What Factors Limit Oxygen Utilization & Aerobic Energy Production During Exercise?

The human body expends either aerobic or anaerobic energy or a combination of both during times of physical exertion. Aerobic energy is energy that is produced with oxygen, and anaerobic energy is produced without oxygen; the latter relies on stored body chemicals such as adenosine troposphere and creatine phosphate. Most exercise programs rely on the production of aerobic energy.

  1. Endurance Exercise and Aerobic Energy

    • Endurance exercise can be defined as a cardiovascular exercise such as distance running, swimming or any exercise that raises the heart rate for an extended period. During endurance exercise, the body is powered primarily by aerobic energy production. Endurance exercise requires the muscles within the body to perform repeated contractions; to accomplish this, the body has to consume an adequate supply of oxygen and have a sufficient fuel supply. Different factors can limit the oxygen used in producing aerobic energy.

    Pulmonary Diffusion

    • The lungs are the means by which oxygen is transferred from the atmosphere to the bloodstream and carbon dioxide is removed from the body. Pulmonary diffusion is the process involving the exchange of oxygen and carbon dioxide between the lungs and the bloodstream. While pulmonary diffusion is not a limiting factor in oxygen utilization for normal individuals, it can limit oxygen utilization in well-conditioned athletes who have much higher cardiac outputs. This is the result of the higher cardiac output of a well-conditioned athlete having a shorter time for oxygen to enter the bloodstream, which in turn could result in reduced blood oxygen saturation levels.

    Cardiac Output

    • Cardiac output by definition is the product of heart rate and stroke volume -- stroke volume being the amount of blood pumped per heartbeat measured in liters. Cardiac output is commonly recognized as the central limiting factor for oxygen delivery and use. Some researchers have concluded that maximal cardiac output can be responsible for 70 to 85 percent of limitations in oxygen utilization. While the maximal heart rate of an individual remains basically unchanged during endurance training, the stroke volume of an individual can be significantly increased from endurance exercise. The heart is a muscle, and as the heart is exercised, it develops a greater capacity to fill with blood. The result for those who participate regularly in a regimen of endurance exercise is that the stroke volume increases to maximum oxygen utilization, which leads to gains in cardiac output and an improvement in endurance performance.

    Blood Volume and Flow

    • During exercise, muscles require a substantially greater amount of oxygen and nutrients. To accommodate these needs, more blood has to be relayed to the muscles during endurance exercise. The oxygen-carrying capacity of the bloodstream can be a factor in oxygen use. If there is an increase in blood volume through regular sessions of intense endurance exercise, the increase in blood volume will reduce the thickness of the blood. The thinning of the blood can improve the blood flow through the blood vessels -- specifically the smallest vessels -- which means improved oxygen delivery to the muscles being exercised. In some individuals, endurance exercise has resulted in an increase in red blood cell volume; this can result in an increase in the oxygen-carrying capacity of the blood.