Total body centre of mass displacement estimated using ground reactions during transitory motor tasks: application to step ascent.

A double integration technique is presented that estimates whole body centre of mass (CoM) displacement from signals of a single force platform, compensating for the drift and low frequency noise inherent in the signals. The technique is composed of two different integration techniques, which may also be used separately, and is applied to transitory motor tasks with known initial and final conditions such as step ascent and descent, single step, etc. First, the lowest frequencies within the force platform signals and considered not to be associated with actual movement are filtered out. Second, a regular and a time-reversed double integration are performed and weighted against each other. The technique's accuracy was assessed using computer generated force platform signals that were artificially perturbed. Experimental data were used to compare the estimated CoM displacement to that obtained from a regular double integration and from segmental analysis performed on stereophotogrammetric data. It was shown that the proposed technique's CoM displacement estimates were more repeatable and up to 50% more accurate than those of a regular double integration. Moreover, the CoM displacement estimated using a single force platform and the proposed technique was found to be not statistically different from that obtained with more demanding measurement and processing techniques such as stereophotogrammetry and segmental analysis.