A Kinematic Index for Estimation of Metabolic Rate Reduction in Running with I-RUN

In this paper, we target multiple goals related to our passive running assistive device, called I-RUN. The major goals are: (1) finding the main reason behind individual differences in benefiting from our assistive device at the muscles level, (2) devising a simple measure for on-line I-RUN stiffness tuning, and creating a lab-free simple kinematic measure for (3) estimating metabolic rate reduction as well as (4) training subjects to maximize their benefit from I-RUN. Our approach is using some extensive data-driven OpenSim simulation results employing a generic lower limb model with 92-muscles and 29-DOF. It is observed that there is a significant relation between the hip joints kinematic and changes in the metabolic rate in the presence of I-RUN. Accordingly, a simple kinematic index is devised to estimate metabolic rate reduction. This index not only explains individual differences in metabolic rate reduction but also provides a quantitative measure for training subjects to maximize their benefits from I-RUN. The simulation results also re-confirm our hypothesis that "reducing the forces of two antagonistic mono-articular muscles is sufficient for involved muscles total effort reduction". Consequently, we introduce a two-muscles EMG-based metric for the on-line tuning of I-RUN.