Effects of Pre-Run Nutritional Supplements During a Fixed-Pace 5 km Treadmill Run

Summary

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.

Detailed Description

This is a randomized, single-blind, placebo-controlled crossover study designed to compare acute physiological and perceptual responses to three pre-run nutritional supplements and placebo during a controlled fixed-pace 5 km treadmill run. Healthy, physically active runners will complete one screening/baseline visit and four experimental visits. Each participant will complete all four experimental conditions in randomized order and will serve as their own control. A minimum washout/recovery period of four days will separate experimental visits. At each experimental visit, participants will receive one of four pre-run conditions: caffeine at 4 mg/kg body weight, L-citrulline at 7 g, an exogenous ketone supplement providing 11.5 g beta-hydroxybutyrate (BHB), or placebo. Study products will be provided in a standardized beverage vehicle, followed by a 45-minute waiting period before the treadmill run. The primary physiological outcomes of interest are running economy and heart-rate drift during the fixed-pace 5 km treadmill run. Additional outcomes include oxygen consumption, carbon dioxide production, ventilation, respiratory exchange ratio, heart-rate recovery, capillary blood lactate and ketone concentrations, rating of perceived exertion, gastrointestinal symptoms, subjective fatigue, energy, focus, and participant-reported perceptions of the assigned supplement condition. A prespecified randomly selected subgroup of up to 12 enrolled participants will use a Dexcom Stelo continuous glucose monitor during the experimental phase. CGM-derived glucose responses will be analyzed as exploratory outcomes within this subgroup only. The study will also evaluate feasibility and tolerability, including visit completion, adverse events, supplement-related symptoms, gastrointestinal symptoms, and completeness of study measurements. The results are intended to characterize within-participant differences among the four conditions and provide preliminary data for future confirmatory studies.

Eligibility Criteria

Interventions