As the body begins exercise there is a greater demand for oxygen, to accommodate for this increase in oxygen demand the body makes a number of changes to meet the new oxygen requirements. The changes that occur to the cardiovascular system which involes the heart and blood vessels happens automatically in response to exercise. It is important to remember that these changes are only temporary and only last for the duration of exercise.
Heart rate is controlled by the autonomic part of the central nervous system, it has two aspects the parasympathetic bracnh which is responsible for decreasing heart rate returning it back to resting levels after exercise. The second branch is the sympathetic system which increases heart rate and is responsible for maintaining a high heart beat during exercise.
The endocrine system produces the hormones adrenaline and noradrenaline during exercise as both hormones play a role in stimulating the heart, increasing heart rate and force of contraction. Adrenaline is also responsible for the slight anticipatory rise in heart rate just prior to commencing exercise as the body anticipates that exercise is about to occur.
Frank Starling Mechanism: Increased amounts of blood returning to the heart (increased venus return) results in an increased force of contraction due to stretching of the muscle wall. There is increased neural stimulation the autonomic nervous system stimulates the heart to push more blood around the body thus increasing stroke volume.
As exercise continues blood vessels dilate to facilitate greater blood flow this also results in less resistance against the blood and greater venus return.
However stroke volume can only be increased to a point as the heart can only pump out so much blood at a time. This limit is usually met a sub-maximal activity at around 50% of VO2 max.
Is the pressure exerted by the blood on the arterial walls as it is ejected from the heart. Normal resting blood pressure being around 120/80 mmHg.
Blood is redistributed from organs and areas that do not require a lot of blood immediately, therefore during exercise some of that blood is redirtcted to the working muscles. Blood is predominately redirected from areas such as the stomach, liver and kidneys to the muscles.
Blood plasma levels decreases due to sweating, evaporation and excretion of metabolic by-products, this can lead to dehydration.
The respiratory system is needed to get in oxygen and expel carbon dioxide in order to increase oxygen supply to the muscles and to remove carbon dioxide the respiratory system sees increases in the respiratory rate, tidal volume and minute ventilation. The aim of these mechanisms is to increase the amount of oxygen getting into and distributed around the body and also to increase the efficiency in the removal of carbon dioxide.
In response to exercise the muscles themselves must become more efficient in their use of fuels in particular oxygen and be able to provide the muscular contractions needed for movement in exercise.
During exercise the body will require a greater number of muscle contractions therefore more motor units and in turn more muscle fibres need to be activated. This is especially true for powerful strength activities that require a lot of force as to provide maximum force a high number of muscle fibres will need to be activated.
During exercise blood is redirected from organs that are not needed for the immediate activity and is redirected to the working muscles.
Enzyme activity is increased this improves the efficiency of the mitochondria and therefore energy can be produced faster.
This is because heat is a by-product of the energy systems. Heat may be helpful to enzyme activity to some extend but if too high may be detrimental and hyperthermia or dehydration could set in.
The muscles cells use more oxygen whilst exercising than at rest as they are engaging in more aerobic respiration whilst exercising. This increased use and uptake of oxygen from the blood results in a greater AVO2(arteriovenus) difference.
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