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Proceeding from a formal definition of heart rate variability, some mathematical and statistical techniques from sampling statistics and time series analysis for the analytical evaluation of heart rate variability for ergonomics purposes are presented and compared. The concept of sampling statistics gives a measure of heart rate variability, arrived at by combining two measures, which were chosen according to a definite criterion. The applicability of this measure is discussed; especially with respect to serial correlation influences when using statistical tests. The two main methods of spectral analysis—the calculation of the transformed autocovariance function and of harmonic analysis–are presented. The influences of interpolations, algorithms and physiological effects are discussed. A possible measure of heart rate variability, calculated by spectral estimates, is proposed and some results are given. [ABSTRACT FROM PUBLISHER]

Heart rate variability is a result of the superimposition of different sources of variation which are systemized. Three parameters are used to describe the phenomenon of heart rate variation. The range of variation of these parameters is discussed using examples from both laboratory and field investigations. Analyses demonstrate a correlation between heart rate and their variability. Discussion of of the variation of the chosen parameters suggests that, when heart rate variability is used as a measure of strain in field research, strain might be under-assessed. [ABSTRACT FROM PUBLISHER]

Information content analysis based on information theory can be used to evaluate stress in controllers. The method is applied to the analysis of radiotelecommunication in air traffic control: ‘ message types ’ are defined and their information content is evaluated using the syntactic level of information. Related to time, the measurements of information provide a stress factor. Preliminary results indicate the usefulness of the method. [ABSTRACT FROM PUBLISHER]

A short system analysis of the air traffic control systems with respect to their purpose and realization shows the role which the human operator plays. The task of man in this system can be determined as information processing. Evaluation of these tasks is important for selection of personal, for job evaluation, and for redesigning tasks and jobs in order to fulfill the tasks of ATC in future. This evaluation of man's tasks can be regarded either from the demands of the job or from their fulfillment and effect for man. Both aspects have to be connected to get objective results which are valid for man. Special research problems arise from the influence of the individual abilities and from the correlation of stress as work load factor and strain as effect of this work load on man. [ABSTRACT FROM PUBLISHER]

Objectives: The aims of the study were to analyze muscular strain and fatigue of urologists during the performance of transurethral resections using direct and video endoscopy and to reduce the muscular effort by an ergonomic arrangement of the operation equipment., Methods: The study was performed before, during and after the introduction of a video-guided resection method. Muscular strain and fatigue were studied by means of surface electromyograms derived from various shoulder and back muscles of surgeons., Results: During direct endoscopy, muscular strain was found to be significantly higher for the shoulder muscles than during monitor endoscopy. The occurrence of muscular fatigue was established for at least one of the muscles under test in all operations during the application of direct endoscopy. A routine use of the video method was facilitated by arranging the operation equipment according to ergonomic principles. This results in a reduction in muscular fatigue, in particular for the trapezius muscle. For this muscle the number of operations accompanied with fatigue was lowered from about 80% before redesign to about 42% after redesign., Conclusion: Muscular strain and fatigue of urologists occurring during transurethral resections is reduced by applying video endoscopy instead of using direct endoscopy. The routine use of the video method requires an ergonomic arrangement of the operation equipment.

An electromyographical fatigue analysis was performed in the operating theatre on four surgeons during 14 urological operations in which 'direct endoscopy' (cf. Luttmann et al. 1996, Part I) was applied. Surface electromyograms (EMG) were derived from the m. trapezius on both sides of the body, the right m. deltoideus, and the left m. erector spinae. The surgeons' activities were documented by simultaneously recording an electrical activity code signal parallel to the EMGs. The electrical activity (EA) was formed from the raw EMG by rectification and continuous averaging. For purposes of spectral analysis, the EMGs were digitized and converted to the frequency domain by Fast Fourier Transformation. During the performance of endoscopic surgery, an increase in EA, as well as a spectral shift towards lower frequencies, are observed for at least one of the muscles under test in all of the operations. This indicates the development of muscular fatigue in the course of the operations. The finding is confirmed by applying a newly developed method for the joint analysis of the spectrum and the amplitude of EMGs (JASA) which permits discrimination between fatigue-induced and force-related changes in the EMG. Utilizing this method, the development of fatigue was confirmed for 11 of the 14 operations in the case of the right m. trapezius. The right trapezius muscle therefore constitutes a bottleneck for the performance of the operations. The endurance time was estimated from the increase in EA and compared with the actual duration of the operations. Since both are of the same order of magnitude, it is concluded that the final part of an operation has to be performed when the muscles are already fatigued. Application of the newly available method known as 'monitor endoscopy' (cf. Part I) can lead to a reduction in muscular strain and fatigue. This, in turn, will enable operations to be performed at less risk to the patient.

An electromyographical field study was performed in the operating theatre on four surgeons during 15 urological operations. In the course of the operations two endoscopic techniques were applied alternately: (1) direct endoscopy, and (2) monitor endoscopy. During direct endoscopy the surgeon looks into the urethra and the bladder via an endoscope. In monitor endoscopy, by contrast, the operating area is observed via a video system consisting of a camera mounted on top of the endoscope and a monitor. During the operations surface electromyograms were derived from both trapezius muscles, the right deltoideus muscle and the left erector spinae muscle. An activity code describing the surgeons' activity was additionally recorded. Analysis of the activity recording reveals that the monitor endoscopic method is preferred in the first third of the operations, whereas preference is given to the direct method in the last third. The electromyographical measurements indicate that during monitor endoscopy the myoelectrical activity of both trapezius muscles and of the right deltoideus muscle is significantly reduced in comparison with the activity for the direct endoscopic technique. A significant influence of the surgical technique on the myoelectrical activity could not be established for the erector spinae muscle. The electromyographical findings reveal that the activity of the shoulder musculature required for the maintenance of the posture and the performance of the operation is significantly lower in monitor endoscopy than in direct endoscopy. Consequently, a clear reduction in muscular strain can be achieved during the performance of endoscopic operations in urology if a video system is employed.

965 workers engaged in working tasks of work intensity grade 2, 3, 4 (based on Chinese National Standard) were investigated on the musculoskeletal disorders with a questionnaire. The lumbar vertebra of 136 randomly chosen workers were also radiologically examined. The result revealed that the prevalence of low-back disorders was 51.2% on average and it was obviously correlated with such factors as age, standing, previous back injury, education level, sport activity, work intensity, working posture, satisfaction with the tools as well as work condition and house work. Heavy work load and unneutral working posture were proved to be the main factors as revealed by the multifactor analysis and further supported by the findings of X-ray examination.

In a work physiology field study, the work flow and the electrocardiogram were recorded throughout whole shifts for six male refuse (garbage) collection workers who transported and emptied 1.1 m3 refuse containers. The work rate (WR), indicated by the number of 1.1 m3 containers emptied per unit of time, and the work pulse rate (WPR) were determined in the data evaluation. The work pulse rate increases with the work rate. The functional relationship can be approximated by a linear regression function (WPR = 20.9 + 35.8.WR). The work pulse rate reaches such high values that it must be assumed that the work cannot be performed continuously throughout the whole working day. Consequently, regular breaks should be provided. When determining the necessary duration of the breaks, it was assumed that an equilibrium between fatigue and recovery should be maintained during the working day. The recovery breaks should be at least long enough for the heart rate to return to the resting level. The necessary duration of the breaks was determined on the basis of the present field study and the laboratory investigations described in the literature. A minimum duration of 10 min per working hour results from the calculations. The breaks should be taken regularly at about hourly intervals. A transportation-capacity model is provided for the planning of the deployment of refuse workers. It permits calculation of the number of 1.1 m3 containers a three-man crew, comprising the refuse collection truck driver and two loaders, can empty during one shift. Both the logistical and ergonomic transportation capacities can be determined using the model. The logistical transportation capacity (TCL) indicates the number of containers which can be emptied per shift by a crew when only criteria such as the optimal utilization of the working time are considered. The ergonomic transportation capacity (TCE) is understood as the number of containers which can be emptied per shift taking into consideration the workers' strain and the recovery breaks they require. TCE amounts to between about 140 and 160 containers per shift depending on the type of city district. TCL is higher by between 20 and 30 containers per shift. In order to meet the demand of protecting workers' health, the number of containers to be emptied per shift by a three-man crew should not exceed the ergonomic transportation capacity.

The health consequences of long-term professional activity in loading for transport were investigated in an epidemiological study. This involved determining the frequency of orthopedic diseases within a series of transport workers and comparing it with the disease frequency in a comparable group with the same age distribution. The frequency of orthopedic diseases in transport workers is about 22% higher than in the other group. Most of the findings relate to the lower lumbar spine. An increase in the number of diseases can be observed in the transport workers even after a short period of professional activity. In order to examine the possible cause for the increased frequency of disease, the load on the lower lumbar spine was determined quantitatively using biomechanical model calculations. A three-dimensional biomechanical model that allows examination of both static and dynamic load was developed for this purpose. The influence of posture, the mass of the load to be transferred, and the acceleration of the load and the body on the mechanical spinal load were examined as typical examples of load manipulation. In the assessment of load, the compressive forces calculated were compared with the strength of the spinal elements. The compression forces on the lower lumbar spine are of the same order of magnitude as the strength. The high mechanical load can therefore be regarded as a possible cause of the high frequency of disease among persons whose professional activity involves lifting heavy loads.

In the terminology of occupational hygiene and the WAO no distinction has been made to date between "load" and "strain". Occupational medicine and ergonomics by contrast, in addition to differentiating between the terms, have been developing the "load-strain approach" since about 1970. After outlining the historical development of the terms and explaining them, the approach is derived and presented in a simple and extended form. Starting from demands made by the WAO, the significance of the approach for the planning and execution of ergonomic investigations is explained. In the approach differentiation between the "description", "assessment" and "judgement" of working conditions is recommended. Possible approaches and criteria for forming a judgment are presented and discussed, with special attention being paid to models for the operationalization of strain. A concept for pragmatic judgment is presented after discussion about the necessity, frequently encountered in practice, of balancing the demands of providing scientific proof and of arriving at decisions relevant to practical problems.

The workload on a physically disabled subject is compared to the load on a non-disabled subjects at identical tasks over a period of 5 shifts each. Various indicators for assessment of the physical working capacity as well as recordings of heart rates during activity are compared. The findings indicate that, in spite of comparable load, the strain may be greater for the disabled person than for the non-disabled, which does however not necessarily entail a difference in output.

Material handling tasks result in high load on the skeletal system. Long-term employment in transportation jobs may therefore cause a high frequency of orthopaedic diseases, particularly in the spinal region. An epidemiological study was performed on employees from a large company in order to test this hypothesis. The medical history of 249 male transport workers was examined by means of statistical analysis of the orthopaedic diseases documented in the record file of their company's health service. For purposes of comparison, the same data evaluation was performed for an age-matched reference group consisting of 267 persons chosen randomly from among the male employees in the same company. The proportion of persons with orthopaedic diseases amounts to 77.1% among the transport workers and 62.9% among the reference persons. It is consequently 1.22 times higher for the transport workers than for the reference persons ("rate ratio RR" = 1.22). The greatest part of all orthopaedic diseases affects the spine. Within the spine, the lumbar region is the most frequently damaged. Both for the totality of all spinal sections as well as for diseases of particular spinal sections (cervical, thoracic, lumbar spine), the proportion of the transport workers with diseases is higher than that of the reference persons (RR between 1.20 and 1.36). The proportion of persons with spinal diseases increases with age in both groups. There is no observable difference between the groups with regard to the frequency of persons with degenerative diseases.(ABSTRACT TRUNCATED AT 250 WORDS)