Gait-dependent integration of neck muscle afferent input.

We investigated the integration of neck muscle afferents during walking and running. Subjects walked or ran straight ahead, with or without an additional mass (20% of body weight). They performed all trials without vibration and with continuous vibration (80 Hz) applied to the lateral aspect of the neck. Vibration systematically caused body deviation toward the side opposite to the stimulation. The amplitude of vibration-induced body deviations was dramatically larger for walking (21.6 +/- 4.6 degrees ) than for running (8.0 +/- 2.5 degrees ). The additional mass marginally straightened body trajectory (average 5.6%), indicating that the gait-dependent effect of neck vibration cannot solely be attributed to differences in body inertia between walking and running. We concluded that neck muscle afferences are selectively gated according to the gait performed.