Ebook: Assessment of the Ergonomic Quality of Hand-Held Tools and Computer Input Devices

The quality of products and the management processes employed for their production, represents an important criterion that can set a company apart from competitors. This among other things is one reason the evaluation and certification of products, companies, and people have become quite popular nowadays. Also, the International Ergonomics Association (IEA) is currently developing standards for Ergonomic Quality in Design (EQUID) which primarily intend to promote ergonomics principles and the adaption of a process approach for the development of products, work systems and services. Whereas certification criteria are being defined which require the comprehensive and systematic application of human factors considerations throughout the product development cycle, hitherto, no specified generally applicable criteria in EQUID exist which address specifically the ability of products to meet user needs and their compatibility with user limitations and capabilities. Probably, in the future this will be difficult to achieve. Furthermore, certification bodies all too often use only formal and clearly understandable criteria because “real” quality is difficult to quantify.

Since the term ergonomics – which suggests quality – is sometimes used arbitrarily in a trend which may be called “Ergomania,” skepticism about so-called ergonomic products is appropriate. People often think that, if they understand, for instance, the size of a person's hand for a hand-held product, then they can call it an ergonomic product. Yet, beneath the surface of a pretty design, the quality of a product which claims to be ergonomic is often questionable. Ergonomics is more than just anthropometric considerations, as many engineers and designers often think. According to the definition of the IEA, it is a scientific discipline concerned with the understanding of interactions among humans and other elements of a system and a profession that applies theoretical principles, data, and methods to design in order to optimize human well-being and overall system performance. Thus, it is important to assess the ergonomic quality of products, hand-held tools and computer input devices via interaction through working processes that represent reality. Well-designed working tools can be expected to reduce or eliminate fatigue, discomfort, accidents and health problems and can lead to improvements in productivity and quality. Furthermore, absenteeism, job turnover, and training costs can positively be influenced by the working tools and the environment. Not all these short-term and long-term issues of working tools can be quantified in pragmatically oriented ergonomic research approaches. But multi-channel electromyography, which enables the measurement of the physiological costs of the muscles involved in handling tools during standardized working tests, and subjective assessments of experienced subjects enable a reliable insight in the essential ergonomic criteria of working tools and products. In this respect it is advantageous to provide a test procedure, in which working tests can be carried out alternatingly both with test objects and reference models.

The introductory Chapter 1 describes a systematic approach for the analysis and ergonomic design of hand-held tools and controls. Striving for holistic rather than sectoral goals and considering interdependencies between the various design criteria, a systematic ergonomic layout of the hand side of tools with respect to shape, dimensions, materials, and surface must always be preceded by a thorough analysis that examines, for example, what needs to be performed with the tool, under what conditions, and where and which type of grip and coupling will be required.

In addition to this European approach, Chapter 2 presents an approach to ergonomics evaluation, design and testing of hand tools from an American point of view. As visualized already by some real-life examples in Chapter 1, for the purpose of this chapter, ergonomics evaluation of a hand tool deals with an existing (non-ergonomically designed) tool of a particular kind to identify the shortcomings or deficiencies for designing or redesigning an ergonomically sound hand tool, in terms of selected criteria. Such criteria are identified as mechanical output of the tool, and impact of the tool on the operator in terms of working posture, fatigue, type of grip used, local hand pressure and injury risk. For a true ergonomic design of hand tools, in both the introductory chapters special emphasis is given to the physiology and anthropometric characteristics of the hand and hand grip. Compatibility between human factors, i.e., the dimensions of the hand, fingers and finger phalanges as well as type and movement range of the joints in the hand-arm-shoulder system, and technical system elements is used as guiding principle.

Chapter 3 describes a knowledge-based system for utilizing electromyography as a powerful objective method for the evaluation of the ergonomic quality of hand-held tools. Utilizing multi-channel recording devices, comprehensive physiological responses of muscles involved in manual work can be quantified in figures and numbers, whereby more or less ergonomically designed tools lead to different physiological costs in terms of muscle strain associated with work.

Since repetitive manual movements have to be carried out both during operating hand-held tools and during materials handling (in assembly lines or in supermarket checkouts), from an ergonomics point of view it is important to reduce strain of the operator by avoiding unfavorable and providing favorable movement directions of the hand-arm system. For this reason, Chapter 4.1 contains fundamental information on electromyographically determined physiological costs associated with translatory movements of the hand-arm system in the horizontal reach. Similarly, Chapter 4.2 presents data on operational output (torque strength) and muscle strain associated with inward and outward rotations of the arm which have to be obeyed for a suitable working technique. The main objective of this study was to quantify the influence of hand preference and rotatory movement direction, i.e., inward and outward rotation of the arm on torque strength as well as physiological costs of the main muscles involved. As for screwing in, a right-handed person normally uses supinations (outward rotations) of the dominant right arm which are weaker than pronations of the subdominant left hand, it would be advisable rather to apply pronations of the subdominant hand. For unscrewing, in any case, the dominant right hand guarantees that a tightened screw can be loosened with less effort.

Chapter 5 deals with conventional and ergonomic keyboards as main computer input devices. Chapter 5.1 provides basic information on the degree of muscle strain of the hand-arm-shoulder system (by standardized Electromyographic Activity sEA [%] of 8 muscles) during alternatingly typing at conventional and ergonomic keyboards in long-lasting working tests. On the one hand, the study delivered consistent results which give statistically reliable insight into the time-varying degree of strain of the various muscles during typing. On the other hand, the results enable an objective evaluation of the keyboards. These were in favor of the ergonomic split keyboard which has been designed with slightly angled keys and a pantile-like inclination of the two keyboard halves to reduce ulnar deviation of the wrist and pronation of the forearm. The positive effects on muscle strain associated with the test keyboard, however, were not as strong as the results shown in Chapter 5.2, i.e., the estimated and experienced subjective assessments via specifically designed questionnaires given to the test subjects prior to and after the working tests.

Chapters 6 and 7 demonstrate that an armrest or also a wrist rest can reduce or even prevent physical complaints which often arise while typing at keyboards that requires longer periods of time. Continuously measured electromyographic activity (EA) of the most important muscles, as indicator of physiological costs, was substantially lower when using the armrest or the wrist rest. Relating EA values without the working aid to those with the working aid, shows that working without the working aid is far more strenuous than working with it. For instance, muscular strain of the descendent part of the trapezius, which keeps the shoulder in position and which always is a bottleneck muscle for sedentary work, is around twice as high as with the two working aids. As a safe sign of a rapidly beginning fatigue, strain of this muscle exhibits an increasing tendency within the 10-min blocks of continuous typing and from one block to another. For the three functional parts of the deltoid muscle which are involved in forward and backward moving, and in abducting of the upper arm, muscle strain is even up to 4 times higher without the armrest. For the wrist rest which reduces muscle strain of the upper arm and shoulder generally less effectively, nevertheless, the effects are statistically significant. This means this working aid also helps to save a lot of physiological costs which otherwise has to be paid by the muscles when working without it. The subjective assessment after the tests under the impression of the own working experience corresponds well with the objectively measured physiological data.

Chapter 8 reports on a detailed study during which an ergonomically designed handle of a mason's trowel was tested in comparison with two standard types. Under well-controlled conditions, physiological costs of muscles associated with mixing and throwing of mortar onto a vertical wall, translatory carrying and depositing of sand on a horizontal wall, rotatory scoping movements with and without an external load of the trowel, and static holding of the tool in different working postures were measured. The ergonomic quality of the handles was rated by means of a questionnaire. The specific relief of strain, e.g., in the grip musculature and the ulnar deviation muscles, when using the ergonomic model, though significantly proven, is much less in scale than was expected from subjective assessments. This makes clear that a numerical quantification of the ergonomic quality based only on subjective rating data of the subjects would have led to an essential overestimation of the ergonomic handle. This handle, no doubt, proved to be better than the standard models; however it was not found to be several times as good as is suggested by the results from subjective rating.

Chapter 9 reports on a similar study focussing on the assessment of the ergonomic quality of file handles. Due to substantial differences between electromyographic, i.e., objective data and the subjective evaluation, inferences have to be drawn that only the combination of subjective surveys and objective measurements represent the opportunely to assess the ergonomic quality of working tools adequately.

Chapter 10 provides useful and important information on screwdrivers, i.e., the most widely used tool which can be found in every toolbox, oftentimes even in several sizes. Although a detailed description of ergonomically optimal screwdriver handles exists for quite a long time, models on the market do not always exhibit, e.g., the shape and dimensions that would follow from the hand's anatomy. As a result, complaints, muscle pain, and blisters oftentimes occur. Chapter 10.1 describes the results of a comprehensive study in which the ergonomic quality of 11 professional-grade tools was tested in terms of maximum achievable torque, physiological strain, and subjective rating of various design criteria and complaints, e.g., pressure marks and blisters in the palm by experienced test persons. Maximum exertable torques and associated muscle strain were not only measured in a power grip during pronation and supination but also when the tool's surface was altered due to practical working conditions from a clean to an oil-contaminated handle. The results of the study, which reflect the advantages and shortcomings of the different models' specific design, were used by several manufacturers to improve their products. The study described in Chapter 10.2 was carried out with a limited set of test models of the preceding chapter as a follow-up investigation into maximum exertable torques and physiological costs. It enabled testing the reliability of methods applied. In the studies described in Chapters 10.3 and 10.4 independent parameters were gender of user, handle (4 and 5 commercially available screwdrivers, respectively) and blade length. The dependent parameters were the maximum supination torque in a static task, physiological responses of the outward rotator of the arm and the grip musculature, and a discomfort rating for the upper extremity under a dynamic task. Amongst other results, it could be shown that blade length is not significantly related to any dependent measure.

Chapter 11 deals with the product-ergonomic evaluation of diagonal cutter handles, i.e., a typical two-legged tool which has to be operated dynamically. The results of the study were gained in the “status nascendi” of a new tool and, therefore, could be used by the manufacturer for improving his product.

Chapter 12 propagates the concept of “snap-on-handles” matched with the proper hand size with a fixed hacksaw blade. The ergonomically designed hacksaw handles were tested/compared with conventional/market handles, in terms of performance or productively, muscular effort, and subjective scores. The experimental results conclusively proved that the ergonomically designed handles were significantly better than the other handles in terms of the stated criteria.

The objective of the studies described in Chapters 13 through 15 was to assess the ergonomic quality of hand tools and working devices which demand bi-manual working in a closed kinematic chain. Since, additionally, several control elements were attached to the tested electrically-powered hedge-clippers, fire fighting nozzles and ambulance cots, this caused complex scheduled test sequences during which the various ways of handling the tools and operating the controls were tested by extensive subjective ratings and work-physiological measurements. Comfort and discomfort as well as considerable details in the design and arrangement of levers, knobs and handlebars could not be evaluated by work-physiological methods but were duly reflected in subjective ratings at bipolar 4-step scales provided for the items of structured interviews. While comparing the results, interestingly, fire nozzles and ambulance cots of producers which pretended to have been designed ergonomically and were even more expensive than others, did not live up to their promise.

The studies in these final chapters are examples of how misleading the term “ergonomic” for a tool can be when the producer does not have a comprehensive understanding of ergonomics. It is not enough to call a hand-held product “ergonomic” when ergonomic considerations, as it is all too common today, are limited to the proper coupling of hand and tool, as it was the case for a pistol grip in a fire fighting nozzle. Ergonomics far exceeds traditional measurements of body parts and involves at the very least an understanding of dynamic situations with respect to the interaction of the user with the product in a comprehensive working environment. To perceive ergonomics as nothing more than an anthropometric consideration is to miss the major part of the point. Instead of this, the term has to be defined as the “study of the efficiency of persons in their working environment”. This amounts to considerably more than percentiles of limb segments, so that the transatlantic term “human factors engineering” seems to be more appropriate.

In the long run, it would be detrimental to the science of ergonomics if the label “ergonomic” would be carelessly handed out by designers or solely on the basis of very popular paper and pencil tests or checklists (as they produce clear yes/no decisions) or based only on relatively simple subjective ratings. Results from subjective ratings, as shown in several chapters of this book cannot substitute fully objective measurements, are not free of bias and uncontrollable transfer effects. Therefore, they must be corroborated, validated, and possibly related via objective measurements, e.g., performance and electromyographic registrations. Only via a multidimensional approach can a more consistent result in the evaluation of a hand tool be reached.

For efficient working with tools, purchasing decisions should not almost exclusively be based on monetary considerations but in the long run, also in due form “physiological costs” which must be “paid” by the operator and subjectively felt complaints have to be considered.

I wish to extend my sincere thanks to all authors and to Dr. Hartmut Irle who did a great job in improving the colored figures and in formatting the book. The cooperation of IOS Press and in particular Dr. Einar H. Fredriksson, Publisher, IOS Press is duly acknowledged.

Prof. Dr.-Ing. habil. Helmut Strasser, Siegen, 2007

To this day, handymen and employees use tools and controls, i.e., hand-operated tools that are freely movable or in a fixed position. In order to avoid cumulative trauma disorders, work-related illnesses, or even occupational diseases especially during repetitive use, the tools must satisfy the equation “suitable for the human body = suitable for the hand.” That is, the aspect of compatibility in the basic ergonomic design must take the characteristics of the human hand-arm system, e.g., the motion ranges as well as the limits of the various joints, into consideration. Accordingly, a systematic ergonomic layout of the hand side of tools with respect to shape, dimensions, materials, and surface must be preceded by a thorough analysis that, for example, examines what needs to be performed with the tool under what conditions and how and where and with which type of grip and coupling it needs to be performed. The analysis as well as the subsequent design must always strive for holistic – rather than sectoral – goals in a systematic fashion and must consider interdependencies between the various design criteria. Several real-life examples in conjunction with evaluation studies to test the ergonomic quality of hand-held tools with electromyographic and subjective methods demonstrate the usefulness of such a systematic approach. It is furthermore helpful for the appropriate selection of truly ergonomically designed hand tools from an assortment of several variants.

A systematic approach to ergonomics evaluation, design and testing of hand tools with particular emphasis on hand-powered tools is presented. Basically, ergonomics evaluation and testing processes used for hand tools are synonymous. However, for the purpose of this chapter, ergonomics evaluation of a hand tool deals with an existing (non-ergonomically designed) hand tool of a particular kind to identify the shortcomings or deficiencies from an ergonomics viewpoint for designing or redesigning an ergonomically sound hand tool of the selected kind. The ergonomics testing of a hand tool deals with an ergonomically designed hand tool, in terms of selected criteria. The ergonomics evaluation of hand tool deals with the characteristics of the tool and the task and the effects of the tool on the operator. The ergonomics evaluation of hand tool is concerned with the mechanical output of the tool, tool mass and centre of gravity, tool dimension and grip, use of different grips and tool surface. In the performance of the hand tool task, the demands on force, precision and task duration must be given due consideration. The impact of the tool on the operator is evaluated in terms of working posture, wrist flexion/deviation angles, machine load and fatigue, type of grip used, local hand pressure and injury risk. In the ergonomics design of hand tool special emphasis is given to the physiology and anthropometric characteristics of the hand and hand grip. In the design of hand-powered hand tool and in particular the design of the tool handle, the relevant factors are: length, size (diameter), shape, material, angulations, snap-on-handles, mechanical output, centre of gravity and weight. For the design of power hand tool, the main issue of concern is vibration. Before conducting ergonomics testing of hand tool, it is necessary to obtain relevant information concerning (tool) functional requirement, work method or motions involved in task performance and working posture through direct observation and/or input from experienced users. The ergonomics testing of an ergonomically designed or redesigned hand tool is performed for functional effectiveness, work performance or productivity, physiological or muscular stress and subjective acceptance or comfort. It should be understood that the details presented under ergonomics evaluation, design and testing are not applicable in each and every situation, only relevant factors need to be considered in a particular situation. The characteristics of hand-powered (hammers, shovels, knives, saws, pliers and screwdrivers) and power (power drills and nutrunners) tools commonly used in industry are presented.

Electromyography enables the measurement of the intensity of muscle exertions which are demanded when working with hand-held tools and controls as well as when performing repetitive manual movements. Utilizing multi-channel recording devices, comprehensive physiological responses of working muscles can be quantified in figures and numbers, whereby more or less ergonomically designed tools lead to different physiological costs in terms of muscle strain associated with work. A computer-based system was developed for the suitable application of electromyography, a technique which requires differentiated and detailed knowledge of the possibilities and limitations as well as a substantial amount of experience. Software packages provide programs for the recording, analysis, and evaluation of myoelectric data. Knowledge about practical methods of appropriate recording and processing of myoelectric data which has been accumulated and further developed during the last decade has been fed into the program system. The same is true for a set of investigations already carried-out and published. Making use of the specifically developed and well-proven software packages which can be loaded into almost all PCs for recording, analyzing, and standardizing electromyographic data, even a user who until now is less familiar with these tasks gains access to electromyography as an efficient and important ergonomic method which is applicable with reasonable expenditure both in the laboratory and in the field.

A study was carried out in order to analyze the influence of different movement directions on muscular strain of the hand-arm system when handling light weights. 11 female subjects had to perform a one-handed lifting task in the horizontal plane, moving repetitively objects of approximately 0 kg and of 1 kg on a table. Thirteen different directions in the frontal area had been provided.

Electromyographic activity (EA) was continuously recorded from 8 muscles of the left hand-arm-shoulder system and the upper trunk. All data were standardized by the activity arising under maximum voluntary contractions (MVC). The EA values were separated into static and dynamic components. Before the test, the subjects had to assess their preference of each direction. After each working direction the actually felt strain was rated on a scale.

Both static and dynamic components of the muscular activity show a strong dependence on the moving direction. The directions around 30° (measured from the body plane) cause less than half of the muscular load in comparison with directions between 90° and 160°, which are often found in real work situations. When moving the weight of 1 kg EA values up to 30 % of the maximum EA were found. According to these findings the strain in the relevant muscle groups dependent on the working direction is not neglectable. When moving the nearly weightless object, the recorded strain was also essential. The pure arm movement seems to be already responsible for a relatively high strain during this kind of work. The subjective ratings before the tests differed considerably from the physiological findings. The ratings after each test, however, corresponded with the measured strain in some important muscles which represent bottlenecks in repetitive manual movements.

The repetitive handling of light weights is often found in industrial workplaces, as for example in supermarket checkouts and in assembly lines. The layout of these workplaces normally refers to static anthropometric data and not to the dynamics of the movements. Especially the direction of the movements is an important parameter for the muscular strain. Almost half of the static strain and considerable part of the dynamic strain of some relevant muscles can be reduced if the workplaces are reconstructed according to the findings of this study.

The focus of this research was to investigate how maximum torque and muscle forces were affected by pronation and supination, i.e., inward and outward rotation of the forearm in a series of screwdriver tests with 6 varied handles. Consecutively, maximum torque for pronation and supination was determined, submaximum isometric levels of torque were demanded, and, finally, an equal dynamic screwing work for all subjects was simulated. Physiological cost of performance was simultaneously measured by registrations of electromyographic activities (EA) from 4 muscles, which were expected to be involved intensively in screwing tasks. Significant and essential differences between maximum torque values produced by pronation and supination of the right and the left arm of the mainly right-handed subjects were found. For clockwise work, as it is necessary e.g., for driving in screws, inward rotations (pronations) of the nondominant hand are at least as strong as outward rotations of the dominant hand. Differences of about 8 % even in favor of pronations were found. Yet, for counter clockwise work involved, e.g., in removing a tightened screw, inward rotations of the dominant hand yielded a much more stronger torque strength than outward rotations of the nondominant hand. Differences of more than 50 % in favor of pronation of the right-handed subjects were measured. Also, EA values of the 4 muscles monitored on the right arm differed significantly. Systematically operational and physiological differences due to the varied screwdriver handles, as results of investigations which were not the main objective of the study, corresponded well with the findings of prior studies.

Manufacturers of ergonomic split keyboards promise maximum effectiveness and comfort as well as a reduction of physical complaints. In order to determine the positive effects claimed, a study was carried out during which 10 male subjects (Ss) participated in standardized working tests. They entered text into a PC, alternatingly using a conventional keyboard and an ergonomic keyboard. Electromyographic activity (EA) of 8 muscle groups was simultaneously recorded during altogether 6 working phases with a duration of 10 min, each. Measurements of the maximum activity, EA_max, via maximum voluntary contractions of the 8 muscles – which were necessary for calculating standardized electromyographic activity (sEA) used to represent muscle strain as a percentage – were always taken at the end of the experiment. Muscle strain varied from muscle to muscle but the level of the sEA values for the different muscles was reproducible and stable. Also, activation of most muscles acting on the shoulder, upper arm, forearm, and the hand showed differences which, though small in amount, could be statistically secured and associated with the keyboard type. The ergonomic design of the tested keyboard led to objectively verifiable and plausible reductions of muscle strain.

At an ergonomically optimized VDU-workstation, a group of 10 test subjects (Ss) carried out a typing task both at the test keyboard and a reference computer keyboard. The participants' personal subjective assessments concerning the working conditions with the two keyboards and the layout of the ergonomic model were recorded via specially designed questionnaires. These were given prior to, and after, the working tests and, therefore, reflected ratings without and with working experience. The posture of the hand, the lower and the upper arm, and the shoulder during text input were evaluated quite differently as a consequence of using the two keyboards. The working posture associated with the conventional keyboard was never assessed positively. The ratings always reached positive values when operating the ergonomic model. The handling of the keyboard and the overall impression were also in favor of the test keyboard as a result of the working tests. Comfort and effort while typing at the keyboards also differed substantially and were in favor of the test keyboard. The same was true for altogether 10 items of the questionnaire, aiming at evaluation of details of the ergonomic keyboard and its overall appearance.

Even when utilizing ergonomically designed flat keyboards, longer lasting periods of work with a word processor or typewriter can cause physical complaints. In this context, a specially developed armrest is said to enable more comfortable working and to prevent physical complaints. Therefore, the objective of this study was to assess the effects of this armrest via an experimental investigation. Ten male subjects (Ss) participated in tests at an already ergonomically optimized VDU workplace where continuous input of the same text was demanded in sections with and without the armrest. Before and after the tests, the subjects had to subjectively rate important criteria of the armrest. During the tests, muscular strain associated with working was measured continuously via electromyographic activities (EA) of 5 muscle groups. These data – as indicators of “physiological cost” – were essentially lower when using the armrest. On the contrary, by relating EA values without the armrest to those with the working aid, it could be shown that working without the armrest is far more strenuous than working with it. Subjective assessments after the tests, as opposed to prior to the tests, corresponded well with the objectively measured physiological data.

This study assessed the effects of a wrist rest for VDT operators via an experimental investigation. Muscular strain associated with the working posture was measured continuously via electromyographic activities (EA) of 8 muscle groups which were involved in the working tasks. The electromyographic measurements yielded a clear systematical effect of the wrist rest while entering text using the 10-finger touch system. Values of the EA – as an indicator of “physiological cost” – were essentially lower with the wrist rest. Working without the wrist rest is at least two times more strenuous than working with it. The differences are statistically highly significant. Less positive and less consistent results were found while working on the prefixed mousepad of the wrist rest. Considering the influence of the working aid on entering text, the results of the subjective assessment after the tests corresponded well with the objectively measured physiological data. Whereas the working aid for entering text was assessed quite positively overall, the integrated mousepad earned a clearly negative rating.

The design and attractive outfit of products and tools very often are cues which encourage somebody to buy them. Yet, the first impression and the succeeding working experience sometimes diverge considerably. Furthermore, stereotypical behavior and traditional habits as well as the lack of numbers and figures indicating the ergonomic quality and the utility values of a product or working tool are obstacles to the introduction of actually innovative items. The same is true for the handle of a mason's trowel, which has been developed some years ago but has not achieved general acceptance in bricklaying. Therefore, the objective of this study was to evaluate the ergonomically designed handle of a mason's trowel in comparison with two standard types, both with a round cross-section of the handle and either a straight neck or a swan's neck. All the tools were equipped with the same blade. Job-specific dynamic and static working elements were performed by 10 subjects in a laboratory. Under well-controlled conditions, physiological cost associated with mixing and throwing of mortar onto a vertical wall, translatory carrying and depositing of sand on a horizontal wall, rotatory scooping movements (supination and pronation of the forearm) with and without an external load of the trowel, and static holding of the tool in different working postures were measured. Electromyographic activity (EA) of the biceps brachii, pronator teres, flexor digitorum, and extensor carpi ulnaris was registered continuously and summed up during all of the test sessions lasting 30 or 45 s, each. All data were standardized by means of maximum EA resulting from preceding job-specific maximum voluntary contractions. Before and after the working sessions, which lasted about 4 h for each subject, the ergonomic quality of the handles had to be rated by means of a questionnaire with 9 items on a bipolar 4-step scale. In accordance with the hypothesis that the ergonomically designed handle should enable a specific relief of the strain in the grip musculature and the ulnar deviation muscles, significantly lower EA values were measured with this model during most of the test phases. But the effect was much less in scale than was expected from the subjective assessment before the tests. Also, subjective rating data after the working sessions differed clearly between the three handles mostly corresponding with the pretest assessment.

In a comparative investigation 3 file handles were evaluated with regard to their ergonomic quality. By means of a mobile measuring system for the recording of peripheral-physiological data, the muscle strain of 9 muscles of the left and right hand-arm-shoulder system was quantified with surface electromyography. A special laboratory device facilitated the standardized execution of the tests. A specific, bipolar questionnaire had enabled the subjective assessment of the design, surface material, general usability, avoidance of pressure marks and blisters, suitability for the exertion of the necessary pressure and pushing forces, and the suitability during hand perspiration. Also, the assessment of more or less favorable body positions to various filing directions was made. From substantial differences in the objective data and the subjective evaluation, the inference has to be drawn that only the combination of subjective surveys and objective measurements represent the opportunity to assess the ergonomic quality of working tools adequately.

In a comparative ergonomic study, which comprised both objective and subjective assessments, 11 types of currently available screwdrivers were tested with respect to their ergonomic quality. In order to objectively record performance (maximum exertable torque) and physical strain during the use of the professional-grade screwdrivers, various test series were carried out (consisting of static torque measurements and dynamic tests of screwdriver use). Twelve male right-handed test subjects (Ss) who were between 22 and 30 years of age participated in the test series. The muscle activity of 4 muscles was recorded via surface electrodes in order to quantify objectively measurable differences in strain during the various screwdriving tests. Each of the Ss had to complete the test series with all screwdrivers under identical, controlled working conditions.

The Ss also assessed in detail the design of the handles via a specifically developed questionnaire. The handles exhibited substantial differences with respect to the 4 most important design aspects: “shape,” “dimensions,” “material,” and “surface.” Items such as working efficiency with clean and oil-covered handles as well as the general design, among others, were also part of the questionnaire. In a special block of items of the questionnaire, the Ss were asked to express also potential physical complaints with respect to intensity, duration, and occurrence in the fingers, hand, and forearm. The same was true for various detailed areas of the palm. The detailed subjective evaluation of the handles by means of approximately 30 questions offered a differentiated view of the impacts of the work situation and reflected the advantages and shortcomings of the different models' specified design characteristics. Additionally, the objective measurements showed that especially an ergonomic shape in conjunction with favorable dimensions and the proper design of the material's friction coefficient of a pressure-anthropomorphic material can contribute to the success of a product.

The use of manual screwdrivers is still an important part of the work of, e.g., car mechanics or in the furniture section. Tightening or loosening screws often requires high torque strength. Therefore, the ergonomic design of the screwdriver handle helps to fulfill the working task by reducing physiological costs for the muscles of the upper extremity as well as complaints like blisters and pressure marks at the fingers and in the palm of the hand. In a series of screwdriver tests with 5 various handles (4 ergonomically designed and one “old-fashioned” handle as reference), bi-directional exertions with clean and oil-contaminated hands were demanded to simulate typical work tasks. Twelve male subjects (Ss), all right-handed, between the ages of 15 and 32, participated in standardized working tests during which the maximum achievable torque was determined. Simultaneously, electromyographic activities (EA) of 4 muscles involved in the working tasks were recorded, processed, and standardized. Significant differences between the standardized electromyographic activities of the muscles investigated were obtained depending on the direction of rotation. Also substantial differences between maximum torque strength were determined for pronation and supination, and for clean and contaminated contact surfaces. The results of this study were mostly consistent with those of the study described in Chapter 10.1 and, therefore, enable testing the reliability of methods applied.

This study evaluated screwdrivers with different handle designs and blade lengths. 10 men and 10 women voluntarily participated. A repeated-measures experiment design was employed. The three independent factors were gender of user, handle (four types), and blade length (130, 170, and 210 mm). The dependent measures were the maximum supination torque under a static task and the %MVC of EMG responses in biceps brachii and flexor digitorum, and a discomfort rating for the upper extremity under the dynamic task. Analysis showed that the in-line screwdriver with the combined characteristics of large handle diameter (3.8 - 4.1 cm), smooth rubber covering handle surface, triangular (or circular) shape, and adequate handle length (11 cm) had the greatest supination torque and a smaller discomfort rating than the screwdriver with the pistol-grip handle. Blade length was not significantly related to any dependent measure.

The objective of this study was to investigate the effect of screwdriver handle design and blade length on maximum torque and muscle activity. Five handle types and three blade length were evaluated. Twenty student subjects (10 males and 10 females) participated in this study. The subjects exerted maximum torque before and after screwing task. Physiological cost was simultaneously measured by electromyographic activities of 2 muscles (biceps brachii and flexor digitorum). The results indicate that handle effect was significant on anterior, posterior maximum torque (p < 0.001), and %MVC of biceps brachii muscle (p < 0.01). On the other hand, the effect of blade length was not significant on all measures. When the diameter of handle was greater, the MVC in anterior and posterior maximum torque exertion was increased, and the %MVC was decreased. The mean anterior and posterior maximum torque of females was 64 % and 62 % of that of males respectively.

For the development of ergonomically optimized types of diagonal cutter handles, 8 typical diagonal cutters were compared and evaluated with respect to the handle design. Eleven male, right-handed test subjects (Ss) between the age of 19 and 35 years repetitively had to cut medium-hard and soft wires according to the test methods of the German Institute for Standardization (published in DIN ISO 5744) at a special device and in a standardized execution. By means of surface electromyography the muscle strain (mean values from 20 cuts) of the m. flexor digitorum, m. extensor digitorum, m. flexor carpi ulnaris and m. biceps in the right hand-arm system were continuously registered. Following these tests, the data were standardized, analyzed and assessed in percentage of the electromyographic activity (EA) associated with maximum voluntary contractions. A complete mobile system for the recording of peripheral-physiological data was used.

Furthermore, specific questionnaires with 35 items were developed with which the Ss subjectively evaluated cutting pliers and handles criteria such as design, material, dimensions, weight, and handling as well as work effects on the human body. The determined objective measured data in combination with the obtained subjective assessments allowed conclusions about design criteria and design approaches for the optimization of the diagonal cutter handles.

Hand-powered hand tools in the past have mainly focused on designing hand tool handles based on ergonomics principles and anthropometric data. No consideration was given to accommodate the hand size of the individual user or the entire male and female populations. The present investigation was undertaken to redesign ergonomic handles for a hand-powered hacksaw to accommodate the entire male and female populations by considering their hand sizes. Based on the ergonomics evaluation of existing hand-powered hacksaws with original/horizontal and conventional/market handles, ergonomically designed hacksaw handles are proposed. To accommodate the entire male and female populations, the hand dimensions are categorized into three groups: small, medium and large. The proposed handles give special emphasis to hand size, length, cross-section dimension and curvature. The three-sized handles for both the preferred (rear) and non-preferred (front) hands are interchangeable to suit the individual hand size. Thus, the concept of “snap-on-handles” with a fixed hacksaw (blade) can be promoted. The ergonomically designed hacksaw handles were tested/compared with original/horizontal and conventional/market hacksaw handles, in terms of performance or productivity (depth of cut), muscular effort or strain (EMG) and subjective scores (acceptance/comfort). The experimental results conclusively proved that the ergonomically designed hacksaw handles were significantly better than the other handles in terms of the stated criteria. The performance or productivity improvements of the ergonomically designed handles were about 25 and 148 %, when compared with the conventional/market and original/horizontal handles, respectively. Furthermore, when the ergonomically designed handle was not matched with the proper or appropriate hand size, there was a significant reduction in performance or productivity, increase in muscular effort and decrease in subjective scores of acceptance/comfort.

Stress and strain during manual tool handling not only depend on factors such as weight to be handled, but are also determined by the design of the man-machine interface. In this study, three different handles of electric hedge-clippers were analyzed. Muscular strain was measured via surface electromyography in laboratory experiments with nine male subjects. The results showed significant differences in physiological cost depending on both work height and the handles' shape, too, despite the fact that all clippers were compensated in respect to weight and location of centre of gravity. One of the handle designs enabled working under varying conditions (work height and direction) at a reduced level of muscular strain of the right arm. Results from the physiological evaluation were partly supported by the working persons' own subjective experience. The results of this investigation show that further ergonomic tool and handle design is necessary.

Firefighters are subject to high physical and psychological stress and fire fighting often requires mastering complicated tasks under adverse conditions. In this job, the handling of the hose/nozzle combination is a central and often performed task. The objective of this field study was to ergonomically evaluate different designs of 3 fire nozzles – a multi-purpose nozzle according to a German standard, a pistol nozzle (AWG), and a supposedly ergonomic nozzle (Quadrafog) – with respect to the muscle strain associated with performing standardized working tests. Eleven firefighters (10 males and 1 female, aged 27-54) used the 3 nozzles in the practice area of a fire station. For 3 different working tasks (straight stream, wide fog, and alternating operation), electromyographic activity was monitored continuously from 7 muscles of the right and left hand-arm-shoulder system using a PC-based mobile data registration system. Specially developed questionnaires provided subjective assessments of the ergonomic quality of the fire nozzles.

The standard nozzle – which is still very frequently used – is only suited for “water go” for extended periods of time, but not for dynamic work. Especially the nozzle operator's arm musculature is subjected to high strain by the hose forces, which depend on water pressure and flow. AWG and Quadrafog led to substantially lower overall strain and smaller static components. Only in pure straight stream fire fighting was there no difference between the standard nozzle and the other models. High static portions characterize straight stream as well as wide fog operation. Both operations required small movements of the body so that the static portions became more noticeable. Overall, the AWG fire nozzle exhibited the most balanced strain profile with non-critical static values and a tolerable overall strain for alternating operations. These results are in accordance with the fire fighters' subjective preference for this model.

It is unfortunate that currently the sole focus remains still on the price rather than the usability, which determines the physiological costs that must be paid by the operator. In the future, more attention should be paid to the compatibility between the characteristics of the human organism and the technical components of the tool.

In addition to work analyses during the use of ambulance cots, the strain on the circulatory system of 12 professional carriers was measured in 4 standardized carrying tests: carrying of the stretcher in a staircase at normal speed and at increased speed, lifting of the stretcher onto the gurney, and loading the ambulance cot into as well as unloading it from an ambulance. Additionally, static and dynamic components of the muscle strain of 6 muscle groups were determined electromyographically. The tests consisted of “normal” carrying as well as explicitly rapid carrying of a dummy (78 kg) up and down a flight of stairs using 3 different commercially available ambulance cots (roll-in systems – stretchers with incorporated transporter which weighed between 48.5 and 50 kg including a pad for the patient). The paramedics had to carry both the front and the rear of all the stretchers. The “normal” carrying times to cover one floor (the typical real-life situation) were approximately 35 to 40 s. Rapid carrying reduced the carrying times by approximately 10 s.

Model-specific influences of the roll-in systems aside, the rapid carrying led to substantially increased strain on the circulatory system (work-related increases of approximately 10 beats per minute (bpm)). The “lifting of the stretcher onto the gurney” and the “loading/unloading of the roll-in system” cause significantly less strain, but still lead to substantial “extra physiological costs” of approximately 50 bpm. The strain on the flexor digitorum, the upper part of the trapezius muscle, and the erector spinae substantially exceeds the strain on the 3 parts of the delta muscle in all tests. Increased speed significantly increases muscle strain. The static components of the standardized electromyographic activity sEA [%] with values of 50 % and more (especially for the flexor digitorum) show that even carrying times of only approximately 30 s cause fatigue. It is well known that just 50 % of maximum output over 30 s already require recovery times of approximately 400 %, i.e., approximately 2 min. Carrying the rear of the stretcher upstairs leads to significantly increased strain on the erector spinae related to the carrying position at the front. Similarly, the carrier at the front of the stretcher experiences substantially higher strain while bearing the stretcher downstairs. Even though model-specific influences cause some differences, they are not displayed consistently across all work elements.

The data can be used by job analysts to grade the level of muscle activity required by different carrying tasks during the transport of a patient, and by product designers to justify changes in the design of ambulance cots to reduce muscular strain on the upper extremities and the back.

In a comparative ergonomic study, three combinations of stretchers with incorporated transporters of brand-name manufacturers – so-called “ambulance cots” or “roll-in systems” – were tested with respect to their ergonomic quality. Twelve male test subjects (Ss) from the invalid transportation sector subjectively assessed the design elements of the stretchers as well as the gurneys via a questionnaire which had been developed specifically for that purpose. Additionally, the Ss were asked to express potential physical complaints resulting from the carrying activity. To that end, the Ss – under controlled conditions – had to carry out 4 different test tasks: carrying in a staircase at two different speeds, attaching of the stretcher onto the transporter as well as loading and unloading of the ambulance cot into and out of the ambulance. For each task, a 78-kg patient dummy was on the stretcher. Thus, differences in strain across the different test objects became visible or could be subjectively experienced. The presentation of results reflects the advantages and disadvantages of the different models' specified design characteristics and possibly permits suggestions for design improvements.

The very detailed subjective assessment of “roll-in systems” and the Ss' subjective evaluation of them via approximately 50 items offer a differentiated view of the work situation. They suggest several concrete changes in order to improve the design. In particular, changes in the design of the different stretchers were recommended in order to reduce the extraordinarily high strain on the paramedics which was also measured via peripheral-physiological methods. It became clear that one system which is widely used in several countries has marked weaknesses. The biggest disadvantage is the unfavorable grip during height adjustments. Furthermore, it is not possible to utilize the so-called “switching technique” in order to relieve the back with the complete ambulance cot. However, even with the other two models, which are similar to each other in terms of the operating elements and their handling, promising approaches to improve these products do exist with respect to the stretchers' weight, their shape and positioning of handles, and the positioning of the release mechanism to adjust the length of the handle.

The results of this study reveal the necessity for industry to manufacture user-friendly and safe ambulance cots for the market. Paramedics cannot risk to use an equipment which is inadequate or works deficiently. Furthermore, an ergonomic design of the product additionally increases the safety and user-friendliness of the system during a rescue operation. Thanks to the ergonomic design, less effort is needed during the transport of the patient, which at the same time means lower physical strain for the paramedics' back and their hand-arm-shoulder system.