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Effects of Pre-Run Nutritional Supplements During a Fixed-Pace 5 km Treadmill Run
Fueling the Kilometers: Effects of Pre-Run Nutritional Supplements on Physiological Responses During a Fixed-Pace 5 km Treadmill Run
Who can join
Ages 18 to 35 · All sexes · Healthy volunteers welcome
Full eligibility criteria
Inclusion Criteria: * Age 18-35 years * Healthy adult * Able to provide written informed consent * Regularly engaged in running-based aerobic training at least 3 times per week for at least 30 minutes per session during the past 3 months * Able to complete a 5 km run in under 30 minutes * Able and willing to comply with treadmill testing, fingerstick testing, dietary standardization, supplement restrictions, and pre-visit instructions * Participants randomly selected for the continuous glucose monitoring subgroup must also be willing to undergo Dexcom Stelo continuous glucose monitor placement and wear Exclusion Criteria: * Known cardiovascular, metabolic, pulmonary, or neurological disease that may increase the risk associated with exercise testing or materially influence study outcomes * Uncontrolled hypertension or another cardiovascular condition that, in the investigator's judgment, makes vigorous treadmill exercise unsafe * Diagnosed type 1 or type 2 diabetes mellitus or another known metabolic disease that may materially influence study outcomes * Pregnant, breastfeeding, or planning pregnancy during the study period * Current use of nitrate medications or phosphodiesterase type 5 (PDE5) inhibitors, including sildenafil, tadalafil, or vardenafil * Known sensitivity or allergy to caffeine, L-citrulline, exogenous ketone/BHB salt products, or any study beverage ingredient * Current use of stimulant medications or other medications that may significantly influence cardiovascular, blood pressure, or metabolic responses to exercise, as determined by the investigator * Musculoskeletal injury or condition that limits safe treadmill running * Smoking or regular use of nicotine products * Recent illness, surgery, or hospitalization that, in the opinion of the investigators, may interfere with safe participation or study outcomes * Unable or unwilling to comply with study procedures or pre-visit standardization requirements * Running fewer than 3 times per week or otherwise not meeting the running-training inclusion criterion
About the study
This study will examine how three commonly used pre-run nutritional supplements-caffeine, L-citrulline, and an exogenous ketone supplement-affect physiological and perceptual responses during a fixed-pace 5 km treadmill run in healthy, physically active runners.
Participants will complete one screening and baseline visit followed by four experimental visits in a randomized order. At each experimental visit, participants will receive caffeine, L-citrulline, an exogenous ketone supplement, or placebo before completing a fixed-pace 5 km treadmill run. Each participant will receive all four conditions and will therefore serve as their own control.
The study will evaluate measures including running economy, heart-rate responses, oxygen consumption, respiratory measures, blood lactate and ketone concentrations, perceived exertion, gastrointestinal symptoms, fatigue, energy, and focus. A randomly selected subgroup will also wear a continuous glucose monitor to explore glucose responses during the experimental visits. The study will also assess the feasibility and tolerability of completing repeated treadmill trials under the four supplement conditions.
What is being tested
- Caffeine (dietary supplement)
- L-Citrulline (dietary supplement)
- Exogenous Ketone (Beta-Hydroxybutyrate) (dietary supplement)
- placebo beverage (other)
Sponsor: St. Louis University · Participants: 20 · Started: 2026-10
Contact the study team
- Hossein Rafiei, PhD, RD, ACSM-CPT · Phone: 314-977-8675
Official record on ClinicalTrials.gov — NCT07854223
Locations in the U.S.
| Missouri | Saint Louis University, Allied Health Building, St Louis |
From ClinicalTrials.gov, data retrieved Oct 6, 2026. Each study sets its own eligibility; the study team decides who can join.