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Objective: To evaluate the effects of wrist splint orthoses (WSOs) on forearm muscle activity and upper extremity/torso postures. Background: WSOs are ubiquitous in industry, but the literature as to their biomechanical effects is limited. Method: Study 1: Participants performed single-plane wrist exertions with or without a WSO while the electromyographic (EMG) activity of the flexor carpi radialis, flexor carpi ulnaris, and extensor carpi ulnaris was captured. Study 2: Participants performed simple computer jumper installation tasks with or without a WSO while upper extremity/torso postures were recorded. Results: Study 1: A significant interaction between WSOs and wrist angle was observed in the response of forearm muscles (e.g., normalized EMG of the flexor carpi radial is increased from 4.2% to 15.9% as flexion increased from 0° to 36° in the orthosis conditions, whereas in the no-orthosis condition it remained 5% at all wrist flexion angles). Study 2: WSOs were found to effect wrist, torso, and shoulder postures, with the orthoses creating a 48% decrease (36° vs. 18.6°) in wrist flexion and 80% decrease (15° vs. -3°) in ulnar deviation but at a cost of increased shoulder abduction of 22% (36.5° vs. 44.5°) and increased lateral bend of torso of 30% (6° vs. 7.8°). Conclusions: WSOs increased forearm muscle activity at large wrist deviation angles and induced awkward shoulder postures in tasks requiring significant wrist deviation. Application: Use of WSOs in occupational settings should be carefully considered relative to task requirements, as orthoses may do more harm than good.

Objective To examine the effects of asymmetry and lower extremity mobility restrictions on the effectiveness of a passive back-support exosuit in short-duration, static trunk flexion postures. Background The effectiveness of trunk exoskeletons/suits for sagittally symmetric trunk posture maintenance has been investigated, but there has been limited study of the effects of asymmetric trunk postures or lower extremity motion restriction. Method Sixteen participants held trunk flexion postures involving trunk flexion (20°, 40°, 60°), asymmetry (0°, 30°), and lower extremity mobility (Free, Restricted) for 3 s. Participants held these postures with and without an exosuit while erector spinae and abdominal muscle activities were collected. Results There were no significant interactions between exosuit and asymmetry or exosuit and lower extremity motion restrictions, indicating no significant effects of these factors on the effectiveness of the exosuit at reducing trunk muscle activity. The exosuit was found to be effective at reducing erector spinae muscle activity regardless of asymmetry of posture or lower extremity restrictions (average 21%, from 11.2% MVC to 8.8% MVC). The magnitude of the erector spinae activity at 60° of trunk flexion with the exosuit was similar to that seen at 20° without the exosuit. Conclusion The exosuit consistently provided biomechanical benefit through reduced activation of the erector spinae muscles and neither asymmetry of trunk posture nor lower extremity restriction influenced this effectiveness. Application Trunk exoskeletons/suits can reduce trunk muscle activation and understanding how characteristics of the trunk postures assumed impact these responses may help target tasks wherein these devices may be effective.

Resistance to change is common in ergonomic interventions, often resulting in negative consequences when the intervention's effectiveness is studied. A lab-based study assessed the effects of positive reinforcement during the intervention process. On Day 1 all participants performed a simple screw-driving task that placed stress on the cervicobrachial region through static loading. On Day 2 a control group received basic information about ergonomics and then performed the task using an ergonomic intervention that has been shown to reduce loading on these muscle groups. The experimental group received the same basic information but also received positive reinforcement while performing the task with the ergonomic intervention. Subjective task assessment surveys and body-part discomfort surveys were administered, and these, along with speed of performance, were assessed in both groups. The results showed a significantly (p < .05) more positive subjective impression of the intervention for the feedback group than for the control group (29%-57% improvement) with no real changes in either the performance or discomfort levels. Applications of this research include improving workers' acceptance of ergonomic interventions in industrial and other settings. The reinforcement technique evaluated in this paper has yielded consistently positive effects in our ongoing ergonomic intervention research.

An experiment was performed to evaluate the motions of the lumbar spine during a constant load velocity lift. For the purposes of this study, a constant load velocity refers to the linear vertical velocity of the load. This vertical load velocity was controlled using a modified angular isokinetic dynamometer, which produced linear isokinetic motion during a lift. A lumbar monitor was used to observe the position, velocity, and acceleration changes that occurred in the lumbar spine during the lifting task. The results indicate that under constant load velocity conditions, significant angular accelerations occur at the lumbar level. The nature of these accelerations was found to depend on several variables associated with a lifting task, such as the load velocity and the asymmetry of the lift. The physical significance of these results would be increased spinal loading above that which would be predicted using a static model.

Awkward wrist posture is generally considered an occupational risk factor for hand/wrist disorders, leading to the ergonomic design principle of "bend the tool, not the wrist." Sixteen participants performed a computer jumper installation task and a simple assembly task while productivity, wrist posture, and shoulder posture were measured. The work surface orientation (vertical and 45°) and the level of constraint placed on the user (constrained grip and unconstrained grip) were also varied. The results indicate that the beneficial effects of the bent-handle pliers are task dependent. In the computer jumper task the bent-handle pliers resulted in 5.3% faster task performance, whereas in the assembly task performance was 4.9% faster with the straight-handle pliers. The bent-handle pliers reduced shoulder deviations by 50% in the jumper installation task, and ulnar deviation was reduced by 12% and 22% for the jumper installation task and the assembly task, respectively (all significant at p < .05). However, allowing participants to hold the pliers in a grip configuration of their choosing (unconstrained technique) often reduced these postural benefits. In applying these results to work place design activities, one should recognize that the ergonomic utility of benthandle pliers can be considerable but that the 3-D kinematics characteristics of the task must be considered.

Repetitive, high-force pinch grip exertions are common in many occupational activities. The goal of the current study was to quantify the relationship between lateral pinch grip span (distance between thumb and index finger) and lateral pinch grip strength. An experiment was conducted in which 40 participants performed maximal lateral pinch grip exertions at 11 levels of grip span distances (0, 10%, ... 100% of maximum functional lateral pinch grip span distance). The results show a significant effect of lateral pinch grip span, with strength at the maximum functional lateral pinch grip span 40% higher than that found at the smallest lateral pinch grip span considered. Between these two endpoints, strength increased monotonically with increasing pinch grip span. The application of these results in pinch grip design criteria for both high-force and long-duration exertions is discussed. Potential applications of this research include the design of hand tools and controls for which significant force is applied by the user.

Jobs with a high degree of variability in manual materials handling requirements expose limitations in current low-back injury risk assessment tools and emphasize the need for a probabilistic representation of the biomechanical stress in order to quantify both acute and cumulative trauma risk. We developed a hybrid assessment methodology that employs established assessment tools and then represents their evaluations in a way that emphasizes the distributions of biomechanical stress. Construction work activities in the home building industry were evaluated because of the high degree of variability in the manual material handling requirements. Each task was evaluated using the Revised NIOSH Lifting Equation, The University of Michigan Three- Dimensional Static Strength Prediction Program™, and the Ohio State University Lumbar Motion Monitor Model. The output from each model was presented as time-weighted histograms of low-back stress, and the assessments were compared. The results showed considerable differences in what were considered high-risk activities, indicating that these 3 assessment tools consider the risk of low-back injury from different perspectives. The time-weighted distribution aspect of this methodology also contributed vital information toward the identification of high-risk activities. These results illustrate the necessity for more advanced low-back injury risk assessment techniques for jobs with highly variable manual materials handling requirements.

A great deal of interest has been generated recently regarding the influence that psychosocial factors may have on the reporting of and disability associated with work-related musculoskeletal disorders. The current study considers the potential influence of one psychosocial factor - personality type - on basic neuromuscular control strategies and biomechanical loading. The study investigated the hypothesis that Type A people exhibit increased muscular antagonism relative to their Type B counterparts. Volunteers participated in an EMG-based biomechanical study to investigate the co-activation patterns of the major muscles that span the elbow joint during elbow flexion exertions. Results showed that, averaging across all conditions, the antagonist muscle activity was significantly higher for Type A individuals than for their Type B counterparts (10% of maximum for Type A, 5.5% of maximum for Type B). Although the study was somewhat limited in its size and scope, the results indicate that certain psychosocial factors may be more than a filter in postinjury response and may directly influence biomechanical loading. A potential application of this research is an increased awareness that certain individuals may be at greater risk of developing work-related musculoskeletal disorders.

Objective To evaluate the effectiveness of passive back-support exosuit on postural control and cognitive performance during a fatigue-inducing posture maintenance task. Background Wearable support systems (exoskeletons/exosuits) reduce physical demands but may also influence postural control and cognitive performance by reducing muscular fatigue. Method Eighteen participants visited on two different days to test an exosuit system and performed dual-task cognitive assessments based on human information processing (information acquisition, information integration, and action implementation) while maintaining a 35° trunk flexion posture for 16 minutes. Center-of-pressure (CoP), cognitive performance, and perceived workload were recorded, while erector spinae muscle activity was captured to quantify muscle fatigue. Results The exosuit was effective in reducing erector spinae muscle fatigue during the static posture maintenance task (61% less in Δmedian frequency: −9.5 Hz (EXO-Off) versus −3.7 Hz (EXO-On)). The fatigue-inducing task increased CoP velocity as a function of time (29% greater: 9.3 mm/sec (pre) versus 12.0 mm/sec (post)), and exosuit use decreased CoP velocity (23% less: 12.1 mm/sec (EXO-Off) versus 9.4 mm/sec (EXO-On)). The exosuit was also effective at mitigating cognitive degradation, as evidenced by a higher hit-to-signal ratio (8% greater: 81.3 (EXO-Off) versus 87.9 (EXO-On)) in the information integration task and reducing perceived workload in all stages of human information processing. Conclusion Exosuit provided benefits of postural control and information integration processing during a 16-min static posture maintenance task. Application Torso exoskeletons/suits can have positive implications for occupations with concurrent physical and cognitive demands.

Objective : To quantify learning percentages for alternative keyboards (chord, contoured split, Dvorak, and split fixed angle) and understand how physical, cognitive, and perceptual demand affect learning. Background: Alternative keyboards have been shown to offer ergonomic benefits over the conventional, single-plane QWERTY keyboard design, but productivity-related challenges may hinder their widespread acceptance. Method: Sixteen participants repeatedly typed a standard text passage using each alternative keyboard. Completion times were collected and subsequent learning percentages were calculated. Participants were asked to subjectively rate the physical, cognitive, and perceptual demands of each keyboard, and these values were then related to the calculated learning percentages. Results: Learning percentage calculations revealed the percentage for the split fixed-angle keyboard (90.4%) to be significantly different ( p < .05) from the learning percentages for the other three keyboards (chord, 77.3%; contour split, 76.9%; Dvorak, 79.1%). The average task completion time for the conventional QWERTY keyboard was 40 s, and the average times for the fifth trial on the chord, contoured split, Dvorak, and split fixed-angle keyboards were 346, 69, 181, and 42 s, respectively. Conclusions: Productivity decrements can be quickly regained for the split fixed-angle and contour split keyboard but will take considerably longer for Dvorak and chord keyboards. The split fixed-angle keyboard involved physical learning, whereas the others involved some combination of physical and cognitive learning, a result supported by the subjective responses. Application: Understanding the changes in task performance time that come with learning can provide additional information for a cost-benefit analysis when considering the implementation of ergonomic interventions.

The effect of warning time (preview) and task symmetry on the trunk muscular response to sudden loading conditions was investigated. Eleven subjects were asked to catch falling weights with four levels of preview (0, 100, 200, and 400 ms) in sagittally symmetric posture and asymmetric posture. For each of the eight muscles sampled with surface electrodes, the integrated electromyographic (EMG) signal was interpreted in terms of its peak value, mean value, onset rate, and lead/lag time with reference to the weight drop. Results show linear relationships between preview times and peak EMG, preview times and mean EMG, and preview times and lead times. The results show significant change when going from symmetric to asymmetric conditions across most dependent measures. Analysis of peak changes in compression were performed across all conditions but yielded unexpected results.