Summary

The effectiveness of antivibration gloves in reducing vibrations transmitted to the hand is currently being evaluated in the laboratory, using the methodology described in ISO 10819:2013. That standard evaluates the transmission of vibrations to the palm of the hand, but does not take into account vibration transmission to the fingers, or how wearing these gloves affects manual dexterity and grip effort. This study aimed to develop a methodology to improve the evaluation of vibration transmission by antivibration gloves to the palm and fingers, factoring in the effects of these gloves on grip strength and manual dexterity. To this end, ten types of gloves from different manufacturers were selected and their mechanical properties were characterized. The gloves selected included five gloves with viscoelastic material (Gel1to Gel5), two gloves with air bladders (Air1 and Air2), one hybrid glove with air bladders in the palm and viscoelastic material in the fingers (Hybrid), one rubber glove (Rubber) and one fabric glove (Fabric).

To assess the influence of antivibration gloves on the contact force exerted on the surface of the hand, a pressure distribution sensor was developed to measure contact force at the hand-handle interface as well as at the hand-glove interface.
Next, tests with five subjects applying nine combinations of grip and push forces on a cylindrical handle were performed with the sensor attached to the surface of the hand to measure the contact force under three different conditions: bare hand (BH), viscoelastic material wrapping the handle (VM) and hand wearing an antivibration glove (GH). When comparing these different conditions, the contribution of grip and push forces on the contact force was, respectively, 11% and 22% higher for the VM condition compared to the BH condition. For the GH condition, the contribution of the same forces was 20% and 32% higher, respectively, compared to the BH condition. The higher contributions were ascribed to the fact that the subject had to bend more materials (viscoelastic material and outer glove shell for the GH condition) using a greater range of motion (for the GH condition, the amount of glove flexion required to grip the cylindrical handle).

With the help of 15 subjects, the transmissibility of vibrations to the palm of the hand for the ten gloves selected was then evaluated according to the provisions in ISO 10819. Vibration transmissibility to the index and middle fingers was also evaluated. Five gloves met the ISO 10819 vibration attenuation criteria: the Air1, Air2, Gel2, Gel5 and Hybrid gloves. For these five gloves, vibration to the palm was attenuated above 30 Hz. The same gloves attenuated vibrations transmitted to the index and middle finger starting at approximately 200 Hz.

Afterward, the medium and gross manual dexterity provided by the gloves was evaluated using two dexterity tests (ASTM F2010 and the Minnesota “Two-Hand Turning and Placing” manual dexterity test), for 11 conditions (the ten gloves selected and bare hand) and 15 subjects. Compared to the bare hand, for the ASTM test, wearing a glove increased completion time by 14% to 73% and for the Minnesota test, by 16% to 70%, depending on the type of glove. The results also showed that, in general, it took longer to complete the Minnesota test than the ASTM test. There was also greater variability with the Minnesota test, in addition to less sensitivity in differenciating between the ten gloves in the study (42% versus 51% for the ASTM test). Furthermore, among the five gloves that met the vibration attenuation criteria of the ISO 10819 standard, two distinct groups could be  identified by the ASTM test: the Air1 glove demonstrated the poorest dexterity performance and the Gel2, Gel5, Air2 and Hybrid gloves demonstrated the best dexterity performance. In the Minnesota test, there were also two distinct groups, constituted by the Air1 glove, with the poorest dexterity performance, and the Gel2 and Air2 gloves with the best dexterity performance. The Gel5 and Hybrid gloves constituted an intermediary group overlapping the other two.

To establish a method to evaluate the effect of antivibration gloves on grip strength, muscle activation was measured using surface electromyography for four muscles in the forearm: the palmaris longus (PL), the flexor digitorum superficialis (FDS), the extensor carpi radialis longus (ECRL) and the extensor digitorum communis (EDC). These measurements were performed for 11 glove conditions (bare hand and the ten gloves selected) with 15 subjects exerting grip forces of 25 and 50 N on a 40-mm diameter cylindrical handle. The root mean square (RMS) values obtained for each muscle for a given glove and grip force were standardized with those obtained by the bare hand condition using the same grip force. The most sensitive measurement strategy (50 N grip: combination of the ECRL and PL muscles) made it possible to identify three glove subgroups that appeared to be equivalent in terms of effort, as measured through muscle activation. The first subgroup consisted of the fabric gloves (RMS value at 122% of that of the bare hand) and rubber gloves (134%), which required the least effort of all the gloves. The second subgroup was made up of Gel1, Gel2, Gel3, Gel4, Air2 and Hybrid gloves, which generated muscle activation ranging from 143% and 151% of that of the bare hand. Finally, the third subgroup was made up of the Gel5 (157%) and Air1 (173%) gloves, which required the most effort. Of the five gloves that met the vibration attenuation criteria of ISO 10819 (Gel2, Gel5, Air1, Air2 and Hybrid), the Gel2, Air2 and Hybrid gloves required the least effort.

Significant correlations between glove thickness and most of the transmissibility measurements suggested that the thicker the glove, the better the attenuation of vibration (thus less stiffness under compression). This association was confirmed by positive correlations between certain transmissibilities and the stiffness of the antivibration material, where less stiffness was associated with lower vibration transmissibility, through a decrease in the resonant frequency of the hand-glove system. The thickness of the glove and the use of stiff materials for the glove shell resulted in intensifying grip effort by increasing, among other things, the stiffness of the glove during flexion. This stiffness also contributed to lengthening the time it took to complete the ASTM and Minnesota manual dexterity tests.