VO2 max is the maximum rate at which the body can take in, transport, and use oxygen during intense whole-body exercise. It indicates maximal aerobic power and is influenced by cardiovascular, respiratory, muscular, genetic, and environmental factors.
VO2 max reflects the maximum capacity of the aerobic energy system to resynthesize ATP. It can be expressed as an absolute value in , or relative to body mass in , which allows fairer comparisons between individuals of different sizes.
The mechanism is explained by the Fick equation:
Here, is maximum cardiac output, while the arterial-venous oxygen difference represents how much oxygen the working muscles extract from the blood. Therefore, VO2 max depends on both oxygen delivery and oxygen utilization.
| Factor | Influence on VO2 max |
|---|---|
| Genetics | Influences heart size, muscle fibre characteristics, haemoglobin concentration, and responsiveness to training. |
| Aerobic training | Increases stroke volume, cardiac output, capillary density, and mitochondrial density. |
| Age | Usually peaks in early adulthood and declines with age, partly because maximum heart rate and muscle mass decrease. |
| Biological sex | Average values differ because of factors such as haemoglobin concentration, heart size, and body composition. Individual variation remains substantial. |
| Body composition | Greater non-functional mass, especially body fat, lowers relative VO2 max because the value is divided by body mass. |
| Altitude | Reduced oxygen partial pressure lowers oxygen availability and initially decreases VO2 max. |
| Exercise mode | The highest values usually occur when large muscle groups are active, such as during running or cycling. |
A common misconception is that VO2 max alone determines endurance performance. Performance also depends on lactate threshold, exercise economy, fuel availability, pacing, and psychological factors.
In an IB SEHS response, define VO2 max, state its units, use the Fick equation, and distinguish central factors such as cardiac output from peripheral factors such as muscular oxygen extraction. Link it explicitly to topic A.2.3 by explaining that it represents the maximum capacity of aerobic ATP production.