Protecting Workers' Health Series No. 5
Preventing musculoskeletal disorders in the workplace: Previous page | 1,2,3

Part 2: Guidance on main risk factors

In this part, some of the main risk factors for the development of musculoskeletal disorders are listed, and examples of tasks and working conditions are provided. Additionally, potential causes for health disturbances and injuries as well as suggestions as to how to avoid these are made.

Risk frequently results from exposure to mechanical loading. The main influencing factors are high forces resulting from lifting and pushing or pulling heavy objects, high repetition frequency, long duration of force execution, unfavourable posture, uninterrupted muscle force exertion or working on or with vibrating machines. In some cases, the degree of handling precision, rather than the actual force exerted, constitutes an additional hazardous factor.

Risk factor: Manipulation of heavy loads

Where are heavy loads manipulated?

Examples are:

• lifting and carrying of heavy objects in transportation jobs, construction sites, etc.,
• transferring persons in health professions, in old-age care and hospital care.

Why are heavy loads harmful?

Holding and moving of heavy loads requires high muscular force; this may lead to acute overload and/or fatigue of muscles. Examples: Repeated manipulation of heavy bricks in construction work, loading of coffee sacks, cement bags or other loads in ships, containers or lorries

During holding and moving of heavy loads, high forces occur in the skeletal system, too. Risk of acute overloading and damage may result. Loadings being incurred over a long period of time may cause or promote degenerative disorders, especially in the low-back area (e.g. when handling loads with a bent back).

For the individual risk of manual materials-handling activities, the functional capacity of the working person plays an important role

How can heavy loads be handled with low risk for harm?

The most important factors concerning the risk are the weight of the object to be manipulated, the horizontal distance between the load and the body and the duration and repetition frequency of task execution. This leads to some important measures for handling objects

Advice to the employee:

• Lift loads close to the body.
• Lift with both hands, symmetrically to the mid-sagittal plane, bring the load as close as possible to the body.
• Lift heavy loads with an upright trunk by extending the initially flexed legs and avoid manipulation of loads in unfavourable postures (e.g. lateral bending or twisting).
• Use cranes, lifters, dollies, hoists, pallet jacks, mobile elevators, or similar devices, if available, for lifting and transporting heavy loads.
• Carry heavy and/or unwieldy loads with two persons.

Advice to the employer:

• Avoid manual handling tasks, especially of heavy loads. If manual handling is still necessary, introduce ergonomic measures to minimize the resulting risk.
• Avoid moving loads over obstacles.
• Avoid carrying over uneven or slippery routes, over steps or stairs.
• Avoid high or frequent handling procedures.
• Avoid large masses (e.g. instead of one heavy sack use two sacks of smaller weight).
• Provide aids (hoists, or similar devices).
• Mark heavy loads.
• Mark non-symmetrical load distribution within the object.
• Mark containers or barrels with movable content (fluids, granules, etc).
• Suggest and carry out training on "handling".

Risk factor: Work with high force exertion

Where is high force exertion found?

Examples are:

Why is high force exertion harmful

The exertion of force requires high muscle forces. This may lead to an acute overloading and/or fatigue of muscles.

During such work high forces also occur in the skeletal system. This may lead to an acute overloading and injury of the skeletal structures. Force exertion, where the force acts distantly from the body, bears a high risk of damage to the lumbar spine tissues. For tasks with long-lasting or frequently repeated high force exertion, there is risk of degenerative diseases especially of the lumbar spine. This is true, in particular, if force exertion is carried out in unfavourable body postures

How can high force exertion be avoided?

Advice to the employee:

• Carry out pushing and pulling in such a way that the force acts close to the body.
• Avoid pushing or pulling with only one hand.
• Avoid pushing or pulling with strong lateral bending and/or twisted trunk.

Advice to the employer:

• Provide conditions for secure standing.
• Provide wheeled vehicles, trolleys, dollies, or similar devices.
• Avoid pushing or pulling in confined rooms because of constrained postures.
• Avoid obstacles and uneven ground

Risk factor: Working in unfavourable body postures

Where do unfavourable postures occur?

Examples are:

• Work overhead.
• Work in constrained positions.
• Work in confined rooms.
• Work in extremely bent, twisted or extended postures.
• Work in a continuously inclined posture (e.g. construction work, concrete reinforcement work).
• Work out of reach.
• Work in a kneeling, lying, crouching or squatting position .

Why are unfavourable postures harmful?

The keeping up of a certain body posture demands high muscle force; acute overload and/or fatigue of muscles can, therefore, be the result.

Examples are:

• Construction work far from the body demands high activation of musculature for holding the arms.
• Twisted or extended body postures demand high muscular strain and tension of trunk muscles.

During unfavourable body postures, high forces occur also in the skeletal system. This may lead to acute overloading and damage of skeletal structures. For long-lasting activities with an inclined trunk, degenerative disorders, especially in the lumbar region, can arise if such work is executed over a period of many years.

Maintaining unfavourable body postures for long periods of time is connected with long-term activation of certain muscles which may lead to muscular fatigue and considerable reduction in blood circulation. Such partial decrease in the functional ability of the musculature leads to a reduced ability to react on sudden impacts and may therefore result in increased accident risk.

How can unfavourable postures be avoided?

Advice to the employee:

• Bring body close to the position where the object must be handled, or where force application is performed.
• Avoid strong lateral bending or twisting of the trunk.
• Approach the working area and body close enough to enable carrying out the task within reach; use aids such as scaffolds and ladders, if suitable.
• Change posture often to activate different muscles alternately while carrying out tasks; consider alternating between standing and sitting postures.

Advice to the employer:

• Offer adjustable equipment: chairs, tables, scaffolds, etc.
• Supply rooms of sufficient size to avoid constrained postures.
• Arrange tools within reach. Set time-limits when constrained postures are unavoidable and/or alternate tasks of different nature.
• Avoid giving tasks that require a kneeling, lying, crouching, or squatting position.

Risk factor: Monotonous repetitive tasks

Where do monotonous repetitive tasks occur?

Execution of similar or identical movements during a large part of the working time with a high rate of repetition (i.e. several times per minute). During the course of work the working person has often little influence on the working pace, speed, task sequence and work and break schedule. Commonly, the working person cannot abandon the workplace without being replaced by another person.

Examples are:

• Assembly line .
• Cash registration .
• Loading of packing machines.

Why are monotonous repetitive tasks harmful?

Long-lasting repetitive muscle load leads to muscle fatigue, which - if sufficient recovery is not guaranteed - may lead to irreversible changes in the muscular structure. Not only high-level forces but also low-level forces may cause such an effect. Repetitive movements are often superimposed with static loading, in particular postural load.

How can monotonous repetitive tasks be avoided?

Advice to the employee:

• Avoid continuous loading of the same muscles for longer periods of time.
• Strive for changes in motion in order to avoid identical muscular activation patterns. For strongly monotonous work, changes in the execution of movements may be limited.
• Change body posture frequently in order to reduce static loading.
• Use rest pauses

Advice to the employer:

• Provide for organizational changes, such as job rotation, job diversification or job enrichment, to reduce the extent of task repetition for individuals.
• Enable autonomous decisions about the timing of breaks
• Mechanize unavoidable monotonous tasks with high load.

Risk factor: Long-lasting loadings

Where do long-lasting loadings occur?

Examples are:

• Maintaining a static posture (e.g. during bricklaying at floor level; concrete rein-forcement work; picking of fruits and vegetables at floor level; writing; typing; work with computer mouse).
• Holding of objects or tools (e.g. drilling in a ceiling; overhead painting; holding of operation instruments in surgery, carrying a tray uninterruptedly) .

Why are long-lasting loadings harmful?

Long-lasting muscle load leads to muscle fatigue. Fatigue without sufficient recovery can lead to irreversible changes in the muscular structure. Even the exertion of low-level forces (for example, long-lasting fixed posture) can lead to over-exertion and fatigue of small muscles or muscle groups. Long-lasting contraction of muscles may result in insufficient blood circulation.

In the skeletal system long-lasting loading (e.g. due to long-lasting work in an inclined posture) can lead to deficient nutrition of the spinal discs.

How can long-lasting loading be avoided?

Advice to the employee:

• Move instead of holding a static position.
• Use tools for holding objects.
• Strive for frequent change in body position.
• Strive for frequent upright positions from inclined positions.
• Stand up from time to time when working in a sitting position, for example, while making a telephone call.

Advice to the employer:

• Provide tools for holding (e.g. screw-clamps; handles, which enable holding with low muscle force).
• Provide scaffolds, ladders, or similar devices.
• Supply arm supports at computer workplaces.
• Supply handles or grips which can be used with right as well as left hand.
• Place handles/grips to enable use in a neutral position of wrist and arm.

Protecting Workers' Health Series No. 5
Preventing musculoskeletal disorders in the workplace: 1,2,3