A simplified model for whole-body angular momentum calculation

Abstract

The capability to monitor gait stability during everyday life could provide key information to guide clinical intervention to patients with lower limb disabilities. Whole body angular momentum (L_body) is a convenient stability indicator for wearable motion capture systems. However, L_body is costly to estimate, because it requires monitoring all major body segment using expensive sensor elements. In this study, we developed a simplified rigid body model by merging connected body segments to reduce the number of body segments, which need to be monitored. We demonstrated that the L_body could be estimated by a seven-segment model accurately for both people with and without lower extremity amputation.

Keywords: Angular momentum; Gait stability; Rigid body model; Wearable system.

Figure 1:

the merging procedure and definition of the merging parameters on the left side of the body and on the trunk and head.

Figure 2.

A), B), and C) The normalized L_body of AB05. Fig. D), E), and F) The normalized L_body of TF01. The L_body calculated from the reference model (blue line), simplified model with the subject-specific optimal merging parameters (red line), and simplified model with the merging parameters shown in Table 2. The steps started from the right heel strike and the dash black lines show the second and the third right heel strike. MVH is an abbreviation of body mass, walking velocity, and body height.

Figure 3:

The angular momentum of the left leg, right leg, and both legs in the sagittal plane. The blue line is from the reference model, the red line is from the optimized model with the thigh, shank, and foot merged together for each leg. The optimization is conducted for each leg separately.