IB Sports, exercise and health science A.2.3.3 Factors Affecting Maximal Oxygen Consumption Notes

Maximal Oxygen Consumption (VO₂max) and Endurance Performance

1. VO₂ max is expressed in milliliters of oxygen per kilogram of body weight per minute (mL/kg/min).
2. VO₂ max is an indicator of aerobic fitness and determines how efficiently the cardiovascular, respiratory, and muscular systems work together to supply and utilize oxygen.
3. A higher VO₂ max means:
   1. Greater oxygen delivery to muscles.
   2. Enhanced endurance performance and delayed fatigue.
   3. More efficient energy production for sustained activity.

Importance of VO₂ Max in Exercise and Sports

1. Determines aerobic endurance capacity: A higher VO₂ max means an athlete can sustain exercise for longer without fatiguing.
2. Measures cardiovascular efficiency: A well-conditioned heart and lungs enhance oxygen delivery to muscles.
3. Used for performance prediction: VO₂ max is a strong indicator of endurance performance in sports like marathon running, cycling, and rowing.
4. Reflects overall fitness: VO₂ max is used in health assessments and athlete monitoring.

The Fick Equation

1. VO₂max captures how well the cardiovascular system delivers oxygen and how well muscles extract it. The Fick equation summarises both sides.
2. VO₂max = Cardiac Output × (Arteriovenous Oxygen Difference)
3. Cardiac output (Q): the amount of blood the heart pumps each minute (Q = heart rate × stroke volume).
4. Arteriovenous oxygen difference (a-vO₂ diff): the difference in oxygen content between arterial blood entering the muscle and venous blood leaving it.
5. Both sides matter: improving either side of the equation raises VO₂max. Training adaptations target both.

Factors Influencing VO₂max

1. Age

1. VO₂ max peaks in the late teens to early 30s and declines at a rate of about 1% per year after 25-30 years of age.
2. The decline occurs due to reduced stroke volume, cardiac output, and muscle efficiency.
3. Lifelong endurance training: preserves VO₂max well above the age-matched average into the sixties and seventies, because aerobic training slows the loss of stroke volume, blood volume, and mitochondrial density.

2. Sex Differences

1. Males typically have 10-20% higher VO₂ max than females, due to three physiological differences:
2. Larger heart and stroke volume: males tend to have a larger left ventricle, which pumps more blood per beat and raises cardiac output. This increases the supply side of the Fick equation.
3. Higher haemoglobin concentration: males carry more haemoglobin per litre of blood, so each litre transports more oxygen to working muscles.
4. Greater muscle mass and lower body fat percentage: more metabolically active tissue means more mitochondria and a higher capacity to extract oxygen from blood at the muscle.
5. However, trained female endurance athletes can still have a higher VO₂ max than untrained males.