Musculoskeletal Disorders, Workplace Ergonomics and Injury Prevention

Abstract

Musculoskeletal Disorders (MSDs) affect body parts, with severity ranging from mild to intense. When MSDs develop in occupational settings, sequel to the physical tasks involved in the performance of work and the condition of the work-environment, they are referred to as work-related musculoskeletal disorders (WMSDs). The development and prognosis of any particular MSDs are modified by multiple risk factors, which are physical, individual, and psychosocial, in nature. None of these factors act separately to cause WMSDs, rather, they interact. The goal of ergonomics is to create an ergonomically sound work-environment, with the view to reducing the occurrence of WMSDs. This is premised on adherence to effective workplace ergonomic principles (WEP). By and large, WEP is more effective when done both at the workplace and during the performance of leisure time activities. Often, WEP involves designing the workplace, with consideration for the capabilities and limitations of the workers, thus promoting good musculoskeletal health, and improving performance and productivity. For favorable outcomes, a three-tier hierarchy of controls (Engineering, Administrative, and use of Personal Protective Equipment) is widely accepted as a standard intervention strategy for reducing, eliminating, or controlling workplace hazards. Failure of this strategy will expose workers to WMSDs.

1. Introduction

Musculoskeletal disorders (MSDs) is used to described injuries or disorders of the musculoskeletal system, like muscles, nerves, tendons, ligaments, joints, and cartilage; including the supporting structures of neck and back, and can affect all parts of the body (Table 1). Musculoskeletal disorders are described as Work-related, i.e. Work-related Musculoskeletal Disorders (WMSDs) when they are caused, and/or made worse or persists longer than expected, by the performance of work/task, vis-a-vis., work-environment and work-conditions [1]. According to the Bureau of Labor Statistics (BLS), MSDs represent one of the largest work-related problems in the United States; with the incidence rate higher among male full-time workers compared with females [2]. And according to the 2020/21 Labour Force Survey (LFS) of the United Kingdom, 470,000 workers are suffering from WMSDs - new or long-standing [3]; the occurrence and pattern of WMSDs in the United Kingdom are as shown in Figure 1. In Nigeria, WMSDs are especially prevalent in certain occupational sectors and industries such as transportation, warehousing, manufacturing/petroleum industry, health care, Communication services, Butchers, agriculture, and construction services [4, 5, 6, 7, 8, 9].

Serial No.	Structures of the Musculoskeletal system	Examples
1	Muscle/Tendon (Including inflammation of the tendons and/or their synovial sheaths)	Muscle Sprain/Strain; Muscles fatigue eg Tension Neck Syndrome; Rotator Cuff Tendonitis; Epicondylitis, Bursitis; Tendon strain
2	Nerve (usually involve the compression of nerve)	Numbness/Tingling; Digital Neuritis; Radial Tunnel Syndrome; Trigger Finger; Carpal Tunnel Syndrome
3	Joint	Joint Pain; Proprioception; Tear; Temporomandibular joint (TMJ) Pain
4	Ligament	Ligament Sprain
5	Cartilage	KOA
6	Vascular (Affectations of the blood vessels)	vibration syndrome
7	Supporting structures of neck and back	Mechanical Back Pain; Stress; Anxiety

Table 1.

Common musculoskeletal disorders.

Figure 1.

Occurrence and pattern of work-related musculoskeletal disorders [3].

Work-related Musculoskeletal Disorders are classified according to the affected musculoskeletal/anatomical structure (Table 1). According to the Bureau of Labor Statistics (BLS), MSDs accounted for 32% of all injury and illness cases in 2014 among full-time workers [2]. Work-related musculoskeletal disorders usually develop over time, in form of cumulative micro-traumas, sustained while working; it development can also be episodic. Additionally, the severity can progress from mild (i.e., Occasional) to severe/intense (i.e., chronic). These disorders are seldom life-threatening but they impair the quality of life of a large proportion of the adult working population.

The National Institute for Occupational Safety and Health (NIOSH) defined WMSDs as those diseases and injuries affecting the musculoskeletal, peripheral nervous, and neurovascular systems and are caused or aggravated by occupational exposure to ergonomic hazards [10]. Ergonomic hazards refer to physical stressors and workplace conditions that pose a risk of injury or illness to workers’ musculoskeletal system. Ergonomic injury risks include repetitiveness and pace of work (i.e., repetitive motions), forceful motions, vibration, extreme temperatures (especially cold conditions), awkward work-posture and movements, caused by the inadequate design of work-stations, tools or other work equipment, and by improper work methods [11]. Other risk factors include, lack of influence or control over one's job, increase pressure (e.g., to produce more), lack of or poor communication, monotonous tasks, and perception of low support (e.g., management or co-workers). Furthermore, MSDs have been reported to be associated with reduced work ability, and decreased productivity among workers, across working populations [4, 7, 8, 9, 12, 13, 14]. According to the Bureau of Labour Statistics of the Department of Labour, MSDs is the diseases and/or disorders of the musculoskeletal system, and connective tissue, when the event or exposure leading to the case is bodily reaction (e.g., bending, climbing, crawling, reaching, twisting), overexertion, or repetitive motion [15]. They are not the result of any instantaneous non-exertion event like slips, trips, falls or similar incidents.

The occurrence of WMSDs has been attributed to the exposure of workers (employees) to physical factors at work, as a result of poor and/or none adherence to Work-place Ergonomic Principles (WEP). The occurrence of WMSDs are basically attributed to the performance of work, and work-environment, furthermore, MSDs are usually made worse and/or longer lasting by work conditions that preclude good ergonomic principles during execution. Therefore, adherence to WEP is essential in preventing the occurrence of WMSDs. Work-place ergonomic principles involves identifying, analyzing, and controlling work-place risk factors, for the purpose of preventing and/or reducing the occurrence of MSDs (i.e. soft tissue injuries), caused by performance of work, vis-a-vis, exposure to sudden or sustained force, vibration, repetitive motion, and awkward posture etc. This is achieved by creating an ergonomically sound work-environment. By and large, adherence to effective WEP helps to create a workplace condition and job demands, that is, at the capacity of the workers (working population), and thus can be very helpful in preventing/reducing WMSDs. Work-place ergonomic principles is particularly recommended in the conduct of all type job descriptions; including materials manual handling, office-work, and patients management, and rehabilitation.

This book chapter is based on detailed literature of the causes and prevention of WMSDs. It described the inherent workplace hazards, workers are exposed to, at the different work-environments; and the benefits of effective preventive strategies, using standard ergonomic principles (i.e., WEP), applicable for materials manual handling work-place, and during patients management/rehabilitation.

2. Musculoskeletal disorders – causes and prevention

2.1 Background

The disorders/injuries of the soft tissues of the musculoskeletal system - muscles, nerves, tendons, ligaments, joints, and cartilage, are commonly referred to by many names, including musculoskeletal disorders (MSDs), repetitive strain injuries (RSI), repetitive motion injuries (RMI), cumulative trauma disorders (CTDs) and overuse injury [16]. The problem with using other terminology other than MSDs, is that they appear to suggest a singular causative factor (e.g. repetition or stress) as the cause of the soft tissue disorders. This is restrictive, because the literature points to multiple causative risk factors for MSDs. The World Health Organization (WHO), has reported that WMSDs has multi-factorial aetiology; indicating that a number of risk factors contribute to causing these disorders [17, 18]. These factors are physical, work organizational, work-environment, work-conditions (i.e. repetition, sudden/forceful exertions - like lifting a heavy object, and repetitive/sustained awkward postures), psycho-social, individual, and sociocultural, in nature [17]. This multi-factorial aetiology is the major reason for the controversy surrounding WMSDs – as both multiple and individual factors have been identified in the development of WMSDs [17, 18]. The development of MSDs has been recognized as having occupational aetiology factors as early as the beginning of the 18th century [1]. However, it was not until the 1970s that occupational factors were examined using epidemiologic methods, and the work-relatedness of these conditions began appearing regularly in the international scientific literature [1].

2.2 Causes of musculoskeletal disorders

The musculoskeletal system (i.e., muscles, nerves, tendons, ligaments, joints, and cartilage) are most effectively utilized, when they are exposed to little or no work-place risk; i.e. one that is within the worker’s capability. The level of risk depends on the intensity, frequency, and duration of the exposure to these work-place risks/hazards. Furthermore, the effects of work-place risks may be amplified by organizational factors such as shift work, work pace, imbalanced work-rest ratios, demanding work standards, lack of task variety etc. Subjecting a worker to work (carry out a task), in an ineffective WEP, is making the worker to work outside his/her body’s capabilities and/or limitations. Simply put, the worker is being asked to put his/her musculoskeletal system at risk. This may lead to body fatigue in the workers, beyond their ability to recover, and which may result in musculoskeletal imbalance, and may eventually, lead to the development of MSDs . Thus, exposure to work-place risk factors, as a result of ineffective WEP, puts workers at risk of developing MSDs (Figure 2). According to the Bureau of Labour Statistics of the Department of Labor, the diseases and/or disorders of the musculoskeletal system (and connective tissue) is described, when the event or exposure leading to the case is bodily reaction (e.g., bending, climbing, crawling, reaching, twisting), overexertion, or repetitive motion [15]. As a matter of facts, “…there is an international near-consensus that MSDs are causally related to occupational ergonomic stressors, such as repetitive and stereotyped motions, forceful exertions, non-neutral postures, vibration, and combinations of these exposures” [19].

Figure 2.

Mechanism development of MSDs.

Work-related Musculoskeletal disorders do not result from instantaneous non-exertion events like slips, trips, falls etc. The main cause of WMSDs is exposure to (ergonomic) “Risk Factors” at the work-place. Thus, the disposition for developing WMSDs is related more to the difference between the demands of work and the worker’s physical work capacity, which decreases with age [20]. Therefore, adherence to an effective Work-place ergonomic principle/design is essential in the prevention of the development of MSDs. Epidemiological studies [1, 21] have categorized work-place ergonomic risk factors into three, namely: (a) Physical factors (like sustained or awkward postures, repetition of the same movements, forceful exertions, hand-arm vibration, all-body vibration, mechanical compression, and cold) (b). Individual factors (like age, gender, professional activities, sport activities, domestic activities, recreational activities, alcohol/tobacco consumption and, previous WMSDs), (c). Psychosocial factors (like work-pace, autonomy, monotony, work/rest cycle, task demands, social support from colleagues and management and job uncertainty). In this book chapter, ergonomic risk factors are broadly divided into two categories: work-related (ergonomic) risk factors and individual-related risk factors.

2.2.1 Work-related risk factors

This is further divided into two - Primary and secondary factors. There are three primary work-related (ergonomic) risk factors, which are basically physical in nature:

1. Sudden/Forceful Exertions: These are work-tasks and cycles, that require high force loads on the human body, like heavy lifting, pulling, pushing a heavy objects, or excessively squeezing a hand tool such as a hammer. During execution by the workers, muscle effort increases, in response to the high force requirements, thus, leading to increased associated fatigue, and subsequent musculoskeletal imbalance, particularly when fatigue overturns workers body’s recovery system. And over time, this will eventually leads to the development of MSDs, as fatigue continues to overturn recovery. A study by a group of Swedish researchers demonstrated, using Doppler ultrasound scans, that chronic (prolonged) contraction of a muscle can cause a narrowing of the blood supply to the muscle due to compressive effect on the muscle [22]; thus reducing circulation to the muscle fibers and increasing the time required for recovery. This can be precipitated by both static and dynamic muscular contraction (loading) and duration, although static loading is a greater risk factor than dynamic loading, since static loading results in increased muscle fiber recruitment and fatigue and decreased blood perfusion. Forceful exertions produce increased muscle effort in response to high task load, thus, leading to more rapid muscle fatigue and overuse which can lead to upper extremity injuries.

2. High (Task) Repetitions: These are work-tasks and cycles that are repetitive in nature, that is, require making the same motions repeatedly. They are frequently controlled by hourly or daily production targets and work processes. A task is considered to be highly repetitive if the cycle time is 30 seconds, or less, or if a task or motion is performed more than 50% of the time it takes to complete the work cycle [23]. Work and rest cycles are the intervals of time measured during one complete task revolution or cycle. The more repetitive the task or cycle is, the less recovery time there is for the muscles and tendons. Inappropriate rest/work cycles are work cycles that do not allow time for sufficient recovery; this may lead to the accumulation of micro trauma, sequel to exposure to ergonomic hazard. Thus, leading to CTDs. When combined with other risks factors (e.g. sudden/forceful exertion and/or awkward postures), high repetition tasks can lead to increased fatigue, and subsequent musculoskeletal imbalance, particularly when the fatigue overturns workers body’s recovery system. And will eventually leads to the development of MSDs, as fatigue continues to overturn recovery, over time.

3. Awkward postures (Repetitive or Sustained): The positions of the wrist and arm are often considered during awkward postures while executing out the tasks, which may be repetitive or sustained. Awkward postures are those in which joints are held or moved away from the body's natural position; like prolonged standing/sitting, significant sideways twisting, reaching above shoulder height, one handed lifting/carrying, kneeling and squatting (Figure 3). The closer the joint is to its end of range of motion, the greater the stress that is placed on the soft tissues of that joint (muscles, nerves, and tendons). The joints of the body are most efficient when they operate closest to the mid-range motion of the joint. Risk of MSDs is increased when joints are worked outside of this mid-range repetitively or for sustained periods of time without allowing for adequate recovery time. Assumption of awkward postures creates an ergonomic hazard, as it place excessive stress/force (overload) on the musculoskeletal structures (i.e. muscle, joints, cartilage, and tendons) in an asymmetrical manner, thereby imposing a static load, and thus reduces nerve and muscle blood flow on these structures. An example is any activity that uses repetitive finger motions with the wrist in an extended position, and in a constrained postures, such as playing a musical instrument or typing. Exposure to this risk factor, in combination with other risks factors like repeated exposure to force, vibration, awkward posture or repetitive lifting of heavy objects in extreme or awkward postures, can lead to increased fatigue, and subsequent musculoskeletal imbalance. This will eventually leads to the development of MSDs, as fatigue continues to overturn recovery, over time. For instance, combined exposure to prolonged sitting in awkward postures may increase the risk. Exposure to these workplace risk factors puts workers at a higher level of MSD risk. That is, high task repetition, forceful exertions and repetitive/sustained awkward postures, fatigue the worker’s body beyond their ability to recover, leading to a musculoskeletal imbalance and eventually an MSD.

Figure 3.

Work-related musculoskeletal disorders risk factors.

NB: The risk of developing MSDs increases with increasing number of (ergonomic) risk factors involved/present in the execution of the job-task. Jobs that combine high force and high repetition, in awkward postures, pose the greatest risk.

Secondary Risk Factors: These include psychosocial factors [like work-pace, autonomy, monotony, work/rest cycle, task demands, social support from colleagues and management and job uncertainty]. Other secondary risk factors include: Static Posture, Contact Stress, extreme temperature [Cold/heat], Vibration, Noise, Physical Stress, Emotional Stress.

2.2.2 Individual-related risk factors

When all work-related (ergonomic) risk factors are addressed, it is imperative that consideration be giving to individual risk factors, in addition to work-related (ergonomic) risk factors; more so because human beings, are multi-dimensional in nature. This is because limitation to a singular cause of MSDs will limit the ability to create a prevention strategy that addresses the multi-dimensional nature of the workers (and their work-environments). Individual risk factors include:

1. Poor Work Practices: Workers should be familiar with the appropriate work practice, using appropriate training strategies, most especially at the entry point. For instance, proper work - practices, body mechanics and lifting techniques, will help avoid unnecessary risk factors capable of leading to the development of MSDs.

2. Poor Overall Health Habits: Workers who exhibit certain poor health habits are at risk of development of MSDs. Poor health status has been reported to increase the effect of exposure to ergonomic hazard, on the musculoskeletal system.

3. Poor Rest and Recovery: Musculoskeletal disorders develop when fatigue outruns the workers recovery system, causing a musculoskeletal imbalance. Workers who do not get adequate rest and recovery put themselves at higher risk.

4. Poor Nutrition, Fitness and Hydration: Workers who do not take care of their bodies are putting themselves at a higher risk of developing MSDs. Also, selection of workers to task station should be based on the capacity of the workers - such that there is no mismatch between the physical fitness level of the workers and the assigned task.

NB: It is imperative to note that, in other to ensure proper balance of work-practice, and subsequently reduce the occurrence of MSDs, both work-related (ergonomic) risk factors, and individual-related risk factors should be adequately evaluated and controlled. And in addition to the adequate control of work-/individual-related risk factors, there is also need for the workers to exhibit: proper work-practice, good health habits, adequate rest (that allows adequate recovery), and a good nutrition, and fitness regimen, otherwise, they will be at greater risk for fatigue, which may outrun their recovery system. Also, having a poor overall health profile, may put workers at greater risk of developing musculoskeletal imbalance and eventually MSDs.

2.3 Prevention of musculoskeletal disorders

Truly, work-place injuries are not inevitable. Therefore, a work-place design plays a crucial role in reducing the development of MSDs in a work-place; and this can be achieved through the application of an effective work-place ergonomic principles (WEP). The main goal of an effective workplace ergonomic principles WEP is to develop or modify work-environment to meet workers’ needs. The design of WEP is directed towards improving ergonomic risk factors in the work-place, following a proper ergonomic evaluation of the workstation design, worker’s capabilities, workers’ physical attributes and habits. The development and implementation of work-place ergonomic controls is based on the correct assessment of the ergonomic risks inhering in the execution of task, with the designs directed to reducing these risk factors.

2.4 Developing and implementing workplace controls

An adequate “prevention strategy”, with better outcomes is usually conducted following a holistic evaluation of the work-environment, work-task, and the worker. The evaluation of any work-task (Job), vis-a-vis., workplace (including Tools), Tasks and workers, should necessarily involved identifying Ergonomic Stressors, like the:

1. Force required to complete the task - whether the completion/execution of the task involves assumption of static-working or awkward postures.

2. Repetitiveness of a task - whether the work-task is repetitive in nature, that is, require making the same motions repeatedly, for at least 30 seconds, or when a task or motion is performed more than 50% of the time it takes to complete the work cycle;

3. Quality of the Task-posture - whether the Task-posture is prolonged, i.e., more than one hour, or whether the posture is considered awkward or not. Awkward postures place excessive force on joints and overload the muscles and tendons around the effected joint.

4. Quality of the worker’s rest period - whether the pace of work (task) allows sufficient recovery between task-movements. Workers need an acclimatization period to become accustomed to their work demands and to be considered work-hardened or task-fit, this is particularly needed if the workload or working conditions are changed, and/or following an extended absence from work.

5. Overall health of the workers - whether the workers exhibit adequate health, including: proper work-practice, good health habits, adequate rest (that allows adequate recovery), and a good nutrition and fitness regimen. It is important to note that, combination of postures, forces and frequencies, increase the chance of developing an MSD.

For adequate outcomes, a three-tier hierarchy of controls (of Engineering, Administrative and use of Personal Protective Equipment), is widely accepted as an intervention strategy for reducing, eliminating, or controlling workplace hazards, including ergonomic hazards. These are:

2.4.1 Engineering controls

This entails, designing the job-task, to take account of the capabilities and limitations of the workers using engineering controls. Engineering improvements/controls include:

1. Rearranging, modifying, redesigning, or replacing the work-station/task-process.

2. Changing the task-process, vis-a-vis., using handles or slotted hand holes in packages requiring manual handling, or changing the way materials (parts/products) are transported - using mechanical assistive devices to relieve heavy load lifting and carrying tasks.

3. Changing workstation layout, including using height-adjustable workbenches or locating tools and materials within short reaching distances - For example, a job that requires sitting for long periods of time, can be modified to have an adjustable seat or foot stool so that the knees are higher than your hips, so as to protect the lower back.

2.4.2 Administrative controls

This involves changing the work practices and management policies, with the view of reducing prevailing workplace risks. Administrative control strategies are policies and practices that reduce WMSDs risk but they do not eliminate workplace hazards. Administrative controls are usually employed as a temporary measures until engineering controls can be implemented or when engineering controls are not technically feasible. Administrative improvements/controls include:

1. Changing work practices or the way work is organized.

2. Providing variety in jobs - say by rotating workers through jobs that are physically tiring.

3. Adjusting work schedules and work-pace - say by reducing shift length or limiting amount of overtime.

4. Providing recovery time (i.e., muscle relaxation time);

5. Modifying work practices.

6. Ensuring regular housekeeping and maintenance of work spaces, tools, and equipment.

7. Regular health education seminar - for training in the recognition of ergonomic risk factors for WMSDs, and instructions in work practices and techniques that can ease the task demands or burden (e.g., stress and strain), avoiding static positions, awareness of proper lifting techniques.

8. Changes in job rules and procedures such as scheduling more breaks to allow for adequate rest, and recovery.

2.4.3 Personal protective equipment (PPE)

Also known as Safety gear, PPE, generally provides a barrier between the worker and hazard source. Examples of PPE include: Respirators, ear plugs, safety goggles, chemical aprons, safety footwear (shoes), hard hats, knee and elbow pads. There are other devices (like braces, wrist splints, back belts, and similar devices), that are capable of reducing the duration, frequency, and/or intensity of exposure of risk factor for MSDs, although evidence of their effectiveness, as regarding offering personal protection against ergonomic hazards remains (i.e. injury reduction) inconclusive. In some instances, these devices may decrease one exposure, but increase another, because the worker has to “fight” the device to perform the work. An example is the use of wrist splints while engaging in work that requires wrist bending.

3. Musculoskeletal health

Soft tissues injuries (STI) of the musculoskeletal system are important cause of musculoskeletal ill health, particularly in working adult life. Thus, work may serve as a contributor to the development musculoskeletal ill health or exacerbator of an existing health condition. According to Health and Safety Executive (HSE), WMSDs exert harmful effects on the life and well-being of workers in all fields, especially those requiring manual labor [24]. These injuries arise sequel to different causation:

1. Distinct damage to tissues - This is caused by instantaneous non-exertion events (i.e., intense physical exertion) like traumatic experiences (such as slips, trips, falls or whiplash following vehicle collisions;

2. Gradual damage to tissues - This is caused sequel to exposure to occupational ergonomic stressors, such as repetitive and stereotyped motions, forceful exertions, awkward postures, vibration, and/or combinations of these exposures. These type of injuries are commonly referred to as WMSDs. Work-related musculoskeletal disorders have been severally reported to impair musculoskeletal health (MSH) due to the pain and lost of physical function while body tissues heal [25, 26, 27].

3. Insufficient interval of rest-time: Sufficient interval of rest-time is generally needed for recovery, particularly between episodes of high usage; this will enhance the ability of the human body to repair itself. It is therefore advisable to incorporate sufficient interval of rest-time (as an ergonomic control) during task execution, in a work-place. Insufficient recovery time, combined with high repetitions, forceful movements and awkward postures, is capable of adversely altering MSH [26, 27].

Musculoskeletal health (MSH) means more than the absence of a musculoskeletal conditions. Good MSH implies that the musculoskeletal system (i.e., muscles, nerves, tendons, ligaments, joints, and cartilage) function well together without pain or discomfort. Thus, people with good MSH can carry out their functional activities (of daily living) with ease, and without discomfort. Poor MSH may be related to multiple risk factors like physical inactivity, being overweight or obese, diets deficient in vitamin D or calcium, smoking, older age and genetic predisposition to some musculoskeletal conditions [27]. Focusing on strategies directed towards reducing threats to MSH, sequel to work-place activities can therefore not be overemphasized; including early ergonomic evaluation of the work-place, to identify the risk (work-place/individual) factors; and early ergonomic intervention - directed at modifying physical work environments and work practices (Figure 4). This may be helpful in promoting MSH at the wok-place, and subsequently help prevent chronic pain, disability and work loss [28]. This is particularly important because there is a complex relationship between work and MSH. While it is true that certain types of work, and work-place conditions may have negative impacts on MSH, and may lead to failure to create a healthy environment and subsequently increase the risk of MSDs; undertaking meaningful work is an important part of an individual’s sense of health and well-being [25]. Also, according to the National Institute for Health and Clinical Excellence (NIHCE), healthy workplaces provide an opportunity to promote good health generally, and musculoskeletal health specifically [26]. Furthermore, Waddell et al. [25] in their study titled “Work and common health problems”, concluded that, overall, the beneficial effects of work outweigh the risks of work, and are greater than the harmful effects of long-term worklessness.

Figure 4.

Workplace ergonomic control of work-related musculoskeletal disorders.

4. Ergonomics principles

The definition of ergonomics (or human factors), as adopted by the International Ergonomics Association (IEA) in 2000 is “Ergonomics (or human factors) is the scientific discipline concerned with the understanding of the interactions among human and other elements of a system, and the profession that applies theory, principles, data and methods to design in order to optimize human well-being and overall system performance” [29]. Ergonomics is looked at from different perspectives; the word “Ergonomics” is derived from two words: Ergon, which means work and Nomos, which means laws. Ergonomics is also known as “human factors” and “human factors engineering”. It supports the workers and their environment; vis-a-vis, the physical, psychological and social needs of the workers. Ergonomics is simply defined as the scientific study of human work (i.e., people at work). It is basically the science of fitting work-place conditions and job demands to the capability of a particular worker or working population, instead of fitting the workers to their work-place [1]. To achieve this, it important to consider the physical (and mental) capabilities, and limits of the worker as s/he interacts with the Tools/Equipment, Work methods, Tasks and Working environment. There are three major areas (or Dimensions) of ergonomics: Physical, Cognitive and Organizational (Environmental) aspects (i.e., dimensions) of ergonomics:

Physical Aspect of Ergonomics: Focuses on the physiological and bio-mechanical effects of work on human being e.g., Working postures, Work-stations, Work-related safety and health, Materials handled and Work-related musculoskeletal disorders.

Cognitive Aspect of Ergonomics: Focuses on the relationship between individual worker and the different systems (in the work-place) that workers (employees) operate with. It concerns the worker’s cognitive processes, and the ability to process information, for instance technological solutions used at work.

Organizational Aspect of Ergonomics: Focuses on organizational processes, structures and policies at workplace, including communication within the workplace, working hours, work processes/methods and co-operation within operators.

4.1 Work-environment

Ergonomics is described in terms of the environment concerned, i.e. Work-Environments. Work is Physical or mental effort or activity directed towards the production or accomplishment of something (Task). It is the basis for skill acquisition; and is needed throughout all developmental stages for successful role function. While Environments include all the physical, chemical, and biological factors extended to human host, and all related behaviours, but excluding those natural environments that cannot reasonably be modified. Thus, Work-Environment describes: Circumstances, conditions, and influences that affect the behavior and performance of people/workers in the workplace. The following Physical factors affect job design - Noise, Vibration, Lighting, Temperature, Humidity, and Air Flow

4.2 Categories of work-environment

In terms of condition of job, there are two work-environments - Office Work Environment (OWE), which specifically deals with the office environment; and Industrial (Factory/Heavy-duty) Work Environment (IWE); which specifically deals with the Factory/Industrial environment.

While in terms of personality of the staff and/or management, there are also two categories: Hostile Environment, here, there appear to be little or no support what so ever, from the management and the direct boss. And Friendly Environment; here the workers received regular supports from the Management and their immediate boss. This may be created as an incentive for the workers.

4.3 Benefits of ergonomics

The primary goal of work-place ergonomics is to reduce workers’ exposure to MSDs risk factors, thereby creating a safer and more healthful work environment. This is achieved through the use of effective WEP, which normally involves engineering and administrative controls. Work-place Ergonomics Principles (WEP) are directed towards designing workstations, tools and work tasks for safety, efficiency and comfort. This is ultimately, to prevent and/or control occurrence of MSDs, associated with the overuse of muscles (through force exertion), repeated tasks and assumption of awkward posture. Thus, effective WEP is directed towards preventing MSDs (injuries) by decreasing musculoskeletal imbalance and fatigue, associated workplace ergonomics risk factors like overuse of muscles (through force exertion), repeated tasks, and assumption of awkward posture; and failure to the workers body’s recovery system, due to the assault of the ergonomic risk factors. This will invariably, result in increasing comfort (of doing work), job satisfaction and safety (of worker and Tools). Other benefits of workplace ergonomic include:

1. Increased productivity.

2. Increased work quality.

3. Increased efficiency at work.

4. Reduced turnover (for both Machine & Human factor).

5. Reduced absenteeism.

6. Reduced presenteeism

7. Increased employee’s morale.

8. Decreased workers’ compensation costs.

9. Increased physical well being of the workers.

5. Work-place ergonomics

Work-place ergonomics involves designing the work-place, with consideration for the capabilities and limitations of the workers, with the view to reduce risk and promoting good musculoskeletal health; and consequently improve human performance and productivity, including office, recreation activities, and manual handling workplaces. According to General Duty Clause (GDC), Section 5(a)(1) of the Occupational Safety and Health Act (OSHA) regulation of 1970, employers have an obligation to keep the work-place free from recognized serious hazards (including ergonomic hazards), although OSHA regulations do not mandate an employer to provide ergonomic equipment such as work stations and chairs [30]. Common work-place risk factors (i.e., ergonomic hazard) include: Poor sitting posture, Awkward posture, Prolonged (stationary) positions, repetitive movements, Poor lifting (material handling), force/mechanical compression/vibration, temperature extremes, glare, inadequate lighting, and duration of exposure.

5.1 Ergonomic hazards at the office workplace

5.1.1 Poor (Sitting/standing posture)

Assumption of neutral postures when sitting (Figure 5a and b) and standing, is advised for ergonomic reasons, as poor postures exert uneven pressure on the spine, and the four natural curvatures of spine/backbone (i.e. cervical, thoracic, and lumbar spine) is preserved and maintained when lying, sitting, and standing. And may lead to uneven distribution of body weight. Therefore, efforts should be made to assume neutral postures, at all time; as this may be helpful in enhancing musculoskeletal health, and eventually help reduce the development of MSDs, like premature joint degeneration, nerve pinching and/or back pain. When assuming “neutral sitting posture”, it is important to always be careful in ensuring that, the:

1. Back is straight with a slight inward curve (lordosis) of the low-back.

2. Neck and head are held upright, with the ears aligned with the shoulders.

3. Shoulders should be pulled back but relaxed.

4. Trunk (upper body) is not twisting or held leaning on one side.

5. Knees are bent at 90° and positioned slightly lower than the hips.

Figure 5.

(a) Three commonly assumed sitting postures a(i) – Ischio-femoral sitting posture, a(ii) – Sacra sitting posture, a(iii) – Sacro-femoral sitting posture [31]. b: Wrong b(i) and correct b(ii) office work-place sitting postures.

5.1.2 Awkward postures

These are the unnatural body positions (wrong postures) assumed at work (including poor manual handling), like bending, twisting, pocking of the neck - say, looking down at your monitor, extending one’s wrists to type, overreaching - say, to operate the computer mouse, and wrong bending - during manual handling (Figure 6). These postures push the affected joints past the mid-range of motion, thereby exposing the joints to ergonomic hazards, and subsequent injuries. Properly optimized workstation will minimize awkward postures, and this essentially involve assumption of good posture while at work. For optimal workstation, the following adjustment may be required:

1. Adjust the monitor height, such that the top line is at the level of the eye.

2. Adjust the chair height, such that the elbows are at an open angle (90 -110°) when typing.

3. Organize the workspace into zones, and keep frequently accessed items within arm’s reach.

4. Set the arm-rests to desk level, this will further enhance better and easy placement of the wrists in neutral position.

5. Move/Swivel the chair instead of twisting the waist when rotating the body.

Figure 6.

(a) Illustration of proper lifting technique – a – starting position, b – bend your knees, keep your low back bowed-in, c – use correct grasp, d – use body weight to advantage, e – keep load close to the body [31]. (b) Some of the factors responsible for the development of MSDs.

NB: When answering a phone call while at the work-station, the worker can use the speaker function instead of using the arm and/or shoulder wrongly, while holding up the phone.

5.1.3 Prolonged stationary position

This is prevalence among workers whose job tasks encourage sedentary lifestyle. Those who stay in the same position, for longer period of time. Usually sitting or standing in the same position for more than one hour is regarded as prolonged position [32]. Thus, prolonged stationary position is an ergonomic hazard; and it is advisable to observe regular breaks; of between 30 seconds to 5 minutes, usually every one hour, for stretching exercises at the work-place (Figure 7).

Figure 7.

Therapeutic exercises at the workplace. (Each exercise is held or carried out for ten seconds, and repeated three times - for a complete bout of exercises).

5.1.4 Frequent repetitive movements

Certain tasks require frequent repetitive movement. At the office space, the most common repetitive movements are performed by the fingers, wrist and arm. This can be observed in task involving the use of (operating) a mouse. The worker get to perform hundreds of small wind-shield movements with the wrist. This can be made worse, when the task is carried in an awkward position, and over a prolonged period of time. Performing repetitive motions repeatedly, however small, can cause microtrauma to the surrounding tendons and tissues, consequently leading to the development of MSDs. Observing regular rest (particularly of the affected part); of between 30 seconds to 5 minutes, usually every one hour, for stretching exercises, in addition to eliminating the awkward posture is imperative. This allows the body to heal itself, making the worker to recover when the fatigue overturns workers body’s recovery system. And will subsequently leads to the reduction in the development of MSDs.

5.1.5 Poor lighting at work

Insufficient lighting, unwanted dark spots and shadows, glare, and improper color temperature are some of the most common examples of poor lighting at work. They can negatively impact your vision, mood, and even productivity. It is important for workplace lighting to conform to good lighting ergonomics. Ensuring good lighting ergonomics includes the following:

1. The office should be arranged for natural light as much as possible.

2. There should be adequate lighting (300–500 lux) around the immediate workspace.

3. A combination of direct and indirect lighting should be used to eliminate shadows.

4. The chair should be positioned, at a right angle from the windows to reduce glare.

5. Optimize your computer screen for good color and lighting contrast.

6. Add diffusers to light fixtures to make them less harsh on the eyes.

7. Monitor filters or computer glasses can be used to reduce blue light and glare.

6. Manual material handling (MMH), including patient handling

Manual material handling (MMH) is the process of routinely moving and handling of objects (including patients) through a series of biomechanical functions, such as; carrying, holding, lifting, pulling, pushing, and stooping on a regular basis. According to Manual Handling Operations Regulations (MHOR), MMH involve “any activity requiring the use of force exerted by a person to lift, push, pull, carry or otherwise move, hold or restrain an animate or inanimate object” [33]. By this definition, MMH does not excessively involve material handling only, it is also an integral to the practice of the physiotherapy, and rehabilitation professional generally, particularly in patient handling [33]. This is because the work-task of rehabilitation professionals (including physiotherapists) often requires the performance of physically demanding therapeutic activities, refers to as, patient handling tasks (PHT), that may constitute risk of developing MSDs. Patient handling tasks in rehabilitation are usually classified as "traditional" or "therapeutic:" Traditional PHT have a practical goal, like transferring a patient from bed to a wheelchair; “therapeutic” PHT, on the other hand, have more targeted goals, like facilitating patient function and independence. By and large, PHT have been widely reported to be capable of exposing rehabilitation professionals to high mechanical loads, particularly, on the spine [33, 34, 35].

Generally, manual handling frequently involve the performance of unsupported static posture, (which are often awkward in nature), during the execution of any particular work-task, including PHT; which usually involve postures like bending, reaching forward, twisting, squatting etc. (Figure 6). During the assumption of these awkward postures, the workers and/or worker’s body parts are positioned away from their neutral position (Figures 6, 8 and 9). Work-place ergonomic control is therefore essentially required; and directed towards maintaining a neutral body position, and to keep arms and legs as close to the trunk as possible (Figures 8 and 9). Also, modern patient handling technology is often recommended as part of a comprehensive safe patient handling programme in therapeutic and rehabilitation settings, in addition to the implementation of a standard and effective WEP [33, 36].

Figure 8.

Common awkward shoulder (Flexion/Extension, Abduction/Abduction/Extension) from neutral.

Figure 9.

Common awkward repetitive motions of the wrist (Radial/Ulnar deviation & Flexion/Extension, from the neutral).

6.1 Principles of safe manual handling

Basically, manual handling includes both transporting a load, and supporting a load in a static posture. The load may be moved or supported by the hands or any other part of the body, for example the shoulder. This may constitute ergonomic risks, particularly, if hazardous manual handling techniques are employed in the execution of the task (manual material and patient handling). In order to avoid work-place injury from hazardous manual handling, manual handling operations regulations require employers to:

1. Avoid hazardous manual handling, as much as possible;

2. Assess the risk of MSDs from any hazardous manual handling, particularly those that cannot be avoided;

3. Reduce the risk of MSDs from hazardous manual handling, where “reasonably practicable’; which is a measure of balancing the level of risk against the measures needed to control the risk in terms of money, time or trouble.

Furthermore, the risk of developing MSDs sequel to manual handling (materials and patients) can also be reduced by avoiding or reducing assumption of awkward postures (i.e., twisting, stooping, stretching etc.). This can be achieved by changing the:

1. Task layout: The best position to manually handle heavier loads is around waist height (Figure 10). Although, lighter loads, may easily be manually handled below knuckle height or above shoulder height, this should be practiced infrequently.

2. Equipment used: This include the use of mechanical assistance as handling aids. Here some manual handling is retained but bodily forces are applied more efficiently, reducing the risk of MSDs. Some examples; for material handling include Hand-powered hydraulic hoist, Roller conveyors, hydraulic lorry loading crane, Truck with powered lifting mechanism; and for patient handling, there are Patient standing hoist, Pulley and sling etc. [33, 36].

3. Sequence of operations: by improving the flow of materials or products. There is a reduction in the individual handling capability, as the hands move away from the body (Figure 10).

Figure 10.

Reduction of individual handling capability as the hands move away from the body [33].

It is imperative to note that the provision of a safe/good handling technique is no substitute for other risk-reduction steps, such as providing lifting aids, or improvements to the task, load or working environment. Example, moving a load (including patient) by rocking, pivoting, rolling or sliding is preferable to lifting it in situations where there is limited scope for risk reduction [33]. The principles of safe manual handling involve effective assessment of the task, and effective planning of execution of task, including, proper positioning of the body for effective handling, thus, ensuring proper positioning of the feet, securing a proper grip, and keeping the load close to the body, use the leg muscles, with the view using body momentum to advantage (Figures 10 and 11). Assessment of manual handling risk is often anchored on four main areas, including the:

1. Nature of the task - including the workplace conditions, for example, the layout of the workstation and the speed of work (especially in conveyor-driven tasks/jobs.

2. Load/Object being handled - Seize, type, weight, and any difficulty to grasp.

3. Working environment the manual handling is taking place in: difficult to grasp, variations in level of floors or work surfaces, Space constraints, floors, temperature, ventilation and lighting

4. Capabilities of the individual worker performing the manual handling. Individual handling capacity reduces as the hands move away from the body. Thus, as the load is moved away from the body, the level of stress on the lower back increases, regardless of the handling technique used (Figure 10). The workplace should be organized, such that the handler is as close to the load as possible. Extra caution should also be taken, when the employee concerns is new on the job, and/or has an underlining significant health problem or a recent injury. Manual handling is safe, when the lifter/handler hands

Figure 11.

Lifting and lowering risk filter – Each box contains a filter value for lifting and lowering in that zone. The filter values are reduced if handling is done with arms extended, or at high or low levels, as that is where injuries are most likely to happen [33].

It is also important to access the weight of the load to be moved, and also to observe standard lifting technique (Figure 10). If it is less than the value given in the matching box, the operation is within the guidelines (Figure 11). If the lifter’s hands enter more than one zone during the operation, use the smallest weight. If either the start or end positions of the hands are close to a boundary between two boxes you should use the average of the weights for the two boxes. According to [33]. The filter for lifting and lowering assumes: (a) the load is easy to grasp with both hands, (b) the operation takes place in reasonable working conditions, (c). the handler is in a stable body position.

NB: A good handling technique forms a very valuable addition to other risk-control measures. To be successful, good handling technique needs both training and practice. This may be helpful in reducing the risk of injury. The effects of these factors are interrelated, and may partly depend on the nature and circumstances of the manual handling operations. If the manual handling operations are carried out in circumstances which do not really change, like in manufacturing processes; the emphasis is particularly on improving the task and working environment. However, if the manual handling operations are carried out in circumstances which change continually, like certain activities carried out on construction sites, in delivery jobs, or in manual patient handling; the handler may offer less scope for improvement of the working environment and perhaps the task. Here, more attention is directed to the load - for example making the Load lighter for easier handling.

Some of the common workplace risk factors (i.e., ergonomic hazard) in Office work-place, are also considered in manual handling work-space, however, there are workplace ergonomics risk factors that are specifically of great consideration in MMH work-space. These include poor lifting techniques (material handling), wrong work-sitting, mix-match work-environment, and force/mechanical compression/vibration etc. (Figures 5a,b and 6a,b)

7. Discussion and conclusion

This book chapter has provided a comprehensive description of Musculoskeletal system, the disorders of Musculoskeletal systems, causes and preventive strategies, using standard ergonomic principles, applicable at both materials manual handling work-place, and during patients management/rehabilitation. Ergonomic risk factors were discussed under two major categories, namely work-related (ergonomic) risk factors and individual-related risk factors. Work-related (ergonomic) risk factors were further discussed under two sub-categories - Primary and secondary risk factors. The primary work-related (ergonomic) risk factors are basically physical in nature, and they included Sudden/Forceful Exertions, High (Task) Repetitions, Awkward postures (Repetitive or Sustained), body vibration. The secondary risk factors include psychosocial factors (like work-pace, autonomy, monotony, work/rest cycle, task demands, social support from colleagues and management and job uncertainty). Other secondary risk factors include: Static Posture, Contact Stress, Cold/heat, Vibration, Noise, Physical Stress, Emotional Stress.

In order to evaluate the possibility of an employee developing WMSD, it is important to include all the relevant activities performed both at work and during leisure time activities (outside work). This is because, most of the WMSD risk factors can occur both at work and during leisure time activities. Also, because these ergonomic risk factors interact and act simultaneously, and has a synergistic effect on the musculoskeletal system, it is advisable and important to take into account this interaction rather than focus on a single risk factor.

Objectives

After studying this chapter readers should be able to:

• Describe the mechanism of the causes and prevention of WMSDs.

• Understand the different workplace environments, and the peculiar multiple risk factors (hazards) for WMSDs.

• Understand the importance of providing (for workers) an ergonomically sound work-environment, in the prevention WMSDs.

• Understand that WEP is more effective when ergonomic control is done at the workplace and during the performance of leisure time activities.

• Describe the advantages of considering the capabilities and limitations of the workers in the design of workplace.

• Identify the benefits of applying a three-tier hierarchy of controls (of Engineering, Administrative, and use of Personal Protective Equipment) as a standard intervention strategy against workplace hazards.

• Have a better understanding of principles of Safe Manual (Material and Patient) Handling.

Acknowledgments

The writing of this book chapter was influenced by the experience gathered from the teaching, particularly, of my Postgraduate students, at the department of Physiotherapy, college of Medicine, of the University of Lagos. Which started in 2009, when the Postgraduate Physiotherapy programme of the University of Lagos started. The author also appreciate Mr. Bamidele O. Olabisi of Biomedical Communication of College of Medicine, University of Lagos, Lagos, Nigeria, for the drawing of the illustrations

Conflict of interest

The author declare that this book chapter was written in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Notes/thanks/other declarations

N/A