Knowledge Base

Cardiorespiratory fitness

Cardiorespiratory fitness (CRF)

Cardiorespiratory fitness (or endurance) is the ability to exercise your entire body for a long time without stopping. It requires a strong heart, healthy lungs, and clear blood vessels to supply your large muscles with oxygen. Examples of activities that require good cardiorespiratory fitness are distance running, swimming, and cross-country skiing. Your cardiovascular system is made up of your heart, arteries (carrying oxygenated blood), veins (carrying deoxygenated blood), and blood. Your respiratory system is made up of your lungs, where oxygen enters your blood, and carbon dioxide is eliminated.

  • Heart: Your heart benefits from exercise and activities, such as jogging or swimming. The heart acts as a pump to deliver blood to cell throughout your body. During high-intensity physical activity (endurance training) needs more oxygen and produce more waste products. 
  • Lungs: In the lungs, oxygen is transferred from the air to the blood for transport to the tissues of the body. Fit people can take in more air with each breath than unfit people because they have more efficient respiratory muscles (diaphragm and abdominal muscles). 
  • Blood: The higher amount of low-density lipoprotein (LDP), often referred to as "bad LDL cholesterol" is more likely to stay in your body and contribute to atherosclerosis. Regular physical activity helps you improve your health and resist disease by reducing your LDL. 
  • Arteries: Each artery carries blood from your heart to another part of your body. Scientists have found that people who exercise regularly develop more branching of the arteries in the heart and people who exercise regularly develop extra coronary arteries (arteries around heart). It supports the performance of your heart and better CRF. 
  • Veins: Each vein carries blood filled with waste products from the muscle cells and other body tissues back to the heart. Regular exercise helps your muscles squeeze your veins efficiently. Lack of physical activity can cause the venous valves, especially those in your legs, to stop working efficiently. 

VO2max and cardiorespiratory fitness

Maximum oxygen consumption, or VO2 max, is the amount of oxygen your body is able to utilise during maximum load and reflects the overall cardiorespiratory fitness of an individual. It is also good for comparing the performance of endurance athletes. VO2max is also widely used at a hospital as an indicator of health. A lower value of VO2max is associated with a high risk of cardiovascular disease and all-cause mortality. Conversely, a good fitness level significantly reduces your likelihood of developing chronic illness. It is necessary to add, that the value falls with age, but it can be improved with the right training.

VO2 max

Changing the VO2 max value in response to training is highly variable – for some people, it will grow to almost double with the impact of training, whereas with others it barely changes. It is usually expressed as an absolute value (litres of oxygen per minute – l/min) or relatively with regard to a person’s weight (millilitres of oxygen consumed per minute per kg – ml/(kg.min)). Normal untrained people will achieve values around 27-31ml/(kg.min) of VO2 max. For endurance athletes, the values achieved are between 75 and 90 ml/(kg.min). 

The VO2 max value is determined by the heart’s performance, the number of red blood cells, the volume of blood, capillary density, and the number of mitochondria in the muscles. High aerobic capacity value is particularly important in sports which last longer or in interval training, such as with most team sports. With high aerobic capacity, the body can easily recover in short pauses, and the athlete can repeatedly perform at high intensity. 


The estimating VO2 max

Measuring VO2max involves a physical effort sufficient in duration and intensity to fully tax the aerobic metabolism. Usually, it involves a graded exercise test (on a cycle ergometer) in which exercise intensity is progressively increased while measuring ventilation and oxygen and carbon dioxide concentration of the inhaled and exhaled air. VO2 max is reached when oxygen consumption remains at a steady state despite an increase in workload. 

The maximum value of VO2 max

The highest known value of VO2 max is around 96–97 ml/(kg.min), measured in the cyclist Oskar Svendsen and the cross-country skier Espen Bjerke. However, the absolute champions are not humans but Siberian racing dogs, whose VO2 max values can reach up to 240 ml/(kg.min).

Measuring VO2 max is often complex, so various estimates are used, which are often not very accurate. Despite this, it can be useful for observing changes in training.

The Uth–Sørensen–Overgaard–Pedersen estimation

To estimate the VO2 max value, the relatively easy-to-measure resting heart rate (HRrest) and maximum heart rate under stress (HRmax) values are used:
VO2max = HRmax /HRrest x 15,3 mL/(kg.min)

The Cooper test

This estimate of VO2 max uses the distance in metres that someone can run in 12 minutes (d12) for the calculation:
VO2 max = (d12 - 504.9) / 44.73.