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

Blood components and oxygen transport

What blood is made of, how haemoglobin loads and unloads oxygen, the Bohr effect, and why haemoglobin mass, iron status and altitude matter for endurance.

Intermediate Evidence: Strong evidence 3 min read Reviewed 2026-10-31 Status: draft

Learning objectives

  • Describe the components of blood and their functions
  • Calculate arterial oxygen content
  • Interpret the oxyhaemoglobin dissociation curve and the Bohr shift
  • Relate haemoglobin mass and iron status to endurance performance

Before this lesson

Why this matters

Oxygen delivery = blood flow × oxygen content. Cardiac output is one half of the story; the other is how much oxygen each litre of blood carries and releases — governed by haemoglobin.

Fundamental concepts: what blood is

ComponentApprox. shareFunction
Plasma~55%Water, proteins, nutrients, hormones, CO₂ transport
Red blood cells (erythrocytes)~40–45% (haematocrit)Carry O₂ via haemoglobin
White blood cells<1%Immune defence
Platelets<1%Clotting
[openstax2022blood]

Oxygen content

CaO₂ = (1.34 × Hb × SaO₂) + (0.003 × PaO₂) [mL O₂ per dL]1.34 = mL O₂ bound per g of Hb; 0.003 = solubility of O₂ in plasma per mmHg.

Example: Hb 15 g/dL, SaO₂ 0.98, PaO₂ 100 mmHg → 19.7 + 0.3 ≈ 20 mL O₂/dL. About 98% is bound to haemoglobin.

The dissociation curve

Oxyhaemoglobin dissociation curve and the Bohr shift An S-shaped curve of haemoglobin oxygen saturation against partial pressure of oxygen. At lung levels near 100 mmHg, haemoglobin is about 97 percent saturated; in exercising muscle with low oxygen pressure, saturation falls steeply so oxygen is released. During exercise, higher temperature, more carbon dioxide, lower pH and more 2,3-BPG shift the curve to the right, releasing more oxygen at the same pressure. exercising muscle lungs extra O₂ released P50 ≈ 27 020406080100 0%25%50%75%100% Partial pressure of oxygen, PO₂ (mmHg) Hb saturation (SO₂) Rest Right shift: ↑ temperature↑ CO₂, ↓ pH↑ 2,3-BPG
Figure 1. The oxyhaemoglobin dissociation curve at rest and shifted right during exercise. — Original diagram, FSHP Academy (schematic, not to scale).

The curve is sigmoid because binding one O₂ increases haemoglobin’s affinity for the next (cooperative binding). The flat top means saturation stays high even if lung PO₂ falls somewhat; the steep middle means small drops in PO₂ in tissues release large amounts of O₂.

Bohr shift: in working muscle, higher temperature, CO₂, acidity and 2,3-BPG reduce affinity, shifting the curve right and unloading more oxygen [openstax2022blood].

Haemoglobin mass and performance

Total haemoglobin mass is strongly related to VO₂max; experimental changes in Hb mass produce corresponding changes in VO₂max [schmidt2010]. This is why altitude training is used — and why blood doping and EPO are effective and banned. Oxygen delivery is the main limit on VO₂max in healthy people [bassett2000].

Endurance training expands plasma volume more than red cell mass, so Hb concentration may fall slightly (“sports anaemia”) even as total Hb mass rises.

Practical application

Common mistakes and misconceptions

Case study

A female 10 km runner reports persistent fatigue and slowing times. Her doctor finds low ferritin. Under medical supervision, iron intake is adjusted; the coach reduces intensity temporarily and monitors recovery of training quality.

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

Blood components

Crash Course

You will understand: plasma, red cells, white cells and platelets

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

Oxygen–haemoglobin dissociation curve

Khan Academy

You will understand: reading the curve and the Bohr effect

Why: Step-by-step explanation.

Knowledge check

Knowledge check · 0/5

1. With Hb 15 g/dL and 98% saturation, arterial O₂ content is about…

Answer C. 15 × 1.34 × 0.98 ≈ 19.7 mL O₂/dL, plus a small dissolved fraction.

2. Which shifts the dissociation curve to the right?

Answer C. Heat, CO₂, acidity and 2,3-BPG reduce Hb affinity, releasing more O₂.

3. Haematocrit refers to…

Answer B. Typically about 40–50% in men and 36–46% in women.

4. Increasing total haemoglobin mass (e.g., through altitude exposure) tends to…

Answer B. Hb mass is closely related to VO₂max; ~1 g change has been associated with measurable VO₂max change.

5. Why can endurance athletes have a slightly low haemoglobin concentration without true anaemia?

Answer A. Training expands plasma volume more than red-cell mass, lowering concentration while total Hb mass may rise.

Short-answer & application questions

  1. Explain why a right-shifted curve benefits exercising muscle.
  2. Which athletes are at higher risk of iron deficiency and why?
  3. Discuss the ethical and health issues of artificially raising haemoglobin.

Key takeaways

  • Blood is plasma plus formed elements (red cells, white cells, platelets).
  • About 98% of arterial oxygen is carried bound to haemoglobin; each gram of Hb binds ~1.34 mL O₂.
  • The S-shaped dissociation curve lets haemoglobin load fully in the lungs and unload steeply in working muscle; exercise shifts it right.
  • Total haemoglobin mass is closely related to VO₂max; iron deficiency impairs performance.

Connected topics

physiology

VO₂ max

physiology

Stroke volume, heart rate and cardiac output

sports nutrition

Micronutrients and hydration essentials

sports nutrition

Avoiding banned substances and doping risks

References

  1. Betts JG, Young KA, Wise JA, et al. (2022). Anatomy and Physiology 2e — Chapter 18: Blood; Section 22.5: Transport of Gases. OpenStax, Rice University. · Link Textbook check pending
  2. Schmidt W, Prommer N (2010). Impact of alterations in total hemoglobin mass on VO2max. Exercise and Sport Sciences Reviews, 38(2):68–75. 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

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