“In a study of rats, a Japanese research team has shown that acetic acid (the main component of vinegar) increases glycogen repletion in both the liver and skeletal muscle.”
Reference:
Fushimi, T., Tayama, K., Fukaya, M., Kitakoshi, K., Nakai, N., Tsukamoto, Y., & Sato, Y. (2001). Acetic acid feeding enhances glycogen repletion in liver and skeletal muscle of rats. Journal of Nutrition, 131, 1973-1977
Abstract: http://www.nutrition.org/cgi/content/full/131/7/1973