Physical exercise, mainly after vigorous activity, may induce gastrointestinal dysmotility whose mechanisms are still unknown. We hypothesized that physical exercise and ensuing lactate-related acidemia alter gastrointestinal motor behavior. In the present study, we evaluated the effects of short-term exercise on gastric emptying rate in awake rats subjected to 15-min swimming sessions against a load equivalent to 5% of their body weight. After 0, 10, or 20 min of exercise testing, the rats were gavage fed with 1.5 ml of a liquid test meal (0.5 mg/ml of phenol red in 5% glucose solution) and euthanized 10 min postprandially to measure fractional gastric dye recovery. In addition to inducing acidemia and increasing blood lactate levels, acute exercise increased ( P < 0.05) gastric retention. Such a phenomenon presented a positive correlation ( P < 0.001) between blood lactate levels and fractional gastric dye recovery. Gastric retention and other acidbase-related changes were all prevented by NaHCO₃pretreatment. Additionally, exercise enhanced ( P < 0.05) the marker's progression through the small intestine. In anesthetized rats, exercise increased ( P < 0.05) gastric volume, measured by a balloon catheter in a barostat system. Compared with sedentary control rats, acute exercise also inhibited ( P < 0.05) the contractility of gastric fundus strips in vitro. In conclusion, acute exercise delayed the gastric emptying of a liquid test meal by interfering with the acid-base balance.