Mark A. W. Andrews, professor of physiology at the Lake Erie College of Osteopathic Medicine
Contrary to expectations, perhaps, bulging veins during exercise have nothing to do with an increase in either blood volume or pressure in these vessels. In fact, both are known to decrease during stepped-up activity, including exercise. To explain the prominence of veins during exercise, it helps to understand the vascular system and its components. Blood that circulates throughout the body is pumped from the left ventricle of the heart. It first enters into the high pressure arteries, where systolic blood pressure, the highest pressure exerted there, is recorded around 120 mmHg (millimeters of mercury), and diastolic pressure, the minimal pressure exerted in these vessels, is recorded at around 80 mmHg. (Thus, normal blood pressure is typically around 120/80 mmHg.) The blood flows into smaller and smaller branches of arteries called arterioles. As it continues along, its pressure decreases due to the resistance of the walls of the arterioles themselves. The blood then enters the capillaries–the smallest blood vessels–which provide nourishment to, and remove waste material from, active cells. There are more than one billion of these in the human body and they are extremely small and thin. The pressure exerted by the blood as it enters the capillaries is approximately 30 mmHg.
This pressure decreases even further as the blood completes its nourishment functions and then leaves the capillaries to flow back toward the heart via the smallest veins–the venules. The venules combine into larger and larger veins until they feed into the right atrium of the heart as the vena cava. By the time blood enters the largest veins, pressure exerted by the blood stream is only a few mmHg and its return to the heart is moved along more by muscle activity and breathing than its own inherent force.
When exercise begins, the heart’s rate and strength of contraction increases and blood is quickly pumped into the arteries. As this is occurring, systolic blood pressure increases linearly with exercise intensity, rising to nearly 200 mmHg during high intensity aerobic exercise (and to more than 400 mmHg during weight lifting). Diastolic pressure, on the other hand, changes very little with aerobic exercise (although it rises during weight lifting). Simultaneously, the internal diameters of veins and venules narrow in a process called venoconstriction, forcing the flow of blood forward to the heart and enhancing their ability to receive blood coming from the capillaries. Overall, this process helps decrease the pressure in the venules and veins to at most about five mmHg.
Venous volume and pressure thereby decrease and are thus not the basis for the bulging. Instead, the process occurring in the capillaries as a result of the rise in arterial blood pressure during exercise causes plasma fluid otherwise resting in these tiny tributaries to be forced out through the thin vessel walls and into compartments surrounding the muscles. This process, known as filtration, causes a swelling and hardening of the muscle that is noticed during exercise. As a result of this swelling, cutaneous veins are pushed toward the skin surface, flatten to some extent, and appear to bulge. Such veins are more visible in persons with less subcutaneous fat. This bulging is neither good nor bad but simply a result of normal physiological mechanisms that result from the rise in arterial blood pressure during exertion.
Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.
Have an amazing project to share? The Electronics Show and Tell is every Wednesday at 7:30pm ET! To join, head over to YouTube and check out the show’s live chat – we’ll post the link there.
Join us every Wednesday night at 8pm ET for Ask an Engineer!
Maker Business — How 3M is able to ramp up production of N95 masks
Wearables — Flip UV on its head
Electronics — To Y5V or not to Y5V?
Biohacking — Vitamin-C + Gelatin for Accelerated Recovery
Python for Microcontrollers — Virtually Maker Faire, HackSpace Magazine, and more! #Python #Adafruit #CircuitPython @circuitpython @micropython @ThePSF
Adafruit IoT Monthly — Quarantine Clock, Smarter Than your Speaker, and More!
Microsoft MakeCode — Arcade Mini Game in a Text Adventure
No comments yet.
Sorry, the comment form is closed at this time.