What is "Cardio"?

Many athletes think the opposite of lifting is “Cardio”. If they spend a day on the track running intervals or piece together a body weight circuit in the weight room, it is automatically pegged as cardio. Yes, training modalities that focus on improving work capacity and muscular endurance can be loosely described as cardio, but it helps to know that there are two systems being stressed during Cardio training.


The system commonly associated with training cardio is the Cardiovascular system. The Cardiovascular system (aka the Circulatory system) can be defined as an organ system that permits blood to circulate and transport nutrients, oxygen, carbon dioxide and hormones. Comprised of the Heart and a complex system of Arteries, Veins, Capillaries, Venioles and Arteriole, the Cardiovascular system is a key transport system in the body. Long-term training of the Cardiovascular system improves the following areas:

  • Increased maximal Cardiac Output (Q)

  • Increased capillary density

  • Decreased resting Heart Rate


The second system (and often the most overlooked) is the Cardiorespiratory system. The Cardiorespiratory system is a sub-system of the Cardiovascular system and consists of the lungs and associated structures. The primary role of cardiorespiratory system is to exchange Oxygen and Carbon Dioxide via the process of diffusion. Long-term training of the Cardiorespiratory system improves the following areas:

  • Increase Oxygen transport to the lungs and subsequent Carbon Dioxide transport away

  • Increased Minute Ventilation

  • Improved gas exchanged rate in the Alveoli

In closing, the more an athlete knows about the training process, the more an athlete may buy into how a given training system works. Being able to describe the “nuts and bolts” of how Cardio works can go along way in helping create understanding and compliance for all the teams and individuals participating in a coaches program.