JINDRICH, Devin L.; BESIER, Thor F.; LLOYD, David G.; Univ. of California, Los Angeles; Stanford University; University of Western Australia: Mechanical constraints on the control of human running turns

To execute movement, neural control systems must work within mechanical constraints imposed by the motor task. Specific force, work and power requirements have been identified for constant-average-velocity locomotion. However, for other aspects of locomotion such as maintaining stability or maneuvering, mechanical constraints have not been identified. We tested the hypothesis that requirement for body rotation to match the change in movement direction constrains leg force production during running turns. Using a simple, algebraic model of maneuverability in the horizontal plane, we hypothesized that braking forces would be required to prevent body over-rotation when humans turn. To test this hypothesis, we analyzed force and kinematic data from 7 male subjects executing 105 sidestep and crossover cuts at average initial running velocities of 3 m s-1. Absent braking, the lateral forces required to turn would result in body rotations 1.4 to 3 times the change in movement direction. The orientation of the body would be substantially mis-aligned with the direction of movement at the end of the step, supporting the hypothesis. The braking forces predicted by the simple model could explain 67% of the variance in braking forces measured during sidestep and crossover cuts of a range of magnitudes. Identifying the mechanical requirements for stability and maneuverability during locomotion can contribute to interpreting motor output and correcting movement pathologies.