Prefrontal cortex oxygenation and cognition in response to thoracic load carriage in normoxic and hypoxic conditions; Influence of biological sex

Authors

Sydney L. KoppingerFollow
Beverley K. Buchanan, James Madison University

Creative Commons License

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

ORCID

https://orcid.org/0009-0006-1949-3919

Date of Graduation

5-15-2025

Semester of Graduation

Spring

Degree Name

Master of Science (MS)

Department

Department of Kinesiology

First Advisor

Nicholas Luden

Second Advisor

Stephanie Kurti-Luden

Third Advisor

Michael Saunders

Abstract

Males and Females have physiological discrepancies with the potential to elicit varying cerebral blood flood and cognitive responses to high altitude and thoracic load carriage Purpose: To determine if biological females have different cerebral blood flow, and cognitive responses to exercise with thoracic load carriage (25kg) and high altitude exposure compared to Males. Methods: Nineteen (19) female (Female n=11) and male (n=8) subjects completed two familiarization trials involving VO_2max tests in normoxia (FIO₂ = 20.9%) and hypoxia (FIO₂ = 13%), followed by four experimental sessions in each combination of loaded/unloaded in normoxia/hypoxia: Unloaded Normoxic (UN), Loaded Normoxic (LN), Unloaded Hypoxic (UH) and Loaded Hypoxic (LH) in randomized order. Cognitive function was assessed by reaction time and accuracy during the Go/No-Go auditory stimulus test, while a Near Infrared Spectroscopy (NIRS) headband was worn throughout the trial to assess changes in hemoglobin (total, oxygenated, and deoxygenated), as indices of perfusion and oxygen delivery. Participants completed 45 min of incline walking at 8% grade with speeds individually adjusted to elicit 65% relative VO_2max, followed by a time to exhaustion sprint at 95% VO_2max without the thoracic load. Results: THb, HHb, and O₂Hb (CBF_i) increased from rest to exercise (45 min phase), and there was a main effect of sex, such that males experienced augmented CBF_i changes from rest than females. There was also a main effect of condition for CBF_i. THb was higher in loaded normoxia (p< 0.05) vs. unloaded normoxia and unloaded hypoxia. Additionally, O₂Hb was higher in loaded normoxia than all other conditions (p< 0.05). O₂Hb was also elevated in unloaded normoxia vs. unloaded hypoxia. HHb was lower in each normoxic trial compared to each hypoxic trial. Importantly, there was no sex x condition interaction, indicating that males and females respond similar to each other across conditions. Reaction time and accuracy during cognitive function tests did not vary between sexes however, reaction time (RT) was slower during exercise compared to rest (p< .05), and most rapid following the TTE trial (p< .01). Accuracy was greater at rest compared to exercise (p< .05) and returned to baseline post TTE (p< .05)). Females completed significantly shorter time to exhaustion trials compared to Males (124.5 ± 30.1 vs. 176.8 ± 80.9) (p< .05). Conclusions: In line with the literature, cerebral oxygenated hemoglobin levels were elevated in loaded conditions compared to unloaded, and lower in hypoxia compared to normoxia. However, males unexpectedly demonstrated elevated levels compared to females. This did not translate to any sex differences in cognitive performance. Accuracy and reaction time both declined during exercise, with accuracy returning to baseline post exercise and reaction time becoming most rapid post exercise. Altogether, these data indicate that although cerebral perfusion is affected by load carriage, hypoxia and biological sex individually, no conditional or sex-based perfusion changes elicited significant alterations in markers of cognition.