Sarasvathi. V

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Choice of tasks and work methods must be based on a thorough understanding of all aspects of the costs of work; we cannot assume that it is always desirable to reduce the energy cost. Individuals vary in their need conserve physical resources and in their standards for achievement. The aims of a study of the work of the work place should be to provide information helpful in assessing the cost of work in terms of resources and to show how the use of certain resources can be minimized. This kind of study should result in improved ability to assess all the costs of work without undue emphasis on the use of any one resource for all families.




The body’s physiological responses to physical workload involve the musculoskeletal and cardiovascular systems. Muscular forces are required to perform the physical work, that is, to hold and move the load from one point to another. Muscular activities during physical work require energy. Supplying the demanded energy creates loads on the cardiovascular system and respiratory system. The heart must pump faster to deliver the increased oxygen demand through blood vessels to the involved muscles.


Ergonomists typically examine energy expenditure rates to assess physiological demand on workers. In theory, if workers are required to exit less 50% of their energy expenditure capacity during the work day, then they should not become physiologically strained during the work day.


In order to provide a margin of safety, many companies and ergonomists recommend that the workload should not exceed 33% of the worker’s capacity for the work day.


According to world health organization (1974), the energy expenditure (kcal per hour) by men and women for

  • Light work 140 and 100;
  • Moderately active work is 175 and 125;
  • Very active work is 240 and 175; and
  •  Exceptionally heavy work is 300 and 225, respectively.

   A planning of energy expended or needed for a task and its management is not possible if one does not take into account the factor of fatigue. Fatigue lessens one’s capacity to perform subsequent work hence one must plan to avoid wastage of precious energy in energy management Fatigue or tiredness results normally if the activity undertaken is beyond one’s capacity. The capacity to work without fatigue varies from person to person. It is also largely dependent upon one’s response to work being done. One tires more easily at work disliked. Fatigue is largely dependent upon one’s approach, postural and muscular strain, concentration involved, skill required, and equipment being used. Fatigue is mainly of two types:


Physiological Fatigue: This results due to the effect of activity on the muscular and nervous system. Any activity undertaken calls for energy, which is provided by the oxidation of nutrient. When there is intense muscular activity the demand for oxygen is higher and the nutrients are reduced to lactic acid (due to incomplete breaking down) and the accumulation of excessive lactic acid in the muscles results in physiological fatigue.


Psychological Fatigue: Psychological fatigue is more concerned with the mental attitude of the worker’s aversion to work. Lacks of interest, boredom are some of the causes of psychological fatigue. Frustration or failure to achieve a goal could also be one of the reasons for this type of fatigue. There are several ways to reduce both physiological and psychological. Some of these are:

  • Providing periods of rest depending upon duration and frequency.
  • Undertaking activities as per one’s capacity (both physical and mental).
  •  Use of energy saving equipment.
  • Working in pleasant environment boredom by looking out for ways of making routine, monotonous.
  • Avoiding nous and repetitive jobs interesting.
  •  Motivation to achieve goals involved.
  •  Avoiding interruptions and unexpected demands.
  •  Mastering work simplification techniques.
  •  Including recreation in the work plan.
  •  Appreciation and feeling of satisfaction.

Categories of Work


Work may be categorized into prolonged or intermittent work, as described below.

  Prolonged Work: Prolonged or continuous work typically involves submaximal efforts (below the AT) for a relatively long period of time (maintained for a few minutes to several hours). During such type of work the oxygen consumption reaches a steady-state level.


Intermittent Work: Intermittent work usually consists of sustained effort for short periods of time followed by periods of rests. There is change in oxygen consumption during typical high-effort intermittent work.During this type of work the level of oxygen consumption does not reach a steady-state condition (does not level off).


Worker – Working Efficiency


Broadly conceived as the cost (in human resources) of worker input may be considered to have four components (Bratton, 1959a):

1.      The affective component. Attitudes, feelings, and interests,

2.      The cognitive component, Knowledge, thought processes, and skills.

3.      The temporal component. The time of the worker and the timing of tasks.

4.      The physical component. The use of the body in the work.


Expenditure of any of these inputs by any member of the family constitutes use of family resource and is a consideration in choice of tasks, work methods and equipment. Any one of these components may assume unusual importance to one and be relatively unimportant to another or to a given worker at one stage and not at another. The worker is in error if she assumes that only two of these, time and physical work, are her concern. The cognitive and affective components of worker input also influence the assessment of costs to the family, the outcome of work study, choice of supplies and materials, and the acceptance of design of equipment. When the focus is on the worker, the knowledge is sought concerning the demands place on the individual by the particular activity and by controlling the interplay with other activities. The number variety and duration of the positions feelings towards the activity and condition for doing it, amount of judgement , skill organisation, attention, effort are studied here.


Knowledge of the effect of different procedures and working conditions on worker input makes possible intelligent choices in efforts to reduce the necessary work to a minimum. Knowledge of the description and measurement of worker input is requisite to controlling the human costs of work. Bodily activity calls for a considerable expenditure of effort


Maximum force of muscle depends on

    o   Age and sex

o   State of training

o   Momentary motivation


Maximum power when sitting at work


1.      hand is more powerful when it turns inwards than it turns outwards

2.      Rotation force is greatest if the hand is grasping 30cm in front of the axis of the body.

3.      Hands is more powerful when it is pulling downwards than pulling upwards

4.      More powerful when pushing than pulling

5.      Pushing power is greatest – grasping 50cm in the front

6.      Pulling power is greatest – grasping 70cm


While standing


1.      Pushing power is greater than pulling

2.     Pulling and pushing power greater in vertical plane and lowest in horizontal plane

3.      Both power are same when arm held out sideway and forwards

4.      Pushing power in horizontal plane for men 16 to 17kg and women 8 to 9kg


The total energy spent on an activity is largely dependent on the following factors:

  •  The number of the part of the body involved in the activity. The energy consumption increases as more parts of the body are involved.
  • Sex of the worker: men expend more energy than women for an activity.
  •  Surface area of the body: larger surface area involves larger expenditure of energy.
  • Posture of body at work: bending requires more energy than reaching.
  •  Height of working surface: this greatly influences energy expenditure.
  •  Sequence of activity: energy spent is influenced by the sequence of activity.
  • Age influences the amount of energy expended. Older people spend more energy than the younger ones.
  • individual differences are also responsible for the amount of energy expended for an activity
  • The concentration required for an activity.
  • Weather – tropical climates can increase energy expenditure by 5 – 20% (shivering in cold can increase).

Guidelines for work layout – principles


1.      Avoid any kind of bent or unnatural posture

2.      Avoid keeping an arm outstretched

3.      Work sitting down as much as possible

4.      Arm movement should be symmetrical or opposition to each other

5.      Working field should be at the best distance from the eyes of the operator

6.      All tools and materials should be in normal work area

7.      Hands should be supported


Workstation Design


A strong relationship exists between the comfort of workers and their productivity. This fact has not yet been accepted by many industrial organizations. This is an indication of a lack of understanding of the concepts of ergonomics and the roles of its principles for designing an effective workplace. Management should understand that worker discomfort due to long standing instead of sitting, for example, puts additional energy demands on the employee that by no means contribute to the worker’s productivity. The goal of ergonomics is not just to reduce effort; it is rather to maximize the worker’s productivity at a level of effort which is not harmful to the worker. For example the dimensions of the desk-top computer table should provide adequate space for keyboards and displays. If sufficient space cannot be provided, an under-table keyboard holder should be used. Use L-shape or cut-in workstations or a special pull-out mouse holder to keep the elbow as close to the body as possible during the use of computer mouse.

Problems results from awkward postures due to poorly designed workstations. The application of ergonomic principles in the design of workstations has significantly reduced such problem. A good workstation allows the operator to assume a good posture.


Ergonomics Principles for Workplace Design


The ergonomic recommendations for determining the dimensions of the workplace (workstations and work spaces) are based on the following three factors, with the first two being the most important:


§    Anthropometric data;

§    The nature of the job;

§    Behavioral patterns of employees.


An effective workstation for the human operator involves incorporation of certain established design principles from the fields of ergonomics and work study. Conducting systems analyses of the job and function allocations – among operators and between workers and machines – helps determine the types and number of tools and equipment necessary for the operators to perform their functions in the work system. Once the required tools and equipment are determined, they must be so arranged or positioned that operators can effectively perform their functions. In general, the workplace design must satisfy the following important criteria;

  • Be economical;
  • Enhance the worker’s efficiency;
  • Allow good working postures; Minimize fatigue;

Minimize health-and-safety risks, such as stresses on the musculoskeletal system. Workplace design based on the dimensions and capabilities of workers can be ergonomically correct. There is no practical to determine universal design specifications for all work space or work station because their dimensions depend upon the physical characteristics of their users as well as their intended applications. The following principles of ergonomics and work study (monition and time study) should be used as general guidelines for workplace/workspace design.


Work spaces must be designed for the expected user population. Thus, all dimensions should be determined based on relevant anthropometric data.

Work spaces must have adequate clearance for the user’s head, torso, arms, knees, and feet.


Bent or unnatural postures should be avoided. Bending the trunk or the neck sideways is more harmful than bending forwards.


Design the work for more sitting than standing. Prolonged work in the same position should be avoided, whether seated or standing.


Arm movements should be either in opposition to each other or otherwise symmetrical.


The location of the working field should be at the best distance from the eyes of the operator.


All tools and parts needed by the worker should be placed in the order in which they are to be used so that the path of the worker’s movement is continuous.


Tools should be prepositioned in such a way that they can be conveniently picked up for use. For example, a power screwdriver that is repeatedly used in a job can be suspended just above the task area using a coil spring.


All tools and parts should be placed within a comfortable reaching distance.


Using Anthropometric Data in Workstation Design


The designers may deal with several interrelated and/or conflicting criteria and try to combine them in some trade-off fashion. In a complex situation, the designer should follow the routine steps of design procedure. The following are the general steps in a systematic design procedure


1)  Preparation:


Collecting all necessary information with regard to the jobs to be performed in the workplace. All capabilities and limitations are assessed. In this step the following information should be collected:


Types of job functions (tasks);

  • The human – machine interfaces;
  • The workplace requirements and constraints; The workplace environmental conditions;
  • The characteristics and requirements of the equipment used in the workplace; The descriptions and capabilities of work populations.

   2)  Identification of all feasible design alternatives:


The collected information is assembled to link the design components together to explore all the feasible design alternatives that effectively combine components to satisfy the design constraints. The following should be considered in these steps:

  • Functional characteristics
  • Compatibility of the functional characteristics with design constraints.
  • Reliability of the alternative designs under the expected conditions.

  3)  Selection of the best design alternative:


All identified alternatives are compared to select the best alternative. the criteria used for comparison of the alternatives and selection of the best alternative should include:

  • Economy of production
  • Efficiency of operations
  • Ease of maintenance

4)  Examination of the final alternative:


The selected final design alternative should be evaluated experimentally to insure that the design objectives have been achieved and the constraints are satisfied. Making a mock up and evaluation of the overall workplace may be necessary to insure that all design tradeoffs are feasible and all problems are resolved. It should be noted that the workplace design problems may not be just of dimensions they can also be safety environmental psychological or other problems.


Recommendations for Seated Workstations


It is inappropriate to determine design specifications for universal seated workstation since its dimensions will vary according to its intended purpose and its user’s specific characteristics.


Recommendation for Sitting Postures

  • The upper arm and lower leg are vertical The forearms and thighs are vertical
  • The feet are flat on the floor
  • The seat backrest supports the inward curvature of the lumbar region of the spine
  • The weight of the upper body is evenly distributed on a large surface area of the buttocks and thighs.

Recommendations for Seat Design Selection


Chairs should be stable and easily adjustable from the seated position. Mobile chairs are not recommended for use on the shop floor where the risk of tipping over is present.


Where mobility is required wheels or castors should be fitted to the chair. Mobility is not recommended for a slippery floor, which makes it difficult to keep the chair in the desired position.


Where wheels or castors fitted the chair should have five legs to decrease the risk of tipping over.


The chair should have padded backrest that is at least 18cm high and 33cm wide. The backrest should be adjustable up and down and forward and backward.


Seat height should be adjustable so that the upper body weight is distributed over the buttocks, not over the thighs by maintaining the thighs horizontal above the floor accommodations about 90% of the US civilian population accounting for shoe allowance.


The depth of seat should be about 38-40cm and its width should be 42-46cm respectively.


There should be enough clearance between the front edge of the front edge of the chair and the back of the knees.


The front of the seat should be of a waterfall shape which provides enough clearance for the flesh of the thighs, thus preventing reduction of blood circulation.

  The seat pan should be slightly slope backward to prevent the ejection effect of seat. The angle between the backrest and the seat should be about 100°.


Both seat pan and backrest should be upholstered and covered with breathable when compressed.


Torso twisting during the task performance should be avoided. If frequent lateral movements are required the seat should be swivel.


Where the seat height is fixed and excessive, footrest should be provided to the users to be able to maintain their thighs horizontally and relieve the pressure under the thighs from the chair front.


If footrest is required it should be slightly angled toward the person. It should support the soles of both feet; a surface of 27-30cm in depth by 40cm in width should be adequate.


Armrest should be covered with an absorbent nonslip material.


Ergonomic Guidelines For Standing Tasks


It is desirable to design the workplace for sit stand work, in which workers can perform their assigned job sitting or standing. Due to the nature of the task sometimes sitting is not possible. For such situation it should be designed for standing.


Recommendations for Standing Postures


Standing still in one place for long periods of time should be avoided. The activity of the leg muscles acts as pump and assists he vein in returning the blood to heart. Prolonged standing stops this pumping action and causes swelling of the lower extremities.


When fully adjustable worktables cannot be provided for standing work or the operating level at a machine cannot be varied the working heights should be st to suit the tallest operation, while the smaller operators can be accommodated by giving them something to stand upon.


When the work requires fine or precise manipulations, working heights must be raised to a level at which operators can see clearly while keeping their back in a natural position.


When the handwork call for great force or much freedom of movement it is necessary to lower the working surface.

Mats provided for the standing operator should have feathered edges to minimize tripping hazard.


Ergonomics in the Workplace


The term ‘ergonomics’ generally refers to, physical ergonomics as it relates to the workplace (as in for example ergonomics chairs and keyboards). Ergonomics in the workplace has to do largely with the safety of employees, both long and short-term. Ergonomics can help reduce costs by improving safety.


Workplaces may either take the reactive or proactive approach when applying ergonomics practices. Reactive ergonomics is when something needs to be fixed, and corrective action is taken. Proactive ergonomics is the process of seeking areas that could be improved and fixed the issues before they become a large problem.


Problems may be fixed through equipment design, task design, or environmental design. Equipment design changes the actual, physical devices used by people. Task design changes what people do with the equipment. Environmental design changes the environment in which people work, but not the physical equipment they use.


The Workplace Characteristics


Most workplace has the following five characteristics in common;


The workplace consists of mechanical and electrical equipments. The industrial workplace usually includes such equipment as lathes, power saws, power presses, grinding machines, and drills the non-industrial( service) workplace also includes mechanical and electrical equipment. Examples of equipment used in the non-industrial environment include typewriters, computers, and copy machines.

Manual tools are often required to perform the job, examples of such tools include screwdrivers, hummers, dollies, pliers, and keyboards.


Jobs are described by standard sets of procedures that must be followed to produce a desired output.


The workers interact with the equipment to perform many necessary tasks that are involved in producing the desired output.


The workplace is serviced by various other facilities. Example of such facilities are waste removal, water, and power, which are necessary to carry out the work activities in the workplace.


The Worker’s Functions


Workers generally perform the following three types of functions:


Performing various physical tasks that are required to complete the job. Example of such tasks are lifting, carrying and lowering materials, positioning the work-pieces for work operations, using tools to perform the job function, and packaging products.


Controlling the processes that are performed by machines. In this conjunction, the worker sets the machines to work. The worker monitors and controls the work processes so that the job is completed properly. Finally, the worker stops the machine at the completion of the process or whenever something in the system goes wrong. To control the process, it is necessary for the worker to monitor the work being performed.


Sharing the work environment with the machine in the workplace. Consequently, the worker is exposed to the potential hazards due to the use of mechanical and electrical equipment in performing the job.


Ergonomics of Human-Machine Systems

  • Ergonomics is concerned with the following aspects of the human – machine systems;
  • The design of tools to match the physical characteristics of the worker with the functioning of the tools;
  • The design of the workplace and work space to meet the physical characteristics of the worker;
  • The design of controls and displays to allow the worker to operate and monitor the work system processes efficiently with minimum errors;
  • The development of job procedures that meet the worker’s capabilities;
  • The minimization of the effects of external factors(i.e., thermal conditions, illumination, noise, and vibration) on the worker in the workplace.



Measurement of the personal costs of work requires not only a broad concept of these costs, but also the use of knowledge about two other dimensions—the work itself and the place of work. The concept of these three dimensions of work- the worker the work and the workplace provides the framework for the studies aimed appraising the use of the human resource. Each dimension may in turn receive major attention, but at the same time knowledge is generally gained about the remaining dimensions. They are interrelated; they cannot be completely isolated. Each affects the other to some extent.


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