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