78 The authors are with the Dept of Kinesiology and Applied Health Science, Human Performance Labora- tory, Indiana University, Bloomington, IN 47405. International Journal of Sport Nutrition and Exercise Metabolism, 2006, 16, 78-91 © 2006 Human Kinetics, Inc. Chocolate Milk as a Post-Exercise Recovery Aid Jason R. Karp, Jeanne D. Johnston, Sandra Tecklenburg, Timothy D. Mickleborough, Alyce D. Fly, and Joel M. Stager Nine male, endurance-trained cyclists performed an interval workout followed by 4 h of recovery, and a subsequent endurance trial to exhaustion at 70% VO 2max , on three separate days. Immediately following the first exercise bout and 2 h of recovery, subjects drank isovolumic amounts of chocolate milk, fluid replacement drink (FR), or carbohydrate replacement drink (CR), in a single-blind, randomized design. Carbohydrate content was equivalent for chocolate milk and CR. Time to exhaustion (TTE), average heart rate (HR), rating of perceived exertion (RPE), and total work (W T ) for the endurance exercise were compared between trials. TTE and W T were significantly greater for chocolate milk and FR trials compared to CR trial. The results of this study suggest that chocolate milk is an effective recovery aid between two exhausting exercise bouts. Key Words: glycogen resynthesis, endurance performance, nutrition, sports drink It is well known that endurance exercise performance is influenced by the amount of stored glycogen in skeletal muscles, and that intense endurance exercise decreases muscle glycogen stores (9, 10, 13, 18), leading to a diminution in performance. The resynthesis of glycogen between training sessions occurs most rapidly if carbo- hydrates (CHO) are consumed within 30 min to 1 h after exercise (9, 13, 17). Indeed, delaying carbohydrate ingestion for 2 h after a workout can reduce the rate of glycogen resynthesis by half (20, 22). To maximize the rate of glycogen resynthesis, it is suggested that 50 to 75 g of CHO be ingested within 30 to 45 min after exercise (1), with ingestion of 1.2 to 1.5 g CHO/kg of body weight/hour for the next few hours (12, 19, 20, 24, 29). Ingesting protein along with carbohydrate (at a CHO-to-protein ratio of 2 to 2.9:1) has been shown to hasten the rate of gly- cogen synthesis and improve endurance performance, especially when the amount of carbohydrate ingested is less than current recommendations (20, 21, 35, 39). Of particular importance is the study of Ivy et al. (23), who found that the ingestion of a solution containing a 4:1 CHO-to-protein ratio improved endurance performance 06Karp(78) 78 2/22/06, 1:11:57 PM