Heart Rate Response to Exercise

The primary purpose of the cardiorespiratory system is to deliver adequate amounts of oxygen and remove waste from body tissues .  The purpose of cardiovascular regulation is maintaining adequate blood flow to all body tissues.  In addition, the circulatory system transports nutrients and aids in temperature regulation.  During exercise, the demand for oxygen to the muscles is 15 to 25 times greater than at rest.  The heart cannot accomplish this by itself, and does not work in isolation.  The respiratory system and the circulatory system function together as a “coupled unit” delivering the body’s oxygen and nutrients and taking away carbon dioxide and wastes to maintain homeostasis.

     During exercise, there is an increase in oxygen demand on body tissues and many things happen in the body such as an increase in blood pressure, heart rate, and respiratory rate.  To meet the demand for oxygen, two major adjustments of blood flow are made, and increase in the amount of blood being pumped per minute by the heart or the cardiac output, and a redistribution of blood flow from inactive organs to the active skeletal muscle.

     The heart has an electrical conduction system makes of two nodes (special conduction cells) and a series of conduction pathways.  The heart begins beating with an electrical impulse from the sinoatrial (SA) node.  The SA node is the pacemaker of the heart, responsible for setting rate and rhythm and is located in the wall of the right atrium.  The impulse spreads through the walls of the atria, causing them to contract.  Then, the impulse moves through the atrioventricular (AV) node (a relay station) located at the junction between the atria and ventricles.  As the impulse travels down the bundles, the ventricles contract and the cycles repeats itself, this cycle of atrial and ventricular contractions pumps blood of the heart to the rest of the body.

     Resting and exercise heart rate are controlled by the sympathetic and parasympathetic nervous system.  The sympathetic division of the autonomic nervous system prepares the body for physical activity by increasing heart rate, blood pressure and respiration.  The sympathetic division also stimulates the release of glucose from the liver for energy.  Once exercise begins, the sympathetic nervous system is activated and the heart rate rises quickly.  Heart rate also rises by simply thinking about exercise, which is referred to as anticipatory heart rate response.

The parasympathetic division helps to slow down heart rate and respiration.  At rest, the heart is controlled by the parasympathetic division, which is why the average resting heart rate is 60 beats per minute or less.  One of the explanations of why endurance athletes have such a low resting heart rate following training is due to increased parasympathetic response.  During exercise, the release of epinephrine and norepinephrine stimulate receptors in the heart which causes heart rate to increase. 

Written By: WST trainer Melissa Robinson