University of Waterloo researchers Kirsten Willms, Richard Wells and Heather Carnahan conducted a study to investigate the effects of glove flexibility, glove thickness, finger posture/geometry and loss of tactile sensitivity on power grip force and effort. (A power grip is a grip that involves the fingers and palm of the hand). In their introduction, they review previous research that indicates a reduction in force production and an increase in effort in gloved power grip manual tasks. Their literature review reveals that decreases in force output have been attributed to:
- loss of tactile sensitivity;
- low glove flexibility or suppleness;
- friction at the glove-object interface;
- glove thickness; and
- and changes in hand geometry/posture.
They also note that other researchers have looked at a variety of types of gloves and glove combinations, and much of the research, including their own study, may not "elucidate why gloves, in general, had a particular effect," but instead often reflects the effects of a particular glove. Nonetheless, the central question they are investigating is:
What is reducing the force exerted and increasing the effort, and which attributes of gloves are responsible?
Primary Findings
They tested eight hypotheses, all of which were found to be true:
- increasing glove thickness and finger spacing will reduce maximum power grip force;
Reductions of up to 31% were observed with increasing glove thickness, and reductions of up to 10% were attributable to increased finger spacing; both findings being consistent with the findings of other researchers.
- increasing glove thickness will increase the force required to perform a standardized submaximal lifting task;
- increasing glove thickness will increase forearm muscle activation while performing a fixed force submaximal power grip task;
- increasing glove thickness will increase forearm muscle activation to produce an unloaded power grip posture;
Forearm muscle activation increased as glove thickness increased for hypotheses 3 and 4. "Interestingly, the extensor muscles of the wrist and fingers all had greater increases in EMG activity than did the flexors, corroborating previous research that found that forearm extensors are more sensitive to exertions made during gripping activities than are flexors."
- increasing glove thickness will increase perceived exertions required for the maximum and unloaded power grip conditions, and the lifting task;
- increasing glove thickness will reduce tactile sensitivity;
- grip circumference required to maintain a constant finger posture will decrease as glove thickness increases; and
- grip force will change when the grip circumference is reduced to maintain the same finger posture across glove conditions.
The authors conclude that:
- A decrease of tactility attributable to the gloves is associated with a small increase in applied grip force and effort during submax efforts.
- Interdigital spacing of the fingers is associated with a small decrease in grip force during maximal efforts [but not submaximal efforts].
- Increases in glove thickness increase the effective grip circumference a small amount, but the decrease in force observed after [adjusting to maintain a constant grip posture] argues that the change in grip size was not responsible for the reduction in grip forces.
- The stiffness of the glove to bending substantially reduces maximum grip force and substantially increases effort during submaximal efforts.
- The reduction in force with increasing glove thickness may be partially caused by a reduction in flexor digitorum profundus activity.
- Snugness did not differ between participants or glove thicknesses.
Readers with a particular interest in this subject are encouraged to read the original research article, cited below, for complete findings.
The Bottom Line — How This Applies to Ergonomists
Ergonomists have long known that gloves can have a significant effect on grip forces. This research gives us additional insight into the factors that result in increasing muscle effort and/or decreasing force output during maximal and submaximal power grip tasks. Gloves are sometimes required due to protect a person from environmental conditions, and this is knowledge we can apply when working with clients to select the best glove and fit attributes for a specific task and population.
Methods
The following basic methodology information is provided. However, interested readers are encouraged to read the original research article, cited below, for complete details.
- Seven conditions were tested: bare hand, three thicknesses of gloves, and three corresponding interdigital spacer thicknesses.
- Rubber gloves designed for electric utility work, which varied in thickness only, were used.
- 20 subjects; 10 male and 10 female with an average age of 5 yrs.
- Spacers equal to twice the glove thickness were used to simulate finger spacing.
- Baseline measurements were made of grip force, perceived exertion and muscle activity using a dynamometer, surface electromyograms (EMGs) for seven forearm muscles. Grip span was adjusted for individual hand anthropometry such that the index finger and thumb lightly touched.
- A Von Frey hair test was used to assess tactility.
- Perceived effort was assessed using a 100 point rating scale.
Reference
Willms, K, Wells, R, Carnahan, H, Glove Attributes and Their Contribution to Force Decrement and Increased Effort in Power Grip, Human Factors, Volume 51, Number 6, December 2009 , pp. 797-812(16). Last retrieved from http://www.ingentaconnect.com/content/hfes/hf/2009/00000051/00000006/art00003 on December 2, 2010.
This article originally appeared in The Ergonomics Report™ on 2010-12-22.