Most of you probably remember L-carnitine being touted as a ‘fat burner' way back in the days when little girls idolized Madonna. Instead, we have found that carnitine may indeed be much more diverse and impressive than previously thought. First off, what is L-carnitine? This ingredient is made in the body from the amino acids lysine and methionine, and is needed mainly to transport fatty acids into mitochondria the powerhouse of cells. Many consider L-carnitine as a "conditionally essential" nutrient. So here's the science of this amazing compound.
Fact: L-carnitine L-tartrate (LCLT) increases androgen receptor content. In this study, 10 resistance-trained men supplemented with LCLT (equivalent to 2 g of L-carnitine per day) or placebo (PL) for 21 days and provided muscle biopsies for AR or androgen receptor determinations. Subsequently, they performed two resistance exercise (RE) protocols: one followed by water intake, and one followed by feeding (8 kcal.kg body mass, consisting of 56% carbohydrate, 16% protein, and 28% fat). They discovered that feeding after RE increased AR content, which may result in increased testosterone uptake, and thus enhanced luteinizing hormone secretion via feedback mechanisms; and 2) LCLT supplementation upregulated AR content, which may promote recovery from RE.(1) In other words, it looks like LCLT can promote anabolic processes by increasing levels of the steroid receptor for testosterone, the AR. Not only can it jack up the AR, but L-carnitine L-tartrate (LCLT) supplementation beneficially affects markers of post-exercise metabolic stress and muscle damage. Eight healthy men were supplemented with 0 g, 1 g, and 2 g of LCLT for 3 weeks and then performed a bout of resistance exercise (5 sets of 15-20 repetition maximum with a 2-min rest between sets) with associated blood draws. They found that both the 1- and 2-gram doses were effective in mediating various markers of metabolic stress and of muscle soreness. Accordingly, the "use of LCLT appears to attenuate metabolic stress and the hypoxic chain of events leading to muscle damage after exercise."(2)
Bottom line: Elevating your blood levels of testosterone is just ONE way to boost your muscle's anabolic processes. By increasing levels of the androgen receptor, which makes it easier for your cells to take in the steroid hormone testosterone, you can in essence sensitive your muscles more so. Thus, turning you into an anabolic, muscle-building machine.
References
1. Kraemer WJ, Spiering BA, Volek JS, et al. Androgenic responses to resistance exercise: effects of feeding and L-carnitine. Med Sci Sports Exerc 2006;38:1288-96.
2. Spiering BA, Kraemer WJ, Vingren JL, et al. Responses of criterion variables to different supplemental doses of L-carnitine L-tartrate. J Strength Cond Res 2007;21:259-64.
