Comparison of inverse dynamics calculated by two- and three-dimensional models during walking.

The purpose of the study was to compare joint moments calculated by a two- (2D) and a three-dimensional (3D) inverse dynamics model to examine how the different approaches influenced the joint moment profiles. Fifteen healthy male subjects participated in the study. A five-camera video system recorded the subjects as they walked across two force plates. The subjects were invited to approach a walking speed of 4.5 km/h. The ankle, knee and hip joint moments in the sagittal plane were calculated by 2D and 3D inverse dynamics analysis and compared. Despite the uniform walking speed (4.53 km/h) and similar footwear, relatively large inter-individual variations were found in the joint moment patterns during the stance phase. The differences between individuals were present in both the 2D and 3D analysis. For the entire sample of subjects the overall time course pattern of the ankle, knee and hip joint moments was almost identical in 2D and 3D. However, statistically significant differences were observed in the magnitude of the moments, which could be explained by differences in the joint centre location and joint axes used in the two approaches. In conclusion, there were differences between the magnitude of the joint moments calculated by 2D and 3D inverse dynamics but the inter-individual variation was not affected by the different models. The simpler 2D model seems therefore appropriate for human gait analysis. However, comparisons of gait data from different studies are problematic if the calculations are based on different approaches. A future perspective for solving this problem could be to introduce a standard proposal for human gait analysis.