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.     

An ergonomic evaluation of lawn mowers'' startability and controls

A laboratory study was conducted to evaluate ten different lawn mowers for ease of starting, operating controls and handling. Ninety-nine paid subjects (50 males and 49 females) from 14 to 71 years of age with prior experience on lawn mowers were selected randomly. Subjects were asked to identify the various controls, start a lawn mower four times, operate it for approximately 50 m and fill out lawn mower questionnaires on startability and controls. Subjective evaluations were supplemented with objective data.

All lawn mowers tested, except one equipped with a primer in place of a throttle, had high startability rates (90–97%). The handle suddenly pulled back in 0–5% cases. However, 70% of the lawn mowers were perceived as less than easy to start and controls were less than easy to operate on 90% of the lawn mowers. Subjects were less than comfortable in the starting position in 9 out of 10 lawn mowers with the rating of perceived exertion ranging from 10 to 12 on the Borg scale. Instructions on 7 out of 10 lawn mowers were rated as less than easy to follow. Ergonomic evaluation found major problems with the location, design, direction of movement and safety in operating various controls. About 95% of the subjects could not identify the safety control lever and the self-propel control on one lawn mower.

Based on ergonomic evaluation and subjective feedback, it is recommended that the starter rope handle should be placed in the middle at the back of the lawn mower at a height of about 70 cm from the floor. The distance of the starter rope handle from the handlebar should be 36 cm and it should be larger in size (about 11.8 cm) to accommodate all four fingers. Both the handlebar and the safety control lever should be semicircular in shape with a diameter ranging from 1.9 to 2.5 cm. The force required to hold the safety control lever should be less than 7 N. Knob-type sliding levers with clear labeling should be used for throttle, self-propel and ground speed controls. These controls should be located near the handlebar for clear visibility, access, reach and ease of operation.

Lastly, detailed studies are needed to determine optimum location of the starter rope handle, direction of pull, length of pull and speed of pulling. Ergonomic principles should not be ignored in the design and placement of controls on lawn mowers.     

Normative data on the one-handed static pull strength of a Chinese population and a comparison with American data

We assess the one-handed static pull strength of a Chinese population and compare it to that of an American sample. Fifty men and 50 women in five age groups were asked to exert their maximum one-handed pull strength in three pulling directions (across, front and side) and from four pulling heights (61 cm, 76 cm, waist height and above-shoulder height). The results showed that women had less pull strength than men under all of the conditions tested. The front and side pulling resulted in the greatest pull strength, with a decrease detected when the pulling height was increased. The American sample exhibited greater strength than the Chinese. Body mass and men’s handgrip force were also associated with the pull strength. These variables should be taken into account in the development of tasks related to one-handed pulling.

Practitioner summary:

In this paper, we report a laboratory-based experiment conducted to assess the one-handed static pull strength of a Chinese population and compare the results with those of an American population. The variables associated with pull strength included gender, pulling direction, pulling height, race, body mass and men’s handgrip force.     

Upper body push-pull strength of normal young adults in sagittal plane at three heights

Twenty young adults (ten males − mean age = 21.1 years; ten females − mean age = 21.1 years) were tested for their two-handed push-pull strength in sagittal plane at heights of 35 cm (low), 100 cm (medium) and 150 cm (high) in isometric and isokinetic modes. The lower extremities of the subjects were stabilized in a custom-designed device at hip, knees and ankle. The twelve experimental conditions (2 activities − push and pull × 3 heights × 2 modes) were randomized. The push-pull strengths were measured using a modified Static Dynamic Strength Tester with a SM 500 load cell. The analogue data were sampled and collected at 50 Hz through a Metrabyte DAS 20 in an IBM XT. Males as well as females were strongest in pulling at medium height in isometric mode. The isometric pushing strengths ranged between 41% to 68%, and 27% to 44% for males and females respectively when normalized against mean pulling strength of males at medium height. The isokinetic strengths were invariably significantly lower than isometric strength (p < 0.01).     

The evaluation of force exertions and muscle activities when operating a manual guided vehicle

A manual guided vehicle (MGV) is used to handle heavy materials in thin film transistor-liquid crystal display (TFT-LCD) manufacturing clean rooms. This study focuses on evaluating the force exertions and muscle activities in MGV operations. The independent variables include gender, force direction, handle height, load handled and wheel diameter of the MGV. The results show the force direction, handle height and load handling effects are significant in most measures except for F_ending (the peak force required to stop the MGV) and the EMG of the anterior deltoid. The wheel diameter had a significant effect on F_initial (the peak force required to move the MGV) and F_ending responses. Gender did not significantly effect any measures. Moreover, the pushing and pulling force is less at 115 cm handle height than at 101.5 cm and 88 cm handle heights. Using 15.3 cm (6 inch) diameter wheels requires less force than 20.3 cm (8 inch) diameter wheels because the two front wheels are fixed and the two rear wheels are rotatable. The design implications are discussed.     

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.     

Maximum endurance time modeling for push and pull tasks considering gender and handle height

The strengths of both push and pull using both hands at handle heights of 75, 90, and 135 cm were measured for 11 female and 8 male participants. In addition, simulated push and pull tasks were performed on one of the three heights as in the strength measurements. In these tasks, the participants either pushed or pulled a swing suspended with one of the two loads (32.5 and 42.5 kg) until they could no longer do so. Then, the strength of push or pull was measured again. The participants also reported bodily discomfort on their body parts on a CR‐10 rating scale. It was found that hands and leading leg had the highest CR‐10 scores among the body parts and were the bottleneck body parts for the push and pull tasks, respectively. Models of maximum endurance time incorporating gender and handle height, in addition to force ratio, were developed. These models may be adopted in predicting the endurance time in job design concerning work/rest arrangement.     

Effects of handle orientation,gloves, handle friction and elbow posture on maximum horizontal pull and push forces

Biomechanical models were evaluated for effects of handle orientation, handle material, gloves and arm posture on maximal pull/push force. Eight healthy subjects performed maximum pull/push exertions on handles with two different orientations and two different surface materials, using bare hand and two types of glove as well as two arm postures. The empirical data supported the proposed biomechanical models: Pull/push forces for the bare hand on a rubber handle decreased 10% when the handle was parallel to the pull/push direction, compared with when perpendicular to it. For parallel handles, pull/push forces further decreased with decreasing hand–handle friction coefficient (simulated by different handle materials and gloves). Pull force exerted by the bare hand was 29% greater when the elbow was extended than when flexed. Pull force was greater than push force (with bare hand and flexed elbow). The biomechanical models suggest that friction between the hand and handle limits pull/push forces for parallel handles. Elbow strength may be responsible for decreased pull force for the flexed elbow posture and decreased force for pull compared with push in the postures examined.

Statement of Relevance: Biomechanical models presented in this paper provide insights for causes of upper extremity strength limitations during pull/push tasks. Findings in this paper can be used directly in the design of workstation and objects to reduce fatigue and risk of musculoskeletal disorders.     

自动割草机器人的设计

介绍自动割草机器人的设计和实现。其硬件系统主要包括单片机系统、电机控制器以及传感器系统三部分。软件部分实现单片机系统的控制以及割草路径的规划。通过对软硬件的整体调试使系统达到设计要求。     

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.     

Effects of work experience on work methods during dynamic pushing and pulling

Pushing and pulling are potential risk factors for work-related low back disorders (WRLBDs). While several studies have evaluated differences in work methods related to work experience, such evidence for dynamic pushing and pulling is limited. Eight novices and eight experienced workers completed dynamic push/pull tasks using a cart weighted to 250% of individual body mass in two different configurations (preferred vs. elbow handle heights). Multiple measures [hand forces, torso kinematics and kinetics, and required coefficient of friction (RCOF)] were obtained to assess WRLBD and slip risks. Experienced workers generated higher medio-lateral hand forces, during both pulls and pushes, though with a more substantial difference during pushes (∼74%), and which involved the use of hand force components other than to move the cart in an anterior-posterior direction. Experienced workers also had lower peak torso kinematics in flexion/extension and lateral bending, and lower torso flexion/extension kinetics. The latter is suggestive of a lower risk for WRLBDs, though levels of exposures to WRLBD risk were low to moderate in both groups and were often relatively small and inconsistent across the task configurations. Group-level differences in RCOF were quite small, indicating a comparable slip risk between the two groups. Thus, it was considered inconclusive whether the work methods used by experienced workers during dynamic pushing and pulling are advantageous regarding WRLBD and slip risks.     

Determination of optimal location for parachute ripcord handle in a suspended position

A number of parachuting fatalities are attributed every year to the inability of the parachutist to pull the ripcord. The purpose of this study was to determine a location for the ripcord handle in parachutes, which would be most compatible with human capabilities. Eight different ripcord handle locations were selected for this investigation. Eighteen male and 18 female subjects participated in the study. The subjects were tested while being suspended 5 cm above floor level wearing a parachute harness. Maximum voluntary force exertions were measured with the subjects pulling the ripcord handle using their left, right and both hands at all locations. The results indicate that the thigh locations are superior in regard to pull forces for all hand applications (left, right, and both). Also, two-handed pulls yield the largest forces at all locations.     

Psychophysical basis for maximum pushing and pulling forces: A review and recommendations

The objective of this paper was to perform a comprehensive review of psychophysically determined maximum acceptable pushing and pulling forces. Factors affecting pushing and pulling forces are identified and discussed. Recent studies show a significant decrease (compared to previous studies) in maximum acceptable forces for males but not for females when pushing and pulling on a treadmill. A comparison of pushing and pulling forces measured using a high inertia cart with those measured on a treadmill shows that the pushing and pulling forces using high inertia cart are higher for males but are about the same for females. It is concluded that the recommendations of Snook and Ciriello (1991) for pushing and pulling forces are still valid and provide reasonable recommendations for ergonomics practitioners. Regression equations as a function of handle height, frequency of exertion and pushing/pulling distance are provided to estimate maximum initial and sustained forces for pushing and pulling acceptable to 75% male and female workers.     

基于智能视觉的割草机自动控制系统设计

为解决传统系统存在的区域切换行为和避障行为能力差、边缘覆盖率低等问题,设计了基于智能视觉的割草机自动控制系统。通过分析割草机自动控制原理,对系统硬件的控制单元、驱动单元、定位单元和供电单元进行优化;系统软件主要依据系统操作流程,构建人机界面,选用GC编程软件实现自动控制程序,完成基于智能视觉的割草机自动控制系统设计。实验结果表明,采用该系统在割草机自动控制方面,其区域切换行为和避障行为能力强,边缘覆盖率高。     

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.     

水稻钵体苗物理机械特性的测试分析

在对水稻钵体苗的质量、含水率、苗高等基本参数测试分析的基础上。测试研究了水稻钵体苗茎叶拉断力、拔苗力以及秧苗抗折断力，并计算了拉断应力。探讨了拉断力与秧苗横断面、拔苗力与起拔角度的关系。     

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.     

Spinal stresses in simulated raking with various rake handles

Five young male subjects performed a simulated raking task by pushing and pulling 14 different rake handles at 60 N and 110 N simulated soil resistance in a random order. The raking action was performed at a self-selected uniform pace over a 60 cm stroke length with initial, middle and final phases marked. During this action the raking force and angle of the rake was measured by a load cell and a potentiometer respectively. The posture was recorded with a video cassette recorder. The posture and force values were used for the determination of the spinal compression load. In rake pulling the 13 modified rake handles generated a spinal compression of only 20% to 50% of the straight handle, whereas in rake pushing the modified handles generated compression up to five times that of the straight handle. The compression generated with the straight handle never reached the action limit, whereas those of the 13 modified handles rarely stayed within the action limit. Therefore, a straight handle is considered the handle of choice.     

A comparison of isokinetic lifting strength with static strength and maximum acceptable weight with special reference to speed of lifting

A laboratory study was conducted to determine the effects of the speed of lifting and box size on isokinetic strength and to compare isokinetic lifting strengths with static lifting strengths and psychophysically determined maximum acceptable weights. Nine male college students lifted three different boxes (250, 380 and 510 mm wide) from the floor to a bench height of 0.8 m using a free-style lifting technique at a rate of 0.2 lifts min^?1. For each lifting task static strength was measured at the origin of lift. Isokinetic lifting strength was measured at 0.41,0.51 and 0.6 ms^?1 using a Biokinetic ergometer and attaching boxes to the load cell. Ratings of perceived exertion were recorded for the low back. There was a progressive decrease in mean and peak isokinetic lifting strengths both with an increase in lifting speed and with an increase in box width (p<0.01). The lifting speed had a much greater effect (29% and 27%) than the box width (18% and 15%) on mean and peak isokinetic lifting strengths. However, high speed lifting was perceived subjectively to be less stressful (RPE = 10.7) than slow speed lifting (RPE = 12.7). Static strength and maximum acceptable weight had higher correlations with mean isokinetic strengm (r = 0.65 and 0.82) than with peak isokinetic strength (r = 0.52 and 0.73). At 0.41 ms^?1, mean isokinetic strength was 6% greater than the mean static strength (p ≥0,05). Extrapolation of mean isokinetic strength data showed that at 0.73 ms^?1 the estimated mean isokinetic strengths were within 6% of maximum acceptable weights. It is concluded that isokinetic strength is highly dependent upon die speed of lifting. At a slow speed (0.41 ms^?1), mean isokinetic strength is equal to mean static strength; and, at a high speed (0.73 ms^?1), it appears to be equal to the maximum acceptable weight. It is recommended that both speed of lifting and box width should be controlled carefully to simulate job-specific isokinetic lifting strength.     

Impact of pulling direction and magnitude of force exertion on the activation of shoulder muscles

Shoulder musculoskeletal disorders (MSD) are frequently associated with the work activities that demand forceful arm exertions in pushing and pulling directions. Considering the ability of shoulder joint to exert forces in nearly any direction, our understanding of the shoulder muscles activation as affected by pushing and pulling exertions is limited. In this study the activation of seven shoulder muscles were studied for 10 male participants during pulling exertions performed in five directions (pull right, pull left, pull back, pull down and pull up) using three force levels (22.24 N, 33.36 N and 44.48 N). Exertions performed in pulling right and pulling up directions produced higher activation and received higher perceived exertion ratings than the exertions performed in the other directions. Rotator cuff and middle deltoid muscles activation were consistently higher during pulling up and pulling right exertions compared to the other muscles. A high correlation was found between the activation of rotator cuff and deltoid muscles and the perceived exertion ratings. The rotator cuff and middle deltoid muscles activation observed during the pulling up and pulling right exertions can be explained by the concavity compression mechanism which stabilizes the glenohumeral joint of shoulder.Relevance to industryThe muscle activation data expressed in terms of Maximum Voluntary Contraction (MVC) and perceived exertion ratings are widely used by the ergonomic practitioners to design and/or evaluate workplace exertions. This study provides such data for several shoulder muscles during pulling exertions performed under different conditions.