The effect of mastoid vibration on joint angles of lower extremities during walking: implication for sensorimotor training for future spaceflight

A spaceflight in microgravity unloads the peripheral vestibular organs and disturbs the vestibular system of astronauts. This disruption of the vestibular system forces astronauts to use different strategies to walk, such as flexing more on their knee joints to increase force to propel their bodies forward on the Moon. It should be noted that this vestibular disruption observed in microgravity cannot easily be replicated on Earth. However, mastoid vibration (MV) has been shown to be an effective alternative method for disrupting vestibular function. The application of MV during walking has been demonstrated to alter gait characteristics regardless of the different terrains. Could these changes in gait characteristics induced by MV also affect joint angle patterns in a similar manner? Therefore, the purpose of this study was to fill this knowledge gap. This study involved fifteen young adults and ten older adults. Two motion capture cylinders were used to record the trajectory of 10 body land markers. Two electromechanical vibrotactile transducers were placed on bilateral mastoid processes to generate the MV at 100Hz. A reduced-light intensity goggle was used to reduce the visual capability during walking. A total of six 2-minute walking trials were randomly assigned to each participant (3 MV: bilateral/unilateral/no MV x 2 vision levels: full/reduced vision). Dependent variables included peak values, range of motion (ROM), and respective hip, knee, and ankle joint variabilities. A significant interaction between the effects of aging, vision level, and different types of MV was observed in the peak hip flexion angle ( p  = 0.001). Post hoc comparisons indicated that 1) applying bilateral MV significantly decreased peak hip flexion of healthy young but increased peak hip flexion of healthy young in reduced vision condition, and 2) applying bilateral MV induced a greater effect on decreasing hip flexion than applying unilateral MV in all participants regardless of whether vision was full or reduced. The findings of this study revealed the important role of hip joints in balance control during gait under vestibular and/or visual perturbation. Also, MV could be used to simulate a vestibular-disrupted environment for astronauts for future sensorimotor training.