Cellular respiration can occur aerobically or anaerobically. This document describes experiments conducted by Sydney University biology students to test aerobic and anaerobic capacity through physical activity. The experiments found that aerobic exercises produced more ATP and were more efficient than anaerobic exercises at replenishing energy stores. However, more research is needed to fully understand how aerobic capacity influences one's ability to perform anaerobic exercises. The studies emphasized the relationship between heart rate and type of physical activity performed.