Biomechanics in Ergonomics | Shrawan Kumar | Taylor & Francis eBooks,

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ABSTRACT

Two important goals of ergonomics are the comfort, and the health and safety of workers. In many ways these are mutually compatible, for where health and safety is jeopardized, the discomfort results. Most work-related injuries can be viewed as biochemical damage to a tissue or organ; ultimately all injuries are sustained by tissues.

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TABLE OF CONTENTS

chapter |1 pages

Figure 5.1 Dependence of muscle force on muscle length. (A) In single frog fibres, under artificial conditions, the force is highest at mid-lengths. The relation has sharp changes in slope (letters A–E), which occur at specific sarcomere lengths (numbers above x-axis), and which correspond to length-dependent changes in overlap of the thick and thin filaments (numbers 1–6, at top) (from Gordon et al ., 1966, by permission of the Journal of Physiology ). (B) Under more natural conditions, force is still higher at mid-lengths, but the relation is smoother and broader, and depends on the level of activation. These data are for cat soleus muscle (from Rack and Westbury (1969), by permission of the Journal of Physiology ).

chapter |1 pages

Figure 5.2 Dependence of steady force on muscle velocity, the ‘force– velocity characteristic’. Positive velocities indicate shortening. Cat soleus muscle (from Joyce and Rack (1969), by permission of the Journal of Physiology ).

chapter |1 pages

Figure 5.3 Factors that affect the worker’s ability to maintain a position while doing a task. The limb rotates around the joint, under control of at least one agonist and one antagonist muscle. Each muscle contributes passive elasticity (pe), crossbridge force (cb), elasticity from structures in series with the crossbridges (se), and viscosity (v). Its activity is controlled by reflexes and volition. The limb has inertia. The task itself may exert forces on the limb, or load the limb with extra mass or elasticity (modified from Winters et al ., 1988).

chapter |28 pages

Generating power

chapter |13 pages

Types of gasp strengths

chapter 8|59 pages

Hand tools

chapter |2 pages

Figure 9.1 The effect of tendon load on tendon radius of curvature through the carpal tunnel. Loading the tendon with 10N force decreased the radius of curvature (Keir, 1995). Figure 9.2 Combined effect of gripping, with time varying postures. The gripping requires tendon tension. The time varying wrist posture creates sliding of the digital flexor (and extensor) tendons. The combined effect is friction and energy input to the tissues. Finger motion will likewise create tendon sliding.

chapter |1 pages

Biomechanical models of carpal canal hydrostatic pressure

chapter |1 pages

Figure 9.3 The effect of wrist posture on carpal tunnel pressure and median nerve contact stress. Hydrostatic pressure was measured by catheter and contact stress by a tubular rubber transducer replacing the excised median nerve (Keir et al., 1997)

chapter |2 pages

Figure 9.4 The effect of tendon tension on carpal tunnel pressure and median nerve contact stress. Flexor tendons loaded with 10N force. Hydrostatic pressure was measured by catheter and contact stress by a tubular rubber transducer replacing the excised median nerve (Keir et al., 1997)

chapter |2 pages

Figure 9.5 Schematic of muscle activity (electromyograms) associated with low and high risk of developing myalgia. Electromyograms are rectified and normalised to a maximum voluntary effort (MVE) and represent a period of about a minute.

chapter |10 pages

References

chapter |2 pages

Figure 10.1 Illustration of the forces acting on the forearm while holding a ball weighing W in the hand. The biceps muscle force, B, acts upward on the ulna. The joint reaction force, R, and weight of the forearm, G, act downward. The vector sum of these forces must be zero to maintain static equilibrium. Similarly, the net moment about the joint centre must also be zero. These two conditions can be written algebraically as Equations 10.1 and 10.2.

chapter |1 pages

(10.7)

chapter |1 pages

WRIST

chapter |1 pages

Figure 10.2 The tendons of the extrinsic finger flexor muscles can be conceptualised as belts wrapping around a pulley. The tension in the tendon, and F are different because of frictional forces acting on

chapter |1 pages

Figure 10.3 The belt–pulley model of the wrist can be used to analyse the effect of wrist size and posture on the normal force, F, acting on

chapter |2 pages

Figure 10.4 The belt–pulley model predicts that wrist posture affects the relationship between tendon tension, F, and the reaction force,

chapter |5 pages

Figure 10.5 Sagittal plane view of a finger model. Finger posture is described by defining the orientations of coordinate systems fixed to each bone relative to each other. Moment and force equilibrium conditions are formulated at each joint of the finger.

chapter |1 pages

Fingertip pulp models

chapter |1 pages

MULTIPLE SEGMENT ARM MODELS

chapter |15 pages

Figure 10.7 Hand–arm vibration can be modelled by a series of masses, springs, and dashpots. An external acceleration can be placed on the distal element of the model, and the resulting mass displacements can be simulated. Energy dissipation by model elements can also be computed (reprinted from Thomas et al., 1996, with kind permission from Academic Press, London, UK).

chapter |2 pages

Figure 11.1 Anterior (A) and posterior (B) shoulder muscles acting primarily as movers of the shoulder joint and (C) rotator cuff muscles acting primarily as stabilisers (redrawn from (Kreighbaum and Barthels, 1996).

chapter |3 pages

Figure 11.2 An example of an EMG recording during 10 seconds of VDU work showing principles of signal analysis. (A) The EMG signals were RMS converted in 0.2 sec windows and normalised in relation to the EMG amplitude recorded during a maximal isometric contraction. The broken line indicates the 0.5 per cent EMG level used for detection of EMG gaps. (B) An amplitude probability distribution function analysis was performed on the RMS amplitudes shown in (A) and the static (p = 0.1), median (p = 0.5) and peak (p = 0.9) levels are indicated with broken lines. (C) An exposure variation analysis of the RMS amplitudes shown in (A) is shown in a three-dimensional graph. Here, the time spent within the indicated exposure levels and time period lengths are indicated.

chapter |1 pages

The term % Max is used no matter whether the original study expressed results in relation to EMG or MVC. * Estimated from graphs.

chapter |1 pages

Figure 11.3 A picture of a cleaning person with markers is shown at the top. After videorecording the body markers were digitalised and the corresponding stickdiagrams at the bottom are depicted repeatedly during one half cycle of a mopping task. The long stick is the mop and the small horizontal stick at the bottom was used to record twisting of the mop.

chapter |1 pages

Figure 11.4 Distribution of EMG levels recorded bilaterally on the upper trapezius muscles during the performance of computer-aided-design work with a mouse. The percentage time is shown, where the EMG level was recorded within level classes according to the exposure variation analysis (EVA).

chapter |3 pages

M = m · d · g · sin(a)

chapter |3 pages

Figure 11.5 Example of muscle activation patterns for one female subject performing forces in a vertical arm position. The curves show the EMG level for 13 shoulder muscles when performing a 10 N force in different directions in the horizontal plane (representing attempted abduction, flexion, adduction, and extension). The 10 N force corresponded to approximately 14 per cent MVC for all force directions. The circles represent a level of 10 per cent EMG.

chapter |3 pages

m. infraspinatus + m. teres minor.

chapter |10 pages

Figure 11.7 Mean EMG amplitudes of 22 subjects recorded at different positions (1 cm distance between electrode positions) across the upper trapezius from near the clavicle (El.A) to near the scapula (El.H) during an isometric shoulder elevation with increasing force (acromion as the point of force application). The EMG amplitudes were plotted against the amplitude recorded at position D corresponding to the standard position approximately halfway between the clavicle and spina scapula (reproduced from Jensen and Westgaard, 1995).

chapter |1 pages

BIOMECHANICAL BACKGROUND

chapter |1 pages

Figure 12.1 Schematic diagram of the bench-top whiplash apparatus. The trauma sled was drawn to the negative horizontal direction with the pneumatic piston and released in the positive horizontal direction. Flexion was defined as positive rotation and extension as negative rotation.

chapter |1 pages

Figure 12.2 Intervertebral rotations from C0–C1 to C7–T1 of a specimen obtained from high speed cinematography during a 6.5g whiplash trauma shown here as a sample data set. Flexion was defined as positive rotation and extension as negative rotation.

chapter |1 pages

Figure 12.3 Movie still photographs and schematics of the trauma shown in Figure 12.2 illustrating starting neutral position (NP) (A), initial response phase with upper level flexion and lower level extension (B), and the subsequent complete extension of the cervical spine (C).

chapter |2 pages

Figure 12.4 Intervertebral trauma motions are shown from the time of whiplash with maximal extensions of the lowest cervical levels C6–C7 or C7–T1 (denoted with #). Physiological ranges are shown on all graphs as a baseline from which to evaluate the trauma induced intervertebral rotations. The figure represents the 2.5g trauma class (n=4) in (A), the 4.5g trauma class (n=2) in (B), the 6.5g trauma class (n=4) in (C), and the 8.5g trauma class (n=2) in (D).

chapter |8 pages

Figure 12.5 Schematic of the trauma shown in Figures 12.2 and 12.3. The spine starts in a neutral position (NP). The 50 to 75 ms time period illustrates the neck forming an S-shaped curvature (Phase I). During this phase, the lower cervical spine intervertebral joints exhibit hyper-extension, exceeding their physiological limits. In the later phase (Phase II), the spine transforms to a C-shape with complete extension. This phase is associated with a lesser degree of the lower level hyper-extension, and thus a lesser potential for injury.

chapter 2|1 pages

CENTRE EPIDEMIOLOGICAL STUDY

chapter |1 pages

Figure 13.1 Impact test system.

chapter |2 pages

Figure 13.2 Transmissibility and gain as a function of frequency.

chapter |1 pages

Figure 13.3 The stadiometer – a means to measure accurately changes in stature.

chapter |9 pages

Figure 13.4 Set-up for unexpected load experiment.

chapter |8 pages

Figure 14.1 Structures of the disc.

chapter |2 pages

Q 250 D 310 BW: body weight, N/R: not reported, D: dynamic, S: static, Q: quasistatic. L3–L4 = between the third and fourth lumbar vertebrae. L4–L5 = between the fourth and fifth lumbar vertebrae. L5–S1 = between the fifth lumbar and first sacral vertebrae. (From Hooper, 1996).

chapter |8 pages

A/P shear 662.2 1000.0 1058.5 Flex 21.5 23.1 23.9 Twist 0.2 0.5 0.7 Lateral bending 0.9 2.4 3.4 (From Hooper, 1996).

chapter |29 pages

References

chapter |6 pages

Falls

chapter |11 pages

External support: standing

chapter |7 pages

BIOMECHANICAL ASPECTS OF SITTING POSTURES

chapter |10 pages

References

chapter |3 pages

Figure 18.1 Relation of elbow and shoulder moments to ladder slant. Figure 18.2 Relation of trip, knee and ankle moments to ladder slant in male subjects.

chapter |14 pages

Foot forces and joint moments/muscle activity

chapter |4 pages

Figure 19.1 General concept of slip resistance.

chapter |1 pages

TRIBOPHYSICS OF SLIPS AND FALLS Footwear–contaminant–floor tribosystem

chapter |2 pages

h = (K u A)/(F (19.3) t)

chapter |3 pages

Figure 19.2 Elaborated friction model for slipping.

chapter |1 pages

Figure 19.3 Gait phases in normal level walking with typical horizontal (F) and vertical force (FV) components and their ratio, F/F, for one

chapter |2 pages

Figure 19.4 Frictional (F) and normal force (F) vectors versus

chapter |2 pages

Figure 19.5 Example of friction utilisation, F/F, data from two typical

chapter |2 pages

pressure Short test distance Operator-dependent

chapter |3 pages

Figure 19.6 Simple biomechanical parameter model for determining slip resistance. The critical parameters should be studied preferably at slip start, at slip continuation, and at fall start.

chapter |11 pages

Loading on the musculoskeletal system