Fast head tilt has only a minor effect on quick compensatory reactions during the regulation of stance and gait

Sudden tilts of the head to the front or rear were induced during stance, balancing, gait and during perturbations of gait. The most prominent response in the leg muscle electromyogram (e.m.g.) to head tilt occurred in the tibialis anterior muscle (latency about 55 ms) following a backward tilt induced during balancing. During stance and gait, the e.m.g. activity related to head tilt was only a minor component of the leg muscle activity normally occurring during gait. When the head tilt was induced shortly after a perturbation of gait (treadmill acceleration impulse), the compensatory reaction in the leg muscles did not significantly differ from that seen after the gait perturbation alone. In addition, the rate of acceleration of the head was tested against the compensatory e.m.g. responses: No correlation of influence could be discerned. The results indicate that sudden head tilts and the resulting head acceleration have little influence on the e.m.g. patterns that occur during gait and perturbations of gait. It is assumed that these patterns are regulated by central programs, and that the compensation for leg perturbation is achieved mainly by spinal reflex mechanisms. It is discussed whether the lack of head tilt responses is the result of an antagonistic vestibular-neck interaction, or whether it indicates a reduced effectiveness of vestibulo- and cervico-spinal reflexes during gait.