Engine Cab Seating

HS was 45 years old. He had been a locomotive engineer since 1974. In June of 1993, he was the locomotive engineer on a run that encountered a rough section of track. HS was sitting in the engineer's seat when the seat suddenly jolted to the side. Shortly, after the incident, he started to experience back discomfort. HS sought medical attention. He was diagnosed as having a lumbosacral sprain with disc protrusions and probable nerve root irritation. In addition, he was listing to the right due to increased muscle tension on the left lateral lumbar muscular mass.

HF Issues: Could an abrupt lateral movement of the engine that is transmitted to the torso with little attenuation increase the risk of back injury for a person who is seated while operating the cab's controls?


Did the engineer's seat provide adequate support for the lower back? (It was reported that the seat was defective -- it tilted to the side and wobbled.)

HF Investigation:

A portable ergonometer was used to assess the relative stress on the lower back of operating the engine cab controls.

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.

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G. David Sloan, Inc., 1999, www.gdsloan.com, Olympia, WA, USA
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