Carnitine (endogenus) is a necessary component of fat oxidation in cells. L-carnitine may improve the aerobic exercise through increasing lipid peroxidation. Carnitine acts in a transport of long-chain fatty acids to the mitochondrial matrix for oxidation thus plays and important role in energy metabolism . Previous studies have shown that oral L-carnitine ingestion does not increase muscle carnitine concentrations [2,3]. However, a new more promising form of carnitine emerged: L-Carnitine L-Tartrate (LCLT). A tartrate is a salt or ester of the organic compound tartaric acid and it is used in some supplements to improve absorption of another substance.
L-Carnitine L-Tartrate Benefits
We will review a few studies conducted with l-carnitine l-tartrate as an enhancer of the hormonal responses to resistance-training and a recovery promoter. However, we should tell you right away that they are all funded by Lonza Inc., a manufacturer of l-carnitine.
Reduced Muscle Damage
Two cross-over, placebo-controlled studies have shown that oral l-carnitine l-tartrate supplementation reduces the amount of exercise-induced muscle tissue damage [4,5]. Kraemer et al.  suspected that less muscle damage would increase the number of intact hormonal receptors. Thus making more of them available for interaction with anabolic hormones (possibly making better environment for muscle growth). Study in professional football players reported that l-carnitine (as LCLT) as well as l-carnitine and l-glutamine beneficially affect markers of muscle damage and muscle soreness .
A study by Barry A. Spiering and associates  noted seemingly contradictory finding that l-carnitine l-tartrate attenuated markers of muscle damage despite reduced tissue oxygenation. It is plausible that lower muscle tissue oxygenation was due to enhanced muscle oxygen consumption. That however, coincides with several studies which reported that carnitine supplementation increased whole-body VO2max during exercise [7,8].
Data collected by researchers from University of Connecticut  demonstrated subtle yet significant increase in luteinizing hormone in response to post-workout feeding and LCLT supplementation. The primary finding of this study was l-carnitine l-tartrate supplementation upregulated resting androgen receptor content; also post-exercise androgen receptor content was greater following high caloric feeding compared with placebo (water). The increase in androgen receptor and simultaneous decrease in testosterone suggests increased cellular uptake of testosterone. So, LCLT is not a testosterone booster it may enhance testosterone uptake via less muscle damage and increased availability of androgen receptor. L-Carnitine levels in the seminal plasma have also been shown to have a positive correlation with serum testosterone 
Results of animal study  showed that l-carnitine tartrate significantly increases serum testosterone levels compared to saline solution. Serum LH and FSH levels were also significantly increased. So, besides affecting sex hormones and reproduction system, it may also improve male reproductive function.
Improved Aerobic Capacity
Very recent study  reported that acute consumption of l-carnitine l-tartrate positively affects lipid metabolism, maximum oxygen consumption, and distance run. 3 g of l-carnitine tartrate was able to significantly elevate lipid metabolism, VO2 max, and distance run while dependent variables were unaffected in the placebo supplemented group. Blood analysis showed that performance was increased by increased lipid metabolism.
Potential for Hair Loss Treatment
Researchers from University of Hamburg  used l-carnitne-l-tartrate to promote hair growth in vitro. Their findings suggested that l-carnitine stimulates human scalp hair growth by supplying energy to the hair follicles.
L-Carnitine L-Tartrate Side Effects
Martyn R. Rubin and others  investigated the effects of 3 week L-carnipure (l-carnitine l-tartrate) ingestion. Using a balanced, placebo, cross-over design on 10 healthy men, LCLT had no adverse effects on metabolic and hematological safety variables.
(Other common names: Vitacarn, Vitamin B(t), L-Carnitine Tartrate, Levocarnitine, L-Carnitina, Beta-hydroxy-gamma-trimethylammonium butyrate, B(t) Factor, Carnitine, Carnitor, D-Carnitine, DL-Carnitine)
Kerner, Janos, and Charles Hoppel. “Fatty acid import into mitochondria.” Biochim Biophys Acta 1486.1 (2000): 1-17.
Barnett, C., et al. “Effect of L-carnitine supplementation on muscle and blood carnitine content and lactate accumulation during high-intensity sprint cycling.” International journal of sport nutrition 4.3 (1994): 280.
Villani, Rudolph G., et al. “L-Carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women.” International Journal of Sport Nutrition 10.2 (2000): 199-207.
Volek, Jeff S., et al. “L-Carnitine L-tartrate supplementation favorably affects markers of recovery from exercise stress.” American Journal of Physiology-Endocrinology And Metabolism 282.2 (2002): E474-E482.
Kraemer, William J., et al. “The effects of L-carnitine L-tartrate supplementation on hormonal responses to resistance exercise and recovery.” The Journal of Strength & Conditioning Research 17.3 (2003): 455-462.
Spiering, Barry A., et al. “Effects of L-carnitine L-tartrate supplementation on muscle oxygenation responses to resistance exercise.” The Journal of Strength & Conditioning Research 22.4 (2008): 1130-1135.
Marconi, C., et al. “Effects ofl-carnitine loading on the aerobic and anaerobic performance of endurance athletes.” European journal of applied physiology and occupational physiology 54.2 (1985): 131-135.
Vecchiet, L., et al. “Influence of L-carnitine administration on maximal physical exercise.” European journal of applied physiology and occupational physiology 61.5-6 (1990): 486-490.
Kraemer, William J., et al. “Androgenic responses to resistance exercise: effects of feeding and L-carnitine.” Med Sci Sports Exerc 38.7 (2006): 1288-96.
Foitzik, Kerstin, et al. “L‐Carnitine–L‐tartrate promotes human hair growth in vitro.” Experimental dermatology 16.11 (2007): 936-945.
Rubin, Martyn R., et al. “Safety measures of L-carnitine L-tartrate supplementation in healthy men.” The Journal of Strength & Conditioning Research 15.4 (2001): 486-490.
- Dehghani, Mostafa, et al. “Effects of L-Carnitine L-Tartrate Acute Consumption on Lipid Metabolism, Maximum oxygen consumption (VO2 max), and distance run Following Aerobic Exhaustive Exercise on Treadmill in Elite Athletes wrestling.” The AYER 2 (2015): 189-195.
- Ahmed, Syed DH, Shahid Ahsan, and Syed IA Burney. “Male fertility: influence of testosterone, luteinizing hormone, and follicle-stimulating hormone on seminal free L-carnitine.” Human Andrology 3.3 (2013): 76-80.
- Eidi, Maryam, et al. “Effect of L-carnitine on Serum LH, FSH and Testosterone Levels in Adult Male Rats.” (2014).
- Mohtadinia, Javad, et al. “Effects of Carnitine with and without Glutamine Supplementation on Markers of Muscle Damage and Muscle Soreness among Football Players: A Randomized Controlled Clinical Trial.” Galen Medical Journal 3.4 (2014): 207-15.