Welcome to the Cardiovascular System (Unit A2 2)
Welcome to your study notes for the Cardiovascular System within Unit A2 2: The Application of Science to Sports Performance. At AS Level, you learned the basic anatomy of the heart and blood vessels. Now at A2, we take that knowledge and apply it directly to training, athletic performance, and physiological adaptation.
Don't worry if physiological calculations or adaptations seem a bit heavy at first. We will break down every formula, adaptation, and exam trap step by step so you can secure top marks in your 2-hour written exam!
1. Key Definitions and Core Calculations
To master this unit, you need to understand how the heart measures work and how blood moves through the body during rest and exercise.
Core Metrics and Formulae
Heart Rate (HR): The number of times the heart beats per minute (measured in beats per minute, or bpm).
Stroke Volume (SV): The volume of blood pumped out of the left ventricle per single contraction or beat (measured in millilitres, mL).
Cardiac Output (\(Q\)): The total volume of blood pumped by the left ventricle per minute (measured in litres per minute, L/min, or mL/min).
The relationship between these three measurements is captured in our primary calculation:
\(Q = HR \times SV\)
Understanding Ventricular Volumes
To understand where stroke volume comes from, we look at the heart's filling and emptying phases:
End Diastolic Volume (EDV): The volume of blood in the ventricles at the end of the filling phase (diastole), right before the heart contracts. Think of this as how much the heart "filled up".
End Systolic Volume (ESV): The volume of blood left behind in the ventricles after the contraction phase (systole). Even a healthy heart does not empty 100% of its blood on each beat.
This gives us the formula for Stroke Volume:
\(SV = EDV - ESV\)
Analogy: Imagine a water balloon. You fill it with \(120\text{ mL}\) of water (EDV). You squeeze it, and \(70\text{ mL}\) shoots out (SV). There is still \(50\text{ mL}\) left inside (ESV). So, \(120\text{ mL} - 50\text{ mL} = 70\text{ mL}\).
Maximal Oxygen Uptake (\(VO_2\text{ max}\))
Maximal Oxygen Uptake (\(VO_2\text{ max}\)): The maximum volume of oxygen the body can take in, transport, and utilize during incremental (increasing intensity) exercise. It is the ultimate benchmark of aerobic cardiorespiratory fitness.
Quick Memory Aid:
• EDV: Diastole = Dilated/relaxed (Filling)
• ESV: Systole = Squeezed (Leftover after contraction)
Key Takeaway for Section 1: Stroke volume is the blood pumped per beat (\(SV = EDV - ESV\)), while cardiac output is the blood pumped per minute (\(Q = HR \times SV\)).
2. Performance Standards and Thresholds
How do these values look in real life when comparing untrained individuals to elite athletes?
Resting Heart Rate Standards
• Average Untrained Individual: \(70\text{ to }72\text{ bpm}\)
• Elite Endurance Athlete: Can be as low as \(30\text{ to }40\text{ bpm}\)
Cardiac Output (\(Q\)) at Rest vs. Exercise
At Rest:
Resting Cardiac Output remains approximately constant at around \(5\text{ L/min}\) for both trained athletes and untrained individuals.
Why? An elite athlete has a much larger Stroke Volume, so their heart needs fewer beats per minute to deliver the exact same \(5\text{ L/min}\) of blood to the resting tissues.
During Maximal Exercise:
• Healthy Adults: \(Q\) rises to \(20\text{ to }25\text{ L/min}\)
• Elite Athletes: \(Q\) can skyrocket up to \(35\text{ to }40\text{ L/min}\)
This massive rise in maximal Cardiac Output is what allows elite athletes to deliver enormous amounts of oxygen to working muscles during competition.
Key Takeaway for Section 2: At rest, \(Q\) stays steady at roughly \(5\text{ L/min}\) regardless of training status. During exercise, trained athletes achieve much higher maximal \(Q\) values (\(35\text{ to }40\text{ L/min}\)) than untrained individuals.
3. Chronic Physiological Adaptations to Training
When athletes train consistently over weeks and months, the cardiovascular system undergoes long-term, chronic adaptations. In CCEA mark schemes, you must clearly distinguish between aerobic (endurance) adaptations and anaerobic (strength/power) adaptations.
1. Aerobic Training Adaptations (Endurance)
Long-duration, continuous, or interval aerobic training produces several major changes:
• Eccentric Cardiac Hypertrophy: The left ventricle chamber cavity increases in size and volume. A larger cavity allows a greater volume of blood to fill the ventricle during diastole, resulting in an increased End Diastolic Volume (EDV).
• Increased Stroke Volume (SV): Because the chamber holds more blood (higher EDV) and the heart muscle contracts more strongly, the heart pumps significantly more blood with every single beat.
• Resting Bradycardia: Bradycardia is defined as a resting heart rate below \(60\text{ bpm}\). This happens because of two factors working together:
1. The greatly increased Stroke Volume delivers required blood in fewer beats.
2. An increase in vagal tone (increased parasympathetic nervous system activity via the vagus nerve slowing the heart down).
• Increased Capillarisation: An increase in capillary density around both the skeletal muscles and the alveoli in the lungs. This shortens the diffusion distance and speeds up gaseous exchange (oxygen and carbon dioxide diffusion).
• Increased Blood Volume: Total blood volume expands due to an increase in blood plasma volume and an increase in red blood cell count (erythrocytes). This boosts total oxygen-carrying capacity and assists with thermoregulation.
2. Anaerobic Training Adaptations (Strength / Power)
High-intensity, resistance, and power training place a very different physical demand on the heart:
• Concentric Cardiac Hypertrophy: The muscular wall thickness of the left ventricle increases, rather than the internal chamber volume. This muscular thickening allows the heart to generate high contractile pressure to overcome high afterload (the high peripheral vascular resistance that occurs during heavy muscle straining).
• Increased Stroke Volume: SV increases primarily through a higher force of contraction (enhanced myocardial contractility), ensuring forceful blood ejection against resistance.
Quick Comparison: Cardiac Hypertrophy
• Aerobic (Eccentric Hypertrophy): Chamber volume/size expands \(\rightarrow\) holds more blood (higher EDV).
• Anaerobic (Concentric Hypertrophy): Chamber wall thickness grows \(\rightarrow\) generates more forceful contractions against resistance.
Key Takeaway for Section 3: Aerobic training creates eccentric hypertrophy (larger chamber volume), resting bradycardia (via high SV and vagal tone), capillarisation, and expanded blood volume. Anaerobic training creates concentric hypertrophy (thicker ventricular walls) to pump against high resistance.
4. Common Exam Pitfalls & Mistakes to Avoid
Be aware of these classic traps that often cost students marks in the A2 exam:
Trap 1: Mixing up Stroke Volume and Cardiac Output
Error: Writing that Stroke Volume is "the blood pumped per minute".
Correction: Stroke Volume is strictly per beat (mL/beat). Cardiac Output is the total volume per minute (L/min).
Trap 2: Saying Cardiac Hypertrophy without Specifying the Type
Error: Stating that "weightlifting makes the heart bigger" without detail.
Correction: Always specify eccentric (chamber size/volume for endurance) vs concentric (wall thickness for strength/power).
Trap 3: Claiming Resting Cardiac Output Increases with Training
Error: Assuming an athlete pumps \(8\text{ or }10\text{ L/min}\) of blood at rest.
Correction: Resting \(Q\) stays steady at around \(5\text{ L/min}\). The athlete simply pumps that \(5\text{ L/min}\) much more efficiently (fewer beats, larger volume per beat).
Trap 4: Forgetting the Nervous System in Bradycardia
Error: Explaining resting bradycardia purely by pointing to heart size.
Correction: You must also mention neurological control: an increase in vagal tone (parasympathetic dominance via the vagus nerve).
5. Chapter Quick Review
Use this checklist to test your recall before the exam:
• Can you state and calculate \(Q = HR \times SV\) and \(SV = EDV - ESV\)?
• Can you define \(VO_2\text{ max}\) accurately?
• Do you remember that resting \(Q\) is \(\approx 5\text{ L/min}\), while maximal exercise \(Q\) can reach \(20\text{ to }25\text{ L/min}\) in untrained adults and \(35\text{ to }40\text{ L/min}\) in elite athletes?
• Can you contrast eccentric hypertrophy (aerobic) with concentric hypertrophy (anaerobic)?
• Can you explain how increased SV and vagal tone produce resting bradycardia (\(< 60\text{ bpm}\))?