Is the behaviour of the leg during oscillation linear?

The linear behaviour of the human leg was studied using a free oscillation method. The lower leg is represented by a simple mass, spring and dashpot m odel. Forty-five subjects underwent free vibration tests on their right leg s. The force amplitude and the time period, for successive oscillations ena bled calculation of the stiffness to mass ratio values. It was found that t he time period of the second oscillation cycle was significantly lower than that of the first, implying a corresponding increase in stiffness. The exp erimental data consistently exhibits these non-linear characteristics, indi cating that the use of non-linear models could be: of benefit For future fr ee oscillation studies. (C) 2001 Elsevier Science Ltd. All rights reserved.