DYNAMIC RESPONSE OF THE STANDING HUMAN BODY EXPOSED TO VERTICAL VIBRATION: INFLUENCE OF POSTURE AND VIBRATION MAGNITUDE

✍ Scribed by Y. Matsumoto; M.J. Griffin

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 354 KB
• Volume: 212
• Category: Article
• ISSN: 0022-460X
• DOI: 10.1006/jsvi.1997.1376

✦ Synopsis

The influence of the posture of the legs and the vibration magnitude on the dynamic response of the standing human body exposed to vertical whole-body vibration has been investigated. Motions were measured on the body surface at the first and eighth thoracic and fourth lumbar vertebrae (T1, T8 and L4), at the right and left iliac crests and at the knee. Twelve subjects took part in the experiment with three leg postures (normal, legs bent and one leg), and five magnitudes of random vibration (0•125-2•0 ms -2 r.m.s.) in the frequency range from 0•5-30 Hz. The main resonance frequencies of the apparent masses at 1•0 ms -2 r.m.s. differed between postures: 5•5 Hz in the normal posture, 2•75 Hz in the legs bent posture and 3•75 Hz in the one leg posture. In the normal posture, the transmissibilities to L4 and the iliac crests showed a similar trend to the apparent mass at low frequencies. With the legs straight, no resonance was observed in the legs at frequencies below 15 Hz. In the legs bent posture, a bending motion of the legs at the knee and a pitching or bending motion of the upper-body appeared to contribute to the resonance of the whole body as observed in the apparent mass, with attenuation of vibration transmission to the upper body at high frequencies. In the one leg posture, coupled rotational motion of the whole upper-body about the hip joint may have contributed to the resonance observed in the apparent mass at low frequencies and the attenuation of vertical vibration transmission at high frequencies. The resonance frequency of the apparent mass in the normal posture decreased from 6•75-5•25 Hz with increasing vibration magnitude from 0•125 to 2•0 ms -2 r.m.s. This ''softening'' effect was also found in the transmissibilities to many parts of the body that showed resonances.