Optimal work-rest schedules under prolonged vibration.
This research was conducted for the purpose of studying the performance and recovery characteristics of men when subjected to low-level, whole-body vertical sinusoidal vibration for durations of one to two hours. Several male subjects performed a vertical compensatory tracking task using a CKT display according to three work-rest schedules under both normal and vibratory environments. The vibratory environment was that of vertical sinusoidal vibration with a frequency of.5 cps and an amplitude- of 0-08 inches resulting in an acceleration intensity of approximately 0.20 g. The working period was divided into equal intervals during which performance was continuously monitored. Decrement of performance was measured using absolute error score. Results and conclusions are presented regarding performance decrement and recovery under varying work-rest schedules. Optimum work-rest schedules and implications of control tasks under a vibratory environment are discussed.
Effects of duration and vibration on performance of a continuous manual control task
An experiment is described in which two independent groups of seated subjects performed a pursuit tracking task for 202·5 min on two separate occasions. For one group, the total duration included 180 min exposure to vertical z-axis, whole-body random vibration with a bandwidth of 1 octave centred on 4 Hz. The weighted acceleration magnitude was 1·4 ms−2 r. m. s., with a crest factor of 4·13. Using the procedures denned in British Standard 6841 (BSI 1987), the motion had a vibration dose value of 20 ms−1·75. The other group received no vibration exposure. Results showed that performance declined as function of duration, but that vibration exposure did not impair performance or interact with the effect of duration. Performance in the second sessions showed less effect of duration than in the first session. The effect of duration was associated with change in both linear and non-linear tracking behaviour. Closed loop system transfer functions showed both reduced moduli and increased phase lags with increasin...
The Effects of Simulated Buffeting on the Internal Pressure of Man
The effects of mechanically induced vibration upon the human abdomen were determined by measuring the pressure in the rectal end of the colon sigmoideum. A technique was developed for transmitting the internal pressure to external recorders, and the amplitudes of the colon pressure fluctuations were determined, when eight human subjects and one Rhesus monkey were subjected to vertical sinusoidal vibration, at vector accelerations of less than one g, in the frequency range of one through twenty c/s. The pressure fluctuations were found to vary with frequency, showing maximum mean “peak to peak” pressure, per one g acceleration, of 57 mm Hg at 4.5 c/s and 4 c/s, sitting erect and sitting relaxed; and 30 mm Hg at 7 c/s in the semi-supine posture of human subjects. These resonances confirm the results of related prior studies of the human body as a mechanical system.