Quantifying supine human discomfort in off-road whole-body vibration

This work presents a new methodology to quantify supine human discomfort during transport when multi-axis whole-body vibration (WBV) and shocks are present. The methodology employs a new scheme to normalise the reported discomfort. Twenty-six human subjects were tested under different off-road conditions and their reported discomforts collected. The paired Wilcoxon signed-rank method was used to investigate the significant differences (p < 0.01) between different track sections on the normalised reported discomfort from the subjects. Analyses based on ISO 2631-1 showed weak correlation with the reported discomfort when significant lateral motions existed. The results with the new formulation showed that discomfort is highly correlated with the vibration dose value at the head of the supine human during WBV (p < 0.001). These results are consistent with previous published work showing that discomfort based on motion at the head-neck region comprises more than 70% of the reported discomfort during supine transport under multiple-axis WBV.Practitioner summary: There are shortcomings in the current approaches to quantifying discomfort of supine humans in multi-axis whole-body vibration where lateral motions are excessive. This study revealed that reported discomfort is strongly related to the vibration dose value at the head of supine subjects rather than the input motion to the body.Abbreviations: WBV: whole-body vibration; RMS: root-mean square; VDV: vibration dose value; PSD: power spectral density; RDn: reported discomfort; NDn: normalized discomfort; : discomfort scaling coefficient; aw(t): frequency-weighted acceleration; wRMS: weighted root-mean square; Aw: weighted root-mean square acceleration; Aw,p: point weighted root-mean square acceleration; Wd: frequency-weighting factor; Wk: frequency-weighting factor; kx: weighed acceleration multiplying factor in x-direction; ky: weighed acceleration multiplying factor in y-direction; kz: weighed acceleration multiplying factor in z-direction; CV: coefficient of variation; VDVp: point vibration dose value; SD: standard deviation; pVTV: point vibration total value.

Enhanced Microscopic Dynamics of a Liver Lipid Membrane in the Presence of an Ionic Liquid

Ionic liquids (ILs) are an important class of emerging compounds, owing to their widespread industrial applications in high-performance lubricants for food and cellulose processing, despite their toxicity to living organisms. It is believed that this toxicity is related to their actions on the cellular membrane. Hence, it is vital to understand the interaction of ILs with cell membranes. Here, we report on the effects of an imidazolium-based IL, 1-decyl-3-methylimidazolium tetrafluoroborate (DMIM[BF4]), on the microscopic dynamics of a membrane formed by liver extract lipid, using quasielastic neutron scattering (QENS). The presence of significant quasielastic broadening indicates that stochastic molecular motions of the lipids are active in the system. Two distinct molecular motions, (i) lateral motion of the lipid within the membrane leaflet and (ii) localized internal motions of the lipid, are found to contribute to the QENS broadening. While the lateral motion could be described assuming continuous diffusion, the internal motion is explained on the basis of localized translational diffusion. Incorporation of the IL into the liver lipid membrane is found to enhance the membrane dynamics by accelerating both lateral and internal motions of the lipids. This indicates that the IL induces disorder in the membrane and enhances the fluidity of lipids. This could be explained on the basis of its location in the lipid membrane. Results are compared with various other additives and we provide an indication of a possible correlation between the effects of guest molecules on the dynamics of the membrane and its location within the membrane.

2D ultrasonic elastography with lateral displacement estimation using statistics

Ultrasound elastography is the method of obtaining relative stiffness information of biological tissue, which plays an important role in early diagnosis. Generally, a gradient-based strain imaging algorithm assumes that motion only occurs in an axial direction. However, because tissue has different relative stiffness, the scatter presents lateral motion under high freehand compression. Therefore, errors occur in estimating the cross-correlation phase in the calculation window. A 2D elastography algorithm with lateral displacement estimation using statistics was proposed to reduce errors. The new method was investigated through simulation, and the experiment confirmed that errors introduced by lateral tissue movement have been greatly reduced with no sacrifice of real-time ultrasonic imaging quality.

Motion-induced interruptions and postural equilibrium in linear lateral accelerations

This study assesses lateral tipping motion-induced interruptions (MIIs) in a simulated motion environment. The objective is to revisit MII occurrence and sway motion relationship by focusing on the frequency and acceleration of the lateral motion stimulus. Results verify that MIIs increase with increasing peak sway acceleration, but the effect of sway frequency is not as clear as that of acceleration. Complex multidirectional motions create more tipping MIIs than unidirectional motion. Research should incorporate acceleration, frequency and motion complexity as factors influencing MII occurrence. To describe a temporary loss of balance without tipping, the term 'probable' MII is introduced. This term fills the gap between the theoretical definition and a human-centred perception of an MII where loss of balance is not a binary phenomenon. The 'probable' MIIs were 16-67% more common than the 'definite' MIIs. The developed mathematical model of MII occurrence versus sway acceleration (amplitude, frequency) approximated the observed MIIs with less than 9% difference.

Physiologic considerations of therapeutic slideboard rehabilitation with an external loading device

CONTEXT

Slideboard exercise is consistent with the American College of Sports Medicine guidelines for exercise intensity of 55% to 90% of maximal heart rate or 40% to 85% of maximal oxygen uptake.

OBJECTIVE

To determine if slideboard exercise while in a leg harness increases the metabolic and cardiorespiratory demands.

DESIGN

Repeated-measures design.

SETTING

Athletic Training Research Laboratory.

PATIENTS OR OTHER PARTICIPANTS

Sixteen volunteers from the university community.

INTERVENTION(S)

Subjects performed 2 graded slideboard exercise tests with and without the leg harness, each 2-minute stage ranging from 46 to 90 slides per minute.

MAIN OUTCOME MEASURE(S)

We measured maximal oxygen uptake, heart rate, blood lactate, respiratory exchange ratio, ratings of perceived exertion, and total time to exhaustion during each session.

RESULTS

Significant decreases in maximal oxygen uptake and blood lactate were observed when the leg harness was used.

CONCLUSIONS

Performance was hindered when subjects wore the leg harness during the slideboard exercise.