You can eat sugar if you exercise. In fact, eating sucrose (a type of sugar found naturally in maple syrup, dates, and honey) may be beneficial for helping maintain and increase muscle glycogen stores, which the body relies on for fuel during exercise [1
However, not all sugar is created equal: natural sugars (found in fruit, milk, and yogurt) differ from refined sugars in that they are digested and absorbed at a slower rate thanks to the fiber and protein present in these foods. This results in more stable glucose levels and a steady supply of energy for cells.
Foods with natural sugars also contain other essential nutrients (like vitamins, minerals, and antioxidants) that are needed for energy metabolism, immune function, and cell health, and more; whereas refined sugars may negatively affect health.