<p> Oxygen deficit</p><p>During the first few minutes of cardiovascular exercise, the anaerobic energy systems (CP-ATP and glycolysis) supplies the ATP needed for this work. The energy produced during this deficit phase of exercise is used until a steady-state (or steady- rate) of oxygen consumption is used. This indicates that mitochondrial (aerobic) respiration is the dominant energy system being used. </p><p>Rest to Exercise Transitions</p><p>Steady State After the onset of exercise, the body has to adjust to the increased demand for oxygen and ATP. Physiologically, the body goes into a state of oxygen deficit. This is the result of anaerobic energy metabolism, which provides the initial demand for ATP (because it is faster and readily available). As the body adjusts, the ATP is produced through the aerobic energy system. This is called steady state, which means that the oxygen supply is meeting the oxygen demand by way of aerobic metabolism.</p><p>Oxygen Deficit Oxygen deficit is the difference between the total amount of oxygen required to perform an activity and the actual amount of oxygen initially available until steady state is reached.</p><p>Recovery from Exercise Once the exercise is over, the demand for oxygen and ATP decreases and the body starts to recover. The recovery period will include the repayment of oxygen debt and the replenishment of the fuel stores (ATP – CP and muscle glycogen).</p><p>Oxygen Debt —Oxygen Recovery Uptake As soon as exercise stops, the muscle and heart contractions slow down but there is still a higher demand for oxygen compared to what the body needs at rest. During this time, the heart rate and breathing rate are still elevated. This oxygen debt can be defined as the amount of oxygen consumed during recovery over and above what is consumed at rest. Higher exercise intensities will result in longer recovery periods.</p><p>The replenishment of fuel stores and removal of metabolic by-products also occurs during recovery. </p>