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EFFECTS OF L-CITRULLINE SUPPLEMENTATION ON LOCALIZED BLOOD FLOW AND POST-EXERCISE MUSCLE REOXYGENATION RATE

Abstract

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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