L-carnitine L-tartrate: Thermogenic or hypertrophic?

You probably know many supplements that promise to build muscle, but do you know about or use L-carnitine L-tartrate? Many compounds produce muscle-building effects rather than simply stimulating it. However, L-carnitine L-tartrate, which is frequently used to help with muscle recovery, has the potential to directly support muscle growth, according to scientific evidence. This happens because, according to some studies, it can increase androgen receptor content in muscle, potentially making your body's testosterone more effective.

L-carnitine L-tartrate: What is it?

L-carnitine L-tartrate (LCLT) is a supplement composed of L-carnitine bound to tartaric acid. Tartaric acid is essentially inert and exists simply to stabilize and deliver L-carnitine more effectively.

In other words, LCLT is essentially a more stable form of L-carnitine.

It is an amino acid used as a muscle recovery supplement and is even among the 5 best L-carnitine supplements of 2021. However, it is currently not known exactly how this happens, although there are three main theories explaining the muscle recovery effect:

• It alters substrate utilization: In other words, it makes the body change the amount of glucose it burns as fuel relative to fatty acids.
• It increases muscle oxygenation: Oxygenation indicates increased metabolic activity. The greater the activity, the more growth and better results.
• It changes a cell's hormonal status: It does this by increasing its androgen receptor content, allowing testosterone to help muscles recover better.

L-carnitine L-tartrate: How does it work?

The main study was a seven-week trial of supplementation with L-carnitine L-tartrate (LCLT).

• A dose of 2.94 grams of LCLT per day was administered, divided into one gram at breakfast and one gram at lunch,
• The study involved 10 healthy adult recreational bodybuilders.

In this double-blind, placebo-controlled crossover study, the athletes did not exercise throughout the supplementation period. At the end of the three-week supplementation periods, they underwent two exercise tests for analysis. Muscle biopsies were also taken to assess the effects on the muscle tissue in question and for further analysis (only to test interactions with supplementation and food). The groups were also given a mixture of sugar and amino acids or plain water after training. No LCLT was added to this particular drink in either group. The primary result came from the leg muscle biopsy, specifically the vastus lateralis muscle. After 21 days of supplementation, L-carnitine L-tartrate was associated with an increased androgen receptor level before exercise.

• The supplement increased androgen receptor levels at rest.
• The exercise-induced increase in the androgen receptor did not inherently increase with supplementation.
• The exercise-induced increase in the androgen receptor (AR) increased further when the supplement was used and sugars and amino acids were added post-workout.

Training: what are its effects?

There is a physiological importance of the androgen receptor (AR) in muscle hypertrophy, emphasizing the importance of exercise for increasing its content, apparently in a fiber-specific manner [1]. Resistance exercise;

• It causes a significant decrease in AR content in type I fibers, which are oxidative and slow-twitch.
• However, it causes a significant increase in type IIb fibers, which are glycolytic and fast-twitch.

Type IIb fibers are white fibers, also known as fast-twitch or fatigable fibers, which are more beneficial in sports where sprints are repeated. These fibers have low myoglobin content, few mitochondria, and few blood capillaries, but contain a large amount of glycogen. These muscles are the main source of energy during short, intense (explosive) bursts. Particularly among novice or intermediate bodybuilders, a single intense weight-training session increases AR mRNA 48 hours after training [2].

• Such an increase correlates with elevated serum testosterone levels and corresponds to significant increases in myofibrillar protein.
• Testosterone is the primary hormone that interacts with skeletal muscle tissue, and when it rises, it leads to greater muscle growth.

However, among high-performance bodybuilders, high-volume, high-intensity training appears to cause a significant decrease in AR content (-46%) 1 hour after exercise, probably due to exercise-related stress-induced protein catabolism [3]. However, such a negative effect appears to be somewhat mitigated by post-workout nutrition, resulting in greater testosterone uptake in the tissue and an increase in luteinizing hormone (LH), which also raises testosterone levels through feedback mechanisms.

L-Carnitine L-tartrate: what are its effects?

L-Carnitine-L-Tartrate supplementation has been evaluated in high-performance bodybuilders as an enhancer of hormonal responses to training and a promoter of recovery [4]. In just a couple of weeks or more, (about 2 g of elemental carnitine/day) it reduces muscle damage caused by a single high-intensity training session in two placebo-controlled crossover trials, the “gold standard,” so to speak, in terms of clinical trials.

• Less muscle damage may have resulted in more hormone receptors being available for binding interactions with anabolic hormones [4].
• With more hormone receptors available for binding interactions with anabolic hormones, the potential for muscle growth also increases.

In particular, this study demonstrated that supplementation with L-Carnitine-L-Tartrate for 21 days induces a significant upregulation of AR content in skeletal muscle, reaching as much as 15% more. The supplement may have worked by reducing exercise-associated muscle damage and thus attenuating the catabolism of muscle-specific proteins (including androgen receptors – AR). Consequently, the supplement may improve testosterone uptake through reduced muscle damage and greater AR availability. So it does not do so through direct stimulation of testosterone secretion (LCLT is not a testosterone-boosting supplement). Based on these considerations, and on the fact that post-workout nutrition stimulates increases in AR content, adding L-Carnitine-L-Tartrate to a post-workout shake improves the hormonal environment and promotes anabolism.

L-carnitine L-tartrate: what about hormones?

The researchers also evaluated a large number of other hormonal factors and found that:

• Testosterone was comparatively lower in the blood when the receptors became more prominent, suggesting that they were using the receptors to enter the cells.
• L-carnitine L-tartrate and those nutrients appeared to reduce cortisol more than the placebo and the same nutrients.
• Luteinizing hormone (LH), involved in the release and synthesis of testosterone from the testes, was influenced similarly to testosterone, although the androgen receptor did not “absorb” LH.
• Sex hormone-binding globulin (SHBG), a molecule that transports and sometimes inactivates excessively high levels of sex hormones, increased at all times with L-carnitine L-tartrate, but did not interact with the other nutrients or the placebo.
• However, the supplement had no influence on follicle-stimulating hormone.

It should be noted that, while an increase in the androgen receptor and testosterone is pro-androgenic, an increase in SHBG is anti-androgenic. The researchers took a measure called the “free androgen index” (FAI) to assess whether a net positive or negative outcome occurred. FAI increased with L-carnitine L-tartrate plus water after training, but decreased when sugar and amino acids were also added to the shake. This means that, while the supplement may have some anti-androgenic properties, they do not appear to be potent enough to negate the androgenic properties; overall, this is a net positive effect.

The 3 theories about LCLT

To evaluate the hormonal theory regarding the effects of L-carnitine L-tartrate, there is only one other study that has investigated this line of thinking. This research evaluated many different hormones and found an increase in one of the insulin-like growth factors, IGFBP-3. . There is only one study on the theory of the supplement's effects on oxygenation that we can compare and contrast with the hormonal theory, but the substrate theory has multiple studies. Two theories are potentially linked to something, since both oxygenation and substrate utilization may be linked to the actual role of L-carnitine in a muscle cell.

• First, it helps transport fat to the mitochondria to be burned as fuel.
• Second, the hormonal effects appear to be more of a secondary effect of an altered energy environment within the cell.

You can see this with the mTOR pathway and the AMPK pathway, which serve as “nutrient sensors” for cells. When energy—that is, the small cAMP molecule—increases or decreases too much, the cell changes what it “asks” the blood for.

• Energy levels that are too low mean that the cell needs more food.
• Here, AMPK draws nutrients into the cell while helping convert those nutrients into energy.

When energy levels are too high, the mTOR pathway tells the cell to start storing it as long-term tissue and repairing muscle tissue. Therefore, observing changes in the androgen receptor when the cell is requesting growth, with apparently greater testosterone absorption (given that the androgen receptor is actually inside the cell, in the nucleus), seems to align with the idea that an energy transformation promotes muscle growth.

How to use LCLT, then

In the most optimistic sense, L-carnitine L-tartrate has potential as a “testosterone synergist.” In other words, it is a supplement that enhances the actions of testosterone and may generally work in younger people. This means that, theoretically, L-carnitine L-tartrate could be more than just a muscle recovery supplement. Rather, it is a supplement that should be respected for its hypertrophic potential, especially by an elite bodybuilder or fitness athlete. Therefore, you can try it, as it is a good molecule for recovery and seems to nourish your muscles rather than being one of those recovery supplements that simply blocks adaptations by acting as a strong antioxidant or anti-inflammatory.

How to take LCLT

You could take 1 to 2 g (depending on your training level and body composition), especially after training. At this point, you should also add a carbohydrate to the protein shake, which may contain glutamine or creatine. Remember that L-carnitine L-tartrate is a potassium salt that allows L-carnitine to be absorbed in greater amounts and reach the bloodstream, helping you build lean muscle. On non-training days, remember to reduce the dose between meals when you do not train. To learn more about L-carnitine and how to use it, watch this video prepared by MASmusculo.