Cardiorespiratory Fitness

Cardiorespiratory fitness is the capacity of the circulatory, respiratory, and muscular systems to deliver and use oxygen during sustained dynamic exercise. It reflects the integrated performance of ventilation, blood oxygen transport, cardiac output, vascular delivery, and the ability of working muscles to use oxygen for aerobic energy production .¹

The reference measure is maximal oxygen uptake, or VO2max, typically obtained during a graded cardiopulmonary exercise test. When a clear physiological plateau is not demonstrated, the highest measured value may be reported as VO2peak. Fitness can also be estimated from submaximal tests, field tests, or non-exercise equations, although estimates are less direct than measured gas exchange .^1,2

Cardiorespiratory fitness is related to, but not identical with, physical activity. Physical activity describes behavior, whereas fitness describes a physiological capacity shaped by habitual activity, genetics, age, health, and training. Someone can temporarily be inactive yet retain substantial fitness, or be physically active without having a high VO2max. The term therefore describes how effectively the body performs aerobic work rather than how much exercise a person reports doing .^1,2