EFFECTS OF CARBOHYDRATE (CHO) AND FAT SUPPLEMENTATION ON CHO METABOLISM DURING PROLONGED EXERCISE

The aim of the study was to examine carbohydrate (CHO) utilization in subjects receiving CHO or CHO + medium-chain triglycerides (MCT) suppl ements during 180 minutes of exercise at 50% maximal aerobic work rate ([Wmax] 57% maximal oxygen consumption [VO(2)max]). In a double-blind crossover design, nine trained athletes cycled four times. Subjects r eceived a bolus of 4 mL . kg(-1) at the start and 2 mL . kg(-1) every 20 minutes during exercise of either a 150-g . L(-1) CHO solution (CHO trial), an equicaloric 70 energy% (en%) CHO-30 en% MCT suspension con taining 29 g MCT (CHO + MCT trial), or a 150-g . L(-1) CHO (high-CHO [ HCHO]) solution plus 29 g MCT (HCHO + MCT trial). A fourth trial consi sted of a C-13-background control trial (CON). The four trials were ra ndomized. Before and after the exercise bout, muscle biopsies were tak en from the quadriceps muscle and muscle glycogen levels were determin ed. During exercise, breath samples were collected for estimation of e xogenous and endogenous CHO oxidation. No significant differences were detected in glycogen breakdown among the trials (277 +/- 14 14 mmol . kg dry weight(-1) CHO, 249 +/- 20 CHO + MCT, and 240 +/- 18 HCHO + MC T) or in the respiratory exchange ratio during exercise. Mean exogenou s CHO oxidation rates during the final hour of exercise were 0.79, 0.6 3, and 0.73 g min(-1), respectively. No differences were observed betw een the trials regarding exogenous or endogenous CHO oxidation. Plasma free fatty acid (FFA) concentrations were elevated during exercise to a level of approximately 500 mu mol . L(-1) and were comparable in al l trials, whereas plasma ketone concentrations significantly increased after MCT ingestion as compared with the CHO trial. It is concluded t hat 29 g MCT co-ingested with CHO during 180 minutes of exercise does not influence CHO utilization or glycogen breakdown. Copyright (C) 199 6 by W.B. Saunders Company