COGGAN, A. R. and S. C. SWANSON. Nutritional manipulations before and during exercise. Med. Sci. Sports Exerc., Vol. 24, No. 9 Supplement, pp. S331-S335, 1992. Key Points: 1) Ingesting CHO during prolonged, moderate-intensity (60–85% VO2max) exercise can improve performance by maintaining plasma glucose availability and oxidation during the later stages of exercise. 2) Plasma glucose may be oxidized at rates in excess of 1 g·min-1 late in exercise. Athletes therefore need to ingest sufficient quantities of CHO in order to meet this demand. This can be accomplished by ingesting CHO at 40–75 g·h-1 throughout exercise or by ingesting ~200 g of CHO late in exercise. Ingesting CHO after fatigue has already occurred, however, is generally ineffective in restoring and maintaining plasma glucose availability, CHO oxidation, and/or exercise tolerance. 3) No apparent differences exist between glucose, sucrose, or maltodextrins in their ability to improve performance. Ingesting fructose during exercise, however, does not improve performance and may cause gastrointestinal distress. 4) The form of CHO (i.e., solid vs liquid) ingested during exercise is unlikely to be important provided that sufficient water is also consumed when ingesting CHO in solid form. 5) Ingesting 50–200 g of CHO 30–60 min before exercise results in transient hypoglycemia early in exercise, but this does not affect the rate of muscle glycogen utilization or, in most people, cause overt symptoms of neuroglucopenia. Whether performance is impaired, unaffected, or enhanced by such pre-exercise CHO feedings remains equivocal. 6) Ingesting 200–350 g of CHO 3–6 h before exercise appears to improve performance, possibly by maximizing muscle and/or liver glycogen stores or by supplying CHO from the small intestine during exercise itself. 7) Relatively few studies have examined the possible effects on performance of ingesting various other substrates (lactate, glycerol, medium chain triglycerides, amino acids) either before or during exercise. None of these substances, however, appear especially promising in their ability to enhance performance.