Endurance refers to a person's ability to continue doing a stressful activity for an extended period of time. This is Sometimes called stamina. What this means that is a person with good endurance or stamina can bike, jog, play, or run for a long time without getting tired. Having a healthy endurance level means that a person has a healthy level of cardiovascular fitness cardiovascular fitness refers to how efficiently the heart and lungs can pump blood (which holds oxygen) to muscles that are being worked. The more efficiently the heart works, the more energy the body has to continue working without a great deal of effort.