Suitability of Sacrum Motion in Computing Dynamic Gait Stability Indices

Gait stability indices are expected to preemptively detect people at high risk of falling. Among these, the margin of stability (MoS) is known as a valid index. Usually, the computation of MoS requires the motion-related information of multiple feature points of the body; however, we have been pursuing the use of only one feature point. We estimated the anterior and mediolateral MoS values from the velocity time series of the sacrum, knee, or toe using principal motion analysis. Based on open gait data for 60 people over 60 years of age, the sacrum was best suited for computing MoS in the anterior and mediolateral directions. The correlation coefficients between the estimated and observed values were 0.77 and 0.73, respectively. Our findings will help establish an easy-to-access and accurate measurement of MoS values using an inertial measurement unit attached to a body feature.