Determination of the step duration of gait initiation using a mechanical energy analysis

The analysis of gait initiation (the transient state between standing and walking) is an important diagnostic tool in the study of pathologic gait and the evaluation of prosthetic devices. Therefore it is important to know the step duration of gait initiation. However, there is little agreement in the literature regarding this step duration, since each author has based their conclusion on a different biomechanical parameter. In this study, gait initiation in seven normal subjects was studied using a mechanical energy analysis. The number of steps necessary to reach steady state was determined based on the fact that in steady-state gait, the net mechanical work of the body over one stride is zero (Winter et al. J. Biomechanics 9, 253-257, 1976). The variance of the work for a stride during steady-state walking was calculated for 100 steady-state trials from a separate database of normal subjects. The stride work was normalized to the subject's body weight (BW) and leg length (LL), and 95% confidence limits were defined from this data at -1.68%BW * LL < epsilon < 1.28%BW * LL. Total body energy during gait initiation was then computed for the seven test subjects. The energy analysis of gait initiation showed that steady state was attained by the end of three full steps. Therefore, a researcher studying gait initiation must allow his/her subject to take three full steps when recording data to ensure that the full event is included.