 They looked at 20 breast cancer patients who had just been diagnosed and therefore had not yet started their cancer treatments. During the study, the patients pedaled a bicycle ergometer for 30 minutes at a resistance of their own choosing. Blood samples were taken from the patients at rest before the pedaling. During exercise and after the exercise, blood samples were analyzed to calculate the amount of many different types of white blood cells. Now, we know the white blood cells are little Pac-Men that attack invaders.