Heart Rate, Stroke Volume and Cardiac Output

This lesson covers heart rate, stroke volume, and cardiac output as required by the OCR GCSE PE specification (J587). You need to understand the definitions of each term, know the key equation (Q = SV x HR), and be able to interpret and apply heart rate data in sporting contexts.

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Key Definitions

Term	Definition	Unit
Heart rate (HR)	The number of times the heart beats per minute	Beats per minute (bpm)
Stroke volume (SV)	The volume of blood pumped out of the left ventricle with each beat	Millilitres per beat (ml/beat)
Cardiac output (Q)	The total volume of blood pumped out of the left ventricle per minute	Litres per minute (l/min) or ml/min

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Heart Rate (HR)

Heart rate is the number of times the heart beats per minute. It is the simplest measure of how hard the heart is working.

Resting Heart Rate

• The average resting heart rate for an adult is approximately 70 bpm.
• A trained athlete will have a lower resting heart rate, often between 40-60 bpm (and sometimes even lower). This is called bradycardia and is a sign of a strong, efficient heart.
• A lower resting heart rate means the heart pumps the same amount of blood in fewer beats — each beat is more powerful and efficient.

Maximum Heart Rate

• An estimate of maximum heart rate can be calculated using the formula: 220 - age.
• For example, a 16-year-old student has an estimated maximum heart rate of 220 - 16 = 204 bpm.
• Maximum heart rate decreases with age.

Heart Rate During Exercise

During exercise, heart rate increases because:

• Working muscles demand more oxygen and nutrients.
• The heart must pump more blood per minute to meet this demand.
• The nervous system signals the heart to beat faster.
• Adrenaline (released during exercise and excitement) also increases heart rate.

Heart Rate Recovery

After exercise, heart rate gradually returns to its resting level. The time this takes is called the recovery time. A fitter person recovers faster — their heart rate returns to resting levels more quickly.

Exam Tip: OCR may ask you to interpret a heart rate graph showing heart rate before, during, and after exercise. Be prepared to identify: (1) the resting heart rate, (2) the increase during exercise, (3) the peak heart rate, and (4) the recovery time.

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Stroke Volume (SV)

Stroke volume is the volume of blood ejected from the left ventricle with each heartbeat.

Condition	Typical Stroke Volume
At rest (untrained person)	Approximately 70 ml per beat
At rest (trained athlete)	Approximately 100+ ml per beat
During maximal exercise	Can increase to 150-200+ ml per beat

Why Does Stroke Volume Increase During Exercise?

• More blood returns to the heart during exercise (increased venous return) because muscles are contracting and squeezing blood back towards the heart.
• The heart muscle stretches more as it fills with more blood, and then contracts more forcefully (Frank-Starling mechanism).
• This means each beat pumps out a greater volume of blood.

Why Do Athletes Have a Higher Resting Stroke Volume?

Regular training causes the heart muscle to grow larger and stronger (a process called cardiac hypertrophy). A larger, stronger heart:

• Can fill with more blood per beat.
• Can contract more forcefully.
• Pumps more blood per beat (higher stroke volume).
• Therefore needs fewer beats to pump the same amount of blood, which is why athletes have lower resting heart rates.

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Cardiac Output (Q)

Cardiac output is the total volume of blood pumped by the left ventricle per minute. It tells you how much blood the heart is delivering to the body in total.

The Equation

Cardiac Output (Q) = Stroke Volume (SV) × Heart Rate (HR)

Or: Q = SV x HR