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L-Citrulline Reduces Time to Exhaustion and Insulin Response to a Graded Exercise Test

HICKNER, ROBERT C.1,2; TANNER, CHARLES J.1; EVANS, CHRIS A.1; CLARK, PAIGE D.1; HADDOCK, AMY1; FORTUNE, CHRIS1; GEDDIS, HEATHER1; WAUGH, WILLIAM2; MCCAMMON, MICHAEL1

Medicine & Science in Sports & Exercise: April 2006 - Volume 38 - Issue 4 - pp 660-666
doi: 10.1249/01.mss.0000210197.02576.da
BASIC SCIENCES: Original Investigations

Purpose: Oral L-arginine supplementation has been shown to improve treadmill time to exhaustion and resting insulin sensitivity in individuals with peripheral vascular disease and type 2 diabetes, respectively. Furthermore, L-citrulline supplementation increases plasma L-arginine concentration to a level higher than that achieved by oral L-arginine supplementation. The purpose of this investigation was therefore to determine whether time to exhaustion during a graded treadmill test, as well as plasma insulin and glucose profiles, could be improved with oral L-citrulline supplementation in healthy individuals.

Methods: Seventeen young (18-34 yr), healthy male and female volunteers performed incremental treadmill tests to exhaustion following either placebo or citrulline ingestion (3 g 3 h before test, or 9 g over 24 h prior to testing).

Results: Steady-state submaximal respiratory exchange ratio and V̇O2max were not significantly different between placebo and citrulline trials. Treadmill time to exhaustion was lower following citrulline ingestion than during placebo trials (888.2 ± 17.7 vs 895.4 ± 17.9 s; P < 0.05; N = 17), which was accompanied by a higher rating of perceived exertion during exercise in the L-citrulline compared with the placebo condition. There was also an increase in plasma insulin in response to this high-intensity exercise in the placebo, but not in the L-citrulline, condition (P < 0.05).

Conclusions: It can be concluded that, contrary to the hypothesized improvement in treadmill time following L-citrulline ingestion, there is a reduction in treadmill time following L-citrulline ingestion over the 24 h prior to testing. The normal response of increased plasma insulin following high-intensity exercise is also not present in the L-citrulline condition, indicating that L-citrulline ingestion may reduce nitric oxide-mediated pancreatic insulin secretion or increased insulin clearance.

1Human Performance Laboratory and 2Departments of Exercise and Sport Science, and Physiology, East Carolina University, Greenville, NC

Address for correspondence: Robert Hickner, Ph.D., Human Performance Laboratory, East Carolina University, Greenville, NC 27858; E-mail: Hicknerr@mail.ecu.edu.

Submitted for publication June 2005.

Accepted for publication October 2005.

©2006The American College of Sports Medicine