Impact Of Higher Aerobic Fitness On Neurocognitive Function During Simulated Military Operational Stress

Abstract

Modern warfare involves a greater reliance on executive functions such as memory, recognition, and reasoning. Greater aerobic fitness has been associated with minimizing decrements in cognitive function during physical stress scenarios. PURPOSE: To determine the effect of aerobic fitness on higher order neurocognitive function during simulated military operational stress (SMOS). METHODS: Fifty-four male service members (SMs) (age: 26.4 ± 5.4 years, height: 177.9 ± 6.5 cm, weight: 85.2 ± 14.0 kg) took part in the 5 day/night protocol. After a day of familiarization testing (D0) including a treadmill VO2peak test, SMs completed one day of baseline testing (D1). On D2 and D3, sleep was restricted to 0100-0300 and 0500-0700 and SMs were allotted 50% of caloric needs based on estimated total energy expenditure. SMs were permitted to sleep from 2300-0700 and received 100% of their caloric needs all other days. Each afternoon after completion of a physical testing battery, SMs completed a neurocognitive test battery: Reading the Mind in the Eyes (RME) to measure emotional recognition, Match to Sample (MATCH) to assess short-term spatial memory, and Grammatical Reasoning (GRAM) to evaluate language-based logical reasoning. SMs were split into aerobic fitness tertiles based on VO2peak (LOW: < 45.0; MOD: 45.0-51.54; HIGH: > 51.54 mL·kg·min-1). Two-way mixed ANOVA and Bonferroni correction for multiple comparisons were used to analyze group*day interaction on average reaction time (RT) and accuracy (ACC) for MATCH and GRAM, as well as RME ACC, across D1, D3, and D4 of the SMOS. RESULTS: There were no significant group*day interaction effects. However, a significant main effect of group was observed in both MATCH ACC (p = 0.023, ηp2 = 0.145) and GRAM ACC (p = 0.032, ηp2 = 0.131). On average, HIGH SMs exhibited 20% higher MATCH ACC (p = 0.046) and 25% higher GRAM ACC (p = 0.036) scores compared to LOW SMs. A main effect of time indicated MATCH (p < 0.001, ηp2 = 0.263) and GRAM (p < 0.001, ηp2 = 0.290) RT decreased throughout the SMOS. RME remained stable through the 5-day protocol. CONCLUSION: SMs with high aerobic fitness performed better at logical reasoning and spatial memory tasks. Increased aerobic fitness is influential to maintaining cognitive functions in response to the physical and cognitive stress observed in military operations.