Cardiorespiratory (CR) fitness, sometimes called CR endurance,
aerobic fitness, or aerobic capacity, is one of the five basic
components of physical fitness. CR fitness is a condition in which
the body's cardiovascular (circulatory) and respiratory systems
function together, especially during exercise or work, to ensure
that adequate oxygen is supplied to the working muscles to produce
CR fitness is needed for prolonged, rhythmic use of the body's large muscle groups.
A high level of CR fitness permits continuous physical activity
without a decline in performance and allows for rapid recovery
following fatiguing physical activity.
Activities such as running, bicycling, swimming,
cross-country skiing, rowing, stair climbing, and jumping rope
place an extra demand on the cardiovascular and respiratory systems.
During exercise, these systems attempt to supply oxygen to the
working muscles. Most of this oxygen is used to produce energy
for muscular contraction. Any activity that continuously uses
large muscle groups for 20 minutes or longer taxes these systems.
Because of this, a wide variety of training methods is used to
improve cardiorespiratory endurance.