Effect of Isotonic Exercise on HR and BP

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Introduction

   With regular exercise a person’s cardiovascular fitness can be immensely increased as cardiac output is increased, therefore enabling a greater rate of O² being delivered to the body’s tissues.  In cases of strenuous exercise, such as with athletes, the cardiac output is found to be double that of a person doing very little exercise, resulting in the enlargement of the heart and increasing the stroke volume.

   During isotonic exercise muscle contractions remain almost constant while the muscle may change in length.

   As a result of exercise, heart rate increases as the demand for oxygen has been made greater.  This is achieved by the means of two different mechanisms.  The first of these mechanisms is the psychological effect as the body prepares itself for the task ahead. The increase of ventilation as a result of anticipation of exercise is known as the neural changes which send excitatory impulses to the inspiratory area in the medulla oblongata in the brain.  Stimulation of the limbic system also occurs as the body begins to prepare itself.  Heart rate increases to ensure that enough blood is being pumped around the body.  This initial response to the impending exercise is equivalent to that of the “fight-or-flight” response.  Nerve impulses, initiated from the hypothalamus in the brain are sent to the sympathetic division of the ANS, which then starts to rapidly organise the body’s essential resources, such as oxygen and glucose, for the onset of physical activity.  Vast amounts of these resources are transported to organs such as the brain, skeletal muscles and the heart.

   The second mechanism is the actual increase in heart rate during exercise.  This is a more complex sequence of events where the increased cellular metabolic processes taking place in active muscles cause relaxation of smooth muscle in the local arterioles.  

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   Arterioles have an essential role in regulating blood flow into capillaries by regulating the resistance; the mechanism used for opposing blood flow.  Resistance is achieved by friction between the blood and the walls of the blood vessel.  When relaxation of the smooth muscle occurs, the diameter of the blood vessel is greater and resistance is reduced as friction has also been reduced.  This is known as vasodilation. In contrast when contraction of the smooth muscle occurs, the diameter of the blood vessel has been reduced and there is an increase in both friction and resistance.  This is known as ...

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