Characteristics of the force applied to a pedal during human pushing efforts: Emergent linearity

The force seated humans exert on a translationally fixed pedal (foot force) may be directed at any angle because the fu;ed distance between the seat a nd the pedal axis kinematically constrains the lower limb. The authors' obj ective in the present work was to characterize such force. Participants (N = 7) generated force with their lower limb by pushing against the pedal in the most comfortable manner. Pushing efforts were repeated randomly 3 times at each of 97 sagittal-plane pedal axis positions and 10 additional times in 9 of those positions (2,895 total pushes). In 87% of the pushes, the mea sured sagittal-plane force exerted on the pedal by the foot changed magnitu de and direction through time, such that the path of the head of the force vector traced a straight line. The linearity of the foot force paths reflec ted directional invariance in the changes of the foot force vector as the m agnitude of the vector increased. The orientation of those linear force pat hs varied with limb posture in a similar manner across participants. The au thors conclude that the emergent linearity of the force path is consistent with minimization of path length in foot force space. Alternatively, the li nearity of the force paths suggests a motor control strategy that simplifie s the control to a monoparametric form.