When one eats a heavy meal, blood flow is directed towards stomach for digestion. If a person begins exercising immediately, blood is suddenly redirected to working muscles, explained Dr Parth Agrawal, Consultant Arthroscopy. This can slow down digestion. It can lead to stomach cramps, nausea, dizziness and acid reflux. "This discomfort can...[make] the workout feel harder than usual," he said.