Ergonomic Principles Lecture PDF

Physical workplace risk factors are those aspects of a job or task that impose biomechanical stress on a worker Construction: lifting, vibrating tools, awkward positions Office work: repetitive keyboarding, lifting, sitting in one position for a long time Restaurant work: lifting, standing for lon...

Physical workplace risk factors are those aspects of a job or task that impose biomechanical stress on a worker Construction: lifting, vibrating tools, awkward positions Office work: repetitive keyboarding, lifting, sitting in one position for a long time Restaurant work: lifting, standing for long periods, repetitive kitchen work healthcare: physical therapist, dentist Others: driving &firefighting Posture and movement play a central role in ergonomics. The body’s muscles, ligaments and joints are involved in adopting a posture, carrying out a movement and applying a force. The muscles provide the force necessary to adopt a posture or make a movement. The ligaments, on the other hand, have an auxiliary function, while the joints allow the relative movement of the various parts of the body. Poor posture and movement can lead to local mechanical stress on the muscles, ligaments and joints, resulting in complaints of the neck, back, shoulder, wrist and other parts of the musculoskeletal system. Postures – both awkward (non-natural) and static Forces- Including heavy, frequent, or awkward lifting Compression Repetition Vibration.  Raising hands above the head or elbows above the shoulders, a common awkward posture in manufacturing and manual material handling Kneeling or squatting, common in maintenance operations Working with back, neck, and/or wrist bent, for example, when using a microscope Sitting with feet unsupported that can cause blood to pool in the feet and flatten the natural curve in the lumbar spine. This problem is common among laboratory technicians who work at high benches Awkward postures are more fatiguing than neutral postures because the muscles, tendons, and ligaments are actively working to maintain the posture the greater the posture deviations from neutral, the higher the stress on the human and resultant risk of injury Holding a posture for extended periods of time is known as a static posture or static muscle loading. Static postures prevent the flow of blood. Blood flow brings nutrients to the muscles and carries away waste products. Holding a muscle in contraction causes waste products to build up and leads to fatigue. These types of exertions put increased load or forces on the muscles or tendons, which contribute to fatigue. Fatigue is considered a precursor to injury.  Gripping tools that cannot be put down Holding arms out or up to perform tasks Standing in one place for prolonged periods. Repetition is a physical risk factor that occurs when the same motion or group of motions is performed over and over again. Different tasks may still utilize the same muscle groups and, therefore, not allow the muscles to rest leading to overuse. Fatigue – cause a reduction in performance due to a period of excessive activity followed by inadequate recovery time. Muscle fatigue is accompanied by a buildup of lactic acid in the working muscle. Repetition alone is not typically a problem, but when it occurs with other risk factors it magnify the exposure. Force refers to the amount of physical effort that is required to accomplish a task or motion. Tasks or motions that require application of higher force place higher mechanical loads on muscles, tendons, and joints and can quickly lead to fatigue. more physical effort may be needed to perform a task when speed is increased or vibration present. Performing forceful exertions requires the application of muscle contraction that may cause them to fatigue quickly. The more force that must be applied, the more quickly the muscles fatigue. Excessive or prolonged exposure also leads to overuse of the muscles and may result in muscle strain or damage. https://en.m.wikipedia.org/wiki/File:Practical_ Demonstrations_of_Ergonomic_Principles.web m Compression or contact stress is a concentrated force on a small surface area. Contact stress can reduce blood flow or cause tissue (e.g. tendon) irritation due to the constant pressure. One of the most common sources of compression is a sharp or hard desk edge creating a compressive force on the forearm or elbows as we rest to stabilize the joint. Nerves in the forearm are close to the skin surface; compression of the forearm impedes nerve conduction. increases the rate of creep in the spinal motion segments. have shown that loss of fluid from the nucleus reduces its incompressibility. An already degenerated disc will respond in this way when exposed to vibration and will experience greater stresses and strains than a healthy disc the likelihood of further disc degeneration will be greater and the facet joints will be exposed to greater loading Duration is the time period in which an action continues or lasts. Continuous exposure to any risk factor may not allow sufficient recovery time for muscles, tendons, and nerves. Duration magnifies the risk factors as does intensity or magnitude. Temperature Extremes Temperature extreme are a contributing factor to the development of WMSDs. Working in cold environments places a greater aerobic demand on the worker, which means they fatigue faster..Workers move more slowly when hot, so simple tasks can take longer, thus increasing the duration of exposure to temperature extremes and other risk factors. Inadequate Recovery Working without rest can cause fatigue and contribute to injury. Muscles need time to rest to re-oxygenate and remove the waste products of muscle metabolism. There are many ways to rest a muscle group Stretching alternating tasks, taking microbreaks. Personal risk factors can also contribute to the development of workplace injury and illness. Age – as we age, the repair process in our body takes longer. Gender – due to anatomical and hormonal differences, certain WMSDs are more prevalent in women. Hobbies – knitting, crocheting, bowling, and computer gaming. Smoking – linked to back pain because smokers tend to heal more slowly due to the decrease in oxygen in the blood stream. Obesity and pregnancy – linked to carpal tunnel syndrome (CTS Obesity impacts are lack of flexibility, fluid buildup, and increased pressure on the disks. weight above the Physical conditions – poor fitness particularly when combined with a body commonly recognized to be “ideal,” is a prime cause of weariness and fatigue, which are factors that can contribute to the onset of musculoskeletal injuries.  Previous injury – puts a worker at risk of an MSD in the same place. Medications – can cause dehydration, swelling, decreased/increased metabolic rates, and a change in electrolyte levels. Early identification of signs and symptoms of WMSDs can eliminate risk or reduce the severity of an injury. Some signs and symptoms are as follows: Painful aching joints, muscles Pain, tingling or numbness Shooting or stabbing pains Swelling or inflammation Warmth Stiffness or difficult moving Burning sensation Pain during the night Loss of strength and mobility A number of principles of importance to the ergonomics of posture and movement derive from a range of specialist fields, namely biomechanics, physiology and anthropometrics. Biomechanical background In biomechanics, the physical laws of mechanics are applied to the human body. It is thereby possible to estimate the local mechanical stress on muscles and joints which occurs while adopting a posture or making a movement. A few biomechanical principles of importance to the ergonomics of posture and movement are outlined below. 1-Joints must be in a neutral position When maintaining a posture or making a movement, the joints ought to be kept as far as possible in a neutral position. In the neutral position the muscles and ligaments which span the joints are stretched to the least possible extent, and are thus subject to less stress. In addition, the muscles are able to deliver their greatest force when the joints are in the neutral position. If the work is too far from the body, the arms will be outstretched and the trunk bent over forwards. The weight of the arms, head, trunk and possibly the weight of any load being held then exerts a greater horizontal leverage on the joints under stress (elbow, shoulder, back). This obviously increases the stress on these muscles and joints The upper part of the body of an adult weighs about 40 kg on average. The further the trunk is bent forwards, the harder it is for the muscles and ligaments of the back to maintain the upper body in balance. The stress is particularly large in the lower back. Prolonged bending over for long periods must therefore be avoided wherever possible. A twisted trunk strains the back.Twisted postures of the trunk cause undesirable stress to the spine. The elastic discs between the vertebrae are stretched, and the joints and muscles on both sides of the spine are subjected to asymmetric stress. 4-Sudden movements and forces produce peak stresses Sudden movements and forces can produce large, short-duration stresses. These peak stresses are a consequence of the acceleration in the movement. 5-Alternate postures as well as movements No posture or movements should be maintained for a long period of time. Prolonged postures and repetitive movements are tiring, and in t he long-run can lead to injuries to the muscles and joints. 6-Limit the duration of any continuous muscular effort Continuous stress on certain muscles in the body as a result of a prolonged posture or repetitive movement leads to localized muscle fatigue, a state of muscle discomfort and reduced muscle performance. 7-Prevent muscular exhaustion The muscles will take a fairly long time to recover if they become exhausted which is why exhaustion must be avoided. In this example, an exhausted muscle needs to rest for 30 minutes to achieve a 90 per cent recovery. Muscles in a half-exhausted state will recover to the same degree after 15 minutes. Complete recovery can take many hours. 8-More frequent short breaks are better than a single long one Muscular fatigue can be reduced by distributing the resting time over the task duration or working day. It is not sensible to accumulate break times until the end of the task or working day. 1-Limit the energy expenditure in a task The majority of the population can carry out a prolonged task without experiencing any general fatigue provided the energy demand of the task (expressed as the energy consumed by the person per unit of time) does not exceed 250W (1W 0.06 kJ min 1 0.0143 kcal min 1). Examples of activities with an energy demand of less than 250 W are writing, typing, ironing, assembling light materials, operating machinery, a gentle walk or leisurely cycle ride. 2-Rest is necessary after heavy tasks If the energy demand during a task exceeds 250 W, then additional rest is necessary to recover. Rest can be in the form of breaks or less demanding tasks. The reduction in activity must be such that the average energy demand over the working day does not exceed 250W.  Anthropometric background Anthropometry is concerned with the size and proportions of the human body. A few anthropometric principles of importance to the ergonomics of posture and movements are given below. 1-Take account of differences in body size The designers of workplaces, accessories and suchlike must bear in mind differences in body size of the potential users. A table height which is suitable for a person of average stature can be unsuitable for a tall or short person. A table height which is adjustable over a sufficient range is the solution if the table is to be used by several people. Sometimes only the shortest users must be considered, for example, in designing a control panel which has to be reached with the arms. In other cases, such as in choosing a door height, the tall users have to be considered instead. 2-Use the anthropometric tables appropriate for specific populations Data for body dimensions always refer to a particular population group and do not necessarily apply to other population groups. for example, shows the body dimensions of British adults. The adult population of Great Britain is relatively tall in comparison with the average world population. Biomechanical background 1 Are the joints in a neutral position? 2 Is the work held close to the body? 3 Are forward-bending postures avoided? 4 Are twisted trunk postures avoided? 5 Are sudden movements and forces avoided? 6 Is there a variation in postures and movements? 7 Is the duration of any continuous muscular effort limited? 8 Is muscle exhaustion avoided? 9 Are breaks sufficiently short to allow them to be spread over the duration of the task? Physiological background 10 Is the energy consumption for each task limited? 11 Is rest taken after heavy work? Anthropometric background 12 Has account been taken of differences in body size? 13 Have the right anthropometric tables been used for specific populations? For any questions feel free to contact me by mail [email protected] Dr\ Hanaa Elsayed Lecturer of physical therapy Sinai university