2.66 Heart Rate & Exercise | Edexcel IGCSE Biology: Double Science Revision Notes 2019

Heart Rate & Exercise

A heart rate is measured by counting the number of times a heart beats in a minute (bpm)
The natural resting heart rate is controlled by a group of cells located in the right atrium called the pacemaker
- The role of the pacemaker is to coordinate the contraction of the heart muscle and regulate the heart rate
- Pacemaker cells send out electrical impulses which initiate a contraction in the cardiac muscle
Other factors can also influence the heart rate, such as the hormone adrenaline

The heart pumps blood around the body in order to supply oxygen and glucose to respiring cells
The blood also removes waste products from the respiring cells
During exercise, the cells of the muscles respire more rapidly in order to provide energy for muscle contraction
- Respiration may be aerobic if exercise is moderate, or anaerobic if exercise is more intense
An increase in respiration means an increase in requirement for oxygen and glucose as well as an increase in production of waste products that need to be removed
The nervous system responds to this requirement by stimulating the following changes
- Heart rate increases to deliver oxygen and glucose and remove waste more frequently
- The volume of blood pumped out of the heart also increases to deliver bigger quantities of oxygen and glucose
Production of the hormone adrenaline increases heart rate as part of a 'fight or flight' response
At the end of a period of exercise, the heart rate may remain high for a period of time as oxygen is required in the muscles to break down the lactic acid from anaerobic respiration
- This is how the oxygen debt is paid off
The time taken for the heart rate to return to the resting rate is called the recovery time
- A physically fit person will have a lower resting heart rate and a shorter recovery time compared to an unfit person