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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Heart Rate and Exercise
Your heart is an amazing muscle that works non-stop to pump blood around your body. When you exercise, your body needs more oxygen and nutrients, so your heart has to work harder. Let's explore how and why your heart rate changes during exercise and what this means for your health.
Key Definitions:
This is your heart rate when you're completely relaxed. For most teenagers, a normal resting heart rate is between 60-100 beats per minute. Athletes often have lower resting heart rates (40-60 bpm) because their hearts are stronger and more efficient.
During exercise, your heart rate increases to meet the higher demand for oxygen. During intense exercise, your heart rate can reach 160-200 beats per minute, depending on your age and fitness level.
When you exercise, your muscles need more oxygen and glucose to produce energy. Your heart responds by pumping faster and harder to deliver more blood to your working muscles. Here's what happens:
Active muscles use more oxygen and produce more carbon dioxide and waste products.
Your body needs more oxygen and nutrients to fuel muscle contraction and energy production.
Your heart beats faster to increase blood flow to muscles, delivering more oxygen and removing waste products.
Your cardiac output (how much blood your heart pumps per minute) depends on two factors:
Cardiac Output = Heart Rate × Stroke Volume
During exercise, both your heart rate and stroke volume increase, dramatically increasing your cardiac output. At rest, your cardiac output might be about 5 litres per minute, but during intense exercise, it can increase to 20-30 litres per minute!
Elite endurance athletes like marathon runners often have resting heart rates as low as 40 beats per minute. This is because regular training makes their hearts stronger, allowing them to pump more blood with each beat (increased stroke volume). This means they need fewer beats to circulate the same amount of blood, making their cardiovascular system more efficient.
You can measure your heart rate in several ways:
Exercise intensity is often measured using heart rate zones, calculated as a percentage of your maximum heart rate:
Your maximum heart rate (MHR) is the highest your heart rate can safely go during exercise. A simple way to estimate it is:
Maximum Heart Rate = 220 - your age
For example, if you're 15 years old, your estimated maximum heart rate would be 220 - 15 = 205 beats per minute.
When you exercise, your heart rate follows a predictable pattern:
Your heart rate begins to increase even before you start exercising, as your body prepares for activity.
During the first few minutes of exercise, your heart rate rises steadily until it reaches a plateau appropriate for the intensity level.
After exercise, your heart rate gradually returns to normal. The time this takes is an indicator of cardiovascular fitness.
Not everyone's heart responds to exercise in the same way. Several factors influence your heart rate response:
You can assess your cardiovascular fitness by measuring how quickly your heart rate returns to normal after exercise:
The greater the drop in heart rate after 1 minute, the better your cardiovascular fitness. A drop of 20 beats or more is considered good.
Regular exercise causes adaptations in your cardiovascular system that improve its efficiency:
While an increased heart rate during exercise is normal, you should be aware of warning signs that could indicate a problem:
Your body has sophisticated mechanisms to control heart rate during exercise:
The autonomic nervous system regulates your heart rate through two branches:
During exercise, sympathetic stimulation increases while parasympathetic influence decreases, causing your heart to beat faster.
Your heart beats about 100,000 times per day, pumping approximately 7,500 litres of blood! Over an average lifetime, that's more than 2.5 billion heartbeats. Regular exercise makes each of those beats more efficient, potentially adding years to your life.
Heart rate is a vital indicator of how hard your body is working during exercise. Understanding the relationship between heart rate and exercise can help you:
Remember that everyone's heart rate response is unique. What matters most is how your heart rate changes over time as you become fitter, not how it compares to others.
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