The Effects of Exercise and Activity Tolerance
The cardiopulmonary responses to exercise include the circulatory functions of the heart and blood vessels and the gas exchange functions of the respiratory system. Collectively, they function to supply oxygen and energy substrates to the working muscle groups and to exchange oxygen and carbon dioxide with the atmosphere. Cardiopulmonary or aerobic exercise involves repetitive and rhythmic movements, uses large muscle groups, and results in the ability to perform vigorous exercise for an extended period. The cardiovascular responses to exercise involve neural regulation (cardiovascular centers in the brain, with their autonomic output to the heart and blood vessels) in tandem with local control mechanisms that further regulate cardiac output, blood pressure, and local blood flow. Blood pressure also increases with exercise. With the onset of exercise, the systolic blood pressure increases because of the increase in cardiac output, while the diastolic pressure remains relatively unchanged because of vasodilatation and increased blood flow to the working muscles. The role of the respiratory system during exercise is to increase the rate of oxygen and carbon dioxide exchange.
The integration of the neurologic and musculoskeletal systems is essential for body movement and participation in activity. To initiate and sustain increased activity, muscle strength, flexibility, and endurance are needed. Skeletal muscles hypertrophy and undergo other anatomic changes in response to exercise training. “Trained muscles” have an increased number of capillaries surrounding each muscle fiber that facilitates the delivery of oxygen to the working muscle cells during exercise. They are able to use oxygen more efficiently, probably because of enhanced enzymatic activity that increases oxidative capacity.
Metabolic and Thermal Responses
To supply the energy needed for increased activity, a person must consume a balanced diet and have adequate hydration. Although proteins are not used for energy sources during increased activity, they have an essential role in the building and rebuilding of tissues and organs. During increased activity and exercise, it is essential that an individual maintain adequate hydration. Increased activity can result in loss of fluids from the vascular compartment. If this is allowed to progress, the person may experience severe dehydration that may lead to vascular collapse. Before and during vigorous activity, a person should replenish body fluids with water and electrolyte solutions.
The body is able to maintain its temperature within a set range. It does this by way of two mechanisms. The first mechanism used by the body to regulate temperature is to change blood flow to the skin. When the blood vessels of the skin dilate, warm blood is shunted from the core tissues and organs to the skin surface, where heat is lost more easily to the surrounding environment. The second mechanism by which the body loses heat is through sweating, in which the evaporation of sweat from the skin surface contributes to the loss of body heat. Depending on training level and environmental conditions, the body may have difficulty regulating its temperature during vigorous exercise.
The gastrointestinal system is affected by intense physical activity. During intense physical activity, blood flow is shunted away from the gastrointestinal tract toward the active skeletal muscles. As a result, gastrointestinal motility, secretory activity, and absorptive capacity are decreased. Evidence suggests that physical activity reduces the risk for colon cancer as well as diverticulosis, gastrointestinal hemorrhage, and inflammatory bowel disease.
Hemostasis and Immune Response
The immune system is stimulated by regular, moderate exercise and impaired with regular, repetitive, and intense exercise. A period of moderate-intensity exercise has been found to boost the immune system for several hours by producing an increase in circulating white blood cells, including neutrophils and lymphocytes. Of special note is the increased activity of natural killer (NK) cells. Chronic, intense, and exhaustive exercise produces different effects on the immune system. Elevation in body temperature, cytokine release, and increased levels of various stress-related hormonesmay result in a temporary depression of the body’s innate immune defenses. Strenuous exercise alters mucosal immunity of the upper respiratory tract. This may explain why elite athletes are susceptible to illness, especially upper respiratory tract infections.
There is a mental component to the performance of increased activity and exercise. The mental aspect entails the motivation to initiate an activity, or exercise program, and the dedication to incorporate the regimen into one’s lifestyle. Positive effects of regularly performed exercise include increased energy and motivation, positive self-image and self-esteem, decreased anxiety, and better management of stress.