GLOSSARY

Deoxygenated blood is blood that has released part of its oxygen in the tissues and carries more carbon dioxide; it is not completely without oxygen.

Characteristics

• Mixed venous oxygen saturation (SvO₂): about 70–75 percent at rest.
• Partial pressure of oxygen (PvO₂): about 40 mmHg.
• Colour: dark red; the blue appearance of veins through the skin is due to how light penetrates and is absorbed, not because the blood is blue.
• Oxygen reserve: about 75 percent of oxygen remains in venous blood and can be extracted when needed, such as during exercise.

Carbon Dioxide Transport

• About 70 percent as bicarbonate.
• About 20–23 percent bound to haemoglobin (carbaminohaemoglobin).
• About 7–10 percent dissolved in plasma.

Relevance to Sport

• During intense exercise: muscles extract more oxygen, and venous saturation from active muscle may fall below 20–30 percent; this widening arteriovenous oxygen difference is one reason VO₂ rises during exercise.
• Bohr effect: rising temperature, CO₂, and acidity in active muscle facilitate oxygen release from haemoglobin.