High-altitude hypoxia alters the visual control of standing balance in lowlanders and Tibetan highlanders.
High-altitude hypoxia affects both visual function and postural control, yet the influence of optic-flow perturbations on standing balance under hypoxic stress remains unclear. Tibetan highlanders (TH) exhibit adaptations to chronic hypoxia, but whether their visually driven postural responses differ from those of lowlanders (LL) has not been investigated. We examined how high-altitude exposure and acclimatization influence static and dynamic visual contributions to balance by delivering sinusoidal optic-flow perturbations in virtual reality at low altitude (1,400 m) and after incremental ascent to high altitude (4,300 m) in acclimatizing LL (n = 15) and TH (n = 14). Anteroposterior center of pressure (AP CoP) velocity and mean power frequency (MPF) were measured during three visual-field conditions (full-, central-, and peripheral-vision) and two optic-flow velocities (peak 1 m/s and 8 m/s at 0.25 Hz). At high altitude, both groups showed attenuated responses to optic flow compared with 1,400 m, reflected by reduced AP CoP velocity and lower MPF across visual-field conditions, consistent with reduced responsiveness to dynamic visual-motion cues under high altitude hypoxia. In contrast, during eyes-open quiet stance [no virtual reality (VR)], TH but not LL exhibited increased AP CoP velocity and MPF at 4,300 m, and no altitude effect was observed with eyes-closed in either group. This finding indicates that TH adopt a visually dependent postural strategy at altitude, whereas LL show minimal changes in static visual balance control but reduced responsiveness to fast dynamic motion. Together, these findings demonstrate that high-altitude hypoxia disrupts dynamic visual processing for balance control in both groups, while revealing group differences in the use of static visual cues during quiet stance.NEW & NOTEWORTHY This is the first study to investigate how high-altitude hypoxia alters visually driven postural control using virtual reality (VR) optic-flow perturbations. We show that hypoxia attenuates sway responses to optic-flow in both lowlanders and Tibetan highlanders, and that visual weighting differs between these groups. These findings reveal altitude- and population-related changes in sensory weighting during standing balance, advancing sensorimotor understanding of postural control in hypoxia.