To fuel exercise, your body uses stored fat and carbohydrates in the form of muscle glycogen. As exercise intensity increases, greater amounts of fat and carbs are oxidized. But the rate of fat oxidation decreases after your reach about 70% of exercise capacity, accelerating the use of glycogen.

A study published in the European Journal of Sport Science examines whether L-carnitine influences this tradeoff. Because of carnitine’s role in transporting fat, researchers theorized that a reduction in muscle free carnitine might be one of the mechanisms behind the switch from fat to carbohydrate energy.

True Strength Moment: Muscle carnitine content can be increased by eating foods like lamb, fish, chicken, asparagus and dairy products. Supplementation can also increase carnitine, which might be important since there seems to be a correlation between carnitine availability and fat oxidation during high-intensity submaximal exercise.