Date of Award

Summer 2025

Document Type

Open Access Dissertation

Department

Exercise Science

First Advisor

Shawn M. Arent

Abstract

This dissertation examines the efficacy of two distinct nutritional supplementation strategies for improving physical and/or cognitive performance under stress. The first study investigated the effects of 150 mg caffeine plus 150 mg theacrine ingestion in tactically trained individuals. Results indicated that the combination of caffeine and theacrine was associated with significant improvements in reaction time, accuracy, and measures of ocular control following high-intensity interval (HII) exercise. The HII exercise protocol consisted of ten repetitions of 60s high-intensity intervals (≥90% maximal oxygen uptake [VO2max]) followed by 120s low-intensity intervals (~40% VO2max) on a treadmill. These benefits were comparable to ingesting 300 mg of caffeine alone, with the added advantage of potentially fewer side effects. Additionally, some of the benefits were more robust to time and the fatiguing effects of exercise, highlighting the benefits of this combination in similar populations.

The second study compared the effects of exogenous beta-hydroxybutyrate (BHB; 50 g total, administered as two 25 g doses) ingestion combined with caffeine (4 mg/kg body mass) to an energy-matched carbohydrate placebo combined with caffeine on cognitive and physical performance during exercise-heat stress. Aerobically fit participants (VO2max ≥ 55 ml/kg/min) completed a 90-minute treadmill protocol at 50% of their velocity at VO2max in a heat chamber (34 °C, 45% relative humidity) while wearing a weighted vest (20% of body mass), followed by a time-to-exhaustion (TTE) test at 90% of their velocity at VO2max, performing cognitive tests before, during, and after the 90-minute treadmill protocol. Results indicated that BHB ingestion significantly improved working memory and sustained attention, as evidenced by enhanced accuracy on the 1-back and 2-back cognitive tasks compared to the carbohydrate placebo. Additionally, participants demonstrated significantly longer TTE durations in the BHB condition compared to the carbohydrate condition. This investigation supports the efficacy of ketone ester supplementation combined with caffeine to preserve cognitive function and enhance physical performance during prolonged exertion in hot environments.

Taken together, this work could provide new evidence for complementary, non-pharmacological nutritional strategies to enhance cognition and performance in challenging operational environments. By exploring the underlying physiological and cognitive mechanisms impacted by caffeine, theacrine, and BHB, this dissertation contributes to a growing body of work seeking safe, effective interventions for military, athletic, and occupational populations facing physically and psychologically demanding conditions.

Rights

© 2025, Blaine Lints

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