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The effect of posture and seat suspension design on discomfort and back muscle fatigue during simulated truck driving.

Wilder-DG; Magnusson-ML; Fenwick-J; Pope-M
Appl Ergon 1994 Apr; 25(2):66-76
The effects of posture and seat suspension design on discomfort and back muscle fatigue during simulated truck driving were examined. The study group consisted of six male volunteers, mean age 28.5 years, who were free of back pain. They sat in a standard spring suspended seat or seat with a gas spring in its suspension (gas suspended seat) while performing a 10 minute simulated truck driving task. They adopted three driving postures: two hands on the wheel leaning forward while resting the forearms on the wheel, two hands on the wheel while sitting upright (upright posture), and seated back against the back rest. During the tasks the subjects were subjected to 1 to 20 hertz whole body vibrations having root mean square accelerations of up to 0.20 meter per second squared. The subjects rated their perceived level of discomfort before and after each trial using a visual analog scale. Electromyographic (EMG) spectra were recorded from the L3 level of the erector spinae muscles. The EMG data were examined every 10 seconds for signs of muscle fatigue. The magnitude and phase of the vibrations transmitted to the seat pans were calculated. Regardless of seat type, the upright posture was always rated to be the most uncomfortable. Seat type did not significantly affect any of the discomfort ratings. Muscle fatigue was detected in every 10 second interval. The level of fatigue was greatest for the upright posture and was not significantly influenced by seat type. The type of seat suspension did not significantly affect the natural frequency or the vibration transmissability. The natural frequency of the upright posture was significantly greater than those of the other postures. The gas suspended seat transferred significantly less motion to the seat pan than the standard suspension only when the subjects were sitting in the upright posture. Vibration transmissability to the seat pan did not differ for any of the other experimental conditions. The authors conclude that under the experimental conditions none of the comfort ratings or muscle fatigue evaluations were affected by the type of seat suspension. The characteristics of vibration attenuating seats should continue to be evaluated by human subjects.
NIOSH-Publication; NIOSH-Grant; Musculoskeletal-system-disorders; Truck-drivers; Vibration-exposure; Vibration-suppressors; Physiological-fatigue; Back-injuries; Ergonomics; Psychophysiology; Electrophysiological-measurements
Orthopedics and Rehabilitation, University of Vermont, Given Building, Burlington, Vermont 05405, USA
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Journal Article
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Applied Ergonomics
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University of Vermont & St Agric College, Burlington, Vermont