Horizontal plane head stabilization during locomotor tasks

Frequency characteristics of head stabilization were examined during locomo tor tasks in healthy young adults (N = 8) who performed normal walking and 3 walking tasks designed to produce perturbations primarily in the horizont al plane. In the 3 walking tasks, the arms moved in phase with leg movement , with abnormally large amplitude, and at twice the frequency of leg moveme nt. Head-in-space angular velocity was examined at the predominant frequenc ies of trunk motion. Head movements in space occurred at low frequencies (< 4.0 Hz) in all conditions and at higher frequencies (> 4.0 Hz) when the ar ms moved at twice the frequency of the legs. Head stabilization strategies were determined from head-on-trunk with respect to trunk frequency profiles derived from angular velocity data. During natural walking at low frequenc ies (< 3.0 Hz), head-on-trunk movement was less than trunk movement. At fre quencies 3.0 Hz or greater, equal and opposite compensatory movement ensure d head stability. When arm swing was altered, compensatory movement guarant eed head stability at all frequencies. Head stabilization was successful fu r frequencies up to 10.0 Hz during locomotor tasks. Maintaining head stabil ity at high frequencies during voluntary tasks suggests that participants u sed feedforward mechanisms to coordinate head and trunk movements. Maintena nce of head stability during dynamic tasks allows optimal conditions for ve stibule-ocular reflex function.