Sarasvathi. V

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Work physiology is a term related with industrial engineering that is concerned how the human body manages with physical stress, work strain, and the working environment. In this field, one study about the physical toll that works takes on a person in order to minimize it. Work physiologists relate their understanding in assessing and designing work spaces that reduce physical fatigue, abolish occupational injuries, and amplify overall productivity. It endows with information about how the body functions under a variety of environmental conditions, the amount of rest it requires, and when it is able to work at peak levels.


Physiologists study few of the body systems that include Metabolism, respiration, and circulation. They also comprise skeletal, muscular, and cardiovascular activity. Work physiology is concerned with the metabolic cost of work and techniques to minimize it by making the work space as ergonomic as possible. This branch of physiology also studies the changes that result in the human body as a result of being exposed to single or multiple instances of work stress. Information gained from work physiology is used to design work spaces that suit an extensive group of people. The objective of work physiology is to make sure that the worker performs his or her task securely in the most resourceful manner possible within the work environment. Human beings come in all sizes and shapes, and this makes it demanding for work physiologists to design environment appropriate to every type. Normally, the environment isn’t a controlled one — there may be loud noises, flying dust particles, and heat, for example, which the body has to deal with. This branch of physiology monitors the amount of energy people spend on their task and ensures that they aren’t pushed beyond their physical capacity to work.


Fundamentals of Work Physiology:


Physiology is the combination of mechanical, physical, and biochemical functions of living organisms. Physiology has traditionally been organisms.


Physiology has traditionally been divided between plant physiology and animal and all living things physiology. Physiology is the study of how the body functions. Capacity of human body to use energy and apply forces depends on:


1.  Capacity of cardiovascular and respiratory systems to deliver required fuel and oxygen to Muscles and carry away waste products

2.  Muscle strength and endurance (depends on cardiovascular and respiratory limitations)

3.  Ability to maintain proper heat balance within the body

Oxygen consumption and heart rate are proportional to energy expenditure in physical activity oxygen consumption (=respiration rate) and heart rate


Muscular efforts:


Physical work is carried out by your muscles and is therefore often called muscular work.


There are two types:


Static or Postural effort:


This is where a muscle remains contracted for a period of time but there is no movement, as in holding a picture against the wall or carrying a bag of shopping. Holding a static or fixed posture can be very tiring as your muscles don’t get time to relax. A muscle which is heavily contracted squeezes against the blood vessels next to it, restricting blood flow. This cuts down the delivery of oxygen to the muscle and the removal of a waste product, lactic acid from the muscle. This results in muscular aches or pain. Any fixed posture will bring on these symptoms, for example, standing to attention or sitting upright.


Dynamic or Rhythmic effort:


This is where there is rhythmical contraction and relaxation of a muscle which does result in movement, as in pulling open a drawer or walking up stairs. Dynamic work is less tiring and more efficient than static work. This is because during dynamic work a muscle contracts and relaxes rhythmically which makes it act like a pump for the flow of blood in the blood vessels, allowing the blood to supply more oxygen and take away more lactic acid than during static work.

Types of muscle:


There are three types of muscle tissue in our body:

Smooth muscle tissue – located within the walls of various body organs. Cardiac muscle tissue – which forms the heart.

Skeletal muscle tissue – which forms the muscle that make us move.

Skeletal muscle is made up of bundles of muscle fibres which can contract together in one direction. During movement, when a muscle contracts, the muscle fibres reduce in length so the amount of movement that the muscle can produce depends on the original length of these fibres. The strength of the muscle will depend on the number of fibres that it contains and the cross-sectional area of the muscle.


Muscular endurance:


It is the ability of a muscle or a muscular group to remain contracted over a period of time.


Endurance can be static or dynamic.


Static endurance can be determined by the length of time a limb can maintain a certain position, whereas


dynamic endurance can be measured by the number of times a limb can perform a movement against a certain resistance.


Muscular strength: It is the maximum amount of force that a muscle can exert under maximum contraction. The amount of force that can be exerted by our limbs depends on body posture and the direction of force. For example, when standing, we can exert more force when pulling backwards than when pushing forwards.


There are several factors that influence our muscle strength and endurance:


Age: our strength increases in our teens and early 20s, reaches its maximum by the middle to late 20s, remains at this level for 5 to 10 years, and afterwards begins to decrease gradually. Sex: in general, women are about two thirds as strong as men. This is because men have greater muscle mass as percentage of body mass compared to women.


Body build: usually the 95th percentile person of a population will be stronger than the 5th percentile person, the athletic or muscular looking person will tend to be stronger than others;among people of equal body size, differences in strength may be due to the amount of muscle tissue, body shape and proportions.


Fatigue: the build-up of lactic acid in the muscles due to static muscle work causes a gradual decline in muscle work causes a gradual decline in muscle strength, fatigue can be delayed by adopting comfortable working postures, changing our posture now and again, decreasing the intensity or duration of muscular effort, training, or practice, having adequate rest periods.


Exercise: we can increase our muscle strength and endurance through exercise up to the limits of our maximum physical potential, which is mainly determined by the genes we inherit from our parents.


Heat: heat, especially when combined with high humidity, decreases muscular performance, especially, especially endurance.


Cold: cold will not affect muscle strength if we wear adequate protective clothing, but it may affect our manual dexterity.


Clothing & equipment: clothing and any equipment we carry will add to our overall weight and therefore we will need extra muscular energy to move.


Motivation & emotional state: fear, anger or excitement can temporarily increase our muscular strength but skill and accuracy may suffer.


Nature of our job: manual workers are significantly stronger than the other types of worker. Postural aids: backrests increase pushing strength by directing all our strength by directing all our strength forwards. Footrests increase pulling strength by allowing us to brace our legs. The amount of force that can be exerted by our limbs depends on our body posture and the direction of force that we apply.


Optimal need of muscle power:


Ø  Avoid any kind of bend.

Ø   Avoid keeping arm outstretched.

Ø   Work sitting down as much as possible

Ø   Arm movement should be opposite or symmetrical

Ø   Working field should be at its best distance from the operator.

Ø   Hand grip, operating levers, materials should be arranged around workplace.

Ø   Hand work can be raised above forehand, elbow.


Seven guidelines


1.    Avoid any kind of bent or unnatural posture bending sideways is more harmful than bending forwards.

2.   Avoid keeping an arm out stretched either forwards or sideways lead to rapid fatigue and reduce skill of operation.

3.  Work sitting down as much as possible.

4.  Arm movements should be either opposition to each other symmetrical.

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

6.  Hand grips, operating levers, material should be arranged around the work place.

7.  Handwork can be raised up by using supports under the elbows, forearms or hands



Principles of Body Mechanics


Body mechanics refers to the way we move during every day activities. Good body mechanics may be able to prevent or correct problems with posture (the way one stands, sit, or lie.). It is the study of proper body movement to prevent and correct posture problems, reduces stress and enhances physical capabilities. Posture is an important component in body mechanics. Good posture generally means the spine is in a ‘neutral’ or ‘resting’ position. The four normal curves of the spine are natural. This position is not static (fixed) and is individual. A neutral spine is one in which the position is comfortably maintained by the discs, bones, and ligaments.


Body mechanics once referred to postural activities only. Generally, the term has been replaced by bio mechanics. The application of kinesiology to the use of proper body movement in daily activities, to the prevention and correction of problems associated with posture, and to the enhancement of coordination and endurance. When we don’t move correctly and safely, the spine is subjected to abnormal stresses that over time can lead to degeneration of spinal structures like discs and joints, injury, and unnecessary wear and tear. Body mechanics protect one from injury by aligning body segments to each other


Using good body mechanics reduces fatigue to prevent strain on the spine. Body mechanics also provide balance and stability.


By standing straight, the main parts of your body (head, chest, and pelvis) are properly aligned one over the other to maintain good balance.


Body alignment is the proper relationship of body parts to each other to avoid unnecessary strain/injury





Provide maximum comfort and relaxation


Aid in normal body functions


Prevent contractures and neuromuscular deformities and complications Conserve maximum possible energy by preventing unnecessary strain


Body mechanics may be defined as  “a science dealing with  body force and motions”.


Among its major principles are:


1.      Using muscles effectively,

2.      Taking advantage of momentum,

3.      Considering the centre of gravity of the body



Using Muscles Effectively:


It includes employing the strongest muscle feasible, setting the muscles that are to do the work before contacting a load, contract muscles slowly and using them rhythmically. Leg muscles, being stronger then back muscles, should be used for lifting loads. This is accomplished by one’s standing with knees slightly bent or kneeling close to the load and lifting with a slow, steady pull.


Study of muscles used in performing workindicates that the smaller once tire more quickly than the larger, thought use of the smaller muscles involves the expenditure of less total energy. Greater tiredness is probably due to fixation. For polishing a horizontal or any large surface, the full arm and even trunk muscles with their large energy costs may be recommended instead of smaller muscles with their lower energy costs. The forearm performs more naturally and comfortably. In this case the energy cost may are should be disregarded.


Muscle exerts its greatest force when extended, and force diminishes as the muscle shortens. Hence when a person is lifting a heavy sofa, the legs are slightly bent before grasping the load, and straightened as the load is lifted. The cost of speed in movement has already be mentioned in the section on pace.


Rhythm in muscular performance may be defined as the repetition of movements at the same tempo. The pleasure experienced in rhythmic movement in songs, dances, and other art forms has been appreciated since the early history of mankind. It is in the province of aesthetics to explain the association of rhythm and joy, but rhythm also has utilitarian uses. Rhythmic work is less tiring than non rhythmic, and the basis for this is the existence of double sets of muscles for accomplishing work. When they work rhythmically, one set rests while the other set works. In non rhythmical work, both sets operate at once, as in a clenched fist.


It is avoiding stops and starts, change of speed, and sharp changes in direction. Free-flowing motions are the least tiring movements because one motion moves smoothly into the next, rather than stopping abruptly and then starting again. The waving of a flag in the breeze is an example of a free-flowing motion. In polishing or dusting a large surface, the end of each movement may be rounded to make the return stroke a continuation of the forward stroke. Bed covers may be tucked in with a long sweeping stroke, avoiding abrupt strokes. Abrupt motions were criticized by a college student janitor: “less intelligent moppers, who push the mop to end of the stroke, have to hang on to stop the thing before reversing its direction, a terrific waste of energy”.


Considering the Center of Gravity:


It is of importance in lifting, pushing, supporting, or carrying a load, and also in reaching to get an object. It is desirable to keep the load, and also in reaching to get an object. It is point, as well as correct alignment. Note how much closer the baby is to the women’s body in the good as compared with the poor method of lifting. The custom of carrying the baby on the mother’s back as the Japanese do, is an example of keeping the load close to the body. That way of carrying a baby is increasingly seen now in the United States, favoured by the use of the flat baby carrier. Applying force to the centre of gravity of a load to be moved is also economical of energy.


In studying housework, it is important to recognize the patterns of time and energy costs of housework not only for the individual and household but also for their wider social and economic implications. Both the external factors, especially the number and age of children in the family and gainful employment of the wife, and the internal factor of attitude toward housework affect time and energy costs. At the same time there is recognition that such costs are affected by the work environment, which is to some extent under the control of the worker. Concern of home managers has broadened from acceptance and/or reduction of time and energy costs for individuals and families, important as these objectives are, to include the relationship of these costs with the near and far environment.


Analysis by elements of motion:


Bratton (1951) studied eight else mends of motions. Including three arm reaches to heights of the 46 inches from inches and 72 inches two trunk bends to 22 inches and 3 inches from the floor and a body pivot combined with arm reach to 36 inches. Energy consumed was in proportion to height of reach and to the depth and type of bend (trunk or knee). Bending the body is more costly than reaching up with the arms because mode of the body weight is moved in bending (Lang worthy and Barrett). This is important information of consider in planning storage for the home or for placing items in existing storage. Strain may be a problem as well as energy cost.


Pace: Pace of activity affects energy costs. In a sturdy of energy cost of walking (Richardson and McCracken) greater speed increased energy expenditure per unit of time. Nevertheless, in relation to distance covered total expenditure of energy was greater with the slow pace, probably because more steps were taken over the same distance:


Thus walking 108 steps per minute compared with 96 steps per minute increased energy expenditure by 3.9 percent. In general, though not in all studies, slowing down has advantages in using less energy (if type of motions reminds and unchanged) and it also advantageous to the heart.


Effective use of the body:


With the focus on time as one of the major resources in family life, improvement of work in the home has frequently emphasized reduction in time used for work activities. There are, however, many any other advantageous in increasing effectiveness of work methods besides conservation of time. The body effectively has advantageous for the individual, notably in relation to health. The body remains the most important item of household equipment and it is the tool that will not change in the foreseeable future. Also, improvement in work methods may reduce overall boredom resulting from long-accustomed routine habits of work. It may reduce frustration that has arisenbecause of lack effectiveness on a job. It may result in the creation of family resources such as increase skill and in more favourable attitudes toward work.


Because of the importance of the body in performance of work, it is well worth the trouble to develop skill in using the body effectively. To do so requires an understanding of how the body functions in activity. Broadening the concept of energy management beyond mere energy expenditure heightens concern for the total use of the body. There are important physical costs of the body use besides energy, such as circulation of the body and strain on the skeletal structure. Feelings of comfort and tiredness are both associated with physical costs.


Body positions and motions are the key to effective body use. Feelings of comfort and/or discomfort result from the use of the muscles and skeleton. Posture, along with the motions of coordinate with lesser amounts of energy expended. For example, Less comfortable position; but though the trunk bend requires less energy than knee bend, it may be uncomfortable and body strain may result.


Posture: Keeping the body parts in alignment results in stability when the various body weights are correctly positioned. Each cantered over the base of support. Considered the pull on back muscles necessary to maintain stability in.”In correct posture whether standing, siting, or using a tool, muscles constructed to do certain things do them. In incorrect posture, muscles not so constructed must do the job”. When any part gets out of line, muscular effort is required to maintain body balance in addition to the work the body is doing. Strain may also result. When there is a problem of maintaining balance, broader base of support is necessary. The feet may be wide apart or parallel with one in advance of the other.


Practice of Body Mechanics helps to maintain Physical fitness


Practicing good posture and good body mechanics will take a while to get used to.


A physical therapist can help you use good body mechanics. If a physical therapist is unavailable, try using a yardstick to keep your back straight as you go about normal daily activities.


Keeping the back straightened will be painful until you get used to it, because more muscles are utilized in standing or sitting upright than when slouching.


The goal of body mechanics is to learn how to move the body so as to prevent further injury to the spine.


Awareness of common mistakes and proper principles can only help to achieve this goal. One such principle concerns posture.


Poor posture is one of the main causes of neck and back injuries.


The chin tucks or, cervical retraction, involves sitting or standing erect while gently pulling your chin back to a comfortable position. Think of a turtle bringing his head back into his shell. This exercise should be performed in sets of ten, starting with one set and working up to two or three sets, several times daily.


Shoulder squeezes or, scapular retractions can also help improve posture. Shoulder squeezes involve bringing your elbows behind you while squeezing your shoulderblades together. Do these ten to twenty times while holding the squeeze for a count of five. This motion increases mobility in your neck and back, making it easier to stand erect. Both of these exercises should be performed pain free. If pain does occur, try decreasing both the number of sets and the frequency. If pain persists, stop the exercise and consult your physician.


Compliance towards the exercises required to maintain or improve posture will lead to proper spine alignment. This in turn, will help decrease the intensity and frequency of painful flare-ups.


Slumped sitting or standing represents faulty body mechanics, and, although it is a common mistake, it must be improved upon.


If both the head and shoulders remain erect and balanced throughout the day, regardless of the activity being performed, then the chance of future back pain has lessened.


Improvement Techniques

  •  Pathway Chart or Flow Diagram
  • Operation Charts
  • Process Charts

An operation chart is similar to a process chart except that it picks up one particular step in a whole process. Operation analysis is detailed study of different operations involved in doing a work. It becomes necessary in order to investigate the shortcomings of the existing method and to develop an improved procedure. It suggests whether some elements should be eliminated or combined or their sequence should be altered in order to obtain effective utilization of existing man power and machinery with minimum fatigue incurred by the workers. The analysis mainly considers the movements of the limbs and aims at finding a simpler and economical method of doing the job. The principles of motion economy acts as a good guide in developing a better and improved method.


The process chart is a step-by-step description of the method used in doing the task. It shows the flows of movement of work and is most helpful in calling attention to unnecessary steps and motion. It is an overall investigation. It requires at least two people to make a process chart, one to do the task and at least one other to observe and record. The time is relatively unimportant, as the focus is upon the flow of work. The chart helps to visualize the sequence of an activity. For charting home tasks, the worker is followed throughout. It is customary, in this method of research, to perform and chart the same task in an original and then in a revised way. The count of symbols of the original way often indicates at a glance where improvement may be made.


The pathway chart is a simple device for making a motion and time study in the home. A floor plan drawn to scale and fastened to a drawing board or wallboard, pins and thread are all that are needed to make such a study. The pathway chart focuses the analysis on overall amount of travel and retracing of steps. The pin and string method of making a pathway chart suggested by Mrs.Gilbreth.




Fundamental information of anthropometric dimensions and biomechanical properties, of the abilities, as well as restrictions, of the human sensory organs and the hand-arm system, i.e., broad work-physiological knowledge of the characteristics of the human organism, always was, and will still in the future linger, a prerequisite for the truly ergonomic design of workplaces and work tools. Work physiology symbolizes the nucleus of today’s work science or ergonomics. Besides the errands and objectives of work physiology in ergonomics education, the principles of work-physiological research approaches are described. When evaluating workplaces and work tools, measuring physiological cost which the organism or the organs have to pay must be measured. Thinking in terms of physiological cost of work guarantees safe guidance in order to achieve human-oriented working conditions. Ergonomics has gained a high rank, but successful ergonomic interactions depend on comprehensive knowledge and experience, and require core competency in work-physiology as well as in ergonomics work design.


Web links


dynamic Meaning in the Cambridge English Dictionary

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  • https://en.oxforddictionaries.com/definition/dovetail
  • https://www.collinsdictionary.com/dictionary/english/waistline
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