Date of Award

12-2025

Degree Type

Honors College Thesis

Academic Program

Biological Sciences BS

Department

Biological Sciences

First Advisor

Jonathon Stavres, Ph.D.

Second Advisor

Stephanie McCoy Smith, Ph.D.

Advisor Department

Human Performance and Recreation; Kinesiology

Abstract

Energy drinks (EDs) are among the most consumed functional beverages, often marketed to enhance focus, alertness, and physical performance. Despite their popularity, the combined cardiovascular and autonomic effects of caffeine and sugar during exercise remain poorly understood. The purpose of this study was to examine the acute cardiovascular, metabolic, and autonomic responses to sugar-sweetened (ED-S), non-nutritive sweetened (ED-NNS), and placebo beverages during submaximal cycling in healthy young males.

Nine male participants (age 22.2 ± 2.4 yrs; BMI 26.2 ± 2.9 kg/m²) completed three experimental visits in a randomized, repeated-measures design. Each visit involved ingestion of one drink (ED-S, ED-NNS, or placebo), followed by a 15-minute rest period and 12 minutes of cycling in a recumbent bike at 20%, 40%, and 60% of predicted VO₂max. Hemodynamic measures, metabolic markers, and autonomic indices were assessed at baseline, post ingestion, and during exercise.

Results indicated significant main effects of workload for HR (p < 0.001), VO₂ (p < 0.001), and RPE (p < 0.001), confirming expected physiological responses to exercise. Blood glucose showed significant main effects of condition (p = 0.020) and a condition by time interaction (p < 0.001), driven by a sharp post-ingestion rise in ED-S. Lactate increased significantly across time (p < 0.001). SBP exhibited significant main effects of condition (p = 0.030) and workload (p = 0.007). No significant differences were observed for DBP, MAP, and PP. Autonomic measures (cBRSup, cBRSdown, cBRSall, HRV total power, LF/HF ratio) remained stable across all conditions (p > 0.10).

Collectively, these results indicate that acute ED consumption did not significantly alter cardiovascular or autonomic function during moderate-intensity exercise in young males. Future research should evaluate chronic consumption, habituation patterns, and include a larger and more diverse cohort of participants. Lastly, alternative ingestion-to-exercise timings would better characterize the physiological effects of EDs

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