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.
THE EFFECT OF LOW FREQUENCY, HIGH AMPLITUDE, WHOLE BODY, LONGITUDINAL AND TRANSVERSE VIBRATION UPON HUMAN PERFORMANCE
Abstract : Two experiments were conducted to determine the effects of horizontal (transverse and longitudinal) vibration upon the seated human being. Such vibration is typically found in ground vehicles. The transverse (side-to-side) vibration experiment utilized frequencies from 1.5 to 5.5 cps, with intensities of 0.15, 0.25, and 0.35 g. Measures were taken before, during, and following vibration exposure. The longitudinal (fore-aft) vibration experiment utilized the same frequencies with intensities of 0.15, 0.25, and 0.30 g. Measures taken during both experiments were of: compensatory tracking ability, choice reaction time, foot pressure constancy, peripheral vision, visual acuity, body equilibrium, bodily transmissibility, oxygen consumption, breathing rate and total ventilation. The results indicate that transverse and longitudinal, whole-body vibration does affect tracking ability, choice reaction time, foot pressure constancy, and peripheral vision, with some performance decrements being related to specific frequencies and to intensity increments. Visual acuity and body equilibrium were not affected. Performance decrements, transmissibility, and respiratory effects are related and discussed.
The Mechanical Impedance of the Human Body in Sitting and Standing Position at Low Frequencies
The theory of the mechanical impedance of systems with one or more degrees of freedom is applied to the human body. A method of measuring mechanical impedance and determining the parameters of the vibrating systems is developed. Impedance curves for longitudinal vibrations of a sitting and standing subject are established for the frequency range of 1 to 20 c/s. The influence of varied posture and restraining systems is investigated. Dynamic movements of body parts are measured, directly or indirectly, and compared with the impedance curves. The responsible elements in the body for the apparent resonances are identified. Correlations between the impedance function of the body and the subjective tolerance curve to vibration are found and the reasons for the tolerance limits are elucidated. The variability of subjective tolerances due to varying posture, restraining systems, cushions, duration of exposure and vibrations are discussed, and conclusions for the development of protective devices are drawn. The correlation between the steady state response of the human body system and the effects of impact is discussed.