Assessment of work-related hand and elbow workloads using measurement-based TLV for HAL

Direct-measurement-based methods for assessing workloads of the hand or elbow in the field are rare. Aim of the study was to develop such a method based on the Threshold Limit Value for Hand Activity Level (TLV for HAL). Hence, HAL was quantified using kinematic data (mean power frequencies, angular velocities and micro-pauses) and combined with electromyographic data (root-mean-square values) in order to generate a measurement-based TLV for HAL (mTLV for HAL). The multi-sensor system CUELA including inertial sensors, potentiometers and a 4-channel surface electromyography module was used. For wrist and elbow regions, associations between mTLV for HAL and disorders/complaints (quantified by odds ratios (OR [95%-confidence interval])) were tested exploratively within a cross-sectional field study with 500 participants. Higher workloads were frequently significantly associated with arthrosis of distal joints (9.23 [3.29-25.87]), wrist complaints (2.89 [1.63-5.11]) or elbow complaints (1.99 [1.08-3.67]). The new method could extend previous application possibilities.

Comparison of the postural and physiological effects of two dynamic workstations to conventional sitting and standing workstations

Increasing evidence is being found for the association of health risk factors with work-related physical inactivity. An increasing number of people are being exposed to this form of inactivity, and as a result, various interventions aimed at increasing physical activity during working hours are being developed. This study aims to investigate the differences in postural, muscular and physical activities resulting from two dynamic workstations, namely an elliptical trainer and a treadmill workstation, compared with a conventional sitting and standing workstation. Twelve participants completed five standardised office tasks in a laboratory setting at all workstations. No significant effect was found regarding changes in posture and the muscular activity was only significantly higher for the trapezius muscle (50th percentile: 8.1 %MVC) at the dynamic workstations. For the dynamic workstations, physical activity ranged from 4.0 to 14.9 × 10(-2) g, heart rate from 14.3 to 27.5 %HRR and energy expenditure from 1.8 to 3.1 METs. Practitioner Summary: Work-related physical inactivity is associated with health risk factors. In this study, physiological and postural effects of dynamic workstations were assessed in comparison to conventional workstations. No significant effects were found regarding changes in posture and muscular activity. Physical activity, heart rate and energy expenditure increased for the dynamic workstations.

Optimization of inertial sensor-based motion capturing for magnetically distorted field applications

Inertial measurement units (IMU) are gaining increasing importance for human motion tracking in a large variety of applications. IMUs consist of gyroscopes, accelerometers, and magnetometers which provide angular rate, acceleration, and magnetic field information, respectively. In scenarios with a permanently distorted magnetic field, orientation estimation algorithms revert to using only angular rate and acceleration information. The result is an increasing drift error of the heading information. This article describes a method to compensate the orientation drift of IMUs using angular rate and acceleration readings in a quaternion-based algorithm. Zero points (ZP) were introduced, which provide additional heading and gyroscope bias information and were combined with bidirectional orientation computation. The necessary frequency of ZPs to achieve an acceptable error level is derived in this article. In a laboratory environment the method and the effect of varying interval length between ZPs was evaluated. Eight subjects were equipped with seven IMUs at trunk, head and upper extremities. They performed a predefined course of box handling for 40 min at different motion speeds and ranges of motion. The orientation estimation was compared to an optical motion tracking system. The resulting mean root mean squared error (RMSE) of all measurements ranged from 1.7 deg to 7.6 deg (roll and pitch) and from 3.5 deg to 15.0 deg (heading) depending on the measured segment, at a mean interval-length of 1.1 min between two ZPs without magnetometer usage. The 95% limits of agreement (LOA) ranged in best case from -2.9 deg to 3.6 deg at the hip roll angle and in worst case from -19.3 deg to 18.9 deg at the forearm heading angle. This study demonstrates that combining ZPs and bidirectional computation can reduce orientation error of IMUs in environments with magnetic field distortion.

A technical support tool for joint range of motion determination in functional diagnostics - an inter-rater study

Background

The examination of joint range of motion (RoM) is part of musculo-skeletal functional diagnostics, used, for example, in occupational examinations. Various examination methodologies exist that have been optimized for occupational medical practice, which means they were reduced to the most necessary and feasible measures and examinations for efficiency and usability reasons. Because of time constraints in medical examinations in occupational settings, visual inspection is commonly used to quantify joint RoM. To support medical examiners, an inertial sensor-based measurement system (CUELA) was adapted for joint RoM examination in these settings. The objective of the present study was to evaluate the measurement tool in functional diagnostics under conditions close to clinical practice.

Methods

The joint RoM of twenty healthy subjects were examined by three physicians, who were simultaneously using the measurement tool. Physicians were blinded to the measurement results and the other physicians. Active RoM was examined on the cervical, thoracic and lumbar spine while passive RoM was examined on the shoulder, elbow, wrist, hip, and knee, resulting in a total of 40 joint examination angles. The means, standard deviations, intraclass correlation coefficients (ICC_3,k), and Bland-Altman-Plots were calculated using MatLab for statistical analysis.

Results

Most measurement results were in accordance with expected joint RoMs. All examinations showed an acceptable repeatability. In active RoM examinations, the ICC of inter-rater reliability varied between 0.79 and 0.95. In passive RoM examination the ICC varied between 0.71 and 0.96, except examination angles at the elbow and knee extension (ICC: 0.0-0.77).

Conclusion

The reliability and objectivity of active RoM examinations were improved by the measurement tool compared with examiners. In passive RoM examinations of upper and lower extremities, the increase of objectivity by the measurements was limited for some examination angles by external factors such as the individual examiner impact on motion execution or the given joint examination conditions. Especially the elbow joint examination requires further development to achieve acceptable reliability. A modification in the examination method to reduce the examiner impact on measurement and the implementation of a more complex calibration procedure could improve the objectivity and reliability of the measurement tool in passive joint RoM examination to be applicable on nearly the whole body.

Effects of a standing and three dynamic workstations on computer task performance and cognitive function tests

Sedentary work entails health risks. Dynamic (or active) workstations, at which computer tasks can be combined with physical activity, may reduce the risks of sedentary behaviour. The aim of this study was to evaluate short term task performance while working on three dynamic workstations: a treadmill, an elliptical trainer, a bicycle ergometer and a conventional standing workstation. A standard sitting workstation served as control condition. Fifteen Dutch adults performed five standardised but common office tasks in an office-like laboratory setting. Both objective and perceived work performance were measured. With the exception of high precision mouse tasks, short term work performance was not affected by working on a dynamic or a standing workstation. The participant's perception of decreased performance might complicate the acceptance of dynamic workstations, although most participants indicate that they would use a dynamic workstation if available at the workplace.

Occupational kneeling and squatting: development and validation of an assessment method combining measurements and diaries

Objectives

As knee-straining postures such as kneeling and squatting are known to be risk factors for knee disorders, there is a need for effective exposure assessment at the workplace. Therefore, the aim of this study was to develop a method to capture knee-straining postures for entire work shifts by combining measurement techniques with the information obtained from diaries, and thus avoiding measuring entire work shifts. This approach was applied to various occupational tasks to obtain an overview of typical exposure values in current specific occupations.

Methods

The analyses were carried out in the field using an ambulatory measuring system (CUELA) to assess posture combined with one-day self-reported occupational diaries describing the durations of various work tasks. In total, 242 work shifts were measured, representing 81 typical tasks from 16 professions. Knee-straining postures were analysed as daily time intervals for five different postures. The accuracy of the method was examined by comparing the results to measurements of entire work shifts.

Results

Unsupported kneeling was the most widely used knee posture in our sample (median 11.4 % per work shift), followed by supported kneeling (3.0 %), sitting on heels (1.1 %), squatting (0.7 %), and crawling (0.0 %). The daily time spent in knee-straining postures varied considerably, both between the individual occupations, within an occupation (e.g. parquet layers: 0.0–88.9 %), and to some extent even within a single task (e.g. preparation work of floor layers (22.0 ± 23.0 %). The applied measuring method for obtaining daily exposure to the knee has been proven valid and efficient randomly compared with whole-shift measurements (p = 0.27).

Conclusions

The daily degree of postural exposure to the knee showed a huge variation within the analysed job categories and seemed to be dependent on the particular tasks performed. The results of this study may help to develop an exposure matrix with respect to occupational knee-straining postures. The tested combination of task-based measurement and diary information may be a promising option for providing a cost-effective assessment tool.

Validity of self-reports of knee-straining activities at work: a field study with 6-month follow-up

Objectives

To measure short-term and long-term validity of self-reported duration of kneeling and squatting at work and to examine the possibility of differential misclassification due to knee complaints.

Methods

Work-related kneeling and squatting were analysed for 190 male subjects (mean age, 35.0 and SD, 11.5) in field by both measurements and questionnaires. Posture capturing was performed with an ambulatory measuring system (CUELA). Immediately after the measurement (t₀), each participant was asked to estimate frequency and duration of five specific knee postures taken during the measurement period. After 6 months (t₁), the survey was repeated (n = 125). Health status of all subjects was recorded by Nordic questionnaire. Statistical analysis was performed by using nonparametric tests, correlations, and Bland–Altman plots.

Results

At both time points, subjects were able to recall the occurrence of knee postures rather well (100.0–57.6 % agreement) but many of them failed in quantifying their knee load. We found poor-to-moderate correlations between measurements and self-reports for all examined postures in both surveys (0.23 < ρ < 0.63). The durations of knee postures were both over- and underestimated but overestimations predominated (t_0, 74.7 % and t_1, 87.2 % overestimations). High-exposed subjects seemed to misjudge their exposure to a greater extent than low-exposed ones, while knee complaints seemed to have no impact on the assessment behaviour.

Conclusions

As our study showed, self-reported knee loading may deviate widely from measured exposure. These limitations of self-reporting emphasise the arguments in favour of using objective data whenever possible, for example by complementing self-reported occurrence of knee postures with quantitative measurement data.

Electronic supplementary material

The online version of this article (doi:10.1007/s00420-012-0758-4) contains supplementary material, which is available to authorized users.

Comparison of four specific dynamic office chairs with a conventional office chair: impact upon muscle activation, physical activity and posture

Prolonged and static sitting postures provoke physical inactivity at VDU workplaces and are therefore discussed as risk factors for the musculoskeletal system. Manufacturers have designed specific dynamic office chairs featuring structural elements which promote dynamic sitting and therefore physical activity. The aim of the present study was to evaluate the effects of four specific dynamic chairs on erector spinae and trapezius EMG, postures/joint angles and physical activity intensity (PAI) compared to those of a conventional standard office chair. All chairs were fitted with sensors for measurement of the chair parameters (backrest inclination, forward and sideward seat pan inclination), and tested in the laboratory by 10 subjects performing 7 standardized office tasks and by another 12 subjects in the field during their normal office work. Muscle activation revealed no significant differences between the specific dynamic chairs and the reference chair. Analysis of postures/joint angles and PAI revealed only a few differences between the chairs, whereas the tasks performed strongly affected the measured muscle activation, postures and kinematics. The characteristic dynamic elements of each specific chair yielded significant differences in the measured chair parameters, but these characteristics did not appear to affect the sitting dynamics of the subjects performing their office tasks.

Office task effects on comfort and body dynamics in five dynamic office chairs

In the present study, we investigated the effect of office tasks on posture and movements in field settings, and the comfort rating for chair characteristics and correlation with type of task. The tasks studied were: computer work, telephoning, desk work and conversation. Postures, movements, chair part inclinations and comfort rating data were collected from 12 subjects. Computer work showed the lowest physical activity, together with upright trunk and head position and low backrest inclination. Conversation shows the highest activity of head legs and low back together with the highest cervical spine extension. In contrast, desk work provoked the most cervical spine flexion and showed the second lowest activity. The telephoning tasks showed medium activity and the highest kyphosis. Conversation showed the highest backrest inclination. Positive comfort relations were found for computer work and a "swing system" chair, for telephoning and an active longitudinal seat rotation, and for desk work and a chair with a three-dimensionally moveable seat.

[Radiological diagnosis of lumbar prolaps with quantitative and morphological criteria]

PURPOSE

The present study examines the differences of radiological diagnosis of lumbar prolaps with quantitative and morphological criteria. Advantages and disadvantages of both methods were analysed.

METHOD

Concerning the "Deutsche Wirbelsäulenstudie" (DWS) 286 male and 278 female patients between 25 and 70 years of age undergoing clinical or ambulant therapy for radicular symptoms and the diagnosis of a lumbar prolaps in CT and/or MRT were integrated into our study. Actual MRT and CT pictures of the patients' lumbar spine were analysed by an independent radiologist (primary radiologist). Radiological diagnosis was concerned with quantitative and morphological criteria. Radiological images of 100 selected patients were reexamined by another radiologist (secondary radiologist). On the basis of these results, the interobserver reliability (kappa) was calculated.

RESULTS

In 95.2% of all segments a prolaps was seen with quantitative and morphological criteria, in 4.5% a prolaps was analysed with quantitative and in 0.3% a prolaps was seen with morphological criteria. The radiological diagnosis of prolaps by quantitative criteria was confirmed by the operative findings. Many prolapses with lateral localisation were seen in these cases. Therefore radiological diagnosis on the basis of morphological criteria could be difficult. For both radiological methods similar interobserver reliabilities were calculated. To sum up both radiological methods are even equivalent. It is also possible to graduate the diagnosis with quantitative criteria. Detrimental effects of quantitative criteria could be difficulties in measurement with non-digital images.

CONCLUSION

Besides several recommendations in the international literature on the radiological analysis of prolaps with morphological criteria, diagnosis with quantitative criteria is also an effective method.