EFFECT OF REDUCED GRAVITY ON THE PREFERRED WALK-RUN TRANSITION SPEED

We investigated the effect of reduced gravity on the human walk-run ga it transition speed and interpreted the results using an inverted-pend ulum mechanical model, We simulated reduced gravity using an apparatus that applied a nearly constant upward force at the center of mass, an d the subjects walked and ran on a motorized treadmill, In the inverte d pendulum model for walking, gravity provides the centripetal force n eeded to keep the pendulum in contact with the ground, The ratio of th e centripetal and gravitational forces (mv(2)/L)/(mg) reduces to the d imensionless Froude number (v(2)/gL), Applying this model to a walking human, m is body mass, v is forward velocity, L is leg length and g i s gravity, In normal gravity, humans and other bipeds with different l eg lengths all choose to switch from a walk to a run at different abso lute speeds but at approximately the same Froude number (0.5), We foun d that, at lower levels of gravity, the walk-run transition occurred a t progressively slower absolute speeds but at approximately the same F roude number, This supports the hypothesis that the walk-run transitio n is triggered by the dynamics of an inverted-pendulum system.