Sheik N. Imrhan

The influence of wrist position on different types of pinch strength.

This study examines the effects of different wrist positions on maximum voluntary (MVC) pinch strength. Peak MVC forces of 30 male adults were measured for lateral, chuck, pulp-2 and pulp-3 pinches, each in five wrist positions-natural, radial deviation, ulnar deviation, dorsiflexion and palmar flexion. The results showed that all the deviated wrist positions degraded pinch strength, with palmar flexion having the greatest effect and radial deviation the least. Strength degradation ranged from 14% to 43%, depending on wrist position and type of pinch. The lateral pinch was less affected than the others. Biomechanical explanations are offered for these measurements, and implications for work and tool designs are discussed.

The effects of pinch width on pinch strengths of adult males using realistic pinch-handle coupling

Abstract This study examined the effects of pinch width on pinch strengths, using more realistic pinching conditions — larger contact area, worktable height pinching level, and freedom to hyperextend the thumb when gripping. Chuck, pulp-2 and lateral pinches were tested at widths within the range of 2.0–14.0 cm among 17 right-handed male volunteers, using the right hand while standing. The results showed that (1) pinch strength was not significantly different between 2.0–5.6 cm for chuck and lateral pinches, nor between 2.0–9.2 cm for pulp-2 pinch, but decreased significantly at wider widths, (2) strength differences between different types of pinches depended on the width of the pinch, (3) chuck pinch was greater than lateral or pulp-2 pinch at all widths, and lateral pinch was greater than pulp-2 pinch from 2.0–5.6 cm width but weaker at greater widths, and (4) pinch strength was much greater under these test conditions compared to the traditional standardized testing conditions, for similar pinch widths. These data may be more relevant to industrial tasks than those in previously published studies.

Modelling wrist-twisting strength of the elderly

This paper presents a biomechanical model of wrist-twisting strength and uses it to explain maximum voluntary contractile (MVC) counter-clockwise torque and force generated by elderly subjects in attempting to unscrew rough and smooth circular screw-type container lids of diameters 31, 55, 74 and 113 mm. Forty-two subjects, aged 60-97 years, were tested. The results indicated-that for-commercially available lids, torque-diameter relationship was linear up to a certain lid size (diameter), and non-linear, with a decreasing trend, beyond that size. The non-linearity was different for lids with rough and smooth grip surface. An optimal diameter for smooth lids has been proposed. For both types of grip surfaces, force magnitudes were similar up to 74 mm. Beyond this diameter the effects of surface finish were manifested. This was explained by the relationship between hand size and type of grip used at the various diameters. Implications of these results for lid design are discussed. Regression models are also...

Hand anthropometry of Americans of Vietnamese origin

Twenty-four dimensions of the right hand were measured in 30 female and 41 male Americans of Vietnamese origin. The mean, standard deviation, range; and 5th, 50th, and 95th percentile values of each measurement are tabulated. The means of the female measurements are also compared with the means of the corresponding measurements in females from Hong Kong, United Kingdom, United States, and Japan - using data from other published studies.

An investigation of finger pull strengths

This paper describes a study to investigate the nature of pull strength with the fingers. Three types of pulls, distinguished by the type of pinch grip used, were investigated. The experiment was performed in two stages, using different subjects (36 male adults in Stage I and 34 in Stage II). The results indicated that finger pull strength depended on the type of pinch grip used but not on the direction of pull (in the saggital plane) nor on hand laterality. Pull forces with the lateral pinch grip were 1.6 times as strong as with the chuck pinch grip, which was, in turn, 1.5 times as strong as with the pulp pinch grip. Ergonomic design applications suggest a larger pinch handle and workspace to accommodate the lateral grip. Finger pull strength could not be predicted very accurately from pure pinch strengths or anthropometric dimensions accurately enough to be of value to designers, even though there were many statistically significant pairwise correlations.

Can self-estimates of body weight and height be used in place of measurements for college students?

A study was conducted to determine how accurately college students can estimate their height and body weight. Four hundred and sixty-nine students (136 females and 333 males) completed a short questionnaire eliciting self-estimates of height and weight, frequency and recency of measuring them, age, and gender. Immediately afterwards, their height and weight were measured. Three hundred and forty-nine subjects were told that they would be measured later; the others were not told that they would be measured. Analysis of the data revealed relatively small absolute errors of estimation (1.00—3.54%); both males and females overestimated height and underestimated weight; females estimated weight less accurately and height more accurately than males; and knowing that ones estimation would be checked by measurement produced slightly more accurate estimations. Simple self-estimates of height and weight are accurate enough to be used in place of measurements.

Hand anthropometry in Bangladeshis living in America and comparisons with other populations

An anthropometric study of a convenience sample of 51 female and 50 male adults of Bangladeshi origin (mean age 41.3 years), living in the United States, but who spent most of their lives in Bangladesh, was conducted. Standard measurements were taken on 24 dimensions of the right hand that were relevant to the design of hand tools, gloves and access spaces using a standard sliding calliper. Analysis of the results showed significant differences in palm and finger segment lengths, breadths and depths between genders in Bangladeshis and also within each gender between Bangladeshis and other populations. The differences between Bangladeshis and other populations were of about the same magnitude as the differences between genders in Bangladeshis. The data gathered may be used for the design of hand tools, gloves, machine access spaces and hand-held devices and for selection of hand tools for use by Bangladeshis. The study also allows inter-population comparisons that can enhance the understanding of hand anthropometry.

Male torque strength in simulated oil rig tasks: the effects of grease-smeared gloves and handle length, diameter and orientation

This paper examines the effects of two glove conditions and selected handle and task characteristics on tightening (clockwise) torques on cylindrical handles in simulated oil rig tasks. Ten males exerted MVC torques with the right hand on nine handles with different length-diameter combinations (3.8, 7.6, and 12.7 cm in length with 3.8, 6.7, and 8.4 cm in diameter) with dry and grease-smeared gloves in two orientations. The results showed a 50% reduction of torque when using grease-smeared glove compared to dry glove; a 15% increase with the long handle compared to the short one; a 25% increase with the medium diameter handle compared to the small one; and a 12% increase with the horizontally oriented handle compared with the vertical one. There were important interaction effects also.

Muscular strength in the elderly - implications for ergonomic design

This paper discusses the need for greater emphasis to be put on the importance of muscular strength for designing jobs, products, and the living environments for the elderly; and on the need for an appropriate strength data base. The published data on strength in the elderly are reviewed and discussed from the point view of their usefulness in ergonomic designs. The discussion emphasizes that most existing strength data on the elderly were done for fitness and clinical applications, and that the structure of those data is of limited value to ergonomists. The few studies with ergonomic applicability deal mostly with hand strength and manual performance in specific tasks; and the data for whole-body tasks in various postures are non-existent.

The effects of arm elevation, direction of pull and speed of pull on isokinetic pull strength

Abstract This study examines the effects of three variables — arm elevation, direcon (or plane) of pull and speed of pull — on isokinetic pull strength, with the preferred arm. Eleven male adult subjects were tested for maximum voluntary contraction (MVC) pulls, while standing, at all 12 combinations of three starting positions of the arm, two directions of pull, and two speeds of pull. The results indicated that all three variables were influential on pull strength; but that there was a significant interaction effect between speed and arm elevation. Speed exerted a greater effect when pulling obliquely upward, starting with the arm below the shoulder (from a stoop-stand posture), than horizontally (at shoulder height) or downward (starting above the shoulder). Also, pulling toward the body was 9% stronger than pulling accoss it. Under the best pull conditions, pull strength was 1.65–2.09 times stronger than under the worst conditions. The mean pull force of the 11 subjects averaged 36%–58% of their body weight, depending on the pull condition (variable combination).