Cardiovascular System During Exercise of Different Intensities and Recovery

Cardiovascular System Response to Exercise

The cardiovascular system includes the heart, blood vessels, and the blood itself. Its main function is to transport oxygen, nutrients, and hormones to and from the cells of the body.
During exercise of any intensity, the cardiovascular system will respond in order to meet the enhanced demand for oxygen and energy by the working muscles.

Heart rate is the frequency of heart contractions, usually measured in beats per minute (bpm). At rest, a normal heart rate can range from 60 to 100 bpm for most healthy adults.
As exercise intensity increases, heart rate also increases to meet the rising demand for oxygen by the working muscles. This response is known as chronotropic response.

Stroke volume refers to the amount of blood ejected by the left ventricle of the heart during one contraction or heartbeat. Stroke volume typically increases during the initial stages of exercise.
At higher intensities, stroke volume plateaus - a phenomenon known as the Frank-Starling Mechanism. The mechanism involves more blood returning to the heart (preload), causing the heart muscle fibres to stretch and contract with more force, thus ejecting more blood.

Cardiac output is the volume of blood ejected by the heart per minute and is calculated as heart rate multiplied by stroke volume.
During exercise of increasing intensity, cardiac output initially increases due to the combined increase in both heart rate and stroke volume.

During exercise, systolic blood pressure (pressure when the heart contracts) typically increases to accommodate the greater demand for blood and oxygen in the working muscles.
Diastolic blood pressure (pressure when the heart relaxes) usually remains the same or may slightly decrease during exercise due to the dilatation of blood vessels.

Over prolonged, steady-state exercise, a phenomenon called cardiovascular drift occurs where heart rate continues to increase while stroke volume decreases. This is largely due to dehydration and an increase in body temperature.

Following the end of exercise, the cardiovascular system will start to return to its resting state during the recovery period.
Immediately after exercise, heart rate and stroke volume will decrease, thus reducing cardiac output. This process happens quickly at first, then more slowly, following a pattern called exponential decay.
During this recovery period, modes of active recovery, such as slow jogging or walking, are beneficial to help maintain venous return and stabilise blood pressure.

After high-intensity exercise, the body experiences a ‘debt’ of oxygen known as EPOC. The body uses more oxygen than is available, and EPOC serves to repay this oxygen debt.
EPOC comprises of two phases - alactic (quick to recover and replenishes the immediate ATP-PC system) and lactic (longer to recover and oxidises accumulated lactic acid).
EPOC leads to a prolonged increase in heart rate and respiration as the body works to restore itself to its restful state, also known as homeostasis.