Human body nonlinearity and mechanical impedance analyses

Abstract

Mechanical impedance techniques have been used by many investigators to evaluate human body dynamics and to imply energy transmission within the body. The use of mechanical impedance as a whole body characteristic requires that the body responds as a linear system for either steady state or transient accelerations. Data presented within this paper indicate the recognition of nonlinearities as seen in the measured response of subjects seated erect in several impact and vibrational environments. Significant variations in the transient impedance occur with a variation in input acceleration for one subject. Steady state force response exhibits nonlinearity in its waveform. To gain an analytical insight into the nonlinear response, a nonlinear whole body model was subjected to a half sine pulse and the response calculated. The transient mechanical impedance indicated that the phase angles achieved were beyond those permitted by a linear system.