Unit D

Module 7 ~ Lesson 2

Heart Rate

Cardiac output is the amount of blood pumped by the heart each minute, usually measured in L/min, and is an indicator of the level of oxygen delivered to the body. The amount of work that a body's muscles can perform depends on the oxygen available to them. Cardiac output is a product of heart rate and stroke volume.

Heart rate is the number of times your heart beats in a minute. Average resting heart rates are around 70 beats/min. On average, your heart (a fist-sized organ) will beat close to three billion times over a lifetime. More than 200 million litres of blood will pass through its chambers.

Stroke volume is the amount of blood that is pumped from the heart with each beat. A strong heart has the ability to pump a larger volume of blood with each beat so does not have to contract as often in order to circulate blood. This results in a lower heart rate and a greater work capacity.

By OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

Due to intense cardiovascular training schedules, elite athletes work at creating the most efficient work output with the least amount of energy. They achieve such low resting heart rates due to the strength of their heart muscles developed as a result of rigorous cardiovascular activities.

Read

Read "Cardiac Output and Stroke Volume" on pages 275 to 276 of your textbook.

Heart Rate Recovery

How long does it take your heart to return to its resting rate? First, find your pulse at your wrist or under your jawbone. Record your pulse for 15 seconds and multiply by 4. This is your resting heart rate. Now, do jumping jacks or another vigorous activity for 1 minute. Immediately take your heart rate at the end of your exercise. Continue taking measurements every minute until your heart rate has returned to your resting rate. Plot these results on a graph of heart rate versus time.


If you have a physical condition that makes it inadvisable to exercise vigorously, try this alternative. After recording your resting heart rate, sit quietly, breathe deeply, and relax your body. After 4 minutes, check your heart rate to see how much you have lowered it. Take readings for every minute until your heart rate returns to its resting rate. Plot these results on a graph of heart rate versus time.

Self-Check

High blood pressure is linked to people with elevated resting heart rates. The heart is not pumping efficiently, while the pressure is increased in the blood.


Blood pressure will increase slightly during exercise to accommodate the need for a faster rate of blood flow.