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

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.