A method of enhancing physical performance during exercise by administering an amount of a grape extract effective to treat a subject. A preferred grape extract comprises a concentration of flavanol monomers of greater than about 5% by weight, and more preferably within a range from about 12% by weight to about 50% by weight, and a concentration of flavanol dimers preferably greater than about 2% by weight, and more preferably within a range from about 6% by weight to about 20% by weight. The flavanol monomers preferably include catechin, epicatechin, epicatechin gallate, and gallic acid. The flavanol dimers preferably include procyanidin B1, procyanidin B2, procyanidin B3, procyanidin B4, and procyanidin B2-O-gallate.