Experimental determination of short-term creep of femoral sheep bones and theoretical estimation of the dissipated energy during walking

The short-term creep of ten fresh femoral sheep bones was determined through an analysis of their strain response in the time interval 10 super(-2)-10 super(3) s, under constant load corresponding to 100% body weight. The strain in the direction of minimum principal stress was measured by strain gauges attached at two points located on the ventral dorsal level at one-half and three-quarters of the bone's length, beginning from the knee joint. The experimental data were analyzed using a three-parameter viscoelastic model consisting of a spring and a Kelvin element in series, and the material constants were calculated. The results indicate that the viscoelastic behaviour of femoral compact bone presents a transition phase with a time constant comparable with that of the normal walking period. Approximating the stress developed under walking conditions by a sinusoidal function, the corresponding strain time function and the dissipated energy due to viscoelastic mechanisms were estimated. According to our estimations the dissipated energy during normal walking conditions (speed 2.5 km h super(-1) and 60 steps min super(-1)) was about 12%.