ERICKSON, M. A., R. J. SCHWARZKOPF, and R. D. MCKENZIE. Effects of caffeine, fructose, and glucose ingestion on muscle glycogen utilization during exercise.Med. Sci. Sports Exerc., Vol. 19, No. 6, pp. 579–583, 1987. Five competitive cyclists were used to determine the effects of fluid intake (16 ml.kg-1) consisting of: (i) non-nutrient control (CON); (ii) fructose (1 g.kg-1) before exercise (FRU); (iii) caffeine (5 mg.kg-1) before exercise (CAF); (iv) glucose (1 g.kg-1) during exercise (GLU); and (v) fructose/caffeine before and glucose during exercise (CFG) on blood glucose, free fatty acids, muscle glycogen, and other parameters. Exercise consisted of 90 min of cycling at 65 to 70% VO2max.Following exercise, blood glucose was found to be significantly (P< 0.05) higher for CFG and GLU (117 and 109 mg%) compared to CON, CAF, and FRU (92, 89, and 86 mg%). Blood free fatty acids rose (P< 0.05) further for CON (1,336), CAF (1,126), and FRU (1,034) over CFG (737) and GLU (714 μmol.1-1). Muscle glycogen utilization was greater (P< 0.05) for CON (91) vs CAF (63) and GLU (62 μmol/g-1wet muscle weight). It was concluded that GLU and CAF decrease muscle glycogen utilization, FRU is likely to cause gastric upset, and ingestion of multiple substances produces the greatest variability in muscle glycogen utilization and may provide added endurance benefits in some individuals.