatest risks for physical injury in the workplace.
One of the great strengths of engineering is the ability to make simplifications in order to calculate how much loading the body is under. If you have limit values available, biomechanical calculations can tell you whether a chosen task, in terms of posture, forces and time, will push the human beyond his or her limits.
These simplifications are the basis for most ergonomics evaluation methods, which are explained. When you can identify unhealthy physical loading based on principles, you can reason your way into better decisions when choosing design solutions for the workplace.
For the system performance improver and work environment/safety specialist striving to identify improvement potentials in a workplace, the anatomical and physiological knowledge may be overwhelming to keep in mind and difficult to separate into analytical components in order to look for risks in a structured way – therefore, this chapter provides an intermediate step along the way to the ergonomics evaluation methods by showing how the body’s reactions to loading can be simplified into some main components that can be systematically observed and later targeted in improvements.
Basic Anatomy and Physiology, the body’s tissues work together to withstand many different types of biomechanical loading. Exceeding the body’s physical ability to handle these loads results in pain and physical injury, which can be either sudden or chronic. But if we regard the problem from an engineering perspective, we need concepts and methods to identify what exactly makes physical loading a risk.
To make this possible, we adopt the view that:
Physical Loading = posture × forces × time
Body posture demands that the body’s muscles actively work to maintain a position, which is a form of internal loading. The posture aspect includes how internal forces are distributed across the different parts of the body (for example, lifting something off the ground with a straightened back engages mostly the leg muscles which are large and strong, while lifting the same object with a bent back loads the upper torso which has smaller, weaker muscles).
External loading occurs as a result of handling weights, e.g. by pushing, pulling, lifting, pressing or dragging something. Generally, when force is counted as a component of loading, we are mainly referring to external loading. In some biomechanical analyses, the weights of the human’s own body parts are sometimes also considered a load, especially if gravity influences the chosen posture.
Finally, time factors describe how long, how often or how frequently the body’s structures are loaded. Since you now know that the muscles and tissues can work for a limited time until they are fatigued and need to rest, the level of risk depends on whether the exposure is suitable for strength- or endurance-type body structures. The time component most frequently focuses on repetitiveness, which is considered a major health risk because the body’s structures are not allowed enough recovery between loadings.
Posture denotes how the body is aligned and positioned, especially in states of activity. A posture can occur as a result of consciously choosing how to position the body, or less voluntarily as a result of adapting to available space, tool sizes, visual demands, pain, etc. Posture may be influenced by the contextual factors
There is a conception of “good” and “bad” posture, stemming from societal norms about keeping the body upright, symmetrical and well aligned. From a work design perspective, good posture is more than keeping your head upright and your back straight – it also includes strong hand postures, equal weight balance between the legs, and deliberately handling external loads close to the centre of the body. As a useful, operative definition for engineering work, we can define good and bad posture as follows:
Good posture is a position where the functional structures of the body are in the best possible position to exert high Force or high-precision movements, as required by the work task. Indications of good posture are balance, symmetrical distribution of forces on the body parts, and skeletal (rather than muscular) loading.
Bad posture is a position where body is in a weak position to perform physically demanding work. Bad posture puts the body tissues under extra,unnecessary physical load that does not contribute to the task at hand. Indicators of bad posture include positions at the outer range or movement (hyperflexion or hyperextension), asymmetry, imbalance between the legs, slumping, and forced muscular loading rather than skeletal loading.