The physiological support systems in the body all work together simultaneously to provide a sustained energy release during physical activity to achieve a specific task. The three major systems which actively participate in this effort are the pulmonary system, cardiovascular system and the neuromuscular system. The Pulmonary system is primarily responsible for controlling breathing and volume of air that enters the lungs. Lung volumes vary with age, gender, and body size, especially stature. As the body becomes more physically fit for endurance, the pulmonary system becomes more efficient in exchanging the volume of gas between its internal and external environment. The process of this exchange is extremely quick with a healthy lung taking about 1 second to exchange gas with blood. The alveoli are the final branchings of the respiratory tree and act as the primary gas exchange units of the lung. The alveoli are the final branchings of the respiratory tree and act as the primary gas exchange units of the lung. The alveolar pressure is determinant to whether air will flow into or out of the lungs. When alveolar pressure is negative, as is the case during inspiration, air flows from the higher pressure at the mouth down the lungs into the lower pressure in the alveoli. When alveolar pressure is positive, which is the case during expiration, air flows out. At end-inspiration or end-expiration, when flow temporarily stops, the alveolar pressure is zero (i.e., the same as the atmospheric pressure). *Did you know that the surface area of the lungs is the same as a tennis court? Carbon dioxide (CO2) is the primary gas which is expelled from the body, while oxygen (O2) is primary gas which is inhaled and absorbed. In an average, moderately fit human being, the exchange of these two gases is very efficient and ventilation capacity is rarely taxed. *Did you know that their are 700 million alveoli in an adult lung? Even during maximal exercise, a considerable breathing reserve exists because pulmonary ventilation at this level of exercise rarely exceeds 85% of a healthy person's maximum capacity for breathing. After only 4 weeks of submaximal training, a considerable reduction in the amount of oxygen needed to maintain the same energy output is observed. *Did you know you lose about 1/2 liter of water a day through breathing? Theoretically, endurance exercise would benefit the pulmonary system for two main reasons: (1) It would reduce the fatiguing effects of exercise on the ventilatory musculature (primarily the lungs), and (2) any oxygen freed from use by respiratory muscles becomes available to the exercising muscles. The Cardiovascular System consists of the heart and blood vessels which develop the vascular circuit of the body. This system serves four important functions during physical activity: 1) It delivers oxygen to the exercising muscles and removes wastes; 2) It returns blood to the lungs for aeration; 3) It transports heat, a byproduct of cellular metabolism, from the body's core to the skin; and, 4) It delivers fuel nutrients to the active issues. *Did you know that 8 million blood cells die every second, and the same number are born each second. The blood is sometimes compared to a river, but the arteries are more like a river in reverse. Arteries are thick-walled tubes with a circular covering of yellow, elastic fibers, which contain a filling of muscle that absorbs the tremendous pressure wave of a heartbeat and slows the blood down. This pressure can be felt in the arm and wrist - it is the pulse. The largest artery in the human body is the aorta which distributes the highest volume of blood. Eventually arteries divide into smaller arterioles and then into even smaller capillaries, the smallest of all blood vessels. One arteriole can serve a hundred capillaries. Here, in every tissue of every organ, blood's work is done when it gives up what the cells need and takes away the waste products that they don't need. Now the river comparison really does apply. Capillaries join together to form small veins, which flow into larger main veins, and these deliver deoxygenated blood back to the heart. Veins, unlike arteries, have thin, slack walls, because the blood has lost the pressure which forced it out of the heart, so the dark, reddish-blue blood which flows through the veins on its way to the lungs oozes along very slowly on its way to be reoxygenated. Back at the heart, the veins enter a special vessel, called the pulmonary arteries, into the wall at right side of the heart. It flows along the pulmonary arteries to the lungs to collect oxygen, then back to the heart's left side to begin its journey around the body again. *Did you know you the adult human body contains 5-6 quarts of blood? Your Physician will regularly measure your blood pressure as an assessment when you go for your annual checkup. Blood pressure is equal to the forces exerted by the blood against the walls of the arteries during a cardiac cycle and is written as systolic/diastolic or, for example, 120/80 mm Hg (stated as 120 over 80). *Did you know you the adult human body contains 5-6 quarts of blood? High blood pressure, or hypertension, imposes a chronic and excessive strain on the normal function of the cardiovascular system. Chronic hypertension that is not corrected can eventually lead to heart failure. Hypertension is defined as: systolic blood pressure (SBP) of 140 mm Hg or greater; or diastolic blood pressure (DBP) of 90 mm Hg or greater. Regular aerobic training brings about modest reductions in systolic and diastolic blood pressure at rest and during submaximal exercise. Systolic blood pressure increases in proportion to oxygen uptake and cardiac output during exercise, whereas diatolic pressure remains relatively unchanged or increases slightly. At the same relative exercise load, systolic pressures are greater when exercise is performed with arms and legs. *Did you know you that your heart beats 40 million times a year? Cardiac output reflects the functional capacity of the circulatory system. Heart rate and stroke volume (quantity of blood ejected with each stroke) are the two factors that determine the heart's output capacity. The relationship is: Cardiac output = Heart rate X Stroke volume. *Did you know you that your heart will increase in size with strength training? Both short and long term cardiac performance and adaptation are significant via aerobic (utlizing O2) and anaerobic (without O2) exercise. Training changes may, enable the heart to function at a lower percentage of its total oxidative capacity during exercise. In addition, exercise may provide some protection from the degenerative process of heart disease. The Neuromuscular System consists of the integrated network of nerves and muscles in the body. Muscles are composed of thousands of individual cells called muscle fibers held together with a network of connective tissue that becomes continuous with the tendons at each end of the muscle. Tendons serve to connect skeletal muscle to bones, and it is through this connection that muscle can actively change its length and produce joint and limb movement. *Did you know you that the strongest muscle in your body is located at your jaw - the masseter? Muscle fibers are innervated by motor neurons. A motor neuron can innervate as few as one or several hundred muscle fibers. When a motor neuron fires, all the fibers that it serves are simultaneously activated and develop force. A motor neuron and all of the muscle fibers that it innervates are referred to as a motor unit, the basic functional entity of muscular activity. The extent of control of a muscle is usually dependent on the number of muscle fibers within each motor unit. Muscles that must function with great precision, such as eye muscles, may have motor units with as few as one muscle fiber per motor neuron. In contrast, the quadriceps, which performs much less precise movements, may have several hundred fibers served by one motor neuron.