D11 Mode Identification

Topic

This identification of the dynamic mode determines, in general, the specific kinematic and kinetic pattern within which the athlete operates at any given moment of their movement—whether walking, running, sprinting, jumping, or executing any other distinct movement pattern.

The most universal criterion for distinguishing between these movement patterns is the presence or absence of a complete aerial phase within each movement cycle: if the athlete maintains simultaneous double contact with the ground during part of the cycle, they are walking; however, as soon as they completely lose ground contact during an aerial phase of the cycle, they are running rather than walking.

The Froude number marks the transition between walking and running in a more quantitative manner than the mere presence or absence of an aerial phase: it compares the athlete's speed against the acceleration due to gravity and the characteristic length of their leg, with the transition occurring precisely when the Froude number crosses a specific critical value. When the athlete's Froude number exceeds this critical value, they shift from the walking pattern to the running pattern.

Finally, the athlete's leg stiffness—combined with the ratio of ground contact time to flight time—determines whether they are operating in an elastic-reactive mode (featuring a brief stretch-shortening cycle similar in spirit to the tendon-based stretch-shortening cycle found in other models) or in a concentric generation mode (characterized by a much more prolonged active muscle contraction). The fact that the athlete's ground contact time is even shorter relative to their flight time means that the athlete operates more clearly within the elastic-reactive mode rather than the concentric generation mode. Consequently, this model—which began by identifying the athlete's dynamic mode at any given instant—allows the force platform, the 3D motion analysis system, and the electrical signals from the athlete's muscles to combine and automatically classify the dynamic mode based on a fully quantifiable biomechanical criterion. The system measures the velocity of the athlete's center of mass, contact time, flight time, and the ground reaction force pattern for each step; based on the aggregate of these measured variables, it determines the athlete's final active mode, as well as the Froude number, leg stiffness, and the contact-to-flight time ratio introduced at the start of the model. Because this combined system measures these variables with an even higher frequency over time, the final identification of the athlete's active dynamic mode becomes increasingly precise at each successive moment of movement.

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