Mechanical design and fabrication of the VHF-gun, the Berkeley normal-conducting continuous-wave high-brightness electron source.

A high repetition rate, MHz-class, high-brightness electron source is a key element in future high-repetition-rate x-ray free electron laser-based light sources. The VHF-gun, a novel low frequency radio-frequency gun, is the Lawrence Berkeley National Laboratory (LBNL) response to that need. The gun design is based on a normal conducting, single cell cavity resonating at 186 MHz in the VHF band and capable of continuous wave operation while still delivering the high accelerating fields at the cathode required for the high brightness performance. The VHF-gun was fabricated and successfully commissioned in the framework of the Advanced Photo-injector EXperiment, an injector built at LBNL to demonstrate the capability of the gun to deliver the required beam quality. The basis for the selection of the VHF-gun technology, novel design features, and fabrication techniques are described.

Changes in muscle geometry during forearm pronation and supination and their relationships to EMG cross-correlation measures.

Geometric artifact may alter the amplitude and frequency of the electromyography (EMG) signal. Artifacts include the changing geometry of muscles with respect to electrodes and potential crosstalk from adjacent muscles. This study addresses: (1) the geometrical relationships between common electrode placement sites for six forearm muscles, (2) the geometrical change of forearm muscles in pronation and supination, and (3) the relationships between EMG cross-correlation and muscle geometry. EMG and ultrasonography images were recorded during pronation, supination, and neutral forearm postures while exerting 20% maximum grip strength. Proportions of anatomical structures were then calculated for 15mm, 20mm, and 25mm radial pick-up zone distances, representing greater than 90% of observed myoelectrical signal energy. We found that guidelines for electrode placements were supported and no single posture maximized the proportion of the target muscle detected. Secondly, other muscles were present in the most conservative 15mm radius pick up zone; it is unlikely that surface EMG can completely differentiate between forearm muscle activities. Thirdly, forearm orientation did not appear to be an important factor in changing the geometrical relationships between surface electrodes and the muscles studied, and fourthly, certain muscles (e.g., FDS) may be more vulnerable to EMG crosstalk.

Multivariate, longitudinal analysis of the impact of changes in office work environments on surface electromyography measures.

PURPOSE: To detect impacts of changes in work environment and worker-equipment interface variables upon surface electromyography (EMG) measures using multivariate, longitudinal analysis. METHODS: For 33 office workers, yearly measurements (1999-2001) were taken during normal work. Independent variables were related to work environment (expert-observed equipment dimensions, work organization on questionnaire) and interface (expert-observed postures, self-reported workstation-equipment relative fit i.e. inside or outside guidelines-informed location, and 30 min video-based task analysis). Internal mechanical exposure (EMG) was recorded bilaterally from extensor carpi radialis brevis (ECRB) and upper trapezius sites, each side, also for 30 min. Dependent variables were amplitude probability distribution functions (APDF 50 and 90%) and gaptime for entire record EMG (over all tasks) and task-specific EMG (for four separate tasks). Multivariate mixed models used independent variables to predict EMG measures (4 muscle sites × (1 entire record + 4 task specific) = 20 models total). RESULTS: Among EMG measures, 9/16 means and 2/16 variances were significantly different across years (p < 0.1). Environment and interface variables explained part of the variation in EMG measures in 13/20 models. The most consistent predictors included: (1) increased monitor distance predicted reduced APDFs and increased gaptimes; (2) wrist extension <20° predicted decreases in left ECRB APDFs; (3) keyboard location within guidelines predicted improvements in all right ECRB EMG measures during keyboarding; and (4) longer task duration predicted higher APDFs and lower gaptimes. CONCLUSION: Longitudinal analysis with multivariate models can detect the impacts of changes in environment and interface exposures on EMG measures among office workers.

Developing common metrics of mechanical exposures across aetiological studies of low back pain in working populations for use in meta-analysis.

OBJECTIVES: One of the challenges of conducting meta-analyses on the relationship between workplace mechanical exposures and low back pain is that mechanical exposures are reported in a wide variety of ways. We aimed to develop common metrics to apply in the translation of literature-based workplace mechanical exposures for use in meta-analyses, and to test the metrics' measurement properties. METHODS: We developed a set of 7-point scales to capture the intensity of important aspects of mechanical exposures that may be related to the development of low back pain in workers. The scales represented three dimensions of mechanical exposures at work: (1) trunk posture, (2) weight lifted or force exerted and (3) spinal loading, and estimated both peak and cumulative loads. Measurement properties of the scales were tested through a survey of experts in biomechanics and ergonomics who were asked to rate literature-based workplace exposure definitions using the scales and provide estimates of their confidence in their ratings. RESULTS: For each dimension the ratings for peak loads tended to be higher than the cumulative load ratings. The inter-rater reliability for the scales ranged from 0.3 to 0.5; we would need to average the ratings of at least four expert raters to have an acceptable level of reliability (>0.7). Inter-expert reliability was positively related to the experts' level of confidence in their ratings. In most cases the ranking of intensity ratings from the experts matched the ranking of exposure intensity from the original articles. CONCLUSIONS: This study provides insight into estimating the intensity of literature-based mechanical exposure metrics using a common set of scales which can be applied across epidemiologic studies. These metrics may be useful to quantify the relationship between workplace mechanical exposure and low back pain in a systematic review and meta-analysis.

Effectiveness of a participatory ergonomics intervention in improving communication and psychosocial exposures.

A participatory ergonomics programme was implemented in an automotive parts manufacturing factory in which an ergonomics change team was formed, composed of members from management, the organized labour union and the research team. It was hypothesized that the participatory nature of this change process would result in enhanced worker perceptions of workplace communication dynamics, decision latitude and influence, which in conjunction with anticipated mechanical exposure reductions would lead to reduced worker pain severity. Utilizing a sister plant in the corporation as a referent group, a quasi-experimental design was employed with a longitudinal, repeat questionnaire approach to document pre-post intervention changes. Nine participatory activities (psychosocial interventions) were implemented as part of the process. Communication dynamics regarding ergonomics were significantly enhanced at the intervention plant compared to the referent plant. However, there were no significantly different changes in worker perceptions of decision latitude or influence between the two plants, nor did pain severity change. Possible explanations for these results include limited intervention intensity, context and co-intervention differences between the two plants, high plant turnover reducing the statistical power of the study and lack of sensitivity and specificity in the psychosocial measures used. Further research should include the development of psychosocial tools more specific to participatory ergonomic interventions and the assessment of the extent of change in psychosocial factors that might be associated with improvements in pain.

Biomechanical and psychosocial risk factors for low back pain at work.

OBJECTIVES: This study determined whether the physical and psychosocial demands of work are associated with low back pain. METHODS: A case-control approach was used. Case subjects (n = 137) reported a new episode of low back pain to their employer, a large automobile manufacturing complex. Control subjects were randomly selected from the study base as cases accrued (n = 179) or were matched to cases by exact job (n = 65). Individual, clinical, and psychosocial variables were assessed by interview. Physical demands were assessed with direct workplace measurements of subjects at their usual jobs. The analysis used multiple logistic regression adjusted for individual characteristics. RESULTS: Self-reported risk factors included a physically demanding job, a poor workplace social environment, inconsistency between job and education level, better job satisfaction, and better coworker support. Low job control showed a borderline association. Physical-measure risk factors included peak lumbar shear force, peak load handled, and cumulative lumbar disc compression. Low body mass index and prior low back pain compensation claims were the only significant individual characteristics. CONCLUSIONS: This study identified specific physical and psychosocial demands of work as independent risk factors for low back pain.

Methanol to hydrocarbons: enhanced aromatic formation using a composite Ga2O3-H-ZSM-5 catalyst.

Addition of beta-Ga2O3 to H-ZSM-5, as a physical mixture, enhances the formation of aromatic hydrocarbons in the methanol to hydrocarbons reaction.

Comparison of four peak spinal loading exposure measurement methods and their association with low-back pain.

OBJECTIVES: This paper examines the performance of 4 different methods of estimating peak spinal loading and their relationship with the reporting of low-back pain. METHODS: The data used for this comparison was a subset of subjects from a case-referent study of low-back-pain reporting in the automotive industry, in which 130 random referents and 105 cases (or job-matched proxies) were studied. The peak load on the lumbar spine was determined using a biomechanical model with model inputs coming from a detailed self-report questionnaire, a task-based check list, a video digitization method, and a posture and load sampling technique. RESULTS: The methods were directly comparable through a common metric of newtons or newton meters of spinal loading in compression, shear, or moment modes. All the methods showed significant and substantial associations with low-back pain in all modes (odds ratios 1.6-2.3). The intraclass correlation coefficients (ICC) showed strong similarities between the checklist and video digitized techniques (ICC 0.84-0.91), moderate similarities between these techniques and the work sampling method (ICC 0.49-0.52), and poor correlations (ICC 0.16-0.40) between the self-report questionnaire and the observer recorded measures. CONCLUSIONS: While all the methods detected significant odds ratios, they cannot all be used interchangeably for risk assessment at the individual level. Peak spinal compression, moment, and shear are important risk factors for low-back pain reporting, no matter which measurement method is used. Questionnaires can be used for large-scale studies. At the individual level a task-based checklist provides biomechanical model inputs at lower cost and equal performance compared with the criterion video digitization system.

Changes in geometry of the finger flexor tendons in the carpal tunnel with wrist posture and tendon load: an MRI study on normal wrists.

OBJECTIVES: (1) To develop a methodology to determine the trajectories of the digital flexor tendons using MRI. (2) To examine changes in tendon trajectories due to wrist posture, with and without pinch force. (3) To calculate the radius of curvature of the flexor tendons and note implications for contact forces on the median nerve. (4) To assess the use of Landsmeer's models at the wrist. DESIGN: Finger flexor tendon centroids were digitized from magnetic resonance images of the carpal tunnel and the tendon paths were determined analytically. Radii of curvature were calculated from the tendon paths. BACKGROUND: Landsmeer's models of joint-tendon interaction (Landsmeer, 1961) have been used to determine moment arms and radius of curvature of the tendon paths about articulations. An explanation for a biomechanical cause of work-related carpal tunnel syndrome originated from these models. METHODS: Three healthy male participants had their right wrist scanned while splinted in four wrist postures (flexed to 20 degrees, 45 degrees, neutral, extended to 20 degrees ) with and without maintaining a 10 N pinch grip. 20-24 cross-sectional images were used for each condition. RESULTS: Volar movement of the tendons was seen with wrist flexion and the opposite was true with extension. Tendon intersection angles were calculated between the tendon as it entered the carpal tunnel and as it exited the tunnel and were 50-65% of the wrist angle (R(2)=0.81-0.96). The radius of curvature was smallest (mean=82-127 mm) with an active pinch grip with the wrist splinted at 45 degrees of flexion (mean actual wrist angle 37 degrees ). CONCLUSIONS: The radius of flexor tendon curvature is not constant as previously assumed and is larger than previous estimates. The addition of tendon force with the wrist flexed acts to reduce the radius of curvature which further increases the contact stress on the median nerve and other wrist structures. The use of MRI to determine the tendon paths has provided new insight into the relationships between the finger flexor tendons and other structures at the wrist. RELEVANCE: These findings provide data for biomechanical models of the carpal tunnel and predict the possible pathophysiology of work-related carpal tunnel syndrome.

Assessment of an EMG-based method for continuous estimates of low back compression during asymmetrical occupational tasks.

Variables, such as peak and accumulated moments and spine compression forces, have been shown to be risk factors for occupational low back pain. Estimates of these forces during prolonged, dynamic, asymmetric tasks using biomechanical models is complex and time-consuming. A simple technique for continuous measurement of these variables over a prolonged period is needed to measure the distribution of spinal loading during both sagittal plane lifts and complex asymmetrical jobs. The aim of this study was to determine whether a linear normalization of erector spinae EMG to spine compression force, called compression normalized EMG (CNEMG), could be used to estimate spinal loading for simulations of asymmetrical occupational tasks. The estimates of spine compression force obtained using the normalized EMG are presented in the form of an amplitude probability distribution function and are compared with estimates of a three-dimensional biomechanical model. The per cent time a worker spends above particular levels of spinal loading of interest, such as the NIOSH action limit for compression, are displayed. Five males performed simulated occupational tasks. The exposure time at a specific level of spine compression force for a combination of three tasks, estimated by CNEMG, was, on average, within 6.5% of the time calculated by the biomechanical model. However, if the task combination was dominated by an axial twisting moment, then the difference was, on average, 13.4%. The difference in magnitude of spine compression at a specific probability was, on average, 14.9% and when axial trunk twist dominated, 30.7%. It is concluded that CNEMG can estimate probability at a specific level of spine compression force when the task combination is characterized by a predominant extensor moment in the sagittal plane. Estimates of spine compression at a specific probability, and estimates obtained during task combinations dominated by an axial twisting moment, are poor.

The effects of tendon load and posture on carpal tunnel pressure.

Two pressure measurement techniques (catheter and bulb) were used to decompose the effects of tendon loads on carpal tunnel pressure (CTP). The catheter technique measures true hydrostatic pressure, whereas the bulb technique is a estimate of contact force or pressure on the median nerve. Eight cadaveric wrists were moved through a range of flexion-extension (0 degrees, 10 degrees, 20 degrees, 30 degrees, and 45 degrees of each) and radioulnar deviation (10 degrees and 20 degrees radial and 0 degrees, 10 degrees, 20 degrees, and 30 degrees ulnar) while CTPs were measured under 4 muscle loading conditions with the thumb, index, and long finger in a pinch-grip posture. The first of these was zero load. Then a 1-kg mass was applied in turn to both flexors of the index and long fingers, the palmaris longus (PL); and the flexor pollicis longus. The hydrostatic pressure was found to be affected by both wrist posture and tendon load. With no load, highest pressures were seen in wrist extension. Muscular loading elevated CPT, particularly the loading of palmaris longus with the wrist in extension and the digital flexors with the wrist flexed. Bulb pressure measurements, related to local contact forces by the digital flexors, indicated the highest loads on the median nerve with the wrist flexed. Palmaris longus loading created the highest pressures in extension and only moderate pressure in flexion, indicating that it may alter the geometry of the transverse carpal ligament. In view of the data from this study, it is necessary to incorporate measures of hydrostatic pressure and local contact forces to describe possible trauma to the median nerve in the carpal tunnel, as neither appears sufficient when used independently.

Disability resulting from occupational low back pain. Part I: What do we know about primary prevention? A review of the scientific evidence on prevention before disability begins.

This is the first of two papers that systematically review available scientific evidence on the causes of disability from occupational low back pain, and the effectiveness of interventions to prevent it-before disability begins (primary prevention-Part I) and after its onset (secondary prevention-Part II). This first paper reviews the risk factors for the onset of pain and associated disability followed by a critical summary of intervention studies attempting to achieve prevention and to evaluate the results.

Disability resulting from occupational low back pain. Part II: What do we know about secondary prevention? A review of the scientific evidence on prevention after disability begins.

This is the second of two papers that systematically review available scientific evidence on the causes of disability from occupational low back pain, and the effectiveness of interventions to prevent it after its onset (secondary prevention). This paper reviews the national history of how back pain and the risk factors for its extension into chronic disability, followed by a critical summary of intervention studies attempting to reduce the duration of this disability, and to evaluate the results.

Passive properties of the forearm musculature with reference to hand and finger postures.

OBJECTIVE: To quantify individual forearm muscle passive forces and evaluate their impact on hand function. DESIGN: The passive force-length properties of the 24 extrinsic hand and wrist muscles were determined in five fresh frozen cadaver arms. BACKGROUND: Muscle force production is a summation of the active and passive force components. The passive properties of the extrinsic finger musculature and wrist musculature appear to strongly affect both hand posture and hand movement. METHODS: The passive force-length properties of extrinsic hand and wrist muscles were determined by applying a slow, continuous extension to each muscle and recording the resulting tension. Each force-length curve was fit using exponential regression and were related to specific joint rotations and seven hand postures by calculating the muscle excursions for those postures. RESULTS: The exponential passive force-length relationship explained over 97% of the experimental variance. The largest passive forces were elicited in the digital extensors in grips involving large flexion angles such as tip pinch, key pinch, and a briefcase grip. CONCLUSIONS: The passive properties of the extrinsic finger musculature and wrist musculature affect both hand posture and movement especially in postures with flexed wrist and fingers.

Method for measuring vertebral kinematics from videofluoroscopy.

Optical distortions and digitizing errors must be minimized to obtain accurate measurements of spine kinematics from videofluoroscopic imaging. This study adapted and evaluated a method for reducing these errors. Image and signal processing techniques were applied to obtain lumbar spine kinematic measures from walking and trunk extension trials. Mean absolute error was conservatively estimated to be 0.69° (sd = 0.43°) for vertebral rotation, independent of angle, and 0.33 mm (sd = 0.25 mm) for linear measurements. Digital filtering was applied to further minimize random errors.

The inappropriateness of helmet drop tests in assessing neck protection in head-first impacts.

Protecting the cervical spine in situations of axial compressive loading is indeed complex. Results from a number of crash simulations suggest that the mechanisms of head impact causing brain damage and those causing neck injury are different. The idea that neck injuries can be predicted from results of helmet drop tests or that the helmet is capable of providing protection to the cervical spine is unsupported. In head-first collisions causing axial compressive loading, the cushioning properties of the helmet alone would dictate the maximum force on the neck if both the head and neck were rigid. Since the head and neck are not rigid and appear to be as stiff or less stiff than the helmet, the cushioning influence of the helmet is minimized, so the forces experienced by the neck are dictated largely by its own properties. The helmet does not have a large influence. To be effective, the helmet would have to be much less stiff than it is at present and would have to maintain this low stiffness under very large loads. These conditions would be difficult to achieve without making the helmet disproportionately larger than it is now.

Postural dynamics in the standing human.

The purpose of this study was to develop a mathematical model of the linkage dynamics in upright standing, and to use this model to study output principles for postural control. The standing human was modelled in the sagittal plane as a three-segment linkage. Mechanical disturbances were simulated as forces which could be applied at various points in this linkage. An iterative approach was used to find joint torque combinations which would restore balance within 80 ms of these mechanical disturbances. The model predicted that a specific proportional relationship was necessary between the hip, knee and ankle torques in order for balance to be restored. This proportional relationship was shown to be a function of the model structure, but independent of the location, direction and amplitude of the disturbance. These predictions were tested experimentally. A disturbance apparatus was designed to apply an impulsive force to the subjects. The joint torque responses of the subjects were in quantitative agreement with the predictions of the model. The results suggest that a fixed relationship between joint torques may be required to restore balance, and this fixed relationship may make the task of postural control simpler for the nervous system.

Postural dynamics of walking in humans.

The dynamics of postural control in human biped locomotion were studied using (1) a model, and (2) experimentally applied impulsive force disturbances. The model was planar, and contained five rigid segments, articulating at frictionless pin joints. The model was used to identify joint torque combinations which would successfully correct for an impulsive force disturbance applied at different points in the walking cycle. The simulation results suggested that (1) early responses (within 80 ms) can be effective in compensating for impulsive disturbances, (2) the same strategies which successfully counteract similar disturbances during quiet standing are also effective in certain phases of the walking cycle, (3) modifications in the response strategies are needed to accommodate differences in the dynamics over the stride cycle, and (4) the swing leg is ineffective in compensating for disturbances in the short term. These model predictions were tested experimentally. Subject responses to an impulsive force disturbance applied during walking were studied. The electromyographic results generally support the model predictions.

Mechanical energy costs of human movement: an approach to evaluating the transfer possibilities of two-joint muscles.

Different methods of calculating the mechanical energy cost of a movement presented in the literature can give results differing by an order of magnitude. The assumptions made concerning the transfer of energy between different parts of the body are part of the problem. This investigation assesses the role of transfer in energy saving and specifically, the possibility of two-joint muscles reducing the mechanical energy cost of a movement compared to a system having one-joint muscles only. An algorithm was developed which recruited one-joint or both one- and two-joint muscles to supply the net joint moments. The work performed under these two conditions was then compared. It was found that activation of both one- and two-joint musculature reduced the mechanical work cost during walking by between 7 and 29% over that required by single-joint musculature alone. This investigation supports suggestions in the literature that one of the functions of two-joint musculature is to reduce the mechanical energy cost and probably the metabolic cost of movement.

Lumbrical function: interaction of lumbrical contraction with the elasticity of the extrinsic finger muscles and its effect on metacarpophalangeal equilibrium.

Since conflicting statements have been made in the literature regarding the influence of lumbrical contraction on the metacarpophalangeal (MP) joint, a study was undertaken to determine the length-tension curve for the index flexor profundus. Four fresh cadaver hands were used. Measurements for the flexor superficialis and for the common extensor were determined in there. The measurements were correlated with measured displacement of these tendons in six finger positions. Isolated lumbrical contraction was then mechanically simulated, acting against spring homologues of the index extrinsic muscles. The finger moved from the rest position toward the intrinsic position with loads of less than 5 N. This demonstrated that in addition to its effect on interphalangeal joint extension, the lumbrical acting alone can cause flexion of the metacarpophalangeal joint.