This interrupted worksheet case study, developed for introductory or intermediate undergraduate physiology courses, aims to eliminate misconceptions that many students have about lactate, lactic acid, and changes in the body during exercise. The case begins with two fictional undergraduate students discussing the causes of muscle soreness; both of these characters have obvious misunderstandings about this issue that are likely to be shared by many students. As the case develops, students are presented with information in a variety of forms including flow charts and work through some of the chemical reactions that take place in actively contracting skeletal muscle cells to better understand the real cause of muscle soreness. By the end of the case, students will have explored this complex issue from multiple angles.