It is known from animal experiments that the vestibulospinal pathway is an effector control of the vestibular nucleus, whose stimulation generates an increase in the muscular tone during the stance phase of walk without affecting the muscular coordination. Increasing movement speed (walk to run) inhibits peripheral vestibular afferents in favour of central automatic motor programs. The aim of this study was to quantify the impact of a transient vestibular tone imbalance (TVTI) on the level of muscular activity and muscular synergies during walking and running, in human.

Eleven asymptomatic participants aged between 20 and 28 years took part in the study. Participants were instructed to walk or run for a distance of 10m with the eyes closed (control conditions). They also were instructed to perform the same tasks after 10 rotations on an armchair at 360°/s, before being abruptly stopped (experimental conditions). For each condition, muscular synergies were extracted by using the non-negative matrix factorization on the surface electromyographic (EMG) signal of 8 lower limb muscles. Additionally, the change in muscle activation (ΔEMG) due to the TVTI in each mode of locomotion (walk or run) was determined by the mean EMG amplitude during the TVTI condition with the one during the control condition. The lateral deviation of locomotion was quantified by a Vicon 3D analysis system.

Muscle synergies were similar across conditions (in number, composition and activation), while ΔEMG of the stance phase during walking was significantly (P=0.038) higher than during running. The TVTI increased the lateral deviation in both modes of locomotion (P<0.001) but this effect was higher in walking than running (P=0.001).

This study corroborated previous findings that vestibular inputs were differentially regulated depending on the locomotion speed but had no effect on the underlying muscle coordination of locomotion. This result could open a new paradigm of rehabilitation of vestibulopathic subjects, by training them to flexibly regulated the weightings among sensory inputs to produce the motor response.