This apparatus monitors the electrical activity of muscles (EMG)
at the location where its surface electrodes are affixed to the
body. The unit provides auditory biofeedback as to the extent
of muscular activity. The surface electrodes were placed on HS's
back as shown in the graphic above.
After the electrodes were affixed and the ergonometer calibrated.
HS was instructed to reach, in turn, for each of the engine cab
controls while seated. A video camera was used to record HS's
actions and the associated auditory correlates to EMG.
HF Analysis: A 3D computer model of HS was generated
in a computer application that can estimate the torques on the
lumbosacral joint for different postures (HumanCad). The model
was placed in a seated position and the torques calculated for
the different postures adopted by HS as recorded on the videotape.
The highest torques were recorded for postures where the engineer
leans forward, rotates his upper torso to the left, and extends
both arms. This was consistent with the EMG data. Additional factors
considered were "seat wobble" and susceptibility to whole-body
lateral and horizontal vibration, and the relation between vibration
and muscular fatigue. Seat design was examined in terms of how
well it supported the engineer's activities and dampened vibration.