Assessing Increased Activities of the Forearm Muscles Due to Anti-Vibration Gloves: Construct Validity of a Refined Methodology.

OBJECTIVE: The primary aim was to test the construct validity of a surface electromyography (EMG) measurement protocol, indirectly assessing the effects of anti-vibration (AV) gloves on activities of the forearm muscles. BACKGROUND: AV gloves impose a relatively higher grip demand and thus a higher risk for musculoskeletal disorders. Consequently, activities of the forearm muscles should be considered when assessing AV glove performance. METHOD: Effects of AV gloves on activities of the forearm muscles (ECR: extensor carpi radialis longus; ED: extensor digitorum; FCR: flexor carpi radialis; FDS: flexor digitorum superficialis) were measured via EMG, while gripping a handle with two grip force levels. Fifteen subjects participated with 11 glove conditions, including one with bare hand. RESULTS: Activities of ECR, FCR, mean of ECR and FCR (ECR_FCR), and mean of all four muscles were sensitive to wearing gloves. Compared with bare hand, combined ECR_FCR activities increased by 22%-78% (mean = 48%, SD = 28%) with gloves. The correlation coefficient (r) of ECR_FCR activities with glove thickness and manual dexterity scores were 0.74 (p < .05) and 0.90 (p < .001), respectively. CONCLUSIONS: A refined EMG methodology was the most sensitive to AV gloves with specific forearm muscles (ECR and FCR) and the 50-N handgrip force. Its construct validity was further substantiated by correlations with glove thickness and manual dexterity. APPLICATION: Assessment of the effect of AV gloves on activities of the forearm muscles can yield design guidance for AV gloves to reduce grip exertion by the gloved hand.

Distributed vibration isolation and manual dexterity of anti-vibration gloves: is there a correlation?

This study focuses on the integrated performance of anti-vibration (AV) gloves in terms of manual dexterity and distributed palm and fingers' vibration transmissibility. Experiments were designed to measure vibration transmission and manual dexterity performance of 10 different gloves using 15 subjects. The results showed all gloves impeded manual dexterity, while five gloves satisfied the AV glove screening criteria. Glove type yielded a significant effect on manual dexterity (p < 0.001) and vibration transmissibility (p ≤ 0.001). Manual dexterity decreased nearly linearly with an increase in glove thickness (p < 0.05), while palm and fingers' vibration transmissibility in high-frequency range was negatively correlated with glove thickness (R2 > 0.70). A strong correlation was evident between glove material stiffness and the H-frequency range palm vibration transmissibility (R2 ≥ 0.8). While the vibration isolation of a glove is strongly related to material properties at the palm, the dexterity performance is dependent on design factors such as thickness and bulkiness. Practitioner summaryAnti-vibration gloves are used to isolate hand from power tools vibration, while these may adversely affect manual dexterity. Vibration isolation was correlated with material properties and thickness, while dexterity was correlated with thickness alone. Glove thickness is a vital parameter for realising a compromise between vibration isolation and manual dexterity. Abbreviations: HTV: hand-transmitted vibration; AV: anti-vibration; MANOVA: multivariate analysis of variance; TR: vibration transmissibility; ASTM: ASTM F2010 standard test; Minnesota: Two-Hand Turning and Placing Minnesota test; rANOVA: repeated-measures analysis of variance; rms: root mean square; CoV: coefficient of variations; S: score.

Evaluation of effects of anti-vibration gloves on manual dexterity.

The purpose of this study was to evaluate the effects of anti-vibration gloves on manual dexterity and to explore factors affecting the manual dexterity. The manual dexterity of ten different gloves was investigated with 15 adult male subjects via performing two different dexterity tests, namely ASTM F2010 standard test and Two-Hand Turning and Placing Minnesota test. Two-factor repeated-measures analysis of variance was conducted to evaluate the main effects of glove type, test method and their interaction effect on manual dexterity. Results suggested that glove type yielded significant effect on manual dexterity (p < .001), while no significant difference was observed between test methods (p = .112). The interaction effect of glove type and test method also revealed a significant difference (p = .009). The manual dexterity decreased nearly linearly with increase in the glove thickness, which further showed a moderately significant difference on the number of drops during the tests. Practitioner Summary: Anti-vibration gloves may adversely affect manual dexterity and work precision, which may discourage their usage. This article presented a study of manual dexterity performance of anti-vibration gloves and the design factors affecting the manual dexterity. The results were discussed in view of a design guidance for improved hand dexterity, which would encourage the use of anti-vibration gloves in the workplace.

Effects of elastic seats on seated body apparent mass responses to vertical whole body vibration.

Apparent mass (AM) responses of the body seated with and without a back support on three different elastic seats (flat and contoured polyurethane foam (PUF) and air cushion) and a rigid seat were measured under three levels of vertical vibration (overall rms acceleration: 0.25, 0.50 and 0.75 m/s(2)) in the 0.5 to 20 Hz range. A pressure-sensing system was used to capture biodynamic force at the occupant-seat interface. The results revealed strong effects of visco-elastic and vibration transmissibility characteristics of seats on AM. The response magnitudes with the relatively stiff air seat were generally higher than those with the PUF seats except at low frequencies. The peak magnitude decreased when sitting condition was changed from no back support to a vertical support; the reduction however was more pronounced with the air seat. Further, a relatively higher frequency shift was evident with soft seat compared with stiff elastic seat with increasing excitation. PRACTITIONER SUMMARY: The effects of visco-elastic properties of the body-seat interface on the apparent mass responses of the seated body are measured under vertical vibration. The results show considerable effects of the coupling stiffness on the seated body apparent mass, apart from those of excitation magnitude and back support.

Comparisons of apparent mass responses of human subjects seated on rigid and elastic seats under vertical vibration.

The apparent mass (AM) responses of human body seated on elastic seat, without and with a vertical back support, are measured using a seat pressure sensing mat under three levels of vertical vibration (0.25, 0.50 and 0.75 m/s(2) rms acceleration) in 0.50-20 Hz frequency range. The responses were also measured with a rigid seat using the pressure mat and a force plate in order to examine the validity of the pressure mat. The pressure mat resulted in considerably lower AM magnitudes compared to the force plate. A correction function was proposed and applied, which resulted in comparable AM from both measurement systems for the rigid seat. The correction function was subsequently applied to derive AM of subjects seated on elastic seat. The responses revealed lower peak magnitude and corresponding frequency compared to those measured with rigid seat, irrespective of back support and excitation considered.

Design and evaluation of a suspension seat to reduce vibration exposure of subway operators: a case study.

Subway operators have complained about discomfort caused by whole-body vibration. To address this problem, a suspension seat with extensive ergonomic features has been adapted to the confined space of the subway operator cab. The suspension was modified from an existing suspension in order to reduce the dominant frequency of the subway vertical vibration (2.4 Hz). The suspension seat has been extensively tested on a vertical hydraulic shaker. These tests have shown that the SEAT value was lower for a higher vibration level, for higher subject weight, and for the suspension adjusted at median height. The seat also produces a lower SEAT value when there was a predominance of the 6 Hz vibration component. The horizontal seat adjustments had no influence on the suspension SEAT value. Removing the suspension damper also decreases the SEAT value for all the tested configurations. The final version of the suspension seat prototype was validated during normal subway operation with 19 different operators having weight in the 5th, 50th and 95th percentile of the operator population. Accelerations were measured with triaxial accelerometers at the seat cushion, above the suspension and on the floor. In addition to the vibration measurements, each operator was asked about his perceived discomfort from vibration exposure. Globally, the suspension seat attenuated the vertical vibration (SEAT values from 0.86 to 0.99), but discomfort due to amplification of the 2.4 Hz component occurred when the suspension height was adjusted at the minimum, even when the global weighted acceleration was lower (SEAT value < 1). These results suggest that in order to reduce the discomfort caused by whole-body vibration, the transmissibility of the seat should also be considered, in particular when there is a dominant frequency in the vibration spectra.

Comparing three methods for evaluating impact wrench vibration emissions.

To provide a means for comparing impact wrenches and similar tools, the international standard ISO 8662-7 prescribes a method for measuring the vibrations at the handles of tools during their operations against a cotton-phenolic braking device. To improve the standard, alternative loading mechanisms have been proposed; one device comprises aluminum blocks with friction brake linings, while another features plate-mounted bolts to provide the tool load. The objective of this study was to evaluate these three loading methods so that tool evaluators can select appropriate loading devices in order to obtain results that can be applied to their specific workplace operations. Six experienced tool operators used five tool models to evaluate the loading mechanisms. The results of this study indicate that different loads can yield different tool comparison results. However, any of the three devices appears to be adequate for initial tool screenings. On the other hand, vibration emissions measured in the laboratory are unlikely to be fully representative of those in the workplace. Therefore, for final tool selections and for reliably assessing workplace vibration exposures, vibration measurements should be collected under actual working conditions. Evaluators need to use appropriate numbers of tools and tool operators in their assessments; recommendations are provided.

Mechanical impedance and absorbed power of hand-arm under x(h)-axis vibration and role of hand forces and posture.

The biodynamic responses of the hand-arm system under x(h)-axis vibration are investigated in terms of the driving point mechanical impedance (DPMI) and absorbed power in a laboratory study. For this purpose, seven healthy male subjects are exposed to two levels of random vibration in the 8-1,000 Hz frequency range, using three instrumented cylindrical handles of different diameters (30, 40 and 50 mm), and different combinations of grip (10, 30 and 50 N) and push (0, 25 and 50 N) forces. The experiments involve grasping the handle while adopting two different postures, involving elbow flexion of 90 degrees and 180 degrees, with wrist in the neutral position for both postures. The analyses of the results revealed peak DPMI magnitude and absorbed power responses near 25 Hz and 150 Hz, for majority of the test conditions considered. The frequency corresponding to the peak response increased with increasing hand forces. Unlike the absorbed power, the DPMI response was mostly observed to be insensitive to variations in the excitation magnitude. The handle diameter revealed obvious effects on the DPMI magnitude, specifically at frequencies above 250 Hz, which was not evident in the absorbed power due to relatively low velocity at higher frequencies. The influence of hand forces was also evident on the DPMI magnitude response particularly at frequencies. above 100 Hz, while the effect of hand-arm posture on the DPMI magnitude was nearly negligible. The magnitude of power absorbed within the hand and arm was observed to be strongly dependent upon the excitation level over the entire frequency range, while the influence of hand-arm posture on the total absorbed power was observed to be important. The effect of variations in the hand forces on the absorbed power was relatively small for the bent elbow posture, while an increase in either the grip or the push force coupled with the extended arm posture resulted in considerably higher energy absorption. The results suggested that the handle size, hand-arm posture and hand forces, produce coupled effect on the biodynamic response of the hand-arm system.