Maneuverability and usability analysis of three knee-extension propelled wheelchairs.

PURPOSE: The purpose of this study was to evaluate the maneuverability and usability of three knee-extension propelled wheelchairs. METHOD: The maneuverability of the knee-extension propelled wheelchairs was determined in a controlled test representing five standard wheelchair activities. The usability of the wheelchairs was evaluated in a field test with elderly residents of an extended care facility in Salt Lake City. RESULTS: The results indicate that the wheelchair designs using a swinging (four-bar linkage) or sliding belt mechanism are preferred to a sliding plate design. CONCLUSIONS: The use of knee-extension propelled wheelchairs is a feasible alternative to hand propelled wheelchairs. Further development and research is needed to address power requirements, maneuverability, and entrance/egress from the chairs.

Biomechanical simulation of manual lifting using spacetime optimization.

Previous optimization techniques for the prediction of lifting motion patterns often require a change in either the number of variables or the order of the mathematical functions used to express the angular displacement of selected joints in response to change in variant conditions. The resolution of predicted results can also be seriously constrained by the number of variables used. These restrictions may often limit the applicability of these methodologies. In this paper, we proposed a new methodology for generating the optimum motion patterns for para-sagittal lifting tasks. A detailed description of this methodology is introduced. An example of an analysis using this methodology is presented. The computer program generated lifting motion patterns with a reduction of the overall objective function values. The actual versus predicted lifting motion patterns are compared. Using this method, constraints can be added anywhere within the lifting cycle without the need of rewriting the whole program. These features provide for a more flexible and efficient prediction of the lifting motion.

Ergonomic risk exposure and upper-extremity cumulative trauma disorders in a maquiladora medical devices manufacturing plant.

Workers at a Nogales, Mexico, maquiladora plant that assembles medical devices were studied to determine the prevalence of upper-extremity cumulative trauma disorders (CTD). Subjects included production workers employed 6 months or longer; of the 148 eligible workers, 145 (98%) participated. Subjects had a mean age of 24.6 years (SD = 5.2; range, 17 to 45) and the mean length of employment was 3.5 years (SD = 2.5; range, 0.5 to 14). Job tasks were videotaped and analyzed for ergonomic risk factors, using pre-defined criteria. All jobs performed by study subjects were found to involve one or more ergonomic risk factors associated with the development of CTD. A CTD questionnaire and screening physical examination format, similar to that used by the National Institute of Occupational Safety and Health (NIOSH) in a chicken processing plant study, were administered. Period prevalence of CTD within the previous year, as reported on the questionnaire, was 28%. Prevalence of CTD was 17%, using data from the screening physical examination. Point prevalence (current pain data from the questionnaire plus positive symptoms on the screening physical examination) was 15%. CTD was reported more frequently in women than men (46% and 25%, respectively; P < 0.05) and in subjects who had worked at the plant less than one year (50%; P < 0.05). Workforce turnover (3% monthly) may have resulted in those affected by CTD leaving employment, reducing the apparent CTD rate in experienced workers.

Testing and evaluation of a hip extensor tricycle for children with cerebral palsy.

The design and testing of a modified tricycle (hip extensor tricycle) designed to isolate and exercise the hip extensor muscles in children with cerebral palsy is presented. Initial laboratory tests involved stability evaluation and EMG studies of two normal children. Field evaluation involved five children diagnosed with cerebral palsy who were given hip extensor tricycles for home use during an 8-week test period. The hip extensor strength and gait pattern of the subjects were recorded at 2-week intervals. The clinical tests indicated that the hip extensor tricycle was more stable, and resulted in more hip extensor muscle activity, than the traditional therapeutic/exercise tricycle. A panel of experts judged that the gait patterns of four of the five subjects improved during the course of the study. Parent evaluations indicated that the use of the hip extensor tricycle improved the subjects' physical condition, coordination, sense of accomplishment, and self-esteem.

Measurement of creep strain of flexor tendons during low-force high-frequency activities such as computer keyboard use.

The aim of this study was to measure tendon strain during low-force, high-frequency activities such as computer keyboard use. Prior to creep strain testing an estimate of flexor tendon force during keyboard use was made. Tendon force was measured indirectly by comparing electromyographic activity of the flexor and extensor digitorum muscles in five human volunteers for various hand activities. Results of the electromyographic study showed that flexor tendon forces during keyboard use may be as high as 60 N. Sixty eight flexor digitorum tendons from 17 fresh-frozen cadaver hands were used for the creep strain tests. Three loading conditions (static, 1 Hz cyclic, (1/4) Hz cyclic) and four load levels (10, 20, 50, 100 N) were used. Results of the creep study showed that for a flexor tendon force of 60 N the total strain of the tendon would be approximately 1.8%. This does not appear to be enough strain to cause permanent damage to the tendon according to current cumulative strain models. RELEVANCE: Recent studies have shown an increase in hand and wrist tendinitis among computer users. At the present time the aetiology is unknown, but risk factors commonly associated with tendinitis are hand forces, wrist postures, and frequency of finger movements. This research looks at tendon creep due to repeated force as a possible aetiology.

Effect of mailbag design on musculoskeletal fatigue and metabolic load.

The need for an alternative mailbag to the conventional U.S. postal mailbag, which hangs at the side over one shoulder, was investigated. Based on the results of a pilot study, two types of alternative mailbags, both including waist support and one that splits the load into two parts, are recommended. The metabolic energy requirement and lateral trunk muscle fatigue resulting from the use of the alternative mailbags were compared with those resulting from the conventional U.S. postal mailbag. The alternative mailbags resulted in no significant change in metabolic load. Both alternative mailbags resulted in significantly less lateral trunk muscle fatigue. It is proposed that this reduction in fatigue would result in reduced musculoskeletal stress and reduced potential for back injury.

Chronic, recurrent low back pain. A methodology for analyzing fitness for duty and managing risk under the Americans with Disabilities Act.

Chronic, recurrent low back pain, although one of the most commonly encountered medical conditions in the workplace, is one of the most difficult to manage. With the passage of the Americans with Disabilities Act, the proper management of the worker with recurrent low back pain poses an even greater challenge. We propose an interdisciplinary methodology to evaluate the worker at high medical risk of recurrent low back pain and determine the potential ergonomic risks of essential function tasks in material-handling work. The proposal considers the ethical and legal liabilities of risk assessment and fitness for duty evaluation that physicians, ergonomists, attorneys, and ultimately business managers and supervisors experience in balancing the societal interests represented by the Americans with Disabilities Act.

Investigation of low-force high-frequency activities on the development of carpal-tunnel syndrome.

The objective of this study was to determine the effects of repetitive motion on the flexor tendons and synovium in the carpal tunnel. One possible mechanism of tendon damage is fraying of the tendons as they slide past each other in the carpal tunnel. Increases in tendon friction were measured in human cadaver arms. The flexor tendons were loaded using pneumatic cylinders while load cells were used to measure tendon force both distal and proximal to the carpal tunnel. Results showed that tendon force distal to the carpal tunnel decreased by over 10% after 6 h, while tendon force proximal to the carpal tunnel remained constant. Two rhesus monkeys were used to further study the effects of repetitive motion. One arm of each animal was subjected to 729000 repetitive cycles over a 3-week period. Results of the animal study showed that highly repetitive motions encountered over a relatively short period of time had little effect on the tissue in and around the carpal tunnel.

Evaluation of a device to exercise hip extensor muscles in children with cerebral palsy: a clinical and field study.

This research includes the effectiveness of a tricycle (hip extensor tricycle) designed to isolate and exercise the hip extensor muscles in children with cerebral palsy. Five children diagnosed with cerebral palsy were given hip extensor tricycles for home use during an 8-week test period. The hip extensor strength and gait pattern of the subjects were recorded at 2-week intervals. Additional recorded information included the time and duration of subject use and a parent evaluation that noted subjective physical and psychological improvements. A panel of experts judged that the gait patterns of four subjects improved during the course of the study. There was an assignable cause for the lack of improvement in the fifth subject. The results of the strength testing were found to be inconclusive. The subjects used the device on a regular basis and enjoyed doing so. Parent evaluations indicated that the use of the hip extensor tricycle improved the subjects' physical condition, coordination, sense of accomplishment, and self esteem. It is recommended that future research implement a longer test period along with improved hip extensor strength measurement methods and focus on improvements in evaluation of gait and physical condition.

Evaluation of the hip-extensor tricycle in improving gait in children with cerebral palsy.

Weakness of the hip extensor muscles contributes to the walking impairment of children with cerebral palsy, but it is difficult to strengthen these muscles. This study demonstrates greater activation of the hip extensor muscles when using a tricycle developed for this purpose than when using a traditional tricycle. The hip-extensor tricycle was also found to be more stable than a traditional tricycle. A 10-week field trial of the hip-extensor tricycle showed that visually analysed gait improved, but hip extensor strength did not. However, children used and enjoyed the tricycle, and parental reports were positive. This tricycle could be used to supplement other means of improving gait in children with CP.

Supermarket checker motions and cumulative trauma risk.

The relationship between specific motions and symptoms consistent with upper extremity cumulative trauma disorders (UECTDs) was investigated in 50 supermarket checkers. Each completed a questionnaire concerning UECTD symptoms; four composite symptom indices were derived: any arm symptoms, hand-wrist-lower arm (S-DIST), upper arm, and symptoms specifically associated with carpal tunnel syndrome (S-SPC). Each participant was videotaped on at least two occasions while performing checking work. Analysis of these tapes assigned each subject a composite motion index for each of the following motions: wrist flexion, wrist extension, body (lumbar) flexion, pronation, grip type, and tendency to lift objects. "Positive" symptom status was defined by a score in the upper quartile for the symptom index. Relationships between an individual's motion indices and symptom indices were analyzed by determining the percent of subjects "positive" for symptoms in each quartile of motion index, by rank correlation, and by regression of symptom scores on principal components of motions. Trends toward relationship of wrist flexion and extension, lumbar flexion, and pronation with S-DIST and S-SPC were noted. Principal components regression confirmed that extension and flexion were related to these two symptom outcomes. This study suggests that postural loading can be determined on an individual basis in a meaningful fashion and that interventions that decrease such loading may be beneficial. It supports the role of certain repetitive motions as causes of UECTD symptoms.

Work-related symptoms and checkstand configuration: an experimental study.

Supermarket checkers are known to be at risk of upper-extremity cumulative trauma disorders. Forty-two experienced checkers checked a standard "market basket" of items on an experimental checkstand. The counter height could be adjusted (high = 35.5, low = 31.5 inches), and the pre-scan queuing area length (between conveyor belt and laser scanner) could be set to "near" or "far" lengths. Each subject scanned under the high-near, high-far, low-near, and low-far conditions in random order. Seven ordinal symptom scales were used to describe comfort. Analysis showed that both counter height and queuing length had significant effects on symptoms. Furthermore, the height of the subject affected the degree and direction of the impact of the checkstand configuration differences. The study suggests that optimization of design may be experimentally evaluated, that modification of postural as well as frequency loading may be beneficial, and that adjustability for the individual may be advisable.

Design of a device to exercise hip extensor muscles in children with cerebral palsy.

Children with cerebral palsy (CP) often have weak hip extensor muscles and gait-related difficulties. Current therapeutic techniques do not provide sufficient exercise for this muscle group. In addition to calisthenics, therapists use a traditional tricycle to strengthen leg muscles, yet the mechanics of traditional tricycles are not effective in exercising hip extensor muscles. A new therapeutic tricycle was designed specifically to exercise the hip extensor muscles, and tests compared the traditional tricycle to the new hip extensor tricycle in effectiveness of promoting hip extensor activity in two subjects without CP. The tests demonstrated that the hip extensor tricycle was more effective in promoting hip extensor activity. Tests are underway to investigate the effect of the hip extensor tricycle in improving hip extensor strength and gait in patients with cerebral palsy. This paper describes the design of the hip extensor tricycle and a preliminary investigation of its effectiveness.

The ergonomic challenge of repetitive motion with varying ergonomic stresses. Characterizing supermarket checking work.

Many jobs leading to a risk of cumulative trauma do not have highly stereotyped motions. This study developed and employed a novel method of ergonomic characterization to describe quantitatively the actions associated with grocery checking. Fifty workers were videotaped for three 15-minute segments each. Eight object types were selected to represent the variety of items in a supermarket. Nine types of motion were coded for each of the eight objects for 10 replications for each subject. The motions coded were: grip type (power versus pinch), wrist flexion, wrist extension, radial deviation, ulnar deviation, supination, pronation, body (lumbar) flexion, and drag versus lift. The results were then weighted according to relative frequency of the object type. In this manner, an ergonomic risk index can be assigned to each specific object type. This method permits identification of objects presenting the greatest risk. It also allows specificity of preventive interventions (object redesign, work practice change) as well as providing a quantitative measure to evaluate work station redesign. Furthermore, it has the potential of quantitatively describing the risk of each individual worker.

Tracking Decrement as a Result of Grip Holding Endurance.

This study explores the feasibility of using the static strength and endurance relationships suggested by Rohmert in 1960 to predict pursuit tracking performance, Ten male subjects are tested on a pursuit rotor before and after being subjected to specific levels of loading on a grip holding device. The loading corresponded to specific levels of each subject's maximum endurance as determined from Rohmert's strength and endurance equation. The hypotheses are: (a) predetermined schedules of strength expenditure cause a systematic decrement in tracking efficiency; and (b) the process of recovering efficiency is dependent upon the expenditure schedules. Resulting data support these hypotheses, suggesting that tracking efficiency can be reliably predicted using some of the strength and endurance relationships postulated by Rohmert.