A geometric analysis of muscle mechanical power with applications to human gait

The interpretation and assessment of the biomechanical behaviour underlying complex movements such as human walking often requires that different time-series representations of the data be mentally combined. Geometrically based data presentation techniques (e.g. phase diagrams) which have been used in the past can sometimes reveal such information more easily through the link of mechanical behaviour to single plot geometries. Yet, examples such as phase or angle-angle diagrams are limited to movement description only (i.e. kinematics). In the present work, a method is introduced which graphs the factors of the muscle mechanical power equation (i.e. net muscle moment of force and relative joint angular velocity). The resulting planar space is called the "power plane" and it offers direct and simultaneous access to the relationship between specific variables associated with both movement and movement cause about a joint from the very plot geometry. In particular, the shape of the power portrait can reveal information about external influences and multiarticular interaction. The power plane diagram extends the phase diagram and is shown to reveal common patterning at the knee joint across various types of human gait which is not evident from the very different time-series plots.