FSHP Academy
Exercise Physiology — all lessons

Muscle Physiology

Muscle physiology: excitation–contraction and the sliding filament modelConcentric, eccentric and isometric muscle actionsMotor units, recruitment and rate codingNeuromuscular adaptations to training

Energy Systems

Energy systems overview: how the body makes ATPThe ATP-PC (phosphagen) systemAnaerobic glycolysis and lactateThe aerobic oxidative system

Cardiovascular Physiology

Heart anatomy and the cardiac cycleStroke volume, heart rate and cardiac outputBlood components and oxygen transport

Aerobic Fitness and Intensity

Aerobic fitness concepts and adaptationsVO₂ maxLactate thresholdHeart rate zones and RPE-based intensity control

Stroke volume, heart rate and cardiac output

How the heart matches blood flow to demand — the determinants of stroke volume and heart rate, the Fick principle, and how endurance training changes them.

Intermediate Evidence: Established consensus 5 min read Reviewed 2026-10-31 Status: draft

Learning objectives

  • Calculate cardiac output from heart rate and stroke volume
  • Explain how preload, contractility and afterload determine stroke volume
  • Use the Fick principle to connect cardiac output with oxygen uptake
  • Describe the cardiovascular adaptations to endurance training and the meaning of a low resting heart rate

Before this lesson

Why this matters

Muscles can only sustain work if oxygen reaches them, and the heart is the pump that delivers it. Cardiac output — the volume of blood the heart pumps each minute — is the central link between the heart and the VO₂ max and endurance performance of an individual [bassett2000]. For trainers, it also explains heart-rate responses, why some clients’ heart rates rise more slowly than others, and what changes with endurance training.

Prerequisite: the structure of the heart and the cardiac cycle (heart anatomy and cardiac cycle).

Fundamental concepts

Q̇ = HR × SVQ̇ in L·min⁻¹; HR in beats·min⁻¹; SV in mL·beat⁻¹ (divide by 1,000 to convert mL to L).
  • Heart rate (HR): beats per minute.
  • Stroke volume (SV): blood ejected by the left ventricle per beat = end-diastolic volume (EDV) − end-systolic volume (ESV).
  • Ejection fraction: SV ÷ EDV — the proportion of filled blood ejected.

Worked example. At rest, HR 70 bpm × SV 70 mL = 4,900 mL/min ≈ 4.9 L/min. During maximal exercise an untrained adult might reach ~195 bpm × ~110 mL ≈ 21 L/min, while elite endurance athletes can exceed 35 L/min, almost entirely because of a much larger stroke volume [joyner2008] [levine2008].

The science: what sets stroke volume and heart rate

Determinants of cardiac output and oxygen uptake Flow diagram. Heart rate is set by autonomic nervous system balance. Stroke volume is set by preload (end-diastolic volume), contractility and afterload. Heart rate multiplied by stroke volume gives cardiac output. Cardiac output multiplied by the arteriovenous oxygen difference gives oxygen uptake, which is the Fick equation. Autonomic balance sympathetic ↑ · vagal ↓ Preload (EDV, venous return) Contractility Afterload (arterial pressure) Heart rate (HR) beats · min⁻¹ Stroke volume (SV) mL · beat⁻¹ (↑ afterload ↓ SV) × Cardiac output (Q̇) L · min⁻¹ = HR × SV a–v̄O₂ difference O₂ extracted by tissues Oxygen uptake (V̇O₂) V̇O₂ = Q̇ × (a–v̄O₂ diff) Fick principle: oxygen uptake = delivery (Q̇) × extraction (a–v̄O₂ difference)
Figure 1. Determinants of cardiac output and their link to oxygen uptake via the Fick principle. — Original diagram, FSHP Academy (schematic, not to scale).

Stroke volume

Three factors determine stroke volume [openstax2022cv]:

  1. Preload — how much the ventricle fills before contracting (EDV). More venous return stretches cardiac fibres, and a stretched fibre contracts more forcefully — the Frank–Starling mechanism. During exercise, the muscle pump in the legs and breathing-related pressure changes increase venous return.
  2. Contractility — the strength of contraction at a given fibre length, increased by sympathetic stimulation and adrenaline.
  3. Afterload — the pressure the ventricle must overcome to eject blood (largely arterial pressure). Higher afterload tends to reduce stroke volume.

Heart rate

The sinoatrial node sets an intrinsic rhythm, which is modulated by the autonomic nervous system: parasympathetic (vagal) activity slows it, sympathetic activity speeds it. At the start of exercise, heart rate rises first through withdrawal of vagal tone, then further through sympathetic activation. Maximal heart rate declines with age and changes little with training — see heart rate zones for prediction equations and their errors.

The Fick principle

V̇O₂ = Q̇ × (a–v̄O₂ difference)a–v̄O₂ difference = arterial O₂ content − mixed venous O₂ content (mL O₂ per 100 mL or per L of blood).

Oxygen uptake is delivery multiplied by extraction. During exercise both rise: cardiac output increases, and working muscles extract more oxygen from each litre of blood. At maximal effort in healthy people exercising with a large muscle mass, maximal cardiac output is the principal limit on VO₂ max [bassett2000] [levine2008].

Worked example. Q̇ = 20 L/min and a–v̄O₂ difference = 150 mL O₂/L → V̇O₂ = 20 × 150 = 3,000 mL/min = 3.0 L/min. For a 70 kg person, that is ≈ 43 mL·kg⁻¹·min⁻¹.

Training adaptations

Endurance training produces a predictable set of changes [joyner2008] [levine2008]:

  • Larger, more compliant left ventricle (more filling capacity) and expanded plasma and blood volume → higher EDV and stroke volume.
  • Lower resting and submaximal heart rate for the same cardiac output, because each beat ejects more blood.
  • Little change in maximal heart rate.
  • Peripheral adaptations — more capillaries and mitochondria — raise the a–v̄O₂ difference.

Practical application

Common mistakes and misconceptions

  • “Training makes your maximal heart rate go up.” Training raises maximal stroke volume; maximal HR stays similar or falls slightly.
  • “Heart rate = intensity.” HR is a proxy influenced by heat, hydration, caffeine, stress, medication and time in the session.

Assessment and practical tools

  • Resting HR: measure on waking, seated or lying, for 60 s, on several days; use the average.
  • HR recovery: the drop in HR in the first minute after stopping exercise is a simple fitness indicator worth tracking over time within the same person.
  • Calculator: use the heart rate zone calculator to set training zones.

Case study

Client: Arjun, 45, sedentary office worker, begins three brisk-walking and cycling sessions per week.

Week 1: resting HR 78 bpm; at a set treadmill speed and incline, HR reaches 148 bpm. Week 10: resting HR 68 bpm; the same workload produces 132 bpm.

Interpretation: The same oxygen demand is now met with fewer beats — consistent with increased stroke volume. The trainer explains this to Arjun as visible proof of progress, re-tests his zones, and increases the workload so sessions continue to provide a training stimulus.

Further learning: video lessons

Video links are only marked “verified” after a human has watched them. Unverified entries open a YouTube search for that channel and topic rather than a guessed link.

Introductory needs verification — opens a YouTube search

Cardiac output, stroke volume and heart rate (overview)

Khan Academy

You will understand: the Q̇ = HR × SV relationship and its units

Why: Clear foundational explanation.
Technical needs verification — opens a YouTube search

Preload, afterload and contractility — Frank–Starling

Ninja Nerd

You will understand: the mechanisms that set stroke volume

Why: Detailed physiology lecture with diagrams.
Practical demo needs verification — opens a YouTube search

Cardiovascular responses to exercise and training

Armando Hasudungan

You will understand: how exercise and training change heart function

Why: Illustrated explanations linking physiology to exercise.

Knowledge check

Knowledge check · 0/5

1. A client has a heart rate of 150 beats/min and a stroke volume of 110 mL. Cardiac output is about…

Answer B. 150 × 110 mL = 16,500 mL/min = 16.5 L/min.

2. Increased venous return stretches the ventricle and increases stroke volume. This is…

Answer B. Greater end-diastolic volume stretches cardiac muscle fibres, increasing the force of the next contraction.

3. Which change accounts for most of the increase in maximal cardiac output after endurance training?

Answer B. Maximal heart rate changes little with training; larger, more compliant ventricles and expanded blood volume raise stroke volume.

4. In the Fick equation V̇O₂ = Q̇ × (a–v̄O₂ difference), the a–v̄O₂ difference represents…

Answer B. It is the difference in oxygen content between arterial and mixed venous blood — how much oxygen tissues removed.

5. Heart rate gradually rises during prolonged steady exercise in the heat while stroke volume falls. This is called…

Answer B. Cardiovascular (cardiac) drift is linked to rising body temperature, fluid loss and redistribution of blood to the skin.

Short-answer & application questions

  1. Calculate resting cardiac output for HR 62 bpm and SV 85 mL, then estimate how stroke volume would change if the same output were maintained at HR 50 bpm.
  2. Explain why heart rate alone can mislead you about exercise intensity on a hot day.
  3. Describe two warning signs during exercise that should make a trainer stop a session and refer the client.

Key takeaways

  • Cardiac output (Q̇) = heart rate × stroke volume; at rest about 5 L/min in adults, rising four- to eight-fold during maximal exercise depending on fitness.
  • Stroke volume depends on preload (filling), contractility and afterload; the Frank–Starling mechanism links greater filling to a stronger contraction.
  • The Fick principle — V̇O₂ = Q̇ × a–v̄O₂ difference — explains why maximal cardiac output is central to VO₂ max.
  • Endurance training mainly raises maximal stroke volume (larger heart chambers, more blood volume), not maximal heart rate.
  • A low resting heart rate is often a sign of fitness, but it must be interpreted in context — it is not a diagnosis.

Connected topics

physiology

VO₂ max

physiology

Blood components and oxygen transport

physiology

Heart rate zones and RPE-based intensity control

physiology

Aerobic fitness concepts and adaptations

metabolic health · planned

Hypertension training guidelines

References

  1. Joyner MJ, Coyle EF (2008). Endurance exercise performance: the physiology of champions. Journal of Physiology, 586(1):35–44. doi:10.1113/jphysiol.2007.143834 Narrative review check pending
  2. Levine BD (2008). V̇O₂max: what do we know, and what do we still need to know?. Journal of Physiology, 586(1):25–34. doi:10.1113/jphysiol.2007.147629 Narrative review check pending
  3. Bassett DR Jr, Howley ET (2000). Limiting factors for maximum oxygen uptake and determinants of endurance performance. Medicine & Science in Sports & Exercise, 32(1):70–84. doi:10.1097/00005768-200001000-00012 Narrative review verified
  4. Betts JG, Young KA, Wise JA, et al. (2022). Anatomy and Physiology 2e — Section 19.4: Cardiac Physiology. OpenStax, Rice University. · Link Textbook check pending

Educational content only — not medical advice. Consult a qualified clinician for diagnosis or treatment.