|Arginine-based pre-workout products are more popular with guys than with girls. Could this be the reason that only women complain about unlovedly rapid muscle gains? ;-)|
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With ~5-6g of arginine being taken before a workout that consists of 3 sets of 8 classic strength training exercises that are performed for 10 repetitions and at an intensity ~75% of the personal 1RM of the 14 strength trained men [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], the researchers from the Faculty of Physical Education & Recreation at the University of Alberta in Edmonton, Alberta, Canada designed an experimental setup which comes "shockingly" close to what the average and extraordinaire gymrat is doing, when he or she is hitting the grind.
|Figure 1: Level of arginine, GHRH and IGF-1 at T = 0, 15, 30, 60 min of rest-recovery + integrated area under the curve for growth hormone (iAUC GH); all values expressed relative to placebo control (Forbes. Nov 2013)|
What do we make of these results?
Most of you will probably remember the often referenced results of West & Phillips, whose 12-week resistance training intervention in the course of which the researchers from the Exercise Metabolism Research Group at the Department of Kinesiology of the McMaster University in Hamilton, Ontario, made the following observations (West. 2012):
Suggested Read: "Anabolic Workouts Revisited!" | more
activities <8 months before the study.
- Significant correlations between GH and the increase in type I (slow twitch, oxidative) muscle fibers, but no correlation between testosterone, IGF-1 and cortisol.
- Significant correlations between GH, as well as cortisol and the increase in type II (fast twitch, gylcolytic) muscle fibers, but no correlation between testosterone and IGF-1.
Is the decrease the result of a previous GH "overload"?
With respect to the possible involvement of an auto-negative feedback, which is another, previously suggested explanation for this phenomenon, of which I had to realize during my research for this article that it has been covered in the literature before (Kanalay. 2008), Forbes et al. remark that their data would basically exclude the possibility that "the GH suppression was not due to a GH or IGF-1 induced autonegative feedback loop." (Forbes. Nov 2013)
|It may not be the perfect muscle builder and maybe not even something you want to take in the vicinity of a workout, but there is still promising data on the metabolic effects of arginine esp. for (pre-)diabetics | more|
If we focus on the available data, the conclusion of the researchers from the University of Alberta is certainly right. If we do take into account that we are talking about post workout supplementation and remind outselves that "the somatotrope is also known to have a refractory period" (Kanaley. 2008), it should be obvious that post-workout measurements, alone, cannot exclude the possibility that the GH spike that's responsible for the auto-negative feedback occurred during, not after the workout.
In other words: Instead of focusing exclusively on the post-workout GH levels, Forbes, Harber and Bell would actually have had to measure the pre & intra-workout GH response, as well. The GH spike that would cause the auto-negative feedback could after all have been caused by a sudden drop in blood glucose in response to the insulin sensitizing effects of arginine and the 'glucose hungry' strength training session.
Auto-negative feedback is still possible, but isn't there something else?
An alternative explanation for the lowered growth hormone response may come from a closer reading of the 'prequel' to this study. In January, Forbes et al. published a paper with the same supplement, but a different exercise protocol. Instead of hitting the weights, their 15 aerobically trained male subjects cycled for 60 min at 80% of their personal VO2max - again, immediately after ingesting 5-6g of l-arginine (0.075g/kg body weight).
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- the rate of fatty acid oxidation at the onset of the workout, which was reduced in the l-arginine group, and
- the levels of the sugar alcohol glycerol at the 45-min time point, which were slightly, but significantly increased
The arginine infusion increased the glucose uptake and blunted the increase in nonesterified fatty acid and glycerol concentrations during 120min of cycling at 72% of the VO2max which were followed immediately by a 15-min "all-out" cycling performance bout (McConell. 2013). Whether it also changed the GH response is however something I can't tell you, because reseachers from the The University of Melbourne did not measure the effect the arginine infusion had on the growth hormone levels of their study participants. I would yet guess that it will have been similar to the one on the cycling study Forbes did. This, in turn, would suggest that the effect depends on (a) duration and energy expenditure, or (b) the substrate utilization during the workout (lifting weights = glycolytic; cycling = rather oxidative). In the end both of these are related to the reliance on fat, not glucose / glycogen to fuel the energetic demands of your workout and as you all know the acute provision of glucose is the prerogative of glucocorticoids (i.e. cortisol), not GH.
- Álvares TS, Meirelles CM, Bhambhani YN, Paschoalin VM, Gomes PS. L-Arginine as a potential ergogenic aid in healthy subjects. Sports Med. 2011 Mar 1;41(3):233-48.
- "blunt, v.". OED Online. September 2013. Oxford University Press. http://www.oed.com/view/Entry/20664?rskey=iZQVcA&result=3&isAdvanced=false (accessed November 19, 2013).
- Forbes SC, Harber V, Bell GJ. The acute effects of L-arginine on hormonal and metabolic responses during submaximal exercise in trained cyclists. Int J Sport Nutr Exerc Metab. 2013 Aug;23(4):369-77. Epub 2013 Jan 8.
- Forbes SC, Harber V, Bell GJ. Oral L-Arginine Prior To Resistance Exercise Blunts Growth Hormone in Strength Trained Males. Int J Sport Nutr Exerc Metab. 2013 Nov 13. [Epub ahead of print]
- Kanaley JA. Growth hormone, arginine and exercise. Curr Opin Clin Nutr Metab Care. 2008 Jan;11(1):50-4. Review.
- McConell GK, Huynh NN, Lee-Young RS, Canny BJ, Wadley GD. L-Arginine infusion increases glucose clearance during prolonged exercise in humans. Am J Physiol Endocrinol Metab. 2006
- Rahim A, Toogood AA, Shalet SM. The assessment of growth hormone status in normal young adult males using a variety of provocative agents. Clin Endocrinol (Oxf). 1996 Nov;45(5):557-62.
- West DW, Phillips SM. Associations of exercise-induced hormone profiles and gains in strength and hypertrophy in a large cohort after weight training. Eur J Appl Physiol. 2012 Jul;112(7):2693-702.