During dynamic exercise, the body’s cardiovascular system undergoes changes to meet the muscles’ increased demand for oxygen. Blood pressure is measured by two numbers: the higher systolic pressure (SBP), which reflects the pressure when the heart beats, and the lower diastolic pressure (DBP), which is the pressure when the heart rests between beats. While SBP rises significantly during exercise, DBP remains remarkably stable or may even decrease slightly. This stability is the result of a precise physiological balancing act that manages blood flow and resistance throughout the circulatory system.
Diastolic Pressure and Resistance
Diastolic blood pressure represents the continuous pressure exerted on the artery walls while the heart ventricles are relaxing and refilling. Since the heart is not actively pumping during this phase, DBP is primarily determined by the resistance blood encounters as it flows through the body’s network of smaller vessels, known as Total Peripheral Resistance (TPR).
The diameter of the tiny arteries and arterioles dictates the TPR. If these vessels are narrow, resistance is high, causing DBP to rise; conversely, if they dilate, resistance drops, and DBP falls. The fundamental reason DBP does not increase during exercise is that the total resistance in the body’s circulation decreases significantly.
Localized Vasodilation in Working Muscles
The immediate trigger for the drop in overall vascular resistance is the metabolic activity within the exercising skeletal muscles. As muscles contract, they consume oxygen and produce metabolic byproducts that act as chemical signals demanding increased blood flow.
The accumulation of compounds like nitric oxide, adenosine, potassium ions, and ATP signals the smooth muscle surrounding local arterioles to relax, a process called vasodilation. This widening of vessels supplying active muscles allows blood flow to increase dramatically (exercise hyperemia). This massive, localized vasodilation in large muscle groups creates a significant drop in peripheral resistance, applying a downward force on the total system-wide vascular resistance and the diastolic pressure.
The Global Maintenance of Blood Pressure
If vasodilation in the working muscles were the only change, the resulting drop in TPR would cause a fall in systemic blood pressure. To prevent this, the body initiates a coordinated response mediated by the sympathetic nervous system, triggering compensatory vasoconstriction in all non-essential body regions.
Blood vessels supplying organs such as the kidneys, the gastrointestinal tract, and inactive muscles constrict significantly. This narrowing in non-working tissues helps redirect blood flow toward the high-demand working muscles. This compensatory vasoconstriction offsets the massive drop in resistance caused by vasodilation. The net effect is that the Total Peripheral Resistance remains relatively unchanged or decreases slightly, maintaining stable diastolic pressure throughout the exercise bout.
What a Rise in Diastolic Pressure During Exercise Suggests
While the normal response to dynamic exercise is a stable or slightly falling DBP, a significant rise can be an important clinical sign. An increase of 10 to 15 mmHg or more above the resting value is considered an exaggerated or abnormal response. This atypical response suggests a failure in the balance between local vasodilation and global vasoconstriction.
The most common underlying cause for a rising DBP is the inability of small arteries to dilate properly in response to metabolic demands. This impaired vasodilation is frequently associated with early-stage cardiovascular issues, such as endothelial dysfunction, hypercholesterolemia, or insulin resistance. In patients undergoing exercise stress tests, an exaggerated DBP increase may also indicate the presence of severe coronary artery disease.