The three immediate adaptations that occur to the body when beginning a cardiovascular program are

This review examines the cardiovascular adaptations along with total body water and plasma volume adjustments that occur in parallel with improved heat loss responses during exercise-heat acclimation. The cardiovascular system is well recognized as an important contributor to exercise-heat acclimation that acts to minimize physiological strain, reduce the risk of serious heat illness and better sustain exercise capacity. The upright posture adopted by humans during most physical activities and the large skin surface area contribute to the circulatory and blood pressure regulation challenge of simultaneously supporting skeletal muscle blood flow and dissipating heat via increased skin blood flow and sweat secretion during exercise-heat stress. Although it was traditionally held that cardiac output increased during exercise-heat stress to primarily support elevated skin blood flow requirements, recent evidence suggests that temperature-sensitive mechanisms may also mediate an elevation in skeletal muscle blood flow. The cardiovascular adaptations supporting this challenge include an increase in total body water, plasma volume expansion, better sustainment and/or elevation of stroke volume, reduction in heart rate, improvement in ventricular filling and myocardial efficiency, and enhanced skin blood flow and sweating responses. The magnitude of these adaptations is variable and dependent on several factors such as exercise intensity, duration of exposure, frequency and total number of exposures, as well as the environmental conditions (i.e. dry or humid heat) in which acclimation occurs.

The acute responses by the cardiovascular and respiratory system are experienced in the transition between rest and the start of aerobic exercise.

Immediately during the start of exercise, the cardiac output (Q) increases because of an increase in stroke volume (SV) and heart rate (HR). Cardiac output is the amount of blood pumped in liters per minute, and is the product of stroke volume and heart rate: [Q = SV x HR].  Obviously, the heart rate increases during exercise, but most people don't realize that it actually starts to pick up right before the start of exercise as a reflex.  The sympathetic nervous system sends an anticipatory stimulation to get the heart ready for exercise.  The stroke volume increases beginning at the onset of exercise, and similarly to heart rate, can increase with the anticipation of exercise.  Stroke volume can increase up to 50% - 60% of the resting value.

Oxygen uptake (VO2), which is the amount of oxygen consumed by the body's tissues, also increases to accommodate the metabolic demands.  At rest, VO2 is 1 met = 3.5 mL/kg/min.  The maximum value for VO2 can be anywhere between 25 - 80 mL/kg/min, depending on age and conditioning level.

There is also an increase in blood pressure and blood flow. Systolic blood pressure is the pressure in the arteries during the heart's contraction, and should increase during exercise.  Diastolic blood pressure is the pressure in the arteries during the rest between heart contractions, and can increase or decrease during exercise.  However, diastolic blood pressure should never increase over 20 mmHg.  

During exercise, there is vasodilation in the active muscles, meaning the blood vessels leading to and in the active muscles dilate to allow more blood to come through and more oxygen to be transported.  At the same time, there is vasoconstriction in the other organ systems as a mechanism of prioritization.

Acute Respiratory

Respiration also increases during aerobic exercise, obviously, to meet the new oxygen demands.  Specifically, there are significant increases in the amount of oxygen delivered to the tissues, carbon dioxide returned to the lungs, and minute ventilation, which is the volume of air breathed per minute.  Minute ventilation increases through an increase in breathing frequency and tidal volume, which is the amount of air inhaled and exhaled per breath.  Essentially this means that you breathe deeper and faster during exercise. There is also an increase in the diffusion of oxygen from the capillaries into the tissues, as well as an increase in diffusion of carbon dioxide from the blood into the lungs.

Aerobic exercise training leads to cardiovascular changes that markedly increase aerobic power and lead to improved endurance performance. The functionally most important adaptation is the improvement in maximal cardiac output which is the result of an enlargement in cardiac dimension, improved contractility, and an increase in blood volume, allowing for greater filling of the ventricles and a consequent larger stroke volume. In parallel with the greater maximal cardiac output, the perfusion capacity of the muscle is increased, permitting for greater oxygen delivery. To accommodate the higher aerobic demands and perfusion levels, arteries, arterioles, and capillaries adapt in structure and number. The diameters of the larger conduit and resistance arteries are increased minimizing resistance to flow as the cardiac output is distributed in the body and the wall thickness of the conduit and resistance arteries is reduced, a factor contributing to increased arterial compliance. Endurance training may also induce alterations in the vasodilator capacity, although such adaptations are more pronounced in individuals with reduced vascular function. The microvascular net increases in size within the muscle allowing for an improved capacity for oxygen extraction by the muscle through a greater area for diffusion, a shorter diffusion distance, and a longer mean transit time for the erythrocyte to pass through the smallest blood vessels. The present article addresses the effect of endurance training on systemic and peripheral cardiovascular adaptations with a focus on humans, but also covers animal data.

What are three cardiovascular adaptations to exercise?

Which adaptations occur in the cardiovascular system?

What are the 3 main acute responses that occur following physical activity?

What are the cardiorespiratory adaptations to exercise training?