Effects of vibration frequency, amplitude, and direction on human gait metrics.

The effect of vibrations on gait is a topic that has not been sufficiently analyzed. Thirty-one volunteers underwent 50 walking trials on a modified treadmill with three degrees of freedom including normal walking and walking in the presence of sinusoidal roll, pitch, and vertical vibration. A full factorial design of experiments was adopted, using two vibration amplitudes (4 or 8 cm for linear displacements, 4° or 8° for angular oscillations), four frequencies (0.25, 0.5, 0.7, and 1 Hz), and two walking speeds (0.7 or 1 m/s). A significant alteration of all the gait metrics was found in the presence of vibration, but the step width and cadence resulted in the most affected. A combined effect of all factors was found, with the major impact on gait in the case of rotational vibration, mainly in the case of roll, at higher amplitude and frequencies. Understanding the most detrimental vibration conditions contributes to updating the ISO standard for whole-body vibration considering exposed walking workers.