Standing balance is preserved despite altered orthostatic cardiovascular responses during high-altitude acclimatization

Millions of people live above 3,500 m, where standing balance and orthostatic tolerance are essential for daily activities. At high altitude, reduced oxygen availability triggers a hypoxic ventilatory response that, with sustained exposure (ventilatory acclimatization), helps to preserve arterial oxygenation but also causes hypocapnia. Although hypoxia increases cerebral blood flow, accompanying hypocapnia may attenuate cerebrovascular reactivity, potentially challenging orthostasis. Evidence for the effects of hypoxia and acclimatization on standing balance is mixed, and the relationship between orthostatic cardiovascular responses and postural stability at high altitude remains unclear. While ascent to high altitude increases sympathetic activity and may help preserve resting blood pressure, hypoxia may pose unique challenges to orthostatic control. Sex-based differences in these responses are also largely unexplored. We therefore tested whether orthostatic cardiovascular responses were associated with standing balance during ascent to high altitude, and whether cardiovascular and postural responses altered with acclimatization in both males and females. Twenty-three participants (11F, 12M; mean age 32 ± 11) completed testing at low altitude in Calgary, Canada (1,100 m; LA), followed by high-altitude testing in La Paz, Bolivia (3,500 m) during early (days 2-3; HA2/3) and late (days 8-9; HA8/9) exposure. Each testing day included 10 min of supine rest followed by a 10 min active stand test on a force plate. Systolic blood pressure (SBP) and center-of-pressure (CoP) metrics (95% ellipse area and jerk) quantified orthostatic blood pressure responses and standing balance, respectively, during the initial (0-10 sec) and recovery (30-60 sec) phases of standing. Heart rate (HR) peak was determined across the full 10 min of standing. Orthostatic changes were calculated as standing minus supine values (ΔSBP: mean within each phase; ΔHR: peak during standing). High-altitude acclimatization significantly increased ΔSBP with standing, with a larger drop at HA8/9 compared to LA during the initial stand phase (0-10 sec; P=0.0073). During recovery (30-60 sec), ΔSBP remained lower at HA8/9 compared to both LA (P=0.0402) and HA2/3 (P=0.0105). In parallel, ΔHR following standing increased at HA8/9 compared to LA (P=0.0018). CoP 95% ellipse area and jerk did not differ between days during the initial phase (P >0.1299). During the recovery phase, CoP jerk was significantly lower at HA8/9 compared to LA (P=0.0013) and HA2/3 (P=0.0361), indicating reduced postural variability with acclimatization. No significant sex differences were observed for any outcome measures (P >0.0990). Despite altered cardiovascular responses with acclimatization, standing balance was preserved with both acute ascent and sustained exposure to high altitude. Together, these findings demonstrate distinct cardiovascular and postural control changes with acclimatization to high altitude and suggest similar control strategies between sexes. ACKNOWLEDGEMENT OF FUNDING Natural Science and Engineering Research Council of Canada Discovery Grants, Mount Royal University, Hotchkiss Brain Institute RHISE and University of Calgary Transdisciplinary Connector Grants. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.