Low frequency self-generated vibration during ambulation in normal men.

An assessment was made of the upper body low frequency steady-state vibration in five normal male subjects during level walking in a straight line. Speed of progression ranged from 0.99 to 2.35 m/s. Through a stereophotogrammetric technique, a three-dimensional measurement of the linear displacement of the longitudinal axis of the trunk and head was done. The relevant accelerations were obtained by double differentiation and described both in the time and frequency domains. The data were compared with those available on the biodynamic properties of body tissues and on the subjective response of humans to externally generated whole-body vibration. The comparison yielded a consistent indication of the characteristics of the vibration stimulus to which the human body may be adapted. As walking speed approached its maximum, the vertical acceleration spectrum increased in magnitude and shifted critically close to frequencies at which body organs are known to undergo resonance. A coordinated movement of the trunk with respect to the pelvis helped to reduce to a minimum the value of the acceleration to which the head was submitted in the antero-posterior direction and to shift the relevant spectrum towards the lower frequencies.