Jonathan DeShaw

Predictive discomfort of non-neutral head–neck postures in fore–aft whole-body vibration

It seems obvious that human head–neck posture in whole-body vibration (WBV) contributes to discomfort and injury risk. While current mechanical measures such as transmissibility have shown good correlation with the subjective-reported discomfort, they showed difficulties in predicting discomfort for non-neutral postures. A new biomechanically based methodology is introduced in this work to predict discomfort due to non-neutral head–neck postures. Altogether, 10 seated subjects with four head–neck postures—neutral, head-up, head-down and head-to-side—were subjected to WBV in the fore–aft direction using discrete sinusoidal frequencies of 2, 3, 4, 5, 6, 7 and 8 Hz and their subjective responses were recorded using the Borg CR-10 scale. All vibrations were run at constant acceleration of 0.8 m/s2 and 1.15 m/s2. The results have shown that the subjective-reported discomfort increases with head-down and decreases with head-up and head-to-side postures. The proposed predictive discomfort has closely followed the reported discomfort measures for all postures and rides under investigation. Statement of Relevance: Many occupational studies have shown strong relevance between non-neutral postures, discomfort and injury risk in WBV. With advances in computer human modelling, the proposed predictive discomfort may provide efficient ways for developing reliable biodynamic models. It may also be used to assess discomfort and modify designs inside moving vehicles.

Comprehensive measurement in whole-body vibration

Accurate measurements of human response to whole-body vibration are essential to any conclusions about the health risks, discomfort, and assessment of suspension systems in vibration environments. While accelerometers are traditionally considered the main measurement tools in whole-body vibration studies, their measurements become questionable when they are attached to inclined surfaces or when the motion has coupled components in multiple directions. Current measurement correction methodologies are subjective and limited to simple cases. A comprehensive correction methodology using inertial sensors was used in this work to quantify human response under single fore-aft, single-vertical, and multiple-axis whole-body vibration of twelve seated subjects with supported-backrest and unsupported-backrest upright posture. Vibration files of white noise random signals with frequency content of 0.5–12 Hz and vibration magnitude of 1.8 m/s2 RMS were used in the testing. The results have shown considerable differences in the transmissibility measurements without proper correction. The work presented has the potential to standardize experimentation in whole-body vibration and make measurements more accurate and defined across labs.

Predictive discomfort and seat-to-head transmissibility in low-frequency fore-aft whole-body vibration

A predictive discomfort measure considering the combined neck and trunk is introduced in this work and compared with the seat-to-head transmissibility and subjective reported discomfort due to fore-aft whole-body vibration of seated subjects under two sitting postures. Five subjects were tested using discrete sinusoidal frequencies in the range of 0.5–12 Hz. All files were run at a constant acceleration of 0.8 m/s2. The subjects were tested with back support and without back support, and their subjective discomfort measure was reported based on the Borg CR-10 scale. The results have demonstrated that the predictive discomfort was invulnerable to the measurement locations and has shown consistency with the subjective discomfort for both sitting conditions. The seat-to-head transmissibility showed less consistency with the subjective discomfort and was sensitive to the locations of the output point on the head and to the components of the motion included in the transmissibility calculation at these locations.

Predictive Discomfort in Single- and Combined-Axis Whole-Body Vibration Considering Different Seated Postures

Objective: The aim of this study was to develop a predictive discomfort model in single-axis, 3-D, and 6-D combined-axis whole-body vibrations of seated occupants considering different postures. Background: Non-neutral postures in seated whole-body vibration play a significant role in the resulting level of perceived discomfort and potential long-term injury. The current international standards address contact points but not postures. Method: The proposed model computes discomfort on the basis of static deviation of human joints from their neutral positions and how fast humans rotate their joints under vibration. Four seated postures were investigated. For practical implications, the coefficients of the predictive discomfort model were changed into the Borg scale with psychophysical data from 12 volunteers in different vibration conditions (single-axis random fore-aft, lateral, and vertical and two magnitudes of 3-D). The model was tested under two magnitudes of 6-D vibration. Results: Significant correlations (R2 = .93) were found between the predictive discomfort model and the reported discomfort with different postures and vibrations. The ISO 2631-1 correlated very well with discomfort (R2 = .89) but was not able to predict the effect of posture. Conclusion: Human discomfort in seated whole-body vibration with different non-neutral postures can be closely predicted by a combination of static posture and the angular velocities of the joint. Application: The predictive discomfort model can assist ergonomists and human factors researchers design safer environments for seated operators under vibration. The model can be integrated with advanced computer biomechanical models to investigate the complex interaction between posture and vibration.

Predictive discomfort of supine humans in whole-body vibration and shock environments.

Abstract This work presents a predictive model to evaluate discomfort associated with supine humans during transportation, where whole-body vibration and repeated shock are predominant. The proposed model consists of two parts: (i) static discomfort resulting from body posture, joint limits and ambient discomfort; and (ii) dynamic discomfort resulting from the relative motion between the body segments as a result of transmitted vibration. Twelve supine subjects were exposed to single and 3D random vibrations and 3D shocks mixed with vibrations. The subjects’ reported discomfort and biodynamic response were analysed under different support conditions, including a rigid surface, a stretcher and a stretcher with a spinal backboard. The results demonstrated good correlations between the predictive discomfort and the reported discomfort for the different conditions under consideration, with R2 = 0.69–0.94 for individual subjects and R2 = 0.94 for the group mean. The results also indicated a strong relationship between the head-neck and trunk angular velocities and discomfort during supine transportation. Practitioner Summary: The quantification of discomfort of supine humans under vibration and shocks by using a predictive model is an important contribution to this field, whereby the efficacy of different transport systems can be compared. The predictive discomfort model can be used as design criteria for ergonomic enhancement in supine transportation of humans.

Effective seat-to-head transmissibility under combined-axis vibration and multiple postures

Effective seat-to-head transmissibility (ESTHT) is introduced in this work to objectively evaluate human biodynamical response in a six-degree-of-freedom input/output vibration environment. In ESTHT the complex transmissibility matrix is transformed to simple forms that can be easily interpreted. In this study, human responses were compared using ESTHT under different seated postures, including an upright seated posture with no backrest, a backrest-supported sitting posture, a backrest-supported sitting posture with forearms resting on armrest supports, and a backrest-supported sitting posture in which participants used the armrest supports and rotated their heads to the side. Twelve healthy males participated in the study and were tested under random-vibration files of 0.5-12 Hz with different magnitudes. The results showed the capability of ESTHT to identify the frequency spectrum at which the motion is magnified. The study also revealed that ESTHT was able to detect differences in human response due to different postures and vibration directions.

Effect of lumbar support on human-head movement and discomfort in whole-body vibration

BACKGROUND: It is well known that prolonged sitting can elicit low back pain as a result of the abnormal shape of the spine. This problem becomes worse in whole-body vibration environments where a rocking motion of the pelvis can occur and may amplify the vibration motion transmitted to the lumbar spine. OBJECTIVE: Although the use of lumbar supports is common in static environments, little is known about how the use of such supports changes the biodynamic response and discomfort of the person in whole-body vibration environments. METHODS: The motion at the head and the discomfort of ten participants were recorded under five back-support conditions, including three commercially available lumbar supports. RESULTS:The results indicated significantly lower head motion and discomfort ( p< 0.05) with the use of the lumbar supports than with a simple flat backrest. CONCLUSIONS: All lumbar supports used in this study combined the advantages of reduced head motion and reduced discomfort during whole-body vibration.

Comparing the Efficacy of Methods for Immobilizing the Thoracic-Lumbar Spine

OBJECTIVE The purpose of this study was to compare the relative efficacy of immobilization systems in limiting thoracic-lumbar movements. METHODS A dynamic simulation system was used to reproduce transport-related shocks and vibration, and involuntary movements of the thoracic-lumbar region were measured using 3 immobilization configurations. RESULTS The vacuum mattress and the long spine board were generally more effective than the cot alone in reducing thoracic-lumbar rotation and flexion/extension. However, the vacuum mattress reduced these thoracic-lumbar movements to a greater extent than the long spine board. In addition, the vacuum mattress significantly decreased thoracic-lumbar lateral movement relative to the cot alone under all simulated transport conditions. In contrast, the long spine board allowed greater lateral movement than the cot alone in a number of the simulated transport rides. CONCLUSION Under the study conditions, the vacuum mattress was more effective for limiting involuntary movements of the thoracic-lumbar region than the long spine board. Moreover, the increased lateral bend observed with the long spine board under some conditions suggests it may be inadequate for immobilizing this anatomic region as presently designed. Should emergency medical service providers choose to immobilize patients with suspected injuries of the thoracic-lumbar spine, study results support the use of the vacuum mattress.

Biodynamics of supine humans and interaction with transport systems during vibration and shocks

This work investigates the effect of the contact surfaces on the biomechanical response of supine humans during whole-body vibration and shocks. Twelve participants were exposed to three-dimensional random vibration and shocks and were tested with two types of contact surfaces: (i) litter only, and (ii) litter with spinal board. The two configurations were tested with and without body straps to secure the supine human. The addition of the spinal board reduced the involuntary motion of the supine humans in most directions. There were significant reductions in the relative vertical accelerations at the neck and torso areas, especially during shocks (p < 0.01). The inclusion of body straps with the spinal board was more effective in reducing the relative motion in most directions when shocks were presented. This study shows that the ergonomic design of the human transport system and the underlying contacting surfaces should be studied during dynamic transport environments.

Dynamic Responses of Experienced All-Terrain Vehicle Operators to Simulated Unexpected Terrain Changes

All-terrain vehicles (ATVs) require “active riding,” meaning operators must rapidly assess changes in vehicle stability and adjust body position to compensate. No previous studies have reported using an ATV simulator to study active riding by human subjects. An ATV was mounted to a computer-controlled platform. Ride-file programs were developed which included sudden vehicle pitch (upward/downward) and roll (side to side) movements. A motion-capture system and accelerometers collected data that were analyzed with 3D modeling software. The posture and dynamic response to simulated sudden terrain changes for five adult males with ATV riding experience were determined. This study provides proof-of-principle for the use of ATV simulation to study active riding. In addition, the response patterns of experienced adult ATV operators can now be compared to that of other groups (e.g. inexperienced operators, children, drivers with passengers) to determine potential differences that might contribute to loss of vehicle control and crashing.