Positive Hysteresis and Negative Hysteresis in Human Gait Transition

The present study investigates the dynamics of human walk-to-run (W-R) and run-to-walk (R-W) transitions. Most particularly, it investigates the difference between the critical velocities (specifically, Froude Numbers) at which walk transitions to run and run transitions to walk, a difference referred to as hysteresis. Its primary theoretical focus is expressing the dynamics that distinguishes between (a) the classically observed positive hysteresis in which R-W critical Froude Number \u3e W-R critical Froude Number and (b) the recently observed negative hysteresis in which R-W critical Froude Number \u3c W-R critical Froude Number. Four experiments on treadmill locomotion of young adults were directed at the dependence of hysteresis on (1) treadmill speed (constantly increasing or decreasing), (2) treadmill slope (0%, 5% and 10%), (3) concurrent cognitive activity (no counting, counting back from a given number by ones, by sevens), and (4) so-called functional distance (report of upcoming transition speed while walking or running on the treadmill versus while standing off the treadmill). In respect to Experiment 1, treadmill speed did not affect critical Froude Numbers and, perforce, degrees of positive hysteresis. In respect to Experiment 2, treadmill inclination affected the critical Froude Numbers but not the degree of positive hysteresis. In respect to Experiment 3, the more difficult the cognitive activity concurrent with treadmill locomotion the larger the positive hysteresis. In respect to Experiment 4, judging the treadmill speed at which a gait transition was expected when standing off the treadmill yielded negative hysteresis in contrast to the positive hysteresis when walking or running on the treadmill. The results of the four experiments were addressed through a synergetic model of positive and negative hysteresis adapted from Lopresti-Goodman et al. (2013). The results were found to be consistent with principles of self- organization