One-handed dynamic pulling strength with special application to lawn mowers

A laboratory study was conducted to determine one-handed dynamic and static pulling strengths of 50 males and 49 females from 14 to 71 years of age. The dynamic strength for a 11m pull was measured to simulate the act of starting a lawn mower engine for four different starting-rope handle locations: on the engine, in the middle, on the right and on the left side of the frame. The last three were located at the back of the lawn mower at a vertical height of 63 cm from the floor and the handle on the engine was located at 42 cm. Static strength was measured for the handle in the middle. Ratings of perceived exertion were recorded for different body parts.

Peak and average dynamic pulling strengths were 55% and 34% of static pulling strengths. Dynamic pulling strengths were highly correlated with peak velocity (r = 0·84). Men in the age group 21-34 years had the highest strength and women in the age group 51-71 years the least strength. Dynamic pulling strengths for women were 62% of strengths for men. Women took 10% longer to pull, had a lower peak velocity (16%), reached peak force faster (17%) and took a longer time (6%) to reach peak velocity than men.

The starting handle located on the engine resulted in the maximum pulling strength and on the left side in the minimum strength. However, two out of three subjects preferred the handle either on the right side or in the middle. Fifty-five percent of the subjects indicated they would prefer a height higher than 63 cm.

Maximum stresses were perceived on the shoulder and upper arm with a mean rating between fairly light and somewhat hard. Graphs of cumulative frequency distributions of average and peak dynamic pulling strengths are presented to aid in the determining forces required to start a lawn mower engine in order to satisfy a desired percentage of the population.     

One-handed dynamic pulling strength with special reference to speed, handle height and angles of pulling

A laboratory study was conducted to determine the effects of pulling speed, handle height and angle of pull from the horizontal plane on one-handed dynamic pulling strength. The dynamic strength of nineteen male subjects for a 1 m pull was measured at four different handle heights (40%, 50%, 60% and 70% of shoulder height), at three different angles above the horizontal plane (15°, 25° and 35°), and at three different speeds of pulling (mean speed = 0.7, 1 and 1.1 ms⁻¹). In addition, ratings of perceived exertion were recorded for elbow, shoulder and back. Also, the subjects were required to rate the overall comfort for the pull.

Pulling speed, handle height and angle all had a significant effect on both mean and peak dynamic pulling strengths (p 0.01). Among the three variables, pulling speed was found to be the most critical. The mean dynamic strength was 360, 250 and 180 N and the peak strength was 600, 425 and 320 N at 0.7, 1 and 1.1 ms⁻¹, respectively. The strengths decreased with an increase in handle height from 100% at 40% shoulder height to 83% at 70% of shoulder height and were the highest at an angle of 25° from the horizontal plane.

The ratings of perceived exertion for all three body parts decreased with an increase in speed of pulling (p 0.01). The high speed pulls were perceived as being more comfortable than low speed pulls (p 0.01). The handles at 50% and 60% of shoulder height and at an angle of 25° were perceived as being more comfortable than those at other heights and angles (p 0.01).

It is suggested that biomechanical stresses need to be considered along with physical strength and ratings of perceived exertion and comfort to determine optimum speed, height and angle of pulling for high speed pulling tasks.     

Human strength capabilities during one-handed maximum voluntary exertions in the fore and aft plane

Maximal static strengths were determined for one-handed exertions in all directions in the fore and aft plane. Data from 12 males and 10 females (mean age 30.7 yrs, standard deviation (SD) = 8.9 yrs, n = 22) were obtained with handle heights of 1.0 and 1.75 m. Twelve of the subjects also performed two-handed exertions at the same handle heights. The ratio of mean strengths of females to that of males ranged from 0.50 to 0.83 (for absolute forces) and from 0.63 to 1.00 for forces normalized to body weight. The ratios of one-handed to two-handed strengths ranged from 0.64 to 1.04. Two-handed strengths commonly exceeded one-handed strengths at the lower handle height, but showed fewer significant strength differences (p less than 0.05) according to direction at 1.75 m. Both female/male and one-handed/two-handed strength ratios were found to be dependent on direction of exertion and handle height. The observed strength dependencies upon number of hands (one or two-handed), direction of exertion, handle height and sex are discussed. The strength data have implications for use in biomechanical models and task analysis.     

Arm lift strength in work space

This study was conducted to determine arm strength values for isometric and isokinetic efforts around the human trunk. Thirty-eight normal young adults (20 male and 18 female) performed a total of 19 tasks. These consisted of one self-selected optimum posture with upright stance and elbows bent at 90 degrees , designated as standard posture for isometric test. In addition, isometric testing was done sagittally symmetrical 30 degrees and 60 degrees lateral planes at half-, three-quarters- and full-reach distances at knuckle height. The isokinetic tests were done between knuckle height and shoulder height in postures identical to isometric tests. The sequence of these tasks was randomised. The peak strength in standard posture was invariably lower than the peak strength at half-reach in isometric condition in all three planes for both sexes with the exception of one condition among females (60 degrees lateral plane, half-reach isometric). Peak and average arm lift strengths of males were significantly higher than those of females (p < 0.01) and ranged between 44% and 71%. For both sexes isometric strength was significantly higher than isokinetic strength (p < 0.01). The peak and average strengths in the sagittal plane were invariably higher than those of asymmetric postures, with one exception among females. With increasing reach distance the strength declined significantly for all conditions among both genders (p < 0.01). The ANOVA showed that the gender, mode of lifting, postural symmetry and reach of lifting, in addition to affecting the peak and average strength individually (p < 0.01), had significant 2-way and 3-way interactions (p < 0.01). All strength values were inter-correlated (p < 0.01). The regressions predicting peak and average strengths from anthropometric characteristics and sagittal plane strengths accounted for 63% to 89% of all variance and were highly significant (p < 0.01).     

Acclimatization to Severe Dry Heat by Brief Exposures to Humid Heat

Abstract

Maximal static strengths were determined for one-handed exertions in all directions in the fore and aft plane. Data from 12 males and 10 females (mean age 30·7 yrs, standard deviation (SD)=8·9 yrs, n=22) were obtained with handle heights of 1·0 and 1·75 m. Twelve of the subjects also performed two-handed exertions at the same handle heights. The ratio of mean strengths of females to that of males ranged from 0·50 to 0·83 (for absolute forces) and from 0·63 to 1·00 for forces normalized to body weight. The ratios of one-handed to two-handed strengths ranged from 0·64 to 1·04. Two-handed strengths commonly exceeded one-handed strengths at the lower handle height, but showed fewer significant strength differences (p<0·05) according to direction at l·75m. Both female/male and one-handed/two-handed strength ratios were found to be dependent on direction of exertion and handle height. The observed strength dependencies upon number of hands (one or two-handed), direction of exertion, handle height and sex are discussed. The strength data have implications for use in biomechanical models and task analysis.     

Ratings of acceptable load and maximal isometric lifting strengths: the effects of repetition

The effects of repetition on psychophysically acceptable loads and maximal isometric lifting strengths were studied in two groups of subjects. In both groups, subjects selected acceptable loads for dynamic lifting between table and floor and were tested for maximal and acceptable lifting strength isometrically at knee and waist levels.

In series I, 33 subjects (15 males, 18 females) were tested 4 times with a minimal interval of 5 days between tests. In series II, 12 subjects (8 males, 4 females) were tested daily from Monday to Friday on 2 consecutive weeks.

Differences in acceptable isometric lifting strength between the two groups appeared to arise from minor differences in the instructions given; but in neither series was there a significant change in acceptable lifting strength, either dynamic or isometric. In series I, no change was noted in maximal isometric lifting strength. But in series II there was a gain in maximal lifting strength at knee level of 25%. Also in series II, the acceptable isometric lifting strength at waist level was consistently found to be 60% of the acceptable dynamic lifting strength.     

The effect of handle height and cart load on the initial hand forces in cart pushing and pulling

The objective of this study was to measure the three-dimensional hand forces people exert to initiate a cart push or pull for two cart loads: 73 and 181 kg, and three handle heights: knuckle, elbow, and shoulder heights. The cart used was equipped with 15.24 cm (6 in) diameter wheels. The floor was covered with carpet tiles. The laboratory-measured hand force exertions were compared to the minimum forces needed to push/pull the cart under the same conditions and to the psychophysical initial push/pull force limits. For pushing and pulling, the measured anterior-posterior hand forces were 2–2.4 times the minimum required forces. For the heavier cart load, lower forces were applied as handle height increased. Pull forces were 7% higher than push forces. The smallest vertical forces were measured at elbow height. Strength capability and gender did not have an effect on the applied forces. The mean strength percentile for the male sample was 64%, while the mean strength percentile for the female sample was 13% as determined from the Adjusted Torso Lift Strength Test and population strength data for this test. The comparison with the psychophysical limits indicated that the tasks were well within the maximum acceptable initial forces for males, but not for females.     

Effects of sitting and standing, reach distance, and arm orientation on isokinetic pull strengths in the horizontal plane

In recent years, isokinetic strengths (dynamic strength exertions at constant speed) have almost replaced isometric (static) strengths in laboratory studies as measures of a person's strength exertion capabilities. Many industries are also showing a keen interest in replacing static strength usage with dynamic strength usage. The increasing acceptance of isokinetic strengths as a more valid and accurate measure of people's strength exertion capability has necessitated the development of isokinetic strength databases. This paper presents one-arm isokinetic pull strength profiles of males, engaged in infrequent exertion in a horizontal plane, as a function of posture (sitting and standing), reach distance (25, 40, and 55 cm for the sitting posture; 45, 65, and 85 cm for the standing posture), and angle of the preferred (stronger) arm from the frontal plane (0—frontal plane, 30, 60, 90, 120, and 150 deg). Twenty-five males participated in the study. The results indicated that more strength is exerted while standing. The strength also increases with the reach distance. The strength exertion becomes stronger as the angle of the arm increases to 90° from the frontal plane (i.e., the arm moves to the sagittal plane) and then weakens.     

Maximum isometric lifting strengths of men in teamwork

This study reexamined the additivity of maximum isometric teamwork lifting strength using experienced and height-matched young male participants. The maximum isometric lifting strength was measured for four exertion heights (45, 75, 105, and 140 cm) and four lifting styles (one-, two, three-, and four-person exertions). The results showed that actual teamwork strength could be greater or lower than the sum of individual strengths. If it was greater, the difference between the two could be either significant or nonsignificant, but if it was lower, there was no significant difference between the two. Actual teamwork strength ranged from 90.0% to 134.8% of the sum of individual strengths, indicating that experienced and height-matched participants could overcome the problem of lack of coordination in isometric teamwork lifting. The results also showed that some teamwork members, especially weaker members, might be forced to exert strengths higher than their maximum individual voluntary strengths in teamwork lifting. To avoid such overexertion in teamwork, it is recommended that the weight of the handled load be controlled and lower than the sum of all members' strengths. Additionally, members with significantly different strength abilities should not be assigned to the same team. Actual or potential applications of this research include designing member assignments in teamwork lifting tasks.     

Development of predictive equations for lifting strengths

The purpose of the study was to determine relationship between lifting strengths of male and female subjects and body posture, type of lift (stoop or squat) and velocity of lift. Thirty normal young adults (18 males and 12 females) volunteered for the study. All subjects were required to perform a total of 56 tasks. Of these, 28 were stoop lifts and 28 were squat lifts. In each of the categories of stoop and squat lifts, the strengths were tested in standard posture, isokinetic (linear velocity of 500 mm/s), and isometric modes at half, three-quarters and full horizontal individual reach distances in sagittal, 30 degrees lateral and 60 degrees lateral planes. The strengths were measured using a static dynamic strength tester with a load cell and an IBM microcomputer with an A/D card. The peak and average strength values were extracted and statistically compared across conditions and gender (ANOVA). Finally a multiple regression analysis was carried out to predict strength as a function of reach, posture and velocity of lift. The ANOVA revealed a highly significant effect of gender, reach, plane and velocity (p < 0.01). All regression equations (108) were significant (p < 0.01), and more than 70% of variance in lifting strength was accounted for by the anthropometric variables and sagittal plane strength values. Such an established relationship allows one to predict the human lifting strength capabilities for industrial application based on simple anthropometric and strength characteristics.     

Lumbosacral compression in maximal lifting efforts in sagittal plane with varying mechanical disadvantage in isometric and isokinetic modes

Nine normal male subjects (mean age 28·2 years and mean weight 72·6 kg) performed 20 standardized maximal effort lifting tasks. They were asked to perform stoop and squat lifts at half, three-quarters and full individual horizontal reach distances in mid-sagittal plane in isometric and isokinetic modes (fixed velocity 60 cm/s). Both stoop and squat lifts were initiated at the floor level and terminated at the individual's knuckle height keeping the horizontal distance constant throughout the lift. The isometric stoop lifts were performed with hip at 60° and 90° of flexion with hands at preselected reach distances. The isometric squat lifts were performed with knees at 90° and 135° of flexion with hands at similarly preselected reach distances. The force was measured using a Static Dynamic Strength Tester with load cell (SM1000). The postures were recorded using a two-dimensional Peak Performance System with an event synchronizing unit. The load cell was sampled at 60 Hz and the video filming was done at 60 frames per second. The force and postural data were fed to a biomechanical model (Cheng and Kumar 1991) to extract external moment and lumbosacral compression. The strengths generated in different conditions were significantly different (p < 0·01). The strength variation ranged by up to 73% whereas the lumbosacral compression varied by only up to 15%. A high level of lumbosacral compression was maintained in all conditions.     

Intelligence,Work Performance,and Inspection Time

The additivity of strengths for teams of two and three untrained female subjects in eam-work was evaluated in static (isometric) and dynamic (isokinetic) terms. Eight healthy college students were tested under laboratory conditions. Four standard values were used to evaluate isometric strengths: arm, leg, stooped back, and composite measures. The isokinetic strength was tested by means of dynamic lift strength and dynamic back extension. Following individual measurement of the subjects, they were tested in two-member and three-member teams. Two-female teams w«re evaluated in terms of 28 combinations for each of the six measures; the three-female teams were tested in 56 combinations among the subjects. With the exception of isometric arm strength, the actual team strengths were significantly lower then the corresponding sums of the team-members' individual strengths. On average, the isometric back, leg and composite strengths were approximately 83·3% for the two-female teams, and 83·9% for the three-female teams. The isokinetic strengths for two-female and three-female teams accounted for about 68·0% and 68·4% of the sums, respectively. These results indicate that lifting strength of females in team-work is generally not additive and depends upon the muscle group in use, and suggests that lifting capacity in team-work will be reduced as the number of team members increases.     

Pushing strengths under restricted space

This study investigates human maximum horizontal isometric pushing strength and rearward foot position while pushing at four different exertion heights (48 cm, 84 cm, 120 cm, and 156 cm) and two exertion spaces (unrestricted and restricted). The restricted space was reduced to an anterior–posterior direction. The results showed that participants' most efficient exertion height and rearward foot position occurred invariably at an exertion height of 84 cm when pushing in an unrestricted exertion space. Restricted space impaired the pushing strength, with a maximal difference of pushing strength between unrestricted and restricted spaces also occurring at the exertion height of 84 cm. The percentages of female to male pushing strength varied little across the four exertion heights. Participants seemed to be prone to utilize only approximately 71% to 82% of the exertion space available while pushing in a restricted space. © 2007 Wiley Periodicals, Inc. Hum Factors Man 17: 95–102, 2007.     

Effects of work experience and exertion height on static lifting strengths and lift strategies of experienced and novice female participants

In this study, 46 female experienced workers and inexperienced novices (23 each) were recruited to determine their maximum lifting strength at 15 exertion heights between 10 and 150 cm from the floor. The results revealed that the experienced workers' strengths at all 15 heights exhibited relatively little fluctuation, and were approximately 50–70 N lower than those of novices when heights were ≤50 cm. No differences in strengths were observed at 60–150 cm between the groups. The experienced workers tended to adopt a consistently deep squat at lower heights (≤50 cm) and a more erect posture with stiffened arms at higher heights (≥70 cm), resulting in lower L4/L5 disc compression forces and shoulder moments than in novices, respectively. In contrast to the lifting techniques adopted by experienced workers to effectively avoid overloading, the findings suggest that novice female workers who lack experience should be cautious and trained for performing lifting tasks.     

Static and dynamic lifting strength at different reach distances in symmetrica] and asymmetrical planes

Postural and therefore biomechanical standardization in strength testing has not been rigorously and consistently applied. To develop a quantitative relationship between strength and posture (body position, symmetry, and reach) 30 normal subjects (18 male and 12 females) were required to stoop and squat lift or exert in the relevant posture against a standardized instrumented handle. The isometric lifting efforts and isokinetic lifts were studied. The isokinetic lifts were done at a linear velocity of 50cm/s of the hand displacement from the floor to the knuckle heights of the respective subjects in stoop and squat postures. The isometric stoop lifting efforts were exerted in two standardized postures: (a) with 60° hip flexion; and (b) with 90° hip flexion. The isometric squat lifting efforts were also exerted in two standardized postures: (a) with 90° knee flexion; and (b) with 135° knee flexion. All isometric lifting efforts and isokinetic lifts were performed at half, three-quarters, and full horizontal reach in sagitally symmetrical, 30° left lateral, and 60° left lateral planes. Isometric stoop and squat lifting efforts were also measured in self-selected optimal postures. These 56 conditions were tested in random order. The analysis of variance revealed that the gender, the mode of lifting, the postural asymmetry and reach of lifting affected the strength significantly (p<0·0001). Most two-way and three-way interactions were significant (p<0·01). Of 108 prediction regression equations, 103 were significant with up to 90% of the variation explained by anthropometric variables and sagittal plane strength. The reach affected the strength most profoundly followed by postural asymmetry and the mode of lifting.     

Risk of neck musculoskeletal disorders among males and females in lifting exertions

Work-related neck disorders are common among various occupational groups. Despite clear epidemiological evidence for the association of these disorders with forceful arm exertions, the effect of such exertions on the biomechanical behavior of the neck muscles is currently not well understood. In this study, the effect of lifting tasks on the biomechanical loading of neck muscles was investigated for males and females. Twenty-six participants (13 males and 13 females) performed bi-manual isometric lifting tasks at knuckle, elbow, shoulder, and overhead heights by exerting 25%, 50%, and 75% of their maximum strength. The activity of the cervical trapezius and sternocleidomastoid muscles was recorded bilaterally using surface electromyography. Higher activity of the cervical trapezius muscle (10% MVC–43% MVC) compared to the sternocleidomastoid muscle (4% MVC–18% MVC) was observed. Females tend to use the sternocleidomastoid muscle to a greater extent than males, whereas, higher cervical trapezius muscle activation was observed for males than females. The main effect of weight and height, and weight by height interaction on the activity of neck muscles was statistically significant (all p < 0.001). The results of this study demonstrate that the neck muscles play an active role during lifting activities and may influence development of musculoskeletal disorders due to resulting physiological changes.     

Static and dynamic lifting strength at different reach distances in symmetrical and asymmetrical planes.

Postural and therefore biomechanical standardization in strength testing has not been rigorously and consistently applied. To develop a quantitative relationship between strength and posture (body position, symmetry, and reach) 30 normal subjects (18 male and 12 females) were required to stoop and squat lift or exert in the relevant posture against a standardized instrumented handle. The isometric lifting efforts and isokinetic lifts were studied. The isokinetic lifts were done at a linear velocity of 50cm/s of the hand displacement from the floor to the knuckle heights of the respective subjects in stoop and squat postures. The isometric stoop lifting efforts were exerted in two standardized postures: (a) with 60 degrees hip flexion; and (b) with 90 degrees hip flexion. The isometric squat lifting efforts were also exerted in two standardized postures: (a) with 90 degrees knee flexion; and (b) with 135 degrees knee flexion. All isometric lifting efforts and isokinetic lifts were performed at half, three-quarters, and full horizontal reach in sagitally symmetrical, 30 degrees left lateral, and 60 degrees left lateral planes. Isometric stoop and squat lifting efforts were also measured in self-selected optimal postures. These 56 conditions were tested in random order. The analysis of variance revealed that the gender, the mode of lifting, the postural asymmetry and reach of lifting affected the strength significantly (p less than 0.0001). Most two-way and three-way interactions were significant (p less than 0.01). Of 108 prediction regression equations, 103 were significant with up to 90% of the variation explained by anthropometric variables and sagittal plane strength. The reach affected the strength most profoundly followed by postural asymmetry and the mode of lifting.     

Adsorptive voltammetry of Hg(II) ions at a glassy carbon electrode coated with electropolymerized methyl-red film

The glassy carbon electrode coated with electropolymerized methyl-red film, 1.2 × 10⁻⁶ m in thickness, (PMRE) showed high sensitivity towards Hg(II) ions. PMREs were adopted to accumulate and detect Hg(II) ions in a pH 2.56 Britton–Robinson buffer solution. Cyclic voltammogram of the accumulated Hg species on PMREs exhibited an anodic wave at 0.64 V and a cathodic wave at 0.13 V, due to the oxidation of accumulated Hg species on PMREs and the reduction of Hg(II) ions in the solution, respectively. For this heterogeneous adsorption of Hg(II) ions onto PMREs, the maximum surface concentration, adsorption equilibrium, and Gibbs energy change were evaluated to be 5.12 × 10⁻⁶ mol m⁻², 3.7 × 10⁵ l mol⁻¹, and −30.1 kJ mol⁻¹, respectively. The anodic peak current at 0.64 V was linear with the concentration of Hg(II) ions in the range of 1.1 × 10⁻¹⁰ to 1.1 × 10⁻⁷ M with a detection limit of 4.4 × 10⁻¹¹ M. The proposed method was utilized successfully for the detection of Hg(II) ions in the lake water.     

Foot Pedal Forces for Seated Operators

The foot controls of spot welding machines were orgonomicnlly evaluated, and redesign recammondations put forward. Ten male and ten female subjects were tested to dotermine the maximum isometric force that a seated operator could exert on a horizontal foot pedal. The experimental results showed no significant strength differences between right arid left legs and mole legs strengths were 9% to 50% greater than female leg strengths depending on the position of the foot pedal.     

The interacting effects of forearm rotation and exertion direction on male and female wrist strength

The accurate estimation of wrist strength is an important component of ergonomics task evaluation, as a vast majority of occupational tasks involve use of the hands to generate forces and moments. The purpose of this study was to examine the interacting effects of forearm rotation (pronation/supination) and wrist exertion direction on strength at the wrist joint in males and females. A total of 24 male and female participants performed maximum isometric wrist exertions while maintaining a non-deviated wrist posture (no flexion/extension or radial/ulnar deviation) and an open hand. Maximum wrist moments were obtained in combinations of three forearm rotations (90° pronation, neutral, 90° supination) and four exertion directions (flexion, extension, radial and ulnar deviation). A greater effect of forearm rotation was observed for males, as strength in the neutral forearm posture was significantly different than pronated and supinated postures in 5 of 8 comparisons. For females, both wrist flexion and extension strengths were higher in neutral, compared to supinated forearm postures. The findings of this study suggest that wrist strength does depend on forearm rotation, and this interaction between axes needs to be accounted for in future strength capability estimates.Relevance to industryThis study shows that wrist strength estimates, currently used by ergonomics software packages in industry, can be improved to more accurately reflect the actual wrist strength capabilities of workers during hand-intensive tasks.