Oxidation of exogenous [13C]galactose and [ 13C]glucose during exercise

amined the oxidation of exogenous galactose or glucose dur-ing prolonged submaximal cycling exercise. Eight highly trained volunteers exercised on two occasions on a cycle er-gometer at 65 % of maximal workload for 120 min, followed by a 6U-min rest period and a second exercise bout of 30 min at 60 % maximal workload. At random, subjects ingested a 8 % galactose solution to which an [lJ3C]galactose tracer was added or a 8 % glucose solution to which an [U-13C]glucose tracer was added. Drinks were provided at the end of the warm-up period (8 ml/kg) and every 15 min (2 ml/kg) during the first 120 min of the test. Blood and breath samples were collected every 30 and 15 min, respectively, during the test. The exogenous carbohydrate (CHO) oxidation was calculated from the ‘3C0#“COZ ratio and CO2 production of the expired air. Peak exogenous CHO oxidation during exercise for galac