L-carnitine may reduce oxidative stress from exercise. (Photo by mikebaird)
The case for carnitine supplements in preserving brain function seems strong enough (especially in animals, but also in humans), but what about carnitine and exercise benefits? In this post, we'll look at the studies on the effects of carnitine in aerobic and anaerobic exercise.
In the studies on carnitine and cognition, the only forms of carnitine that were used were L-carnitine and acetyl-L-carnitine. In the studies below, glycine propionyl-L-carnitine and L-carnitine L-tartrate are mentioned as well. Glycine propionyl-L-carnitine (GPLC) is a propionyl ester of carnitine that includes an additional glycine component for better absorption. L-carnitine L-tartrate (LCLT) is a salt form of L-carnitine, which is used mostly because it's not as easily degraded.
Carnitine and exercise performance
Aging results in an atrophy of the muscle fibers, an increase in fat mass, and a decrease in skeletal muscle oxidative capacities. When Bernard et al. fed old rats with L-carnitine at 30 mg/kg body weight, the L-carnitine levels and oxidative activity of muscle cells was restored. A positive change in body composition was also seen: the carnitine-fed rats decreased their abdominal fat mass and increased muscle capabilities.
According to Panjwani et al., L-carnitine in a dose of 100 mg/kg body weight improved exercise endurance of rats both at sea level and high altitude conditions. The effect was more pronounced during the latter.
Thalassemia is an inherited blood disease that is associated with poor physical fitness. El-Beshlawy et al. report that when thalassemic patients were given L-carnitine at 50 mg/kg body weight or placebo for 6 months, oxygen consumption, cardiac output, and oxygen pulse at maximal exercise increased significantly in the carnitine group. The authors note that L-carnitine works better the younger the patients are.
Jacobs et al. looked at glycine propionyl-L-carnitine and its effect on high-intensity cycling performance in healthy, trained individuals. The authors conclude that short-term oral supplementation enhanced peak power production and decreased post-exercise blood lactate accumulation.
Spiering et al. gave healthy resistance-trained men 2 grams of LCLT or placebo for 23 days. In the participants receiving carnitine, forearm muscle oxygenation was reduced. At the same time, malondealdehyde levels decreased. The authors propose that this seemingly contradictory effect may have been due to enhanced oxygen consumption.
On the other hand, Eroğlu et al. saw no difference in the metabolic and blood lactate values of male and female badminton players after taking 2 grams of L-carnitine prior to exercise. Bloomer et al. studied the effects of 1-3 g GPLC on aerobic and anaerobic exercise performance in healthy men and women. No difference was seen between the treated and placebo groups.
Carnitine and oxidative stress from exercise
Later, Bloomer & Smith looked at how GPLC affects oxidative stress from aerobic and anaerobic exercise. Both forms of exercise increased oxidative stress even in those receiving the carnitine supplement. However, GPLC reduced resting levels of malondialdehyde, which is a marker for oxidative stress.
In a study by Broad et al., twenty active males were given either 2 grams of L-carnitine L-tartrate or placebo for two weeks. When comparing the results from a 90-minute exercise test before and after treatment, no change was seen in fat, carbohydrate and protein contribution to metabolism in either group. Plasma ammonia tended to decrease in the carnitine group, however, which may suggest a potential reduction of metabolic stress from exercise.
In a study by Volek et al., 2 grams of L-carnitine L-tartrate for three weeks resulted in a reduction of post-exercise levels of malondialdehyde. Muscle disruption, markers of purine catabolism and cytocosolic proteins were also attenuated, suggesting that carnitine is effective in assisting recovery from squatexercises.
Kraemer et al. looked at how LCLT supplementation and post-exercise feeding affect hormonal and androgen receptor responses. Before exercise, LCLT upregulated androgen receptor content. Resistance exercise increased androgen receptor content in the placebo group only, while post-exercise feeding increased it in both groups. The authors suggest the upregulation of androgen receptors by LCLT may promote recovery from resistance exercise (I suppose the androgen-related effect might also be of interest to those worried about hair loss).
While the evidence for the effects of carnitine on exercise is inconclusive, carnitine may improve physical fitness in old or unhealthy people. Furthermore, the studies suggest carnitine reduces markers of exercise-related oxidative stress, especially malondialdehyde.
For more information on exercise and carnitine, see these posts:
L-Carnitine, Acetyl-L-Carnitine and Cognitive Function in Humans
L-Carnitine, Acetyl-L-Carnitine and Cognitive Function in Animals
Green Tea Extract Increases Insulin Sensitivity & Fat Burning during Exercise
Coenzyme Q10, Exercise and Oxidative Stress