Blood pressure is the force blood exerts against artery walls as it circulates. It is presented as two numbers: systolic and diastolic pressure. Systolic pressure is the peak pressure when your heart contracts to pump blood. Diastolic pressure indicates the pressure in your arteries when your heart rests between beats. During physical activity, systolic pressure increases, but diastolic pressure often remains stable or decreases.
Understanding Diastolic Pressure
Diastolic blood pressure represents the minimum pressure exerted on arterial walls during the heart’s relaxation phase, known as diastole. This is when the heart’s ventricles refill with blood. It reflects the resistance within peripheral blood vessels, providing insight into the overall tone of the circulatory system. It indicates the constant pressure within the arteries that maintains blood flow to organs even when the heart is not actively pumping, which is important for continuous tissue perfusion. This pressure is influenced by arterial wall elasticity and overall resistance to blood flow.
The Body’s Response to Exercise
When physical activity begins, working muscles demand more oxygen and nutrients. To meet this heightened metabolic need, the cardiovascular system undergoes significant adjustments, including an increase in cardiac output. This ensures that the active tissues receive a greater supply of blood, facilitating metabolic processes necessary for sustained effort.
A primary adjustment involves selective vasodilation, the widening of arterioles within active skeletal muscles. This physiological response allows for a dramatic increase in blood flow to these specific areas. This enhanced perfusion delivers abundant oxygen and glucose while efficiently removing metabolic waste products. Local factors produced by contracting muscle fibers contribute to this relaxation of adjacent blood vessels, causing them to relax and expand. While the sympathetic nervous system also influences blood vessel tone, the localized vasodilation in active muscles is the predominant mechanism for increasing their blood supply.
How Vascular Resistance Changes
Vascular resistance refers to the opposition blood encounters as it flows through the circulatory system. Total peripheral resistance (TPR) represents the cumulative resistance the heart must overcome to pump blood throughout the entire body. This resistance is primarily determined by blood vessel diameter; narrower vessels create more resistance, and wider vessels reduce it. The length of the vessels and the viscosity of the blood also play roles in influencing TPR.
During exercise, a significant physiological shift occurs in vascular resistance. Despite some blood vessel constriction in less active areas, such as the digestive tract and kidneys, widespread vasodilation within active skeletal muscles profoundly impacts overall resistance. The relaxation of arterioles in these muscles creates numerous low-resistance pathways for blood flow, allowing for a substantial increase in local perfusion. This extensive widening of blood vessels in the exercising muscles is so pronounced that its effect on resistance largely outweighs the vasoconstriction occurring elsewhere. As a result, the net effect during dynamic exercise is a significant decrease in total peripheral resistance across the systemic circulation. This reduction in resistance is a fundamental cardiovascular adjustment, enabling efficient blood distribution to meet the heightened metabolic demands of working muscles.
Why Diastolic Pressure Decreases
The decrease in diastolic blood pressure during exercise is a direct consequence of reduced total peripheral resistance. Diastolic pressure is largely maintained by the resistance offered by arterioles and the elastic recoil of large arteries, which push blood forward during the heart’s resting phase. When total peripheral resistance drops due to vasodilation in working muscles, the pressure against which the heart rests lessens considerably. This allows for a more efficient and rapid “runoff” of blood from the large arteries into the capillary beds of the highly active muscles.
The heart does not need to maintain as high a pressure to ensure continuous blood flow to tissues during diastole, contributing to the observed decrease in the lower blood pressure reading. This physiological adaptation permits the heart to pump a much larger volume of blood through the circulatory system, increasing cardiac output, without causing a significant rise in mean arterial pressure. It ensures that the greatly increased blood flow to active tissues is facilitated by lower resistance, preventing strain on the cardiovascular system and supporting oxygen delivery during physical exertion.