Influence of the kinematic constraints on dynamic residuals in inverse dynamic analysis during human gait without using force plates

Abstract

The conventional use of inverse dynamics applied to gait analysis involves the estimation of joint forces and moments based on kinematic data, anthropometric parameters and force plate data. The procedure uses the measured ground reactions and, beginning with those segments in contact with the ground, calculates joint forces and moments at each successive segment. However, this procedure cannot always be applied. There are laboratories that do not have force platforms, or situations in which measurements must be made outside the laboratory. Force plate data only gives the ground forces and moments resultants. When using multi-segment foot models, additional assumptions must be made to distribute the resultants among the different segments in contact with ground. In these situations, a possible solution is the use of inverse dynamics based only on kinematics. This procedure usually starts with the non-contact segments (head, hands, swinging foot in single support phase) and ends with the foot or feet in contact. In the double-support phase of gait, the ground reaction forces include 12 unknowns, which makes the inverse dynamics problem indeterminate. To solve the indeterminacy, the Smooth Transition Assumption (STA) was used in this work. This algorithm is based on the assumption that the reaction forces and moments at the trailing foot decay according to a certain law that combines exponential and linear functions, reducing the number of unknowns to six. In this work, ground reaction force and moments calculated using different body pose reconstruction methods were compared to data provided by force plates. Results depend greatly on the body pose reconstruction method used. Results show that the imposition of kinematic constrains can lead to worse results in the kinetic results if the multibody model is too simplistic. To get good comparison results between inverse dynamics methods based only on kinematics and classical procedures using force plates data, dynamic residuals should be as small as possible. In the single support phase, differences will be identically equal to the dynamic residuals, but higher in the double support phase because of the errors introduced by the transition functions.