Oral L-arginine before resistance exercise blunts growth hormone in strength trained males.
Acute resistance exercise and L-arginine have both been shown to independently elevate plasma growth hormone (GH) concentrations; however, their combined effect is controversial. The purpose was to investigate the combined effects of resistance exercise and L-arginine supplementation on plasma L-arginine, GH, GH secretagogues, and IGF-1 in strength trained participants. Fourteen strength trained males (age: 25 ± 4 y; body mass: 81.4 ± 9.0 kg; height: 179.4 ± 6.9 cm; and training experience: 6.3 ± 3.4 y) participated in a randomized double-blind crossover design (separated by ~7 days). Subjects reported to the laboratory at 08:00 in a fasted state, consumed L-arginine (ARG; 0.075 g·kg-1 body mass) or a placebo (PLA) before performing an acute bout of resistance exercise (3 sets of 8 exercises, 10 repetitions at ~75% 1RM). Blood samples were collected at rest, before exercise, and at 0, 15, 30, and 60 min of rest-recovery. The ARG condition significantly increased plasma L-arginine concentrations (~120%) while no change was detected in the PLA condition. There were no differences between conditions for GH, GH-releasing hormone, ghrelin, or IGF-1 at any time point. GH-inhibiting hormone was significantly lower in the ARG condition. However, integrated area under the curve for GH was blunted in the ARG condition (L-arginine = 288.4 ± 368.7 vs. placebo = 487.9± 482.0 min·ng·mL1, p < .05). L-arginine ingested before resistance exercise significantly elevated plasma L-arginine concentration but attenuated plasma GH in strength trained individuals despite a lower GHIH. Furthermore our data shows that the GH suppression was not due to a GH or IGF-1 induced autonegative feedback loop.
Faculty of Physical Education & Recreation, University of Alberta, Edmonton, Canada.
Scott C
SC
Forbes
Vicki
V
Harber
Gordon J
GJ
Bell
D000284:Administration, Oral; D000328:Adult; D019540:Area Under Curve; D001120:Arginine / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D019382:Human Growth Hormone / Q000097:blood*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D053580:Muscle Strength; D010809:Physical Fitness / Q000502:physiology; D055070:Resistance Training; D012146:Rest / Q000502:physiology; D013004:Somatostatin / Q000097:blood; D055815:Young Adult
D019382:Human Growth Hormone; D013004:Somatostatin; D007334:Insulin-Like Growth Factor I; D001120:Arginine