Search Results

You are looking at 1-10 of 23

Fig. 2.; Joint reaction forces across all postures and helmet conditions. A single asterisk denotes significant differences at P < 0.05, double asterisks P < 0.01, and triple asterisks P < 0.001. A) Compression. The dashed horizontal line indicates 10% of the estimated compressive tolerance (390 N) of the C5-C6 functional spinal unit (3.9 kN). B) Anteroposterior shear acting on C5. These can be thought of as the required anteriorly directed force sustained by the joint to prevent C5 from accelerating posteriorly. The bold dashed line (50 N) indicates 10% of the estimated shear tolerance (500 N) of the C5-C6 functional spinal unit. C) Mediolateral shear.

Jeff M. Barrett,

Colin D. McKinnon,

Clark R. Dickerson,

Andrew C. Laing, and

Jack P. Callaghan

Fig. 2.

Joint reaction forces across all postures and helmet conditions. A single asterisk denotes significant differences at P < 0.05, double asterisks P < 0.01, and triple asterisks P < 0.001. A) Compression. The dashed horizontal line indicates 10% of the estimated compressive tolerance (390 N) of the C5-C6 functional spinal unit (3.9 kN). B) Anteroposterior shear acting on C5. These can be thought of as the required anteriorly directed force sustained by the joint to prevent C5 from accelerating posteriorly. The bold dashed line (50 N) indicates 10% of the estimated shear tolerance (500 N) of the C5-C6 functional spinal unit. C) Mediolateral shear.

Posture and Helmet Configuration Effects on Joint Reaction Loads in the Middle Cervical Spine

Jeff M. Barrett,

Colin D. McKinnon,

Clark R. Dickerson,

Andrew C. Laing, and

Jack P. Callaghan

Article Category: Research Article

Volume/Issue: Volume 93: Issue 5

Online Publication Date: May 01, 2022

DOI: 10.3357/AMHP.5830.2022

Page Range: 458 – 466

. 7 , 43 Investigations into chronic neck pain, helmeted occupations, and electromyography (EMG) of both the superficial and deep musculature of the neck have found modest increases in muscle activity (2–3% maximum voluntary exertion) from donning NVGs. 29 , 37 However, these authors have yet to contextualize these findings with respect to direct mechanical exposures, such as cervical joint compression or shear forces. To date, there have been few investigations aiming to quantify the loads on the cervical spine with helmet conditions. Snijders et al

Download PDF

Fig. 1.; A) Experimental set-up for MVE trials. The robotic arm was attached to the posterior aspect of the helmet and subjects performed exertions in flexion, extension, rotation, and lateral bending from this position. B) (Top row) The helmet conditions examined in this study. From right to left, No Helmet, helmet only (hOnly), helmet and night vision goggles (hNVG), and the helmet, night vision goggles, and counterweight (hNVG + CW). (Bottom row) The OpenSim cervical spine model demonstrating the five posture conditions used in the study. There is no representative geometry for the helmet, but it is represented mathematically.

Jeff M. Barrett,

Colin D. McKinnon,

Clark R. Dickerson,

Andrew C. Laing, and

Jack P. Callaghan

Fig. 1.

A) Experimental set-up for MVE trials. The robotic arm was attached to the posterior aspect of the helmet and subjects performed exertions in flexion, extension, rotation, and lateral bending from this position. B) (Top row) The helmet conditions examined in this study. From right to left, No Helmet, helmet only (hOnly), helmet and night vision goggles (hNVG), and the helmet, night vision goggles, and counterweight (hNVG + CW). (Bottom row) The OpenSim cervical spine model demonstrating the five posture conditions used in the study. There is no representative geometry for the helmet, but it is represented mathematically.

Fig. 4.; Center of mass (CoM) positions for the helmet only condition (hOnly) compared to the night vision goggles (hNVG) without and with (hNVG + CW) conditions.

Jeff M. Barrett,

Colin D. McKinnon,

Clark R. Dickerson,

Andrew C. Laing, and

Jack P. Callaghan

Fig. 4.

Center of mass (CoM) positions for the helmet only condition (hOnly) compared to the night vision goggles (hNVG) without and with (hNVG + CW) conditions.

Fig. 3.; Changes in the flexion-extension moment with posture and helmet condition. Significance is annotated as indicated in Fig. 1, with a single asterisk denoting P < 0.05, double asterisks P < 0.01, and triple asterisks P < 0.001.

Jeff M. Barrett,

Colin D. McKinnon,

Clark R. Dickerson,

Andrew C. Laing, and

Jack P. Callaghan

Fig. 3.

Changes in the flexion-extension moment with posture and helmet condition. Significance is annotated as indicated in Fig. 1, with a single asterisk denoting P < 0.05, double asterisks P < 0.01, and triple asterisks P < 0.001.

Venous Thromboembolism in Exploration Class Human Spaceflight

Sophie Levasseur,

Nina Purvis,

Sophia Trozzo,

Seok Hoon Chung,

Matthew Ades, and

Laura M. Drudi

Article Category: Review Article

Volume/Issue: Volume 95: Issue 1

Online Publication Date: Jan 01, 2024

DOI: 10.3357/AMHP.6290.2024

Page Range: 45 – 53

. Lowered shear stress, such as in reduced or low flow situations, has been associated with thrombosis via upregulated proinflammatory changes and prothrombotic markers, overriding the protective mechanisms, such as fibrinolysis, usually present with wall shear stress. 36 , 49 Additionally, this increase in inflammatory components upregulates the Von Willibrand factor and other coagulation factors, activating the coagulation cascade while promoting arterial atherogenic events. 8 It is currently unclear how weightlessness affects endothelial shear stress in both venous

Download PDF