Effects of hand span size and right-left hand side on the piano playing performances: Exploration of the potential risk factors with regard to piano-related musculoskeletal disorders

This study used biomechanical techniques to objectively investigate the effects of the size of hand span and right/left hands on the kinematic and kinetic performances when playing the piano. Twenty pianists were recruited and assigned to two hand-size groups. The parameters of interest, such as ratio of maximal digit-to-digit abduction angle (RD-D_abd), range of motion (ROM) of finger and wrist flexion-extension (F/E), radial-ulnar deviation (R/U), and movement units of F/E of finger joints (MU_F/E), were measured while striking the piano keys. The fingertip force was also estimated by a kinetic model. The RD-D_abd was significantly larger for the small hand-span pianists when playing both chords and octaves. The ROM of wrist F/E was significantly larger for small hand-span pianists when playing chords. There was no significant difference in the fingertip force between two groups. However, the values for MU_F/E and fingertip force of the right hand were significantly larger than those of left hand. Pianists with a small hand-span should aware that they have higher exposure risks for hand injuries while playing the piano.Relevance to industry: Hand anthropometric issue might be one of potential risk factors which result in piano-related musculoskeletal disorders. This study provides preliminary evidence that can be used to aid in injury prevention and music education for pianists as well as to reconsider issues with regard to the piano design.     

Wrist discomfort levels for combined movements at constant force and repetition rate

Sixteen male subjects each performed a repetitive, downwards, non-prehensile wrist exertion task with the arm pronated, at a rate of 15 times per minute and with a force of 10N?±?1N in 49 combinations of flexion/extension and radial/ulnar deviation to 0%, 18%, 38% and 55% of the Range of Motion (ROM) for 5 min each. The dependent measure was discomfort measured on a 100 mm visual analogue scale and for most of the analyses these were standardized by using the min?-?max procedure of <citeref rid="b20">Gescheider (1988)</citeref>. These Standardised Discomfort Levels (SDLs) were fitted to mathematical equations from which iso-discomfort contours were derived relative to the percentages of flexion/extension and radial/ulnar-deviation ROM used. The lowest standardized discomfort was found for the neutral wrist posture, followed by 18% extension with neutral radial/ulmar deviation. The results reveal interesting features of the processes involved and provide useful avenues for further research.     

Isokinetic strength characteristics in wrist flexion and extension

A laboratory experiment was conducted to measure strength characteristics in dynamic (isokinetic) wrist flexion and extension. Twenty four college-age males exerted their maximum torque in both concentric flexion and extension at 60, 120, and 180°/s of angular velocity through a ±60° range of deviation from wrist neutral. Results show that velocity and motion direction significantly effected both peak torque as well as the postural displacement of peak torque. The value of peak torque decreased with an increase in velocity and the wrist angle at peak torque generally moved to a more deviated, flexed posture (from neutral) with increasing velocity as well. Peak torque for all velocity and motion-type conditions tested occurred in a flexed posture relative to neutral. It is anticipated that these results may be of use as biomechanically based considerations in the evaluation and design of upper extremity tasks involving wrist flexion/extension as well as to perhaps give insight into functional characteristics of the wrist. Finally, regression equations were developed to aid in the prediction of peak torque based upon task, individual and/or population parameters.

Relevance to industry

Results from this study should enhance the overall understanding of wrist functioning. Specifically, motion type, velocity of movement and wrist posture are important ergonomic design considerations. These results can also be used to modify existing biomechanical models that do not consider wrist variables.     

An evaluation of the ergonomics of three computer keyboards

The influence of keyboard design on hand position, typing productivity and keyboard preference was evaluated by comparing two segmented alternative designs with the linear standard keyboard. The FIXED alternative keyboard featured a split angle of 12 degrees and a moderate lateral inclination angle of 10 degrees. The adjustable OPEN alternative keyboard was used with a 15 degrees split setting, which resulted in a marked 42 degrees of demiboard lateral inclination. Sixteen typists, who completed 10 h of training on both alternative keyboards, were videotaped while typing set texts on all three keyboards. Forearm and wrist angles based on three-dimensional video analyses were significantly different (p<0.05) among the three designs tested. Both alternative keyboards placed the forearm and wrist closer to neutral positions than did the standard keyboard. While the OPEN keyboard reduced pronation, it simultaneously increased radial deviation. The FIXED keyboard kept the forearm in moderate pronation and the wrist closer to neutral. More time was spent in neutral and moderate ranges of wrist motion when subjects typed on the FIXED compared with the other two designs. With respect to the standard keyboard, typing productivity was reduced by 10% on the FIXED and 20% on the OPEN designs. No significant difference in preference was found between the standard and FIXED keyboards, both of which were preferred over the OPEN. It was concluded that, of the three keyboards evaluated, the FIXED design incorporated moderate changes to the standard keyboard. These changes promoted a more natural hand position while typing thereby reducing the potential for cumulative trauma disorders of the wrist. In addition, the FIXED design preserved a reasonable level of productivity and was well accepted by users.     

Biomechanical effects of wearing high-heeled shoes

A survey of 200 young women wearing high-heeled shoes indicated frequent complaints of leg and low back pain. Consequently, an empirical study examined the biomechanical effects of three heel heights (0, 4.5, and 8 cm), while standing stationary and while walking in five, healthy, young women. Four major biomechanical effects were observed. As heel heights increased, the trunk flexion angle decreased significantly. Similarly, tibialis anterior EMG, low back EMG and the vertical movement of the body center of mass increased significantly while walking with high-heeled shoes. Due to these added stresses, wearing of high heels should be avoided.

Relevance to industry

In addition to the normal physical job stresses, women workers may experience additional biomechanical stresses placed on them by fashion demands such as high heels. All these effects can significantly increase discomfort levels in those wearing high heels.     

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.     

Design and evaluation of a curved computer keyboard

Conventional, straight keyboards remain the most popular design among keyboards sold and used with personal computers despite the biomechanical benefits offered by alternative keyboard designs. Some typists indicate that the daunting medical device-like appearance of these alternative ‘ergonomic’ keyboards is the reason for not purchasing an alternative keyboard design. The purpose of this research was to create a new computer keyboard that promoted more neutral postures in the wrist while maintaining the approachability and typing performance of a straight keyboard. The design process created a curved alphanumeric keyboard, designed to reduce ulnar deviation, and a built-in, padded wrist-rest to reduce wrist extension. Typing performance, wrist postures and perceptions of fatigue when using the new curved keyboard were compared to those when using a straight keyboard design. The curved keyboard reduced ulnar deviation by 2.2° ± 0.7 (p < 0.01). Relative to the straight keyboard without a built-in wrist-rest, the prototype curved keyboard with the built-in padded wrist-rest reduced wrist extension by 6.3° ± 1.2 (p < 0.01). There were no differences in typing speed or accuracy between keyboards. Perceived fatigue ratings were significantly lower in the hands, forearms and shoulders with the curved keyboard. The new curved keyboard achieved its design goal of reducing discomfort and promoting more neutral wrist postures while not compromising users' preferences and typing performance.     

Wrist and forearm posture from typing on split and vertically inclined computer keyboards

A study was conducted on 90 experienced office workers to determine how commercially available alternative computer keyboards affected wrist and forearm posture. The alternative keyboards tested had the QWERTY layout of keys and were of three designs: split fixed angle, split adjustable angle, and vertically inclined (tilted or tented). When set up correctly, commercially available split keyboards reduced mean ulnar deviation of the right and left wrists from 12 degrees to within 5 degrees of a neutral position compared with a conventional keyboard. The finding that split keyboards place the wrist closer to a neutral posture in the radial/ulnar plane substantially reduces one occupational risk factor of work-related musculoskeletal disorders (WMSDs): ulnar deviation of the wrist. Applications of this research include commercially available computer keyboard designs that typists can use and ergonomists can recommend to their clients in order to minimize wrist ulnar deviation from typing.     

Effects of combined wrist deviation and forearm rotation on discomfort score

The aim of the study was to examine the pattern of the change in discomfort for combined wrist deviation and forearm rotation as joint angles increased away from neutral in a repetitive task. There were five levels of wrist deviation (neutral, 35% and 55% of the range of motion (ROM) in radial and ulnar deviation) and five levels of forearm rotation (neutral, 30% and 60% of the ROM in pronation and supination). Twenty-five participants performed a repetitive flexion task with a force of 10 N +/- 1 N at a frequency of 15 exertions per min, with replication after 1 week for six of the participants. A visual analogue scale was used for recording the discomfort scores. Repeated measures analysis of covariance with the Greenhouse-Geisser correction, where necessary, was used on transformed values of the discomfort scores. Grip test endurance time at 50% of maximum voluntary contraction was included as a covariate. Wrist deviation (p = 0.007) and forearm rotation (p = 0.001) were found to have significant effects. Interactions of the main factors were not significant and nor was the covariate. Quadratic regression equations were derived and were used to generate iso-discomfort contours, which show a useful area of low discomfort around the central neutral zone of wrist postures, but with steep increases in discomfort at the extreme combinations of wrist ulnar/radial deviation with forearm pronation/supination. Discomfort equations and contours, showing wrist and forearm postures, which are either acceptable or potentially injurious, are useful for the design of industrial tools, machine controls and workspaces. Reference to these can help to reduce the risk of musculoskeletal injury associated with the tasks or tools by avoiding poor postures with unacceptable deviations from neutral posture.     

An evaluation of arborist handsaws

A review of the scientific literature reveals little research on the ergonomics of handsaws and no literature on the specific challenges of arborist saws (saws for cutting and pruning living trees). This study was designed to provide some insight into the effects of saw design and height of sawing activity on the biomechanical response of the upper extremity. Eighteen participants performed a simple sawing task at three different heights using six different arborist handsaws. As they performed this task, the electromyographic activity of several muscle groups of the forearm (flexor and extensor digitorum), arm (biceps brachii long and short heads) and shoulder girdle (posterior deltoid, infraspinatus and latissimus dorsi) were sampled. Also gathered were the wrist postures in the radial/ulnar plane at the beginning and ending of the sawing stroke, the time to complete the sawing task and a subjective ranking of the six different saws. The results show an interesting mix of biomechanical and subjective responses that provide insight into handsaw design. First, there were tradeoffs among muscle groups as a function of work height. As work height increased the biceps muscles increased their activation levels (∼19%) while the posterior deltoid activity decreased (∼17%) with the higher location. The results also showed the benefits of a bent handle design (average 21% reduction in ulnar deviation). The subjective responses of the participants generally supported the productivity data, with the saws demonstrating the shortest task completion time also being the ones most highly ranked.

Relevance to Industry

Understanding the stresses placed on the upper extremity during sawing activities, and design features that can reduce these stresses, may help saw designers to create products that reduce the risk of injury in workers who use handsaws.     

A stress-strength interference model for predicting CTD probabilities

A model for predicting the incidence rate of carpal tunnel syndrome (CTS) for a given job, was developed using known biomechanical data, mechanical properties of human tendons and reliability engineering techniques to simplify the problem. In addition, time-dependent stress-strength interference theory was used to quantify the stress on the tendons during a job cycle, based on wrist position and grip strength and to estimate the tendon failure rate (or CTS incidence) for a given job. Higher failure probabilities were predicted for greater wrist deviations, for higher grasp forces, for females as compared to males, for wrist extension as compared to wrist flexion, and for two-fingered pinches as compared to four-fingered grasps. The predictions closely matched previously reported CTS incidence rates for a poultry thigh boning task.     

Effects of keyboard tray geometry on upper body posture and comfort

The effects of a downward-tilting (DT) keyboard tray on wrist posture, seated posture and self-assessed musculoskeletal discomfort were investigated in a field experiment. Thirty-eight professional office workers were studied. A pretest assessed how they typed using either a conventional keyboard on a desk or on an articulating keyboard tray, and with or without wrist rests. Workers were randomly allocated to a control (n = 15) or test group (n = 23) that used their existing keyboard in a DT system. A post-test was conducted 3 weeks later. Results showed no significant changes in wrist posture, seated posture or reports of musculoskeletal discomfort for the control group, and approximately 50% of typing wrist movements put the hand in a neutral zone. There were significant improvements in wrist posture, seated posture and upper body musculoskeletal discomfort for the test group using the DT system. Over 80% of typing wrist movements put the hand into a neutral zone with the DT arrangement. Reactions to using a conventional keyboard on a DT system were positive.     

Comparison of Infant Car Seat grip orientations and lift strategies

The rear-facing Infant Car Seat (ICS) is designed to meet federal requirements for transporting children less than 1 year old. Typical use includes transfer in and out of a vehicle, which is shown to be a difficult lift. Despite the frequency of this lift, manufacturers provide little guidance for users. Review of relevant literature suggested an ICS featuring an angled handle, promoting a neutral wrist posture, would increase grip stability and decrease lifting effort. Popular press suggested a foot-in-car stance for the ICS lift would do the same. An experiment was conducted in which wrist deviations from neutral posture were recorded along with lifting muscle activation levels (multiple flexor muscles and biceps brachii) and overall perceived exertion for straight versus a new bent handle design and conventional stance versus foot-in-car. Foot position was examined to test the recommendations in the popular press. Surprisingly, wrist deviation was not significantly affected by the new bent handle design (due to compensatory behavior with the straight handle) but was related to foot placement (p=0.04). Results revealed the bent handle to significantly reduce flexor activation compared with the straight handle (p=0.0003); however, the level of biceps activation increased. Biceps activation also significantly increased for foot-in-car stance (p=0.035) but not flexor activation. In general, the bent handle enabled the user to lift the ICS with a steadier grip and less effort.     

leanTAP: Lean tableau-based deduction

prove ((E, F), A, B, C, D) : - !, prove (E, [F A], B, C, D).prove ((E; F), A, B, C, D) : - !, prove (E, A, B, C, D), prove (F, A, B, C, D).prove (all(H, I), A, B, C, D) : - !, + length (C, D), copy_term ((H, I, C), (G, F, C)), append (A, [all (H, I)], E), prove(F, E, B, [G C], D).prove (A,_, [C D] ,_, _) :-((A= – (B); – (A) = B)) -> (unify(B, C); prove (A, [], D,_,_)).prove (A, [E F], B, C, D): - prove (E, F, [AB], C,D).implements a first-order theorem prover based on free-variable semantic tableaux. It is complete, sound, and efficient.     

Occupational biomechanics—a basis for workplace design to prevent musculoskeletal injuries

This paper proposes that occupational biomechanics is the growing discipline necessary to improve workplace design. As such it focuses on the rapidly expanding body of biomechanics knowledge on workplace situations that cause musculoskeletal injuries and disabilities. Several new methods for evaluating the bio-mechanical consequences of workplace designs are reviewed, including computerized biomechanical models of workers and the use of general design guidelines to improve workplace design. Examples of how workplaces can be redesigned to reduce musculoskeletal stresses on the lower back, wrist and shoulder are provided, to illustrate how occupational biomechanics is being applied in several different industries to prevent musculoskeletal injuries and disabilities.     

Different computer tasks affect the exposure of the upper extremity to biomechanical risk factors

In order to determine differences in biomechanical risk factors across computer tasks, a repeated measures laboratory experiment was completed with 30 touch-typing adults (15 females and 15 males). The participants completed five different computer tasks: typing text, completing an html-based form with text fields, editing text within a document, sorting and resizing objects in a graphics task and browsing and navigating a series of intranet web pages. Electrogoniometers and inclinometers measured wrist and upper arm postures, surface electromyography measured muscle activity of four forearm muscles and three shoulder muscles and a force platform under the keyboard and force-sensing computer mouse measured applied forces. Keyboard-intensive tasks were associated with less neutral wrist postures, larger wrist velocities and accelerations and larger dynamic forearm muscle activity. Mouse-intensive tasks (graphics and intranet web page browsing) were associated with less neutral shoulder postures and less variability in forearm muscle activity. Tasks containing a mixture of mouse and keyboard use (form completion and text editing) were associated with higher shoulder muscle activity, larger range of motion and larger velocities and accelerations of the upper arm. Comparing different types of computer work demonstrates that mouse use is prevalent in most computer tasks and is associated with more constrained and non-neutral postures of the wrist and shoulder compared to keyboarding.     

Different computer tasks affect the exposure of the upper extremity to biomechanical risk factors

In order to determine differences in biomechanical risk factors across computer tasks, a repeated measures laboratory experiment was completed with 30 touch-typing adults (15 females and 15 males). The participants completed five different computer tasks: typing text, completing an html-based form with text fields, editing text within a document, sorting and resizing objects in a graphics task and browsing and navigating a series of intranet web pages. Electrogoniometers and inclinometers measured wrist and upper arm postures, surface electromyography measured muscle activity of four forearm muscles and three shoulder muscles and a force platform under the keyboard and force-sensing computer mouse measured applied forces. Keyboard-intensive tasks were associated with less neutral wrist postures, larger wrist velocities and accelerations and larger dynamic forearm muscle activity. Mouse-intensive tasks (graphics and intranet web page browsing) were associated with less neutral shoulder postures and less variability in forearm muscle activity. Tasks containing a mixture of mouse and keyboard use (form completion and text editing) were associated with higher shoulder muscle activity, larger range of motion and larger velocities and accelerations of the upper arm. Comparing different types of computer work demonstrates that mouse use is prevalent in most computer tasks and is associated with more constrained and non-neutral postures of the wrist and shoulder compared to keyboarding.     

基于Voronoi图的障碍不确定数据的聚类算法

数据采集过程中普遍存在不确定性,并且在现实地理空间中,不确定数据之间可能存在障碍物间隔。为解决障碍空间中不确定数据的聚类问题,提出APPGCUO算法,该算法包括三个过程:在障碍物约束下采用R树节点最小最大值方法提出的RPT-OUCure算法,用以生成局部最优解,提高生成局部最优解的效率;继而利用近似骨架的理论提出GIABO算法,以局部最优解生成有效初始解,避免划分聚类算法中任意初始解的不足;最后结合Voronoi图的特性提出VPT-KMediods算法,减少不确定数据的积分运算量。实验结果表明,APPGCUO算法具有较高的聚类效率和质量。     

The effects of container design and stair climbing on maximal acceptable lift weight, wrist posture, psychophysical, and physiological responses in wafer-handling tasks

Despite the high level of automation in semiconductor manufacturing processes, many manual operations are still involved in the workplace. Due to inadequate human–machine interface design, stairs are frequently used to help operators perform wafer-handling tasks. This study was designed to evaluate the effects of climbing stairs and carrying wafer containers (pods) on psychophysical responses (maximal acceptable weight of lift—MAWL, and ratings of perceived exertion—RPE), physiological responses (oxygen consumption—VO₂, and heart rate—HR), and wrist posture (ulnar and radial deviations). Each of 12 subjects (six males and six females) performed six sessions (3 climbing stairs×2 pods types). The results indicate that climbing stairs had a significant influence on MAWL and VO₂ (p<0.01). The type of pod effect on wrist posture was significant (p<0.01). Gender effect differences on MAWL, VO₂ and wrist posture were also significant (p<0.05). Job design implications are discussed.