A workplace hazard is a potential source of harm to a worker. The harm, in this case, is the development of MSD. MSD hazards typically appear when the way that work is organized brings the worker and the workspace together.
Basic MSD hazards are:
At work, these basic hazards occur in combination. For example:
Generally, the more basic hazards are combined, the higher the likelihood of developing MSD.
One or more of these basic hazards are seen in tasks such as lifting from the floor; twisting when lifting; working with arms overhead; gripping or holding objects or tools for extended periods, especially in a pinch grip; using vibrating tools; prolonged standing and long hours working with a computer.
The basic MSD hazards are described below. Remember that they occur together in different combinations when people are at work. This makes it difficult to know their combined risk of developing MSD by watching unless one of the basic hazards is very large. Observational and comprehensive assessment tools use scoring systems or equations to account for the combined effect of the basic hazards.
Examples of force include the force exerted on a box during lifting or the grip force to hold a hand tool. The loads lifted and grip forces exerted are called external forces.
If the external force is high then muscles around the joints must contract forcefully and create internal forces that loads the bones, muscles, ligaments etc. It is high forces inside the body that can lead to the development of fatigue or MSD.
For example, a worker can hold a tool in either a power grip or a pinch grip. The worker has to use the same force (external force) to do the job using both grips. The forces in the muscle and bones are much higher when using the pinch grip. A power grip is good for tasks with high force. A pinch grip gives better precision BUT the forces in the muscles and bones are much higher. This can increase fatigue and the risk of developing MSD in pinch grips.
The back is wonderfully versatile. Damage or disorders of the low back occur when the forces exerted on the spine overload its bones, ligaments, cartilage and discs...
Posture is the position of the body and its joints – an elbow is bent (flexed) or straight (extended). Some positions of a joint are stronger and healthier than others. These are sometimes called neutral postures. An awkward posture is one where the joint is weaker and where it does not function as well as in neutral posture. These awkward postures, over time, can lead to fatigue and increased risk of developing MSD.
The hand is wonderfully versatile and can use a wide range of grips at work. Also, the wrist joint works together with the fingers to create strong natural grips. MSD posture hazards are seen when tools, equipment, products or the workspace require a worker to use poor grips and awkward postures. The grips are also weaker in this case.
Videos and graphics show the hand at work. What the colours mean (Info bubble)
To find tools that help identify Hand and Wrist hazards and to assess work using hands go to the Tool Picker. Use these videos and graphics to help use the tools.
Videos and graphics show the shoulder at work and MSD hazards for the shoulder:
To find tools that help identify Shoulder hazards and assess work go to the Tool Picker. Use the examples above to help use these tools
Videos and graphics show the back at work and MSD hazards for the back:
To find tools that help identify low back hazards and assess work go to the Tool Picker. Use the examples above to help use these tools.
Repetition describes how the postures and forces vary over time. Does the person spend a long time bent over (a static posture), or are they frequently bending over then standing up (repetitive work)? There can be repetition of a posture or repetition of a force. Closely related concepts include recovery (does the body have sufficient rest time) and duty cycle (the percentage of time that the body is working or exerting force).
Different studies and tools use slightly different concepts to describe repetition. Each way of describing it has merit. More recent studies and tools use concepts of duty cycle and recovery more frequently.
Organizations need to establish an effective risk assessment process that allows systematic hazard identification and risk assessment for hazards including those related to MSD.
How to do it?
Repetition is the same or a similar task or subtask being performed on a regular (periodic) cycle. Based upon earlier scientific studies, High repetition work is customarily defined as having a repeating cycle or sub-cycle with a cycle time of less than 30secs or having more than 50% of the cycle time performing the same kind of fundamental cycles.
Duty cycle is defined as the percentage of time a muscle is generating force. For example, a Highly Repetitive job has a work cycle 10 seconds long. The task requires the worker to use a hand tool for 6 seconds. The duty cycle of the hand force is 6/10 or 60%.
Hand Activity Level is a measure developed for the hand that includes both the duty cycle and repetition.
Recovery is the concept that after an effort by a limb or joint, recovery to its original strength occurs. If full recovery has taken place, the cycle of effort and recovery can continue for a long time. If the rest is not long enough, recovery will not be complete, fatigue will occur and strength will continue to drop.
The duration of work has an effect on the risk of developing MSD. A work shift may be 8 hours in length but it may be 2 hours or as long as 12 hours. Many assessment methods include its effects.
Follow this link to learn about the importance of work organization and MSD.
A worker may be exposed to vibration in two main ways:
A tool that digs into a worker’s hand or the pressure on the kneecap when kneeling both create local contact stresses. These contact stresses can, over time, injure the skin or cause blisters or injure the muscles, ligaments or bones underneath the skin.
There is some evidence that working in cold temperatures is associated with an increased risk of developing MSD. Different mechanisms have been proposed. However, working in the cold often requires a worker to wear gloves, which can greatly increase the effort required to grip objects.
For the Quick Start Guideline, key MSD prevention strategies have been extracted from the literature. The approach of the Quick Start Guideline was to identify the strongest and most common MSD hazards and show how these could be eliminated or reduced in common tasks. The mini-posters in the Quick Start Guideline therefore function as combined hazard identification and control guides.
Note: The Quick Start Guideline mini-posters do not include all MSD hazards. Please refer to the section on Workplace MSD Hazards for a more in-depth description.