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Biomedical subjects

A Freivalds

Publications and source records attributed to A Freivalds.

18 recordsLinked to original sources
PubMed2000

Optimum pinch grips in the handling of dies.

Handling roller-press dies has caused numerous work-related musculoskeletal disorders in the leather industry. The dies are quite large (0.61 x 0.30 m), heavy (3.5 kg) and are difficult to handle because of the large pinch span requirements (up to 16 cm). The purpose of this study was to determine the optimum pinch span and optimum crossbar angulation to minimize die handling forces. Five-finger pulp-pinch forces were measured on five males and five females with a force-sensitive-resistor instrumented glove while handling a simulated adjustable die. Maximum pinch forces occurred at pinch spans between 1.27 and 3.81 cm, with average female strengths being 57% of average male pinch strengths. Minimum pinch forces to hold the die occurred at a 45 degrees angulation and increased linearly as the angle approached 90 degrees or the normal vertical orientation. The simplest solution to redesigning the dies is to: (1) decrease the distance between the braces to less than 4 cm and (2) slant the braces at 45 degrees.

Ergonomics↗
PubMed1999

Relationships between clinical symptom severity scales and nerve conduction measures in carpal tunnel syndrome.

This study examined the severity of symptoms in carpal tunnel syndrome (CTS) in relation to nerve conduction measures of the median nerve. Clinical symptom severity and nerve conduction studies were evaluated for 64 hands with CTS in 45 patients. We found the following: (1) significant relationships identified among the clinical scales resulted in a dichotomous symptom classification scheme into primary and secondary symptoms, with the former being more specific for those symptoms usually seen in association with nerve injury; (2) there were significant relationships between symptom severity and nerve conduction abnormality; (3) the primary symptom scale correlated more strongly with the electrodiagnostic measures of nerve injury than did the secondary symptom scale. Based on these findings, we believe that these clinical scales have biological significance and reflect median nerve injury. This would support their potential utility for evaluating the outcome of CTS treatment and developing a model for exposure-severity relationship.

Adult↗
PubMed1999

Effect of carpal tunnel syndrome on grip force coordination on hand tools.

This study investigated coordination of the grip force on and force applied with a hand tool using a precision pinch grip. A simulated hand tool was developed to measure grip force exerted on the tool as a function of the force transmitted from the tool to an external object in a dynamic force matching paradigm. Grip force coordination measures reflected subjects' abilities to modulate grip force in parallel with the tool application force and their abilities to minimize excessive grip force. These measures were calculated for seven subjects with a diagnosis of carpal tunnel syndrome (CTS) and seven age- and gender-matched controls. The absolute magnitude of excessive grip force (safety margin) was unreliable because of the high intrasubject variability in coefficient of friction measurements. Linear regression equations predicting coefficient of friction from pinch force magnitude had low r2 coefficients of determination and were generally not statistically significant (p > 0.05). Relative comparisons of grip force control showed that individuals with CTS exhibited a statistically significant (p < 0.05) increase in ratio of grip force to application force (54% higher than controls) and a significant (p < 0.05) decrease in modulation of pinch force with application force (12% lower than controls). These results suggest that individuals with CTS lose some ability to coordinate efficiently grip force on hand tools and exert higher grip forces on tools, at equivalent application forces, than controls. This is believed to be a result of tactile sensibility deficits associated with CTS. As a result, workers with CTS may be at increased risk of accelerating the progression of their musculoskeletal disorder.

Adult↗
PubMed1997

An instrumented glove for grasp specification in virtual-reality-based point-and-direct telerobotics.

Hand posture and force, which define aspects of the way an object is grasped, are features of robotic manipulation. A means for specifying these grasping "flavors" has been developed that uses an instrumented glove equipped with joint and force sensors. The new grasp specification system will be used at the Pennsylvania State University (Penn State) in a Virtual Reality based Point-and-Direct (VR-PAD) robotics implementation. Here, an operator gives directives to a robot in the same natural way that human may direct another. Phrases such as "put that there" cause the robot to define a grasping strategy and motion strategy to complete the task on its own. In the VR-PAD concept, pointing is done using virtual tools such that an operator can appear to graphically grasp real items in live video. Rather than requiring full duplication of forces and kinesthetic movement throughout a task as is required in manual telemanipulation, hand posture and force are now specified only once. The grasp parameters then become object flavors. The robot maintains the specified force and hand posture flavors for an object throughout the task in handling the real workpiece or item of interest. In the Computer integrated Manufacturing (CIM) Laboratory at Penn State, hand posture and force data were collected for manipulating bricks and other items that require varying amounts of force at multiple pressure points. The feasibility of measuring desired grasp characteristics was demonstrated for a modified Cyberglove impregnated with Force-Sensitive Resistor (FSR) (pressure sensors in the fingertips. A joint/force model relating the parameters of finger articulation and pressure to various lifting tasks was validated for the instrumented "wired" glove. Operators using such a modified glove may ultimately be able to configure robot grasping tasks in environments involving hazardous waste remediation, flexible manufacturing, space operations and other flexible robotics applications. In each case, the VR-PAD approach will finesse the computational and delay problems of real-time multiple-degree-of-freedom force feedback telemanipulation.

Biomechanical Phenomena↗
PubMed1994

An oculomotor test to measure alcohol impairment.

Drunk driving continues to be one of the nation's most serious safety problems. On the premise that oculomotor control provides a quantitative measure that is very sensitive to alcohol impairment, an oculomotor test previously developed as a portable hand-held Viewmaster viewer with specially designed grating patterns as images was used to stress the oculomotor system. Test scores decreased with increased alcohol impairment along with a large dependence on individual lateral phoria scores. Unfortunately, there was a large amount of interindividual variability, which may limit use of the test for the population at large unless other individual characteristics are included.

Adult↗
PubMed1993

Reaction torques and operator stress while using powered nutrunners.

Reaction torque measures of six different nutrunners were correlated with EMG measures and subjective ratings of perceived exertion for different work surface orientations, joint stiffnesses, rpm levels, air pressure levels and handle configurations. Using an underpowered tool or using a softer joint resulted in larger impulses and worse ratings. A pulse-type shut-off mechanism produced the lowest reaction torque and the best rating. Overall, ratings correlated directly with the impulse level. The subjects were good judges of stress levels, and subjective ratings were valid measures of operators stress.

Journal Article↗
PubMed1993

Topographical patterns of ERP elicited by different visual information-processing tasks.

Topographical patterns of event-related potentials were compared on a visual display terminal for a data-input task and a number-comparison task. Maximum negative peaks were found in the frontal and central regions for the former but at midline locations for the latter. Latencies were shorter in the occipital regions than in the frontal regions for the former and the opposite pattern was found for the latter. An analysis of variance indicated that hemispheric location significantly affected the amplitude of peaks. On the other hand, latencies were affected by the task, frontal and occipital regions, and their interaction. These results suggest that a pattern of the topographic display of event-related potentials can be used as an objective means for classifying visual tasks.

Adult↗
PubMed1991

Ergonomics evaluation of a foam rubber grip for tool handles.

An important consideration in tool design is the avoidance of hand discomfort and a reduction of work efficiency by using proper grip designs. To measure grip force distribution on a tool handle, Force Sensing Resistors were calibrated, placed on two different types of grip (wood and foam) and interfaced to a personal computer. The results, using six common garden tools - loppers, hedge shears, shovels, leaf rakes, hoes, garden rakes - indicated a very uneven distribution in grip force, but with the foam grip providing a more uniform distribution. Unfortunately, in most cases, the tool grip force was greater for the foam grip due to the deformation of the foam and a 'loss of control' feeling in the subjects. However, most subjects strongly preferred the foam grips.

Journal Article↗
PubMed1991

Multiple criteria decision-making for the resolution of conflicting ergonomic knowledge in manual materials handling.

The ergonomic design of manual materials handling tasks typically utilizes one or more of three approaches; biomechanical, physiological, and psychophysical. Unfortunately, a comprehensive design is rarely obtained because of the difficulty of resolving the conflicting guidelines and criteria for each of the three approaches. This paper describes a methodology utilizing the multiple criteria decision-making (MCDM) process for resolving this conflict. This approach calculates the ratio of the contribution from each type of stress to an overall stress level as determined by the unacceptability of this stress to the user. An example is presented to demonstrate this technique.

Adult↗
PubMed1991

Biodynamic simulations of the effect of a neck-mounted air bag on the head/neck response during high G acceleration.

New helmet-mounted devices (such as night-vision goggles, laser eye protection, etc.) have created new safety hazards for pilots during ejection or high G maneuvering. In order to prevent the resulting head/neck injuries, this study extends the air-bag protection system developed for ground vehicles to a neck mounted system for aircrew personnel. Results, carried out by computer biodynamic simulations using the Articulated Total Body Model (ATB), showed that: 1) helmet weight had little effect on head/neck torque, contact force and flexion angle; 2) initial head/neck position and center of gravity offsets of the helmet-mounted devices had significant effects on head-neck torques, contact forces, and neck flexion angles; and 3) the neck mounted air bag significantly reduced neck torques, contact forces, and neck flexion angles. We conclude that the neck-mounted air bag system could significantly reduce the severity of head/neck injuries to pilots during ejection or high G maneuvering.

Acceleration↗
PubMed1990

Blade size and weight effects in shovel design.

The shovel is a basic tool that has undergone only nominal systematic design changes. Although previous studies found shovel-weight and blade-size effects of shovelling, the exact trade-off between the two has not been quantified. Energy expenditure, heart rate, ratings of perceived exertion and shovelling performance were measured on five subjects using five shovels with varying blade sizes and weights to move sand. Energy expenditure, normalised to subject weight and load handled, varied quadratically with the blade-size/shovel-weight (B/W) ratio. Minimum energy cost was at B/W = 0.0676 m2/kg, which for an average subject and average load would require an acceptable 5.16 kcal/min of energy expenditure. Subjects, through the ratings of perceived exertion, also strongly preferred the lighter shovels without regard to blade size. Too large a blade or too heavy a shovel increased energy expenditure beyond acceptable levels, while too small a blade reduced efficiency of the shovelling.

Journal Article↗
PubMed1989

Visual performance on CRT screens and hard-copy displays.

Three experiments examined the effect of hard-copy print and CRT screens of different resolution/addressability ratios (RAR) on accommodation and visual search performance. Three different display modes were generated with an IBM personal computer and a Princeton Graphics Terminal: capital letters in high-RAR mode, capital letters in low-RAR mode, and capital letters in high-RAR mode programmed to simulate the low-RAR mode. Same-sized letters were also presented on hard-copy print. Experiment 1 demonstrated that accommodation to hardcopy print and high-RAR screens was more accurate than to low-RAR screens. In Experiment 2 the spatial frequency channels activated by each display were evaluated by measuring the effect of display adaptation on the contrast-sensitivity function. The results suggested that high-RAR screens and hard-copy print activated higher-frequency channels than did low-RAR screens. In Experiment 3 significantly better visual search performance was obtained for high-RAR screens and for hard-copy print than for low-RAR screens. It was concluded that screen RAR is an important variable to consider in the design of CRTs.

Accommodation, Ocular↗
PubMed1987

Comparison of United States (NIOSH Lifting Guidelines) and European (ECSC Force Limits) recommendations for manual work limits.

In the early 1980's two different guidelines for manual lifting were established: the NIOSH Work Practices Guide for Manual Lifting and the European Coal and Steel Community's Force Limits in Manual Work. A comparison of the two guidelines indicates some discrepancies in their predictive capabilities and a significant nonlinear relationship between the two limits. These discrepancies may be explained by differences in respective predictive equations, assumptions and underlying concepts.

European Union↗
PubMed1984

A dynamic biomechanical evaluation of lifting maximum acceptable loads.

A biomechanical evaluation of the job-related stresses imposed upon a worker is a potential means of reducing the high incidence rates of manual material handling injuries in industry. A biomechanical model consisting of seven rigid links joined at six articulations has been developed for this purpose. Using data from cinematographic analysis of lifting motions the model calculates: (1) body position from articulation angles, (2) angular velocities and accelerations, (3) inertial moments and forces, and (4) reactive moments and forces at each articulation, including the L5/S1 joint. Results indicated effects of the common task variables. Larger load and box sizes increased the rise times and peak values of both vertical ground reaction forces and predicted L5/S1 compressive forces. However, boxes with handles resulted in higher L5/S1 compressive forces than for boxes without handles. Also, in lifting the larger boxes the subjects did not sufficiently compensate with reduced box weights in order to maintain uniform L5/S1 compressive forces. Smoothed and rectified EMG of erector spinae muscles correlated significantly with L5/S1 compressive forces, while predicted and measured vertical ground reaction forces also correlated significantly, indicating the validity of the model as a tool for predicting job physical stresses.

Humans↗
PubMed1983

Quantification of human performance circadian rhythms.

The quantification of worker performance changes during a shift is critical to establishing worker productivity. This investigation examined the existence of circadian rhythms in response variables that relate most meaningfully to the physiological and neurological state of the body for three subjects maintaining a resting posture for 25 hours on five separate occasions. Significant circadian variation ranging from 3% to 11% of the mean value was detected for elbow flexion strength, physiological tremor, simple reaction time, information processing rate and critical eye-hand tracking capacity.

Adult↗