Saturday, December 10, 2016

Limitations and Adaptations of Oxygen Consumption

During exercise we all try to push ourselves to work harder and reach new limits and milestones in our training. But no matter how hard we push, we are limited physiologically because maximal oxygen uptake is limited by the cardiorespiratory system’s ability to deliver oxygen to the muscles.2 During bouts of exercise with increased intensity, minute ventilation (the volume of air breathed per minute) increases due to increased depth and frequency of breathing, which leads to increased oxygen consumption and CO2 production.1 And as discussed in an earlier blog, decreases performance. During high intensity exercise, the partial pressure of oxygen lowers and carbon dioxide increases, which causes the gas exchange due to diffusion to happen more rapidly.1  
Oxygen is transported through the blood by a protein found in red blood cells known as hemoglobin, the binding of these two forms oxyhemoglobin. The amount of oxygen that can be transported in the blood in dependent on the concentration of hemoglobin. The binding of these two sensitive to things like pH and temperature. A decrease in blood pH (increased acidity) causes a weaker bond between oxygen and hemoglobin, which results in increased unloading of oxygen into the blood. An increase in temperature will cause a weaker bond between oxygen and hemoglobin, resulting in an increase of oxygen unloading in working muscles. Another factor that can affect hemoglobin concentration is a byproduct of red blood cell glycolysis called 2- 3 DPG. 2-3 DPG can combine with hemoglobin and reduce the hemoglobin’s ability to bind to oxygen. 2- 3 DPG are known to increase in climates with high elevation and in individuals with anemia.3
With an increase in exercise intensity, the respiratory system becomes limited, even in trained individuals.4 However, there are adaptations that can occur due to cardiorespiratory training that can work in favor of a higher VO2 max and more efficient oxygen consumption. Aerobic exercise allows for the increase in size and number of mitochondria, capillaries, and an increase in myoglobin content. Mitochondria are responsible for aerobically producing ATP. The ability to have increased density of mitochondria and greater concentration of myoglobin allows for a greater utilization of oxygen extraction.1

Limitations of performance are bound to happen, it’s just human physiology. But the great this is, adaptations to overcome those limitations naturally occur as well through cardiorespiratory training.2 But as the level of competition rises many of athletes search for a way to expedite the process of training adaptations, while sedentary individuals are sometimes plagued by life choices or illness and fall even further below the curve.

1Baechle, T.R. and Earle, R.W. Essential of Strength and Conditioning. National Strength and Conditioning Association. 2008; (3):124-130.
2Bassett, D. R., Howley, E. T. Limiting factors for maximum oxygen uptake and determinants of endurance performance. Med Sci Sports Exercise. 2000; 32(1): 70-84.
3Powers, S.K. and Howley, E. T. Exercise Physiology. Theory and Application to Fitness and Performance. 2015; (9): 71-77,216-239.
4Xu, F., Rhodes, E.C. Oxygen uptake kinetics during exercise. Sports Med. 1999; (5): 313-327.

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