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.
Human Performance under Vibrational Stress
Blindfolded subjects, restrained by standard harness, sat on a modified Air Force chair, which was programmed to move in random patterns in pitch and roll, the subjects counteracting these motions by using a control stick. The whole device was itself mounted on a mechanical shake table producing vertical sinusoidal motion at frequencies ranging from 2 c/s to 20 c/s and at amplitudes corresponding to about one-third of the subjective tolerance limits. The angular deviations from the upright position were evaluated relative to the disturbing input for both pitch and roll, one minute during the vibration experience and one minute after cessation of the vibration. Some individual subjects were not influenced by the vibration; others showed performance decrements. In the mean, these measures of human performance reflect all mechanical resonances within the body, previously established by other methods. The frequencies most affecting performance were found to be between 3 and 12 c/s. Residual effects were detected by the measurements after vibration.
Deformation of the Human Body Due to Uni-Directional Forced Sinusoidal Vibration
The effects of forced vibration upon the human body were determined in the form of circumferential strain of chest, abdomen, pelvis and thigh. Sixteen human subjects, in the sitting erect, sitting relaxed and semi-supine positions, were exposed to vertical sinusoidal frequencies above two c/s at vector accelerations below 1 g. The maximum body strain occurred at 6.7 c/s in the semi-supine position and between 4 c/s and 6 c/s in the sitting positions. In the semi-supine position the mean strain of chest and abdomen at resonance was found to be 0.040 and 0.053 in./in./g, respectively, when standardized to a table acceleration of 1 g. In the sitting positions this strain was only half as large. The strain of the pelvis, on the other hand, was 0.013 in./in./g in the semi-supine posture, and 0.032 in./in./g in the sitting positions. All subjects showed maximum body strain near 7 c/s in the semi-supine posture. Since tolerance to vibration decreases with increasing body strain, the human body on a space couch must be protected against vibrations transverse to the couch axis in the range around 7 c/s.