Evaluating the impact of writing surface and configuration on muscle activation level during a handwriting task: An exploratory study.

BACKGROUND: Tablets are ubiquitous in workplaces and schools. However, there have been limited studies investigating the effect tablets have on the body during digital writing activities. OBJECTIVE: This study investigated the biomechanical impact of writing interface design (paper, whiteboard, and tablet) and orientation (horizontal, 45°, and vertical) on tablet users. METHODS: Fourteen adults (7 male, 7 female) participated in a study during which they performed simple writing tasks. Surface electromyography (sEMG) sensors were used to measure upper extremity muscle activation. RESULTS: Results indicate that the effects of writing surface type were most pronounced in forearm muscle activation. Specifically, in the extensor carpi radialis (ECR), where muscle activity was lower on the tablet PC surface. The effects of writing configuration were prominent in the shoulder and forearm. The activation of the flexor carpi ulnaris (FCU) and trapezius muscles was significantly lower in the 45° configuration. An exception to the efficacy of this configuration was the anterior deltoid muscle, which exhibited the lowest muscle activity in the horizontal orientation. CONCLUSIONS: Tablet surface and the 45° configuration resulted in the lowest muscle activation levels. Future studies should include longer experiment duration to investigate the effects of continuous writing.

Evaluating biomechanics of user-selected sitting and standing computer workstation.

A standing computer workstation has now become a popular modern work place intervention to reduce sedentary behavior at work. However, user's interaction related to a standing computer workstation and its differences with a sitting workstation need to be understood to assist in developing recommendations for use and set up. The study compared the differences in upper extremity posture and muscle activity between user-selected sitting and standing workstation setups. Twenty participants (10 females, 10 males) volunteered for the study. 3-D posture, surface electromyography, and user-reported discomfort were measured while completing simulated tasks with each participant's self-selected workstation setups. Sitting computer workstation associated with more non-neutral shoulder postures and greater shoulder muscle activity, while standing computer workstation induced greater wrist adduction angle and greater extensor carpi radialis muscle activity. Sitting computer workstation also associated with greater shoulder abduction postural variation (90th-10th percentile) while standing computer workstation associated with greater variation for should rotation and wrist extension. Users reported similar overall discomfort levels within the first 10 min of work but had more than twice as much discomfort while standing than sitting after 45 min; with most discomfort reported in the low back for standing and shoulder for sitting. These different measures provide understanding in users' different interactions with sitting and standing and by alternating between the two configurations in short bouts may be a way of changing the loading pattern on the upper extremity.

Effects of Epinephrine Auto-Injector Shape and Size on Human Factors Influencing Drug Delivery.

OBJECTIVE: The aim of this study was to assess the effects of (a) auto-injector form factor on maximum applied force capability and (b) auto-injector design and instructions on force production and orientation. BACKGROUND: Effective delivery of epinephrine through an auto-injector is the result of a multitude of design factors. At minimum, the design needs to allow the user to apply sufficient force for the needle to penetrate clothing and tissue. METHOD: Trainer devices for three commercially available epinephrine auto-injectors with different form factors (cylindrical, elliptical, prismatic) were tested in a laboratory-based repeated-measures experiment with 20 adults. Participants applied their maximum force onto a force plate positioned over their thigh and practiced an injection using the trainer device after viewing training videos. Participants also rated force confidence and preference. RESULTS: The maximum force varied significantly across devices. The greatest force observed was 64 newtons with the elliptical device, and the lowest force was 61 newtons with the cylindrical device. Participants reported the highest force confidence when using the elliptical and cylindrical devices, ranking the elliptical as their preferred device. CONCLUSION: Force capability results for the elliptical device suggest that it may be more successful in achieving the necessary force for drug delivery in a larger set of adult users. APPLICATION: Results suggest that the auto-injector with the elliptical form may enable more successful drug delivery among a larger set of users.

Effects of torsion on intervertebral disc gene expression and biomechanics, using a rat tail model.

STUDY DESIGN: In vitro and in vivo rat tail model to assess effects of torsion on intervertebral disc biomechanics and gene expression. OBJECTIVE: Investigate effects of torsion on promoting biosynthesis and producing injury in rat caudal intervertebral discs. SUMMARY OF BACKGROUND DATA: Torsion is an important loading mode in the disc and increased torsional range of motion is associated with clinical symptoms from disc disruption. Altered elastin content is implicated in disc degeneration, but its effects on torsional loading are unknown. Although effects of compression have been studied, the effect of torsion on intervertebral disc gene expression is unknown. METHODS: In vitro biomechanical tests were performed in torsion on rat tail motion segments subjected to 4 treatments: elastase, collagenase, genipin, control. In vivo tests were performed on rats with Ilizarov-type fixators implanted to caudal motion segments with five 90 minute loading groups: 1 Hz cyclic torsion to ± 5 ± 15° and ± 30°, static torsion to + 30°, and sham. Anulus and nucleus tissues were separately analyzed using qRT-PCR for gene expression of anabolic, catabolic, and proinflammatory cytokine markers. RESULTS: In vitro tests showed decreased torsional stiffness following elastase treatment and no changes in stiffness with frequency. In vivo tests showed no significant changes in dynamic stiffness with time. Cyclic torsion upregulated elastin expression in the anulus fibrosus. Up regulation of TNF-α and IL-1ß was measured at ±30°. CONCLUSION: We conclude that strong differences in the disc response to cyclic torsion and compression are apparent with torsion increasing elastin expression and compression resulting in a more substantial increase in disc metabolism in the nucleus pulposus. Results highlight the importance of elastin in torsional loading and suggest that elastin remodels in response to shearing. Torsional loading can cause injury to the disc at excessive amplitudes that are detectable biologically before they are biomechanically.

Effects of enzymatic digestion on compressive properties of rat intervertebral discs.

Enzymatic treatments were applied to rat motion segments to establish structure-function relationships and determine mechanical parameters most sensitive to simulated remodeling and degeneration. Rat caudal and lumbar disc biomechanical behaviors were evaluated to improve knowledge of their similarities and differences due to their frequent use during in vivo models. Caudal motion segments were assigned to four groups: soaked (control), genipin treated, elastase treated, and collagenase treated. Fresh lumbar and caudal discs were also compared. The mechanical protocol involved five force-controlled loading stages: equilibration, cyclic compression-tension, quasi-static compression, frequency sweep, and creep. Crosslinking was found to have the greatest effect on IVD properties at resting stress. Elastin's role was greatest in tension and at higher force conditions, where GAG content was also a contributing factor. Collagenase treatment caused tissue compaction, which impacted mechanical properties at both high and low force conditions. Equilibration creep and cyclic compression-tension tests were the mechanical tests most sensitive to alterations in specific matrix constituents. Caudal and lumbar motion segments had many similarities but biomechanical differences suggested some distinctions in collagenous structure and water transport characteristics in addition to the geometric differences. Results provide a basis for interpreting biomechanical changes observed in animal model studies of degeneration and remodeling, and underscore the need to maintain and/or repair collagen integrity in IVD health and disease.

In vivo remodeling of intervertebral discs in response to short- and long-term dynamic compression.

This study evaluated how dynamic compression induced changes in gene expression, tissue composition, and structural properties of the intervertebral disc using a rat tail model. We hypothesized that daily exposure to dynamic compression for short durations would result in anabolic remodeling with increased matrix protein expression and proteoglycan content, and that increased daily load exposure time and experiment duration would retain these changes but also accumulate changes representative of mild degeneration. Sprague-Dawley rats (n = 100) were instrumented with an Ilizarov-type device and divided into three dynamic compression (2 week-1.5 h/day, 2 week-8 h/day, 8 week-8 h/day at 1 MPa and 1 Hz) and two sham (2 week, 8 week) groups. Dynamic compression resulted in anabolic remodeling with increased matrix mRNA expression, minimal changes in catabolic genes or disc structure and stiffness, and increased glysosaminoglycans (GAG) content in the nucleus pulposus. Some accumulation of mild degeneration with 8 week-8 h included loss of annulus fibrosus GAG and disc height although 8-week shams also had loss of disc height, water content, and minor structural alterations. We conclude that dynamic compression is consistent with a notion of "healthy" loading that is able to maintain or promote matrix biosynthesis without substantially disrupting disc structural integrity. A slow accumulation of changes similar to human disc degeneration occurred when dynamic compression was applied for excessive durations, but this degenerative shift was mild when compared to static compression, bending, or other interventions that create greater structural disruption.

Validation of lower limb surrogates as injury assessment tools in floor impacts due to anti-vehicular land mines.

The aim of this study was to assess the ability of lower limb surrogates to predict injury due to floor/foot plate impact in military vehicles during anti-vehicular land mine explosions. Testing was conducted using two loading conditions simulated to represent those conditions created in the field. The lower condition was represented by a 24-kg mass impactor with a velocity of 4.7 m/s. The higher loading condition was represented by a 37-kg mass impactor with a velocity of 8.3 m/s. Two biomechanical surrogates were evaluated using the loading conditions: 50th percentile Hybrid III foot/ankle and Test Device for Human Occupant Restraint THOR-Lx. Comparisons of the force-time response were made to established corridors. Results show a better correlation to the corridors with the THOR-Lx; however, future improvements to the THOR-Lx are recommended.