Acetyl L-carnitine is an interesting substance that has been in the sports supplement industry since at least the early 90's. Carnitine, the molecular base to which an acetyl group is attached, has been in sports supplementation since a decade prior. Carnitine had been touted as a way for endurance athletes to have increased energy production due to its use in the Krebs energy cycle. This would allow the body, if it had a limit rate to carnitine production or usage, to hopefully be augmented and enhanced by supplemental carnitine. It's tale that will be told in a later article... in this one we see a much more powerful version of carnitine, one where an acetyl group has attached to the carnitine molecule, which readily allows it to pass over the mysterious "blood-brain barrier" and enter into the brain where it is a particularly powerful supplement for neurons, who CAN use the supplemental amount of carnitine and has been found to be one of the most powerful cognitive enhancers ever found (also covered in a future article). For exercisers, it seems to allow the brain to continue proper function for signaling to hormone-secreting glands even under severe stress, which usually compromises that signaling system and causes hormones, particularly testosterone, to crash and cortisol to ramp up: neither good for muscle growth or even retention.

Our first study relevant to exercisers was done in 1987, the participants being horses (unfortunately most human research using ALC is done on cognition and fertility, NOT on exercising humans). After two treadmill tests, muscle biopsies were done to determine the level of different carnitines in the muscle tissue. What was found was that free carnitine fell markedly, with an almost equivalent rise in acetylcarnitine. The researchers stated that carnitine was used to maintain the ratio of acetylcarnitines to CoA. Supplemental acetyl-carnitine may possibly blunt this conversion, and thus allow body supplies of carnitine to to be preserved for muscle energy utilization functions.¹

IN 1990 another study on horses was done. They ran for 2 minutes duration and the intensity was increased throughout. It was found that Co-A (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for energy production. Scientists found no rate limit on either CoA or Alc, so it does not appear the body, at least for this duration of intense exercise, has the need for supplemental acetylcarnitine. Thus we can probably safely infer that your workouts must be quite intense for ALC to benefit in blunting the ALC-Co-A conversion for the body to maintain the proper ratio. ²

IN 1993, a study was done that is more directly applicable to athletes. Pre-trained animals (and this is nice, as untrained animal and human studies don’t have much relevance to well-conditioned athletes) that “carnitine preparations such as L-carnitine, mildronate, and acetyl-L-carnitine used for 10 days statistically significantly increased the maximum running speed and its endurance”. effects of the carnitines was proportionate to their antioxidative activity. This would strongly suggest that acetylcarnitine and carnitine have possible very strong antioxidant capacities, at least on muscle systems.³

In 1993, an oft-quoted study on rats exposed to a chronic swimming test (basically one that threatened their lives, to be honest) after 10 days of ALC at dosages of 10mg a day. It was found that “the treatment with ALC prevented the decrease in plasma testosterone levels after chronic swimming stress”. Now this study has been used before to sell acetyl L-carnitine, and I believe it still can be used to provide at least one experiment that is an extremely high stress event and a near miraculous effect (as the non treated rats has a twofold decrease in testosterone).⁴ But how much is 10mg a rat as far as humans go? Let's assume Male Wistar rats at 42 days of life at an average weight of 300g. The average 200 pound male is 90.9 kilograms, or 90900 grams. He is 303 times the rat’s weight. So take our little 10mg dose for the rat and we have 10mg x 303 - 3030 milligrams, approximately 3 grams. Thus, we see the amount typically recommended, which is usually 500 to 1000 mg a day, is far too low, if you're training is sufficiently taxing (to failure with every set, or increasing intensity of time or speed if an endurance athlete).

Another interesting study which will be included in the Fertility article on ALC is important to this discussion.

Many males supplement with testosterone as they age, both for sexual function but also for diminishing muscle issues (sarcopenia). This (placebo-controlled) study in 2002 found that supplemental acetyl l-carnitine was just as effective as supplemental testosterone. So here we have a substance that can outperform testosterone itself in many of the effects is has on the body!⁵ The rational explanation for this is that supplemental testosterone causes a bio feedback loop that causes its stimulating hormones (like luteinizing hormone) to be affected negatively, whereas ALC is stimulating testosterone through normal hormone channels that are activated by a brain that is operating optimally (thus creating optimal levels of luteinizing hormone most likely).