L. Wehrman1, C. Bennett1, N. Gorham1, K. Jacob1, J. Pauly1, S. Sallee1, E. Donovan2, and D.B. Thorp1

1Gonzaga University, Spokane, WA, 2Northern Arizona University, Flagstaff, AZ

L-citrulline is an amino acid that is a common ingredient in many pre-workout supplements and is marketed as a vasodilator. Prior studies have shown L-citrulline promotes vasodilation in various clinical populations and older adults, but limited data exists on L-citrulline's efficacy in young, healthy adults. PURPOSE: To determine L-citrulline's effect on blood flow and muscle reoxygenation rate before, during, and after exercise in healthy, college-aged individuals. METHODS: Participants (n=12; 6 male and 6 female) supplemented with L-citrulline for 7 days (6g/day) and visited the lab twice (pre- and post-supplementation); the same experimental protocol was repeated for both visits. Brachial artery diameter and blood flow velocity were measured via ultrasound before, during, and after the completion of a handgrip exercise. Blood flow rate was calculated as area*velocity. Subjects completed 15 forearm contractions at 1Hz with a resistance set to 15% of their maximum grip strength (MGS). Following recovery, subjects were instructed to complete as many reps as possible (AMRAP), also at 15% MGS. Muscle reoxygenation rate (%SmO2/second) was measured in forearm flexors via NIRS for 30 seconds immediately following the AMRAP. Paired t-tests were used to compare reoxygenation rate and the number of repetitions completed during AMRAP, while repeated measure ANOVA was used to compare blood flow rates using SPSS. RESULTS: Post-AMRAP muscle reoxygenation rate increased from 0.272 ± 0.251 %/sec to 0.602 ± 0.613 %/sec (p<0.05) following supplementation. There was no difference in recovery blood flow rate (16.3 ± 7.3 vs. 16.1 ± 8.2 mL/s, p=0.66), or in the in the number of repetitions completed during the AMRAP test (126.8 ± 60.2 vs. 161.5 ± 99.5 repetitions, p=0.07). There was no difference in mean arterial pressure (99.2 ±15.6 vs. 94.1± 15.7 mmHg, p=0.26) or blood flow rate before or during exercise. CONCLUSION: L-citrulline did not promote vasodilation or increase blood flow in our subjects. With no change in recovery blood flow rate, increased muscle reoxygenation rate may suggest that L-citrulline could improve muscle oxygen uptake via increased oxygen extraction rather than delivery. An increase in post-exercise reoxygenation rate may lead to increased endurance and shorter rest times needed between bouts of exercise.

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