Page 31 - JSOM Fall 2018

logs and streams, and used pulley­based systems to hoist and FIGURE 2 Teams pulled the litter across the ground.
lower the litter over the steepest terrain. The rescue litter,
Sked (Skedco, https://skedco.com/), was composed of flexible
®
plastic, which became rigid upon patient loading and immo­
bilization, as described in Army Training Publication 4­25.13
Casualty Evacuation (Figures 1–3). 4

FIGURE 1 Pulley systems used to hoist the litter.

FIGURE 3 Teams carried the litter across streams.

Accelerometer
A low­mass, wireless, shock and vibration data logger using a
capacitive MEMS triaxial accelerometer (Slam Stick C; Midé
Technology, https://www.mide.com/) was used for data acqui­
sition. This accelerometer digitally recorded acceleration of
the device across three dimensions (x, y, z). Each acceleration
data point was logged with the time of measurement and di­
rection of acceleration. For these trials, the accelerometer sam­
pled at a rate of 1650Hz.

Accelerometer Placement
The accelerometer must be mounted firmly to obtain valid
measurements. The accelerometer used in this study required
3M 950 adhesive tape (https://www.3m.com) to validate man­
ufacturer calibration and, therefore, could not be mounted
on a human patient. Two trials were measured to compare
accuracy of different sensor placements. As seen in Figure
4, during trial 1, the accelerometer was affixed to the inside
surface of the Sked corresponding to the patient’s lumbar re­
gion. For trial 2, the accelerometer was mounted within the
chest cavity of the mannequin. During the Sked­mounted trial,
the x­axis paralleled the superior­inferior axis of the patient.
During the mannequin­mounted trial, the y­axis paralleled the
superior­inferior axis of the patient. In both trials, the z­axis
paralleled the anterior­posterior axis of the patient.

Mechanical Forces During Movement in Mountainous Terrain | 29