Exercise refines the ability of the cardiorespiratory system to take oxygen from air inspired into the lungs, and then load and transport it more effectively. Greater efficiency in the movement of blood through the cardiovascular system allows greater amounts of oxygen to be transferred from the respiratory system and also lung size does not increase due to exercise by any estimable degree.When you are exercising your respiratory system responds by increasing the respiratory rate and tidal volume as you start to breathe heavily, deeper and quicker, so that a greater supply of oxygen can get to the muscles. In contrast when you finish exercising your respiratory rate and tidal volume will decrease and gradually return to baseline. The increase in the respiratory rate and tidal volume in response to exercise leads to an increase in the pulmonary ventilation and thus greater delivery of oxygen to the alveoli to meet the increased demand of the exercising muscles. It also ensures greater removal of carbon dioxide which is produced by the increased workload of the musculature.
Responses to Anaerobic Exercise
In order to immediately meet the unexpected higher energy demand, stored ATP is the first energy source. This lasts for approximately 2 seconds.
Muscles begin to fatigue when ATP resynthesis can no longer match requirement.
If the exercise continues at a high intensity, and so Oxygen is not available at a fast enough rate to allow aerobic metabolism to take over, the production of lactic acid will reach the point where it interferes with muscular function. This is called the Lactate threshold.
When stored ATP is broken down into ADP + P, the rising ADP level excites Creatine Kinase to begin the breakdown of Phosphocreatine (PC).
The ATP-PC system can only last 8-10 seconds before PC stores are decreased.
The lactic acid system (Anaerobic glycolysis) must then take over as the predominant source of energy production. High intensity (but sub-maximal) exercise can last for between 3 and 5 minutes using this system
Responses to Aerobic Exercise
Due to the necessity of Oxygen being present for aerobic metabolism, the first few minutes of low to moderate intensity exercise are powered by anaerobic metabolism as described above.
The intensity and duration of exercise determines which fuel source is used. Fat metabolism is a slow process and so can only be used as fuel for exercise at less than 60% VO2 max.
The intensity of exercise which can be maintained drops as fat cannot supply the required amount of energy.
Continued low to moderate intensity exercise is then fuelled by carbohydrate and fat stores using aerobic metabolism.
Carbohydrate is a much faster fuel source and so can be used for exercise up to 80% (in trained individuals).
Carbohydrate stores within the muscle and liver can fuel exercise for up to 80 minutes. As carbohydrate stores get lower, the body has to rely more and more on fat stores.
The effects of exercise training on the respiratory system :
During exercise of the muscle cells, the organism use more oxygen and produce increased amounts of carbon dioxide. So after the exercise of the muscle cells your lungs and heart have to work harder to supply the extra oxygen and remove the carbon dioxide.Eventually your breathing rate increases and you breathe more deeply and also heart rate increases in order to transport the oxygenated blood to the muscles.

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Muscle cell respiration increases , more oxygen is used up and levels of carbon dioxide rise. The brain detects increasing levels of carbon dioxide and a signal is sent to the lungs to increase breathing. Breathing rate and the volume of air in each breath increase, which means that more gaseous exchange takes place. The brain also tells the heart to beat faster so that more blood is pumped to the lungs for gaseous exchange. More oxygenated blood is gets to the muscles and more carbon dioxide is removed.
A conditioned athlete gradually develops increased maximum oxygen consumption (VO2 max) and lung capacity, which are contributors to being fit and healthy.
Moreover, athlete who has not properly trained their cardiovascular system is likely to incur other injuries more easily by the rapid onset of fatigue and the consequent lowering of motivation and mental awareness. For anyone emulating at varying altitudes, they must allow themselves a considerable period to acclimatise before an event. Even climbing to a moderate altitude decreases the maximum uptake by 7% to 8% due to the change in atmospheric pressure. This decrease in oxygen being supplied to the muscles may decrease performance by 4% to 8% depending on the duration of emulation, a considerable disadvantage at the finish line.
Finally, athlete who prepares and acclimatises well may still not match natives of high altitude areas such as the Andes, who have a larger chest capacity, more alveoli, larger capillary beds and higher red blood cell count.Thenceforth, people may suffer from altitude sickness when moving from low to high altitudes, sufficient time must also be allowed for these symptoms to vanish before starting intensive training.
Conclusion :
Biological control mechanisms increase ventilation in response to exercise to meet the demand for increased gas-exchange rates and to maintain PaCO2, pHa and PaO2 during moderate exercise and heavy exercise. Finally all humans possess specific kinds of muscle fibers, each of which is allotted relatively evenly throughout the muscles of the body in keeping with the genetic makeup of the individual. The two general muscle fiber types are fast twitch and slow twitch fibers. The definition between fast and slow is determined by the frequency with which the neuron that dominates the impulses that control the contraction of the particular fiber. Fast twitch neurons begin at a rate of approximately 10 times greater frequency than does a slow twitch neuron.Also the effective function of fast twitch fibers is necessary to anaerobic sports such as sprinting and jumping. Specialized exercise, such as plyometric programs, can increase the performance of fast twitch fiber. The proportion of slow twitch muscle fibers, the backbone to the muscle function in stamina sports such as marathon running and cycling, will increase in proportion to fast twitch fibers when the athlete undergoes vigorous stamina training.