CHAPTER 2ANATOMY, POSTURE AND BODY MECHANICS

Lectures ObjectivesIntroductionMuscle Structure and FunctionsFunctions of the Skeletal and Muscular SystemsStability and SupportPostureLifting

IntroductionANATOMYGreek ana = up, and tome = a cutting, hence cutting up of a body.The art of dissecting, or artificially separating the different parts of any organized body, to discover their situation, structure, and economy.Dissection.The science that deals with the form and structure of organic bodies; anatomical structure or organization.http://en.wiktionary.org/wiki/anatomyhttp://www.anatomy.usyd.edu.au/glossary/

IntroductionHuman body is a mechanical system which obeys physical laws - designed to perform a variety of functions in daily life.

The skeleton plays the major role in the body all other parts are attached, directly or indirectly.

The body may be stable/unstable and able to withstand a limited range of physical stresses.

Introduction (cont.)Function of Ergonomist - to use principles of anatomy and biomechanics to design the working environment in order to: minimize undue stress preserve health improve performance.

Muscle Structure and FunctionsMuscles make up to 45% of the total body weight.

Human body consists of more than 600 muscles. These can be divided into 3 types - Skeletal muscles; Cardiac muscles and Smooth muscles.

Human MusclesSkeletal muscles : These are connected to the bones and provide the force and movement needed to carry out external tasks. The structure of these muscles largely determines human physical capabilities and limitations .Cardiac muscles : It is an integral part of the heart and helps it to pump out the blood for circulation. Smooth muscles : These are connected to internal organs such as stomach, intestines, blood vessels, etc.

Functions of the Skeletal and Muscular Systems

Skeletal SystemMuscular System1. Support.2. Protection (the skull protects the brain and the rib cage protects the heart and lungs).3. Movement (muscles are attached to bone and when they contract, movement is produced by lever action of bones and joints).4. Homopoiesis (certain bones produce red blood cells in their marrow).Produce movement of the body or body parts.2. Maintain posture.3. Produce heat (muscle cells produce heat as a by-product and are an important mechanism for maintaining body temperature.

Muscular System

Stability and SupportA stable posture can be maintained only if the various body parts are supported and maintained in an appropriate relation to the base of support, such as the feet or the squab of the seat.

The size of the base of support determines the stability and postures.

It is important to provide sufficient space around standing operators and plenty of room for the feet to avoid losses of balance.

Static EquilibriumUpward forces (from floor) must equal downward forces (body weight + any object held).

Forward forces (e.g. bending forward) must equal backward forces (extensions of back muscles).

Static Equilibrium (cont.)Clockwise torques (e.g. from asymmetric loads) must equal counterclockwise torques (back and hip muscles).

Some Aspects of Muscle FunctionThe function of skeletal muscles is to exert tension between the bony points to which they are attached

Tension is exerted when a muscle changes from its resting to its active state in response to impulses from the central nervous system.

Muscle contraction the physiologically active state of the muscle, rather than its physical shortening.

ContractionTwo types of contraction :

1. Static or Isometric contractions

2. Dynamic contractions

1. Static or Isometric ContractionsMuscle can produce force without changing its length, that is, isometric contraction. In such a case, no external work is done. Static contraction, at its maximum can only be maintained for a short period (about 10s or so). Many examples of this type of contraction can be seen in daily life - maintaining a posture, holding a weight or standing at a place without any movement.

2. Dynamic ContractionsDynamic contraction (work) is characterised by a contraction period followed by a relaxation period. In dynamic contraction, blood supply to the muscle is not affected. Due to a contraction-relaxation cycle, blood is pumped in and out the muscle, thereby removing waste products of the energy metabolism - the muscle acts more like a blood pump.

Stress

Postural Stress vs Task-induced Stress

Postural stress : the mechanical load on the body by virtue of its posture (the average orientation of the body parts, with respect to each other, over time)

According to Grieve and Pheasant (1982) :

Postural stress

Postural stress

Postural Stress vs Task-induced StressTask-induced stress : Results from the performance of the task itself, i.e. repetitive movement of wrist or fingers.

Posture and Strength PosturePosture can be defined as the orientation of the body and its parts in relation to each other. Posture has considerable influence on a person's ability to exert force. Posture affects the length-tension relationship.

Posture

StrengthStrength can be divided into two types :1. Static (isometric) strength 2. Dynamic strength

1. Static StrengthThe maximum steady force or torque which an individual can exert in static exertion of short duration (3-5 secs).

This is also known as maximum voluntary contraction (MVC).

1. Static Strength (cont.)Strength is influenced by a number of factors such as : Age: Strength decreases with age Sex: Females on average have less muscular strength Training: Training can improve muscular strength Motivation: Under highly motivated condition a person can improve strength Medical condition, illness, time of the day, sleep deprivation, nutrition etc

2. Dynamic StrengthDynamic strength, unlike static strength, is difficult to define due to : Acceleration / velocity / impulse movement/jerk effects on force exerted by a muscle Muscle length changes with joint motion

2. Dynamic Strength (cont.)Dynamic strength can be measured under two conditions : Constant velocity (isovelocity) using isokinematic devices. Constant force (isotonic) where force is kept constant. This is very difficult to achieve in real life as muscle length changes during movement, the force also changes.

Causes of Back InjuriesStrain from improper sitting or standing postures, sometimes due to poor workplace design.Sudden or frequent twisting and/or bending of the back.Sudden strain on generally unused muscles or jerking of the object.

Causes of Back Injuries (cont.)Lack of exercise, causing muscles to lose their strength, flexibility and length.Manual materials handling tasks, lifting, loweing, pulling and pushing.Stress !!Smoking and many different types of illness.

Lifting

Factors Affecting Lifting (cont.)The following factors influenced the ease and safety with which lifts can be performed :Force and amount of weight liftedLocation of the load in relation to the bodySize of the loadFrequency of liftingStability of the loadHandles or handholdsGeometry of the workplaceEnvironmental factorsPersonal factors

Lifting TechniquesManual materials handling involves a very complex combination of moving body segments, changing joint angles, tightening muscles and loading the spinal column.

Lifting Techniques (cont.)

Lifting Techniques (cont.)

Source: http://www.msha.gov

Lifting RecommendationsEnsure that workers assigned manual lifting tasks are in good physical shape.Place material conveniently within reach (have handling aids available)Train workers to get a good grip on the load and test the weight before trying to move it.

Lifting Recommendations (cont.)Do not twist the back or bend sideways.Do not hesitate to get mechanical help or from other person.Do not continue heaving when the load is too heavy.

ConclusionEvaluation of the physical workplace requires a basic knowledge of human anatomy and body mechanics.It is essential to observe a workers postural behavior and stress, i.e. lifting a material.Skilled workers use postural strategies to minimize fatigue and to exert large forces efficiently.

Posture and Strength PosturePosture can be defined as the orientation of the body and its parts in relation to each other. Posture has considerable influence on a person's ability to exert force. Posture affects the length-tension relationship. Chapter 2*

STANDING POSTUREChapter 2*

SITTING POSTUREChapter 2*

Something, somewhere went terribly wrong!Chapter 2*

Chapter 2*

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Posture for data input taskPosture for long periods of using computer*

Its funny, leaning back has traditionally been the lazy persons posture, and hunched forward is a sign of diligence. Researchers in Alberta and Aberdeen have suggested that we want a spinal angle that is more than 90 degrees.Chapter 2*

Health Postures Stance ChairChapter 2*

Health Postures Stance Chairhttp://www.bluehen.com/health-postures-stance-chair-p-453.html#description1KneelingForward Tilt Sitting Reclined StandingNeutral Posture Chapter 2*

Cool Stuff!USB HubVariable Balans Ergonomic Knee ChairErgo-Comfort - Flat Panel Monitor ArmKeyboard Tray with Adjustable Arm and Mouse PadChapter 2*