Does carnitine supplementation increase endurance performance?
Fat is an important fuel source during endurance exercise. To burn fat for energy (fat oxidation), fatty acids have to be transported into mitochondria (the powerhouses of cells). Carnitine helps fatty acids get into mitochondria. Therefore, carnitine supplementation might increase fat oxidation during exercise.
Carnitine can also help prevent some metabolites (acetyl-Coa) from building up during intense exercise, which may facilitate further energy production.
This study investigated the impact of long-term carnitine supplementation on metabolism during different exercise intensities and on endurance performance. Subjects supplemented with 2 g carnitine or placebo twice a day. Carbohydrates were co-ingested with the meals, because insulin improves carnitine uptake in muscle.
On three visits (before, 3 months in, and after 6 months of supplementation), subjects exercised for 30 min on a low intensity (50% Wmax), 30 min on a higher intensity (80% Wmax), and finally performed a 30 min all-out time trial test.
During low intensity, carnitine supplementation indeed increases fat oxidation and thereby spared muscle glycogen (stored carbohydrates).
During high-intensity exercise, carnitine appeared to prevent metabolite build up which allowed more carbohydrates to be used as fuel (this is a good thing during high-intensity exercise as saving muscle glycogen is not the primary concern).
Finally, carnitine supplementation resulted in a higher work output during the time trial.
Notably, carnitine supplementation did not significantly increase muscle carnitine levels, metabolism, or performance after 3 months. Therefore, it appears that long-term supplementation is a required before effects become apparent.
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