In this physical activity, groups of learners act as blood cells traveling through the circulatory system. They model picking up oxygen at the lungs, traveling through the heart, and delivering oxygen to a leg muscle. From the leg muscle they pick up carbon dioxide, travel through the heart and deliver carbon dioxide to the lungs so it can be expelled. Learners are encouraged to repeat the activity and time themselves as a contest. When learners set up a free account at Kinetic City, they can answer bonus questions at the end of the activity as a quick assessment. They can also keep track of their progress in all of the Kinetic City activities, and compare their progress to other participants worldwide.