Essay on Oxygen Debt and the Beneficial Effects of Exercise

During muscular exercise, blood vessels in the muscles dilate and blood flow is increased in order to increase the available oxygen supply, to allow the muscles required to function properly. Up to a point, the available oxygen is sufficient to meet the energy needs of the body. However, when muscular exertion is very great, oxygen cannot be supplied to muscle fibres fast enough, and the aerobic breakdown of pyruvic acid cannot produce all the ATP required for further muscle contraction.

During such periods, additional ATP is generated by anaerobic respiration by glycolysis. In the process, most of the pyruvic acid produced is converted to lactic acid. This can only be done for a short time as the acid produced is toxic to the body, very quickly the muscles will begin to cramp and exercise cannot continue.

Ultimately, once adequate oxygen is available, lactic acid must be catabolised completely into carbon dioxide and water. After exercise has stopped, extra oxygen is required to metabolise lactic acid; to replenish ATP, phosphocreatine, and glycogen; and to pay back any oxygen that has been borrowed from haemoglobin, myoglobin, air in the lungs, and body fluids.

The additional oxygen that must be taken into the body after vigorous exercise to restore all systems to their normal states is called oxygen debt

The need for oxygen to replenish ATP and remove lactic acid is referred to as the "Oxygen Debit" or "Excess Post-exercise Oxygen Consumption" (EPOC) - the total oxygen consumed after exercise in excess of a pre-exercise baseline level.

In low intensity, primarily aerobic exercise, about one half of the total EPOC takes place within 30 seconds of stopping the exercise and complete recovery can be achieved within several minutes (oxygen uptake returns to the pre-exercise level).

Recovery from more strenuous exercise, which is often accompanied by increase in blood lactate and body temperature, may require 24 hours or more before re-establishing the pre-exercise oxygen uptake. The amount of time will depend on the exercise intensity and duration.

The two major components of oxygen recovery are:

„h Alactacid oxygen debit (fast component)

„h the portion of oxygen required to synthesise and restore muscle phosphagen stores (ATP and PC)

„h Lactacid oxygen debit (slow component)

„h the portion of oxygen required to remove lactic acid from the muscle cells and blood

Recovery following Maximal exercise

Effect of Exercise on Cancer

A number of studies have indicated that regular, even moderate, exercise may reduce the risk of colon cancer and, in fact, any cancer related to obesity. A number of studies have also suggested that regular exercise, particularly if it is vigorous, reduces risks against breast cancer in women and prostate cancer in men. Indeed, a 2004 study showed that prostate cancer cells have a 27% reduction in growth when exposed to exercise serum (blood serum taken from patients who exercise) compared to control serum, suggesting that exercise changes blood chemicals to be less hospitable to cancer cells.

Several studies are underway to measure the effect of exercise on patients who have been diagnosed with cancer. Even though preliminary, they already suggest that exercise has a positive physical, mental, and emotional effect. Exercise can improve physical strength, functional capacity, and the ability to battle the negative side effects of chemotherapy, including nausea and fatigue. More studies are warranted.

Effects on the Gastrointestinal Tract

Endurance athletes often report gastrointestinal distress, such as bloating, diarrhea, and gas, even at rest. Experts suggest, however, that moderate regular exercise, might reduce the risk for some intestinal disorders, including ulcers, irritable bowel syndrome, indigestion, and diverticulosis. For example, in one 2000 study, exercise was associated with a lower risk for ulcers in men (although not in women.) Older people who exercise moderately may have a lower risk for severe gastrointestinal bleeding.

Effects on Neurologic Diseases and Mental Decline

A 2001 study reported that older people who regularly exercised had lower rates of mental deterioration, Alzheimer's, and dementia of any type. Aerobic exercise is linked with improved mental vigor, in all people, including reaction time, acuity, and math skills. Exercising may even enhance creativity and imagination. According to one study, older people who are physically fit respond to mental challenges just as quickly as unfit young adults. Another study found that walking regularly protects women from mental decline, and in fact, the more they walked per week, the more protection they enjoyed. (Stretching and weight training appear to have no such effects.) A 2004 study showed that exercise can reverse a high-fat diets harmful effects on neurologic function.

People with existing neurologic diseases, such as multiple sclerosis, Parkinsons disease, and Alzheimers disease, should be encouraged to exercise. Specialized exercise programs that improve mobility are particularly valuable for Parkinson's patients. Patients with neurological disorders who exercise experience less spasticity as well as reduction in, and even reversal of, muscle atrophy. In addition, the psychological benefits of exercise are extremely important in managing these disorders. Exercise machines, aquatic exercises, and walking are particularly useful.

Effects on Emotional Disorders

Some research has suggested that exercise may have antidepressant effects. Although there is little strong evidence that exercise can help manage depression, a number of studies have suggested benefits. The following are some examples:

„h In a 2000 study 30 minutes of brisk exercise three times a week was as effective as medication in relieving the symptoms and reducing relapse in many patients with mild to mild to moderate depression.

„h A 2002 study reported that over half of older women with depression that did not respond to medication improved with 10 weeks of exercise. (About a third of women who did not exercise also improved during that time.)

„h Studies on elderly, depressed patients report some modest but still significant benefits from exercise, including in patient who do not response to antidepressants. (Simply participating in a group activity may help improve mood.)