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Abstract

Static biomechanical modeling has revealed that human reaching and object movement capabilities are dependent on both torso and upper extremity muscle strengths, and the ability to maintain balance throughout the movement. This paper describes data and biomechanical models that can be used to understand the dynamic motions of people with and without thoracic level spinal cord injuries (SCIs) while moving objects around in their environments. This paper also discusses how data gathered in the Human Motion Simulation (HUMOSIM) Laboratory from volunteer subjects performing various seated tasks are used in multi-joint inverse biomechanical models to predict both shoulder moments and body center of pressure locations. The results demonstrate that when symptomatic control subjects moved a box from a small table in front of them to a shoulder-high shelf, it was performed in a smooth fashion that could be well modeled and understood with the use of sequential static biomechanical models. The motions of those subjects with thoracic and high lumbar level SCIs, however, contained an additional dynamic component. The dynamic component revealed that healthy, active SCI subjects were quite capable of extending the distance over which they can move objects to rigid shelves by using a ballistic motion technique. This dynamic motion allows them to move objects to shelves located over twice the distance predicted by static models of such motions, but also raises questions of safety due to failing forward if the object being moved does not land securely on the shelf. These types of motions also are shown to cause much higher (by about 30%,) shoulder moments, thus raising the risk of injury to shoulder tissues in people with SCIs.

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... This definition is common in the standing literature (as will be discussed in the next sections) and is making its way into the limited body of seated balance literature as well (Seelen, Potten, Drukker, Reulen, & Pons, 1998;Campbell et al., 2001;Chaffin, Woolley, Dickerson, & Parkinson, 2004). ...
... Additionally, the seat itself affects stability since a seatback and/or side-bolsters limit excursion rearward and laterally. When not encumbered by the seat, Chaffin et al. (2004; hypothesized that the seated base of support was restricted laterally by the location of the ischial tuberosities (IT) and rearward by the coccyx. Pelvis geometry from Reynolds et al. (1981) can be used to calculate an IT breadth that is the hypothesized functional stability limit for seated near-lateral reaches. ...
... Detailed information about the data collection and processing procedures is available in Chaffin and Woolley (2001) and Chaffin et al. (2004). A brief description of relevant equipment and procedures is given below. ...
Thesis
Seated reach capability is limited by the strength, range of motion, and balance capabilities of the individual. In forward reaches people are able to maintain balance by generating forces and torques at their hips, supporting themselves over their legs. In contrast, lateral reaches, particularly those in which torso motion is required, are frequently limited by balance. A model-based study and two experiments involving human participants investigated the effect of task characteristics (motion duration, torso recruitment, and hand load) on the differences in static and dynamic analyses and the magnitude of the center of pressure excursion. The results indicate that static, terminal posture analysis is sufficient for evaluation of most seated tasks. An additional experiment used center of pressure excursion measurement to quantify the balance-maintenance capability of thirty-eight adults ranging in age from 21 to 74 years. While the excursion capability decreased with age when a handle was not used, the use of a handle by the contralateral hand allowed older participants to produce lateral excursions similar to those of the younger participants. Three examples of how the results of this dissertation can be applied are presented. The first demonstrates how motion and postural prediction can be affected by integration of balance considerations. In the second, balance prediction and the capability estimates are used in the design of a vehicle environment. The third is an evaluation of the forward-reaching motions and strategies of people with spinal cord injury.
... The researchers hypothesized that they did this so that they could ease into their limit and not lose their balance. Seelen et al. (1998) and Chaffin et al. (2004), found that people with a thoracic-level spinal cord injury had a reduced capacity for moving their center of pressure, which translated into a reduced reach capability. Kerr and Eng (2002) demonstrated the repeatability of this type of measure-an essential attribute for clinical and design purposes. ...
... Additionally, the seat itself affects stability since a seat-back and/or side-bolsters limit excursion rearward and laterally. Chaffin and Woolley (2001) and Chaffin et al. (2004) hypothesized that the seated base of support was restricted, when not encumbered by the seat, laterally by the location of the ischial tuberosities (IT) and rearward by the coccyx. Pelvis geometry from Reynolds et al. (1981) can be used to calculate an IT breadth that is the hypothesized functional stability limit for seated near-lateral reaches. ...
... Seated, forward-reaching tasks are not addressed in this paper since the legs provide support as the CoP shifts forward. The net result is that forward reaches are more likely to be limited by upper-body strength or range of motion than balance (Chaffin et al., 2004;Curtis et al., 1995;Dean et al., 1999a,b). Forward-reaching tasks can be balance-limited for some populations, however (e.g., those with spinal cord injury) (Chaffin et al., 2004;Seelen et al., 1998). ...
Article
Full-text available
Seated center of pressure excursion capability can be used for patient evaluation in a clinical setting and in universal design. A quantification of excursion capability across age and anthropometry has not been previously reported, although some research suggests that the ischial tuberosities are the support structure limiting the excursion. Thirty-eight neurologically healthy adults ranging in age from 21 to 74 years and including 12 obese persons performed a series of 6 lateral-reaching tasks. Participants sat on a platform such that their feet did not touch the ground, leaving their legs free to provide counterbalancing support. Data recorded from a force plate under the platform allowed calculation of the center of pressure throughout the trial and the maximum excursion for each condition was recorded. The average excursion capability for the healthy, experimental population was 148 mm or 37% of seated hip breadth. Taller participants had larger maximum excursions, on average, than shorter participants, and older participants had smaller excursions than younger participants. The greater trochanter of the femur-rather than the ischial tuberosities-appears to be the primary support structure limiting center of pressure excursion in lateral, balance-limited reaches without contralateral support. These measures and concepts can be used for design, accommodation, and clinically for patient assessment.
... Compression force and moment on L4/L5 Three Dimensional Static Strength Prediction Program (3DSSPP) software is one of the most widely used digital human modelling for biomechanical analysis during manual handling tasks. For example, it has been utilised in the automotive industry, patient transport and ability to move objects by people with and without spinal cord injury (Mazloumi et al. 2012;Waters et al. 2012;Chaffin et al. 2004). The input data in 3DSSPP include factors such as sex, height, weight, hand-applied force, body dimensions, and the posture of the participants in standing, sitting, stopping, squatting, and pulling/pushing activities. ...
Article
The purpose of study was to determine the biomechanical, physiological, and subjective effect of a Passive Exoskeleton device (called Ergo-Vest) among 20 waste collectors in the working environment. Compression force and moment on L4/L5 related to 400 critical postures of the participants were estimated using the 3DSSPP software. The heart rate and energy expenditure are measured as the physiological strain using the Polar RS400 Heart Rate Monitor. Borg scale perceived exertion, system usability scale, and ergonomic design indicators of the device were collected as the subjective parameters. Compression force and moment on L4/L5 disc were decreased when the Ergo-Vest was utilised. There was no significant difference in energy expenditure and heart rate with and without the device. The workers' perceived physical exertion was decreased while using the Ergo-Vest. From the perspective of end users, the usability and ergonomic design features of the Ergo-Vest was acceptable. Practitioner summary: The prevalence of musculoskeletal disorders is high among the Iranian waste collectors. To mitigate this occupational problem, the effect of a passive exoskeleton for lower-back support (Ergo-Vest) was investigated on the workers' spine loading, physiological parameters, and perceived physical exertion. The result shows spine force reduction and lower subjective responses.
... Measures of COP or COM were used to assess balance during all four taskssitting, [45][46][47][48] standing, 17,49 walking 44 and transfers. 50 EMG was utilized to evaluate muscle activity during sitting 50-52 and standing. ...
Article
Context Comprehensive balance measures with high clinical utility and sound psychometric properties are needed to inform the rehabilitation of individuals with spinal cord injury (SCI). Objective To identify the balance measures used in the SCI population, and to evaluate their clinical utility, psychometric properties and comprehensiveness. Methods Medline, PubMed, Embase, Scopus, Web of Science, and the Allied and Complementary Medicine Database were searched from the earliest record to October 19/16. Two researchers independently screened abstracts for articles including a balance measure and adults with SCI. Extracted data included participant characteristics and descriptions of balance measures. Quality was evaluated by considering study design, sampling method and adequacy of description of research participants. Clinical utility of all balance measures was evaluated. Comprehensiveness was evaluated using the modified Systems Framework for Postural Control. Results 2820 abstracts were returned and 127 articles included. Thirty-one balance measures were identified; 11 evaluated a biomechanical construct and 20 were balance scales. All balance scales had high clinical utility. The Berg Balance Scale and Functional Reach Test were valid and reliable, while the mini-BESTest was the most comprehensive. Conclusion No single measure had high clinical utility, strong psychometric properties and comprehensiveness. The mini-BESTest and/or Activity-based Balance Level Evaluation may fill this gap with further testing of their psychometric properties.
... Measures of COP or COM were used to assess balance during all four taskssitting, [45][46][47][48] standing, 17,49 walking 44 and transfers. 50 EMG was utilized to evaluate muscle activity during sitting 50-52 and standing. ...
... Measures of COP or COM were used to assess balance during all four taskssitting, [45][46][47][48] standing, 17,49 walking 44 and transfers. 50 EMG was utilized to evaluate muscle activity during sitting 50-52 and standing. ...
Article
Context/Objective The study objectives were to evaluate the test-retest reliability, convergent validity, and discriminative validity of the Activities-specific Balance Confidence (ABC) scale in individuals with incomplete spinal cord injury (iSCI). Design Prospective, cross-sectional study. Setting Laboratory. Participants Twenty-six community-dwelling individuals with chronic iSCI (20 males, 59.7 + 18.9 years old) and 26 age- and sex-matched able-bodied (AB) individuals participated. Interventions None. Outcome Measures Measures of balance and gait were collected over two days. Clinical measures included the ABC scale, Mini-Balance Evaluation System’s Test, 10-meter Walk Test, SCI Functional Ambulation Profile, manual muscle testing of lower extremity muscles, and measures of lower extremity proprioception and cutaneous pressure sensitivity. Biomechanical measures included the velocity and sway area of centre of pressure (COP) movement during quiet standing. Results The ABC scale demonstrated high test-retest reliability (intraclass correlation coefficient = 0.93) among participants with iSCI. The minimal detectable change was 14.87%. ABC scale scores correlated with performance on all clinical measures (ρ=0.60-0.80, P<0.01), with the exception of proprioception and cutaneous pressure sensitivity (P=0.20–0.70), demonstrating convergent validity. ABC scale scores also correlated with overall COP velocity (ρ=-0.69, P<0.001) and COP velocity in the anterior-posterior direction (ρ=-0.71, P<0.001). Participants with iSCI scored significantly lower on the ABC scale than the AB participants (P<0.001), and the area under the receiver operating characteristic curve was 0.95, demonstrating discriminative validity. Conclusion The ABC scale is a reliable and valid measure of balance confidence in community-dwelling, ambulatory individuals with chronic iSCI.
... Yet the motions associated with tasks that require persons to brace themselves, reach or look into confined areas, or exert unusual forces are not well modeled. More specifically, the compensatory type of motions often used by people with back or other musculoskeletal impairments or by people working close to their physical capacities are not predicted well (Chaffin, Woolley, Dickerson, & Parkinson, 2004;Larivière, Gagnon, & Loisel, 2000;Lindbeck & Kjellberg, 2001). ...
Article
Full-text available
Digital human modeling (DHM) technology offers human factors/ergonomics specialists the promise of an efficient means to simulate a large variety of ergonomics issues early in the design of products and manufacturing workstations. It rests on the premise that most products and manufacturing work settings are specified and designed by using sophisticated computer-aided design (CAD) systems. By integrating a computer-rendered avatar (or hominoid) and the CAD-rendered graphics of a prospective workspace, one can simulate issues regarding who can fit, reach, see, manipulate, and so on. In this chapter, I briefly describe the development of various DHM methods to improve CAD systems. Past concerns about early DHM methods are discussed, followed by a description of some of the recent major developments that represent attempts by various groups to address the early concerns. In this latter context, methods are described for using anthropometric databases to ensure that population shape and size are well modeled. Efforts to integrate various biomechanical models into DHM systems also are described, followed by a section that outlines how human motions are being modeled in different DHM systems. In a final section, I discuss recent work to merge cognitive models of human performance with DHM models of manual tasks. Much has been accomplished in recent years to make digital human models more useful and effective in resolving ergonomics issues during the design of products and manufacturing processes, but much remains to be learned and applied in this rapidly evolving aspect of ergonomics.
... Detailed information about the data collection and processing procedures is available in Chaffin et al. (2004) and Chaffin (2001). Only a portion of the data collected is presented in this paper. ...
Article
Full-text available
In many task analyses using digital human figure models, only the terminal or apparently most stressful posture is analyzed. For reaches from a seated position, this is generally the posture with the hand or hands at the target. However, depending on the characteristics of the tasks and the people performing them, analyzing only the terminal posture could be misleading. This possibility was examined using data from a study of the reaching behavior of people with spinal cord injury. Participants performed two-handed forward reaching tasks. These reaches were to three targets located in the sagittal plane. The terminal postures did not differ significantly between those with spinal cord injury and those without. However, motion analysis demonstrated that they employed distinct strategies, particularly in the initial phase of motion. The location of the center of pressure throughout each motion was calculated using inverse dynamics and was found to be a good indicator of the strategies employed and the behavior differences between the two groups.
Article
Loss of hand function severely impacts the independence of people with spinal cord injuries (SCI) between C5 and C7. To achieve limited grasps or strengthen grip around small objects, these individuals commonly employ a compensatory technique to passively induce finger flexion by extending their wrist. Passive body-powered devices using wrist-driven actuation have been developed to assist this function, in addition to advancements in active robotic devices aimed at finger articulation for dexterous manipulation. Nevertheless, neither passive nor active devices see wide adoption and retention in the long-term. Here we present an unconventional system for combining aspects of both passive and active actuation and show that actively modulating the relationship between passive wrist and finger movement can impact both performance and kinematic metrics of upper body compensation. This study comprises six unique case studies of individuals with C5-6 SCI because morphology and response can vary widely across this population. While only some individuals’ performance improved with the shared system over passive-only operation, all six participants stated that they preferred the shared system, regarding added motorization with a sense of trust and embodiment. This outcome motivates the ongoing study of how motors can alter body kinematics to augment body-power without replacing it.
Conference Paper
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The process of scientifically developing selection screening or test batteries for jobs that require high physical demands and specific human characteristics or capabilities has received increasing attention globally over the past decade. ERGOnomics TECHnologies (ERGOTECH) have been responsible for the development of test protocols to collect data for functional body strength including lifting and carrying strength, hand and finger strength as well as neck strength on representative samples of the South African National Defence Force (SANDF) population. The implication of the gender differences in functional body strength is that tasks must either be designed to be gender independent or a specific selection process based on physical demands of the job must be implemented. These data together with scientific processes including the update of physical demands for post profiles, the determination of user limitations and the heaviest of the physical task demands are currently being used in two domains in order to provide scientifically based selection criteria and equipment evaluation tools for posts within the SANDF. Firstly this method has been used in the development of a selection criteria test battery for armour crews. Secondly the results are being used to develop biomechanical models representative of the SANDF population in terms of biomechanics characteristics. These models are to be used in the evaluation of tasks required by specific post profiles as well as the evaluation of equipment prior to field trials in order to access safety and accommodation of the end user population. The paper will present the methods for all three research focus areas including the collection of the strength data, the development of the selection criteria test battery as well as the biomechanical modelling.
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In this thesis we are interested in the definition of the human models for their integration in the working situation definition during the design phases of industrial systems. Various modes of interventions of the man (normal, damaged, maintenance, breakdown service, etc.) and all aspects of its intervention (ergonomics, safety, respect of the standards, etc.) are considered. Within these frameworks, we consider and classify the various human models in the working situations by indicating their specificities and their applications in the various fields. We then proposed a more integrated model, gathering essential aspects (mathematical, social sciences, descriptive models and virtual reality) with a mixed interface of fuzzy and traditional logic. Lastly, we particularly studied the models actually built for virtual engineering in order to improve the current applications to add new points of sights, more general, more flexible and more realistic within the tools used for system design.. We propose a new approach to define danger zones of working situation in a virtual or augmented reality environment. Our final proposal is a set of models and processes of applicable performance evaluation methods within the framework of computer-aided production engineering environments.
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The purpose of this study was to characterize functional limitation in seated manual transfer tasks for low back pain (LBP), spinal cord injury (SCI), and control subjects. Seated subjects performed either two- or one-handed transfer tasks to one of three targets 87cm above the hip-point at 0, 45, and 90° azimuths. Three torso angles (flexion, lateral bending, and axial rotation) were obtained from captured motions and modeled by combinations of B-spline base functions. The results demonstrated that 1) the SCI and LBP subjects exhibit smaller torso flexion than controls; 2) the SCI subjects tend to move the torso (lateral bending and extension) away from the target; and 3) these group differences are reduced in one-handed transfers and light load conditions. The movement patterns suggest that SCI patients may have adapted strategies to compensate for the limited control of upper body balance, while LBPs may limit torso motion to avoid pain.
Article
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This paper addresses the complex issues affecting the postures people choose to use when attempting moderate load lifting exertions. In essence, lifting exertions are known to require a person to utilize muscle strength capabilities at each joint while also maintaining balance. As loads in the hand are located further away from the person both muscle and balance requirements increase. By setting population limits to accommodate both a 90%tile muscle strength capability and a functional balance capability within the University of Michigan's 3D Static Strength Prediction Program, it was possible to run a set of trials which demonstrate the importance of both constraints when lifting loads in one and both hands placed at different horizontal distances away from the body. A small study showing the effects of one handed bracing was also performed. Results indicate that subtle changes in body postures and or hand bracing can affect the maximum distance a moderate load can be lifted. This demonstrates the general nature of the biomechanical strength and balance problems associated with the horizontal location of a moderate load, even when one handed bracing is possible.
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This report presents a three-dimensional description of adult female and male pelvis from the Hamann-Todd skeletal collection, Cleveland Museum of Natural History. Based on a linear height/weight matching strategy and the 1961- 1964 U.S. Health and Examination Survey (HES) data, specimens were selected to represent the small female, medium male, and large male pelvic sizes. One hundred and twenty-three anatomically defined points are used to describe the spatial pelvic geometry in a pelvic-anatomical axis system. A statistical summary of means and standard deviations is presented as X, Y, and Z coordinate value sets to identify each point in three-dimensional space. Full-scale models for each size category were produced for design modeling of anthropomorphic test devices. These data will also be useful as comparative standards for forensic investigations of air crashes and quantitative information on size and shape variability of adult human pelvis.
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This study begins the exploration of the relationship between shoulder external moments and perceived exertion levels for submaximal delivery tasks. Twenty subjects were recorded while performing hand load movement tasks to specified targets. After each exertion, subjects were asked to rate the effort required to perform the task. The recorded motion profiles were processed using a biomechanical upper extremity model, from which resultant external shoulder moments were calculated. Average resultant shoulder moments, stratified by exertion level, were also calculated. Several individual subject moment/exertion profiles showed identifiable trends. It was demonstrated that while no strong relationships exist for individual task exertion effort prediction based on resultant shoulder moments, there is a general trend in the overall data sample, as is shown by a high correlation between mean integrated resultant shoulder moment by exertion level and exertion levels.
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Many existing job analysis tools for ergonomics have concentrated on the potential adverse effects of force, posture, and repetition, as these appear to be traditionally recognized risk factors in the workplace. Recent investigations have indicated that this pragmatic approach may be overly simplistic, and thus miss prediction of risk factors associated with certain motions. This article reviews some of the research under way in the University of Michigan's Human Motion Simulation Laboratory to develop a set of human motion prediction models. To produce these models, over 37,000 motions of 100 men and women from 18 to 78 years in age have been measured with a motion capture system. The motions are typical of people reaching and moving light to moderate load objects while either seated or standing. A 17-link kinematics model has been developed to resolve the dynamics of the motions. Thus far, initial motion algorithms have been developed that capture well over 95% of the between participant repeatability. Advantages and limitations of the methods and data being used are discussed and illustrated.
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This paper describes a study of lumbar and sacrum orientations in select standing postures with the patient holding different loads in the hands. Vertebral rotation data were gathered from two young, healthy men and two young, healthy women while they performed static lifts at two load levels and in postures ranging from erect standing to deep squatting. The results disclosed a predictable reorientation of the sacrum and lumbar spine for both men and women as a function of torso and knee angles. Nonlinear second-order regression models of torso angle and knee angle versus reorientation angle were fit to the data with resulting r2 values of about 0.89. Load was not found systematically to affect the sacrum/lumbar reorientation.
Article
The development of new patterns of postural control in patients with a complete thoracic spinal cord injury (SCI) during their active clinical rehabilitation was studied. Especially the role of non-postural muscles, like the latissimus dorsi (LD) and the trapezius pars ascendens (TPA), in maintaining and restoring sitting balance during standardized bimanual task performance was investigated. Twelve patients, diagnosed with an acute complete thoracic SCI between spinal cord level T2 and T12, participated in a longitudinal experimental study. Changes in the centre of pressure (CP) and electromyographic activity of the erector spinae (ES) at level L3, T9 and T3, the LD, the TPA, the pectoralis major (PM), the serratus anterior and the oblique abdominal muscles were investigated at several moments in the rehabilitation process. Results show a gradual development of specific muscle activation patterns for both high and low thoracic SCI patients. These patterns seem to be related to a combination of restoration of function of the ES-L3 and ES-T9 in the low thoracic SCI subjects and increased compensatory muscle use of the LD, TPA and PM in high SCI patients. The range in which low thoracic SCI patients can actively vary their CP increased slightly during rehabilitation.
Article
To compensate for postural muscle function loss spinal cord injured (SCI) people have to use parts of the sensorimotor system which are still intact. In this study, postural control was investigated in high and low thoracic SCI people and in able-bodied controls, using a bimanual forward-reaching task. Muscle activity was recorded bilaterally from the erector spinae (ES) at level L3, T9 and T3, latissimus dorsi (LD), ascending part of the trapezius muscle (TPA), serratus anterior (SA), sternocostal head of the pectoralis major (PM) and the oblique abdominal muscles (OA) by means of surface electromyography. Sitting balance was monitored by measuring the changes in the location of the centre of pressure (CP) using a force platform. Muscle activity analyzed in different phases of the movement showed that SCI people adopt different postural adjustments to face the balance changes due to the reaching movement. SCI people make alternative use of non-postural muscles like the LD and TPA to maintain their sitting balance.
Article
Spinal cord injured (SCI) people try to compensate for the loss of postural muscle function by increased use of non-postural muscles. Such alternative muscle use, however, may necessitate important modifications in motor control. In this study motor programming processes were investigated in three groups, i.e. in high thoracic SCI, low thoracic SCI and non-SCI subjects. A bimanual forward-reaching task, in which graded sitting balance perturbation was systematically invoked, was presented to the subjects as a visual precue choice reaction time (RT) task. Effects of movement preparation were examined by precuing reaching distance information. RT and movement times were recorded. Centre of pressure (CP) displacement was used as an indicator for sitting balance perturbation. Results indicated that high thoracic SCI subjects programmed balance-perturbing reaching movements as fast as did non-SCI subjects. Low thoracic SCI subjects, on the other hand, showed substantially longer programming times. This latter outcome is consistent with the hypothesis that the low thoracic SCI subjects adopted a more complex postural control strategy involving residual motor functions in an attempt to actively compensate for loss of postural muscle function. High thoracic SCI subjects, on the other hand, appeared to adopt a less complex and thus easier to programme postural control strategy.
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