Elbow Height Research Articles

Measuring anthropometric data for designing hand tools in handicraft industries

This research manuscript presents anthropometric data of handicraft industries of Jaipur, Rajasthan (north western region of India). It comprises of 160 male workers (age group 18–60 years). The data were analysed by computing mean, standard deviation, range and coefficients of variation. The correlation coefficients were also estimated in-order-to find out the relationship among various anthropometric measures. It is observed that measurements in the vertical direction viz. stature, shoulder height, eye height, and elbow height; are highly correlated among each other. Further, the anthropometric dimensions of workers of this region were compared with those of the other regions (north-eastern, southern and eastern) of India and other ethnic group of populations. The aim of this study is to provide the data to manufactures/ designers, so that they are able to design specifically suited tools for the workers. Further, the recommendations about the anthropometric data/values for development of workstation and hand tools of handicraft industries are suggested.

Effects of a vertical console position on operator muscular stress during ultrasonic diagnosis.

Ultrasound examinations tend to put sonographers in unnatural postures, which may lead to musculoskeletal disorders. In this study, we focused on the height of the operation panel of the diagnostic ultrasound system to quantitatively assess the effects of panel height (work plane height) on musculoskeletal stress during scanning in a sitting position. Eight subjects were asked to perform a simulated scanning task that involved touching nine points on the operation panel at four different panel heights. Electromyogram, left wrist joint angle, and subjective evaluation on ease of manipulation, etc., indicated that the optimum height of the operation panel during scanning in a sitting position is elbow height.

Shoulder and neck muscle activities during typing with articulating forearm support at different heights

Use of forearm support is known to reduce physical stress of computer users, but research about how to properly position the forearm support is insufficient. This study was aimed to determine whether the height of forearm support influences muscular loads during typing. Twenty four subjects performed a typing task with a pair of articulating forearm support at three different heights as well as without any support, while shoulder, neck and forearm muscle activities and posture data were recorded. Typing with the support at resting elbow height produced significantly (p < 0.05) lower shoulder and neck muscle activities than that of no support condition. Typing with the support at heights higher than the resting elbow height produced significantly greater shoulder and neck muscle activities compared to the no support condition. Results suggest that forearm support can help computer users lessen physical stress in typing, but only when the supports are positioned at resting elbow height. Practitioner Summary: Use of forearm support is known to alleviate physical stress of PC users in computer works such as typing. This experimental study addressed the importance of proper positioning of forearm support by comparing neck and upper extremity muscle activities between conditions with varying heights of forearm support in keyboard typing.

A field experiment comparing mechanical demands of two pruners for flower cutting

Manual flower cutting requires repetitive forceful movements that may explain the high incidence of upper-extremity MSDs among workers of the Colombian flower industry. Force demands may be caused by the use of pruners that have not been designed for Colombian workers. We conducted a repeated measures field experimental study (n=16, 69% women, 20 to 60 years old) to compare the mechanical demands during rose cutting of two different pruners (Traditional vs. alternative pruner) at two different cutting heights (elbow vs. over-shoulder). Demands included the perceived comfort, perceived effort and upper limb's muscular activity and posture. Workers perceived their traditional pruner as more comfortable but requiring more effort than the prototype tool. No benefits were observed regarding ulnar deviation with the alternative pruner. The wrist extension and related muscular activity of the wrist extensors were higher with the prototype pruner. The prototype pruner resulted in reduced muscular load of the wrist flexors; the biceps when working at the elbow height; and the deltoids when working at the shoulder height. However, Moderate results may be explained by the lack of time for workers' adaptation to the alternative tool. New design developments must focus on reducing extension and ulnar deviation of the wrist.

Anthropometric aspects of body seated in school

This study aimed to assess the student-furniture interface from anthropometric parameters of the sitting posture. The sample was composed of 887 students from two public schools in the State of Parana-Brazil, which attended children from 7 to 17 years of age. The data collection used anthropometric measures of the sitting position, a questionnaire containing a human body diagram for indication of discomfort areas and photographic records to verify postural and ergonomic inadequacies in classroom. The following anthropometric variables were measured: popliteal height, sacro-popliteal length, hip width, lumbar support height, and elbow and thigh height. Percentiles 5 and 95 of anthropometric variables showed differences statistically significant, with variation coefficient greater than 30%. In relation to body discomfort, the highest occurrences were recorded for ankle, knees and shoulder joints as well as for spine and buttocks. It was concluded that children use school furniture that does not meet their anthropometric standards, which favored the adoption of incorrect postures and contributed to the emergence of musculoskeletal problems that can interfere with their educational process.

Anthropometric Database for the Learning Environment of High School and University Students

This paper presents an anthropometric database of high school and university students from Kuala Lumpur, Malaysia. Forty-one high school participants (21 males and 20 females), 13–17 years old, and 143 university students (74 males and 69 females) took part in the study. Twenty-one static body dimensions were measured. The greatest mean differences in the anthropometric data between male and female high school students were found in the sitting elbow height. In addition, a comparison of anthropometric data of male and female university students showed that data for males and females were significantly different, except for buttock–popliteal length, sitting elbow height and thigh clearance. The primary aim of this study was to develop an anthropo-metric database that could be used as a primary reference in designing products, devices and equipment for ergonomic learning environments.

Effects of armrest height on the neck and shoulder muscle activity in keyboard typing

Use of forearm support during typing is known to alleviate biomechanical stresses on user’s neck and upper extremities but it is not known how the change in the armrest height influences the efficiency of the support. The purpose of this study was to investigate the effects of armrest height on the myoelectric activity (EMG) of neck extensors, upper trapezius muscles and forearm muscles during keyboard typing. Twenty-four subjects performed a simple typing task with each of four different armrest conditions (no support, armrests at resting elbow height, armrests at 25% and 40% above resting elbow height) while their EMG amplitudes were periodically collected. Results found significantly greater (p<0.05) mean activity of neck and shoulder muscles associated with elevated armrest heights. Armrest at resting elbow height produced the lowest mean activity. Findings of this study indicate the importance of proper positioning of arm support during typing.

The Influence of Installation Height and Screen Tilt Angle of Touch-Sensitive Screen on Its Usability and Arm Burden during Operation

Recently, touch-sensitive screen has been in widespread use as interface with high usability in public facilities. However, it is pointed out that installation height and screen tilt angle are not inequable for its user because there is a difference of the body type. In this study, for the purpose of taking the knowledge applicable to the design guide of touch-sensitive screen, we investigated the relationship between installation position of touch-sensitive screen and operability. Moreover, we measured maximum torque ratio of upper limb to examine the effect of installation position to arm burden. We asked examine to operate on touch-sensitive screen in nine conditions. Three conditions depend on the height of center of touch-sensitive screen (height of shoulder, elbow and lower back), and the other three conditions depend on the screen tilt angel (0°, 45°, 90°). The result showed that installation height and screen tilt angle of touch-sensitive screen have an influence on pointing time and arm burden. From this study, we suggest the installation positions that are easy to operate and lightly-loaded.

Does elevating and tilting the input device support surface affect typing force and postural exposures of the wrist?

Compare wrist kinematics and typing force during computer work across two workstations, one configured according to recommended guidelines with the keyboard support surface flat and near resting elbow height, the other according to users' actual setup and preference, with an elevated, and positively tilted support surface. Twenty participants completed a standard computer task at the two workstation configurations. A thin profile force plate, placed under the keyboard recorded keyboard reaction forces. Twin axis electro-goniometers (SG65 Biometrics Ltd, London, UK) affixed to the back of the right and left hand of each subject continuously measured wrist extension/flexion and ulnar/radial deviation. Typing force and wrist kinematics were similar between the two configurations with only 10th percentile ulnar deviation for the right hand showing a borderline significant difference of 1° between the two configurations. Elevating and tilting the input device support surface does not necessarily affect typing force and kinematics of the wrist. The combination of the input device support surface and user upper extremities form a complex kinematic system with several degrees of freedom. Wrist postures during computer use are a function of multiple factors other than simply keyboard tilt.

Differences in lifting strength profiles between experienced workers and novices at various exertion heights

This study compared lifting strength patterns between experienced workers and novices at various exertion heights. Twenty-one experienced workers and 21 novices were recruited to determine their static-lifting strength under various heights (10–150 cm in increments of 10 cm) using two exertion methods (vertically upward lifting, VUL, and toward body lifting, TBL). Testing posture was also recorded by a motion analysis system for comparing with the corresponding strength values. Results showed that strength during VUL were much higher than strength during TBL at 15 height positions ( p < 0.001). Strength in all 30 task combinations showed no difference between the two groups except for the VUL at heights of 100–120 cm. On the average, strength exerted by novices during VUL was 4.57–7.61 kg lower than that of workers while lifting at 100–120 cm heights (all p < 0.05). The strength during TBL consistently decreased with increased heights of lifting. When workers performed VUL, the strength surprisingly remained nearly unchanged throughout the heights of interest. The postures adopted by workers during VUL were also highly differentiated from novices while performing near-floor positions, but the strength was equivalent to each other. This study demonstrated that the static-lifting strength of novices were significantly lower than those of experienced workers while upward lifting near the participant’s elbow height. It was concluded that workers tend to adopt a safer (i.e., more flexed knees) and more skillful technique than novices to generate forces, resulting in lower spinal loads during both methods of lifting. Relevance to Industry Many studies have established the human strength data based on student participants who do not have experience in manual materials handling. The present findings clearly suggest that lifting strength data collected on novices (e.g., on students) should be carefully applied in the task (re)design at the workplace as their strength profiles and the postures adopted during lifting differ from workers.

Understanding the Physical Risk Factors Affecting Cervical Musculoskeletal Disorders

In spite of strong epidemiological evidence associating neck or cervical spine disorders with forceful arm exertions common at workplaces, effect of such exertions as causative of neck musculoskeletal disorders (MSD) is currently not well understood. In this study the effect of isometric lifting tasks at elbow, shoulder and overhead heights on the activities of two major neck muscles, sternocleidomastoid (anterior neck muscle) and upper trapezius (posterior neck muscle), was evaluated by using electromyography (EMG). Thirty healthy participants performed isometric lifting tasks exerting 25%, 50% and 75% of their respective maximum strengths at neutral and extended neck postures. Activities of sternocleidomastoid and upper trapezius increased with the increase in the lifting weights and heights. Extended neck posture caused a higher load on the neck musculature than the neutral posture. In conclusion, this study demonstrates a positive load-response relationship between forceful arm exertions and activation of the neck muscles.

Weight and age at puberty and their correlations with morphometric measurements in crossbred breed Suffolk ewe lambs

The objective of this study was to identify and to correlate parameters that characterize puberty and estimate the age and weight of Suffolk ewe lambs in Mato Grosso do Sul. This study was carried out with twenty-two Suffolk ewe lambs for 256 days. Blood samples were collected from the jugular vein and centrifugated and the plasma were stored at -20°C until analysis of progesterone (P4) concentration by radioimmunoassay (RIA). The morphometric measurements included: head length and width, body length, elbow height, chest perimeter, back-sternal diameter, croup length, width and height, cannon bone perimeter and shoulder and hip width, using a tape. The animals became pubertal when the plasma progesterone concentration was &gt;1.0 ng/mL, at 34.1 ± 5.2 kg and 39.5 ± 8.5 weeks of age. Meanwhile, the lambs that did not reach puberty (37.7 ± 11.4 weeks of age) were lighter. The morphometric measurements has medium to low correlations with age and weight at puberty.

Mismatch between classroom furniture and anthropometric measures in Chilean schools

Children spend about five hours per day sitting down while doing their school work. Considering this as well as the potential inadequate use of school furniture, it is likely that some anatomical–functional changes and problems in the learning process may occur. The aim of this study was to compare furniture sizes within three different schools with the anthropometric characteristics of Chilean students in the Valparaíso region, in order to evaluate the potential mismatch between them. The sample consisted of 195 volunteer students (94 male, 101 female) of the 8th grade, ranging from 12.5 to 14.5 years of age from 3 different schools. Regarding the methodology, 6 anthropometric measures (Stature, Popliteal height, Buttock-popliteal length, Elbow height while sitting, Hip width, Thigh thickness and Subscapular height) were gathered, as well as 8 dimensions from the school furniture. For the evaluation of classroom furniture a match criterion equation was defined. After considering the existing classroom furniture dimensions in each match criterion equation, the anthropometric characteristics of the considered population were compared in order to determine the mismatch between them. Results indicated that seat height, which should be considered as the starting point for the design of classroom furniture, was appropriate for students' popliteal height in only 14% of the 2 out of the 3 schools, and 28% in the third. Seat to desk height was too high and mismatched 99% of the students in one school and 100% in the others. Therefore, it was possible to conclude that the classroom's furniture was inadequate in almost all the analyzed cases and subjects. It is possible that the high mismatch percentage found between furniture and students' anthropometry can be associated to the fact that the acquisition and selection of the furniture was made without any ergonomic concern or criteria.

Skeletal forelimb measurements and hoof spread in relation to asymmetry in the bilateral forelimb of horses

Research has highlighted a high frequency of skeletal asymmetries in horses. In addition, research into hoof asymmetries has shown that within a bilateral pair, the hoof with the smaller angle is often subjected to greater loading. There has been limited attention paid to understanding compensatory mechanisms for skeletal asymmetries in the horse; the dynamic structure of the hoof could potentially be acting in a compensatory capacity. To investigate the relationship between morphometry of forelimb segments and hoof spread and their incidence of asymmetry. Ten bilateral measurements of the hoof and forelimb were taken from 34 leisure horses. The relationship between hoof spread and forelimb segment measurements were analysed using a generalised linear model (GLM). In relation to left hoof spread, the GLM identified significant negative relationships with left side measurements (third metacarpal length, elbow height), and significant positive relationships with right side measurements (fetlock height, third metacarpal length, elbow height). In relation to right hoof spread, the GLM identified significant negative relationship with left elbow height, and significant positive relationships with right side measurements (fetlock height, point of shoulder). The difference between the number of horses larger to the left or to the right was found to be significant for point of shoulder height (chi2 = 4.8, P < 0.05), and highly significant for heel height (chi2 = 953, P < 0.01) and the third metacarpal length (chi2 = 7.26, P < 0.01). The study demonstrated considerable asymmetry in left-right morphometry of the equine limb. The fact that measurements of hoof spread were significantly associated with limb segment measurements could possibly indicate that an interaction exists. Any asymmetry in hoof spread measurements may suggest unequal loading of the limbs, which in turn may contribute to injuries and reduced performance.

The effects of split keyboard geometry on upper body postures

Split, gabled keyboard designs can prevent or improve upper extremity pain among computer users; the mechanism appears to involve the reduction of awkward wrist and forearm postures. This study evaluated the effects of changes in opening angle, slope and height (independent variables) of a gabled (14°) keyboard on typing performance and upper extremity postures. Twenty-four experienced touch typists typed on seven keyboard conditions while typing speed and right and left wrist extension, ulnar deviation, forearm pronation and elbow position were measured using a motion tracking system. The lower keyboard height led to a lower elbow height (i.e. less shoulder elevation) and less wrist ulnar deviation and forearm pronation. Keyboard slope and opening angle had mixed effects on wrist extension and ulnar deviation, forearm pronation and elbow height and separation. The findings suggest that in order to optimise wrist, forearm and upper arm postures on a split, gabled keyboard, the keyboard should be set to the lowest height of the two heights tested. Keyboard slopes in the mid-range of those tested, 0° to −4°, provided the least wrist extension, forearm pronation and the lowest elbow height. A keyboard opening angle in the mid-range of those tested, 15°, may provide the best balance between reducing ulnar deviation while not increasing forearm pronation or elbow separation. These findings may be useful in the design of computer workstations and split keyboards. The geometry of a split keyboard can influence wrist and forearm postures. The findings of this study are relevant to the positioning and adjustment of split keyboards. The findings will also be useful for engineers who design split keyboards.

Comparisons of Seated Postures between Office Tasks

Seating is an active area of ergonomics research; however, little research has been performed that evaluates seated body postures for a variety of tasks and chairs. The goal of this study was to evaluate the effects of common office tasks on head, upper extremity, torso, hip, and leg postures. Prolonged awkward postures may contribute to musculoskeletal pain and disorders. Twenty-five participants performed four office tasks using four office chairs while postures were recorded using a 3D optical marker system. The tasks were typing on a desk fixed at 73.7cm (29“), typing with the desk adjusted to be slightly above elbow height, reclined movie watching, and a forward leaning writing task. Head angle, pelvis-to-head angle, thoracic cage angle, and pelvis angle were all significantly different between tasks ( p = &lt;0.0001). This method for full body posture measurement will allow further research into the effects of tasks and chairs on seated posture.

Ergonomic assessment of optimum operating table height for hand-assisted laparoscopic surgery

To investigate the influence of the working surface height on task performance and muscle workload in hand-assisted laparoscopic surgery. The standard task used was closure of 5-cm enterotomy inside a hand-assisted laparoscopic surgery trainer. Surgeons were instructed to place the sutures 3-5 mm apart and from the enterotomy edge. Ten surgeons participated in each experiment and one task was performed with each level. The first experiment compared the quality of task performance and muscle workload with the working surface at: elbow level, 10 cm above, 15 cm above and 10 cm below the elbow. Further narrower levels (5 cm below, at the elbow and 5 cm above the elbow) were investigated in the second experiment. Outcome measures were execution time (s), placement error score (mm), leakage pressure (mmHg), number of execution errors, muscle workload as measured by integrated electromyography (mV x s) and visual analogue score of back discomfort (mm). The first experiment showed that 15 cm above the elbow level was associated with the longest execution time and similar quality of task performance. This level resulted in a higher workload of the deltoid of the extracorporeal limb, the arm extensor of the intracorporeal side and the trapezius and paraspinal muscles of both intra- and extracorporeal limbs. Also, the 10 cm above the elbow level was associated with increased muscle workload of the deltoid of extracorporeal limb and the trapezius of both limbs compared with the elbow height. The 10 cm below the elbow level was associated with increased back discomfort. The second experiment showed that 5 cm below the elbow height was associated with increased muscle workload of the arm flexor group of the intracorporeal dominant limb. The optimum table height for hand-assisted laparoscopic surgery allows the working surface of the extracorporal instrument handle to be at or 5 cm above the elbow level.

A biomechanical analysis of anterior load carriage

Front load carriage is a common occupational task in some industries (e.g. agriculture, construction), but, as compared to lifting tasks, relatively little research has been conducted on the biomechanical loading during these activities. The focus of this study was to explore the low back biomechanics during these activities and, specifically, to examine the effects of load height and walking speed on trunk muscle activity and trunk posture. Eleven male participants participated in two separate front load-carriage experiments. The first experiment called for carrying a barbell (with weight corresponding to 20% of elbow flexion strength) at three heights (knuckle height, elbow height and shoulder height) at a constant horizontal distance from the spine. The second experiment called for participants to carry a bucket of potatoes weighing 14 kg at the same three heights, but with no further restrictions in technique. In both experiments, the participants performed this task while either standing still or walking at a self-selected speed. As they performed these tasks, the activity levels of the right-side muscle of the rectus abdominis, external oblique, biceps brachii, anterior deltoid and three levels (T9, T12 and L3) of the erector spinae were sampled. Mid-sagittal plane trunk posture was also quantified using three magnetic field-based motion sensors at T9, T12 and L3. The results showed a significant effect of both walking speed and load height on trunk posture and trunk muscle activity levels in both the barbell and bucket experiments. In the barbell experiment, the walking trials generated 43% more trunk muscle activity than the standing trials. Trials at shoulder height produced 11% more muscle activity than trials at elbow height in the T9 erector spinae muscles and 71% more muscle activity in the anterior deltoid. In the bucket experiment, trunk muscle activity responded in a similar fashion, but the key result here was the quantification of the natural hyperextension posture of the spine used to balance the bucket of potatoes. These results provide insight into muscle activation patterns in dynamic settings, especially (load) carrying biomechanics, and have implications in industrial settings that require workers to carry loads in front of their bodies.

Reaching Kinematics to Measure Motor Changes After Mental Practice in Stroke

Objective: To examine mental practice (MP) efficacy using a new kinematics reaching model. Method: This was a prepost, case series conducted at an outpatient rehabilitation hospital of 5 patients who experienced stroke >1 year before study entry (3 males; mean age = 52.6 ± 15.4 years [range, 38–76 years]; mean time since stroke = 51.2 months [range, 13–126 months]) exhibiting upper limb hemiparesis on their dominant sides. Participants received 30-minute therapy sessions emphasizing activities of daily living (ADLs) using their affected arms, which occurred 2 days/week for 6 weeks. After therapy, participants received 30-minute MP sessions requiring MP of the ADLs. The main outcome measure was 3-D Motion Analysis (kinematics), in which patients performed 2 functional reaching tasks consisting of reaching and grasping a plastic cylinder positioned at either elbow height (reach out) or shoulder height (reach up). Dependent variables included horizontal reaching distance, hand velocity, elbow range of motion, and shoulder range of motion. Results: Prior to intervention, the mean horizontal reaching distance was 8.3 ± 1.7 cm and 10.9 ± 2.2 cm for the reach-up and reach-out tasks, respectively. Upon completion of the intervention, ability to reach up significantly improved to 9.9 ± 1.6 cm (p <.001). Horizontal reach distance also improved during the reach-out task (11.7 ± 2.2 cm, p = .366). No statistically significant change was observed in linear hand velocity. Patients also exhibited greater shoulder flexion and elbow extension during both the posttest reach-up and posttest reach-out tasks. Discussion and Conclusion: Kinematics appears to offer a precise, objective way of quantifying MP-induced motor changes during ADL performance. MP appears to improve several aspects of affected arm reaching.

Musculoskeletal problems in Iranian hand-woven carpet industry: Guidelines for workstation design

Long hours of static work with awkward posture at traditionally designed looms can cause high prevalence of musculoskeletal disorders (MSDs) among carpet weavers. A comprehensive study was conducted in this industry with the objectives of determination of MSDs symptoms prevalence; identification of major factors associated with MSDs symptoms in carpet weaving occupation; and development of guidelines for weaving workstation design. In the present paper, this ergonomics study is presented. The study consisted of two phases. In the first phase, MSDs symptoms in nine Iranian provinces were surveyed by questionnaire among 1439 randomly selected weavers. Working posture and weaving workstations were ergonomically assessed as well. The results of this phase revealed that symptoms from the musculoskeletal system occured in high rate among weavers with the prevalence significantly higher than that of the general Iranian population ( P < 0.001 ). It was found that the majority of ergonomics shortcomings originated from ill-designed weaving workstation. Based on the findings, some general guidelines for workstation design were presented. In the second phase, considering the general guidelines, an adjustable workstation was designed and constructed. To develop quantitative guidlenes for optimizing workstation set-up, in the laboratory, nine sets of experimental conditions were tested, and working posture and weavers’ perceptions were measured. The results of this lab work showed that working posture was acceptable for both the researchers and the weavers when the weaving height was adjusted 20 cm above the elbow height and a high seat with forward slope was used. By combining the results of the two phases, guidelines for weaving workstation design were presented. In this ergonomics-oriented workstation, loom is vertical. Seat, loom and weaving heights are adjustable. There is enough leg room under the loom. The seat with 10° forward slope is adjusted 15 cm above the popliteal height of the weaver. Weaving height is set at 20 cm above the elbow height. It is believed that the recommended workstation improves working posture and results in reduced postural stress on weavers’ bodies and, consequently, reduced prevalence of MSDs symptoms.