Dear BLOG readers and loyal PEAK customers,

Every well-known supplement manufacturer offers at least one product that is marketed as an NO booster (nitric oxide booster). Many people know that these supplements contain arginine and have something to do with blood flow. Very few, however, know exactly what nitric oxide is or how it works, and they buy the supplements in good faith based on the promising advertising claims in trade magazines.

This situation prompted me to take a closer look at nitric oxide (NO) and our blood circulation in general, in order to provide readers with some background information and a better understanding. Anyone who takes the time to read my admittedly not-so-simple two-part series will certainly have a significant knowledge advantage over most of their competitors at the gym.

Part 1 covers the basics of blood circulation and ways to positively influence it through training

Part 2 focuses specifically on nitric oxide, its associated enzymes, and ways to increase this substance—and thus blood circulation in our bodies—through enhanced synthesis.

BASICS – Blood Circulation

To better explain the effect of nitric oxide on blood flow, we must first briefly discuss blood flow in general. For a better understanding, some key terms need to be explained and clarified.

Definition of Blood Circulation (Perfusion)

Blood circulation refers to the supply of blood to organs and parts of organs. Blood is supplied via arteries and drained via veins. Through this process, all tissues are supplied with oxygen and nutrients, and metabolic waste products such as CO₂ or lactate are removed. Blood flow (perfusion) is defined as the volume of blood that flows through an organ or tissue per unit of time.

We broadly distinguish between two different types of blood flow: resting blood flow and maximum possible blood flow. In both cases, organs and tissues receive varying amounts of blood. At rest, the kidneys receive the largest share of blood; during maximum exertion, it is the muscles and the skin.

The adaptation of blood flow to meet demand is influenced by complex regulatory mechanisms. The brain, kidneys, and gastrointestinal tract are supplied autonomously. We have direct control over blood supply to the muscles via our vasomotor nerves and the associated nervous system (sympathetic and parasympathetic nervous systems). Here, neurotransmitters and catecholamines (norepinephrine and epinephrine) act as signaling molecules.

Definition of Vasodilation

Vasodilation refers to the widening of blood vessels. This widening can occur either actively, through the relaxation of vascular smooth muscle, or passively, through an increase in blood volume. The interaction of nerves and muscles during active vasodilation is referred to as vasomotor function. Vasodilation occurs primarily in response to changes in nitric oxide concentration.

Definition of Vasoconstriction

Vasoconstriction refers to the narrowing of blood vessels. It is responsible for an increase in flow resistance in the arterial portion of the vascular system, thereby causing blood pressure to rise. Vasoconstriction is a mechanism for regulating blood flow to organs and tissues. It is primarily triggered by hormones in the blood vessels. These hormones bind to specific receptors (binding sites) present there, known as α/β receptors.

Vasoactive substances (which trigger vasoconstriction) include angiotensin I and II, serotonin, endothelin (produced by peripheral tissue cells), norepinephrine, and—in very high concentrations—epinephrine, which normally has a vasodilatory effect.

The flow-time volume

Cardiac output is defined as the volume of blood that flows through a specific segment of a blood vessel per unit of time. It plays a crucial role in the blood supply to organs and muscles.

The flow-time volume increases when vasodilation reduces the flow resistance in the vessel, or when the pressure difference between arterial and venous pressure increases.

Flow resistance

Flow resistance is the frictional resistance between the various layers of fluid as they slide past one another. It is determined by the vessel length, the vessel radius, and the viscosity (thickness) of the blood.

Viscosity

Viscosity, in turn, depends on the blood marker hematocrit (the proportion of cellular components in the blood volume). It indicates how thick or thin the blood is.

Our blood becomes thicker as temperature rises and during strength training.

During endurance training, although the number of particles in the blood (mainly red blood cells) increases, the fluid content also increases—and to a greater extent—so that overall viscosity decreases.

Endurance training thins the blood; strength training thickens it.

The greatest influence on flow resistance—and thus on blood flow—comes from changes in the vessel radius, that is, whether the blood vessels dilate or constrict.

Blood Pressure

Blood pressure indicates the pressure of the blood within a blood vessel. Normal values are 120/80 mmHg; values up to 140/90 mmHg are considered safe. A systolic value between 140 and 160 mmHg and a diastolic value between 90 and 95 mmHg indicate so-called borderline hypertension. If readings are higher, blood pressure-lowering medications or measures should be used.

How is blood pressure generated?

The heart’s cycle consists of a systole (contraction phase) and a diastole (relaxation phase). During systole, blood is ejected from the ventricles; during diastole, the heart relaxes and refills. Normally, this would mean that the body’s organs are supplied with blood in bursts. This must not happen, as some organs depend on a relatively constant pressure. Therefore, the aortic arch (the curve of the aorta) expands and fills with blood. This reduces the heart’s ejection pressure, thereby relieving the strain on the blood vessels. During diastole, the aorta then contracts again so that the pressure does not drop completely. This phenomenon of the aorta is called the “windlass function.”

Important:

Systolic and diastolic blood pressure can only be measured in the arteries

How does blood pressure change during physical exertion?

Blood pressure rises depending on the amount of force exerted and the level of exertion.  

The greater the force exerted, the greater the rise in blood pressure.

In strength training, readings of up to 400/300 mmHg have been recorded. In endurance sports, the increase occurs gradually as the cardiovascular system is stressed.

How is blood pressure regulated?

Pressoreceptors

As is often the case in the body, receptors here also detect and transmit signals to regulate blood pressure. In this case, these are known as pressoreceptors. They detect the current vascular tension and relay this information to the brainstem. Via the vagus nerve, they can thus cause the blood vessel walls to dilate (vasodilation)—thereby lowering blood pressure—or constrict (vasoconstriction)—thereby raising blood pressure—by releasing the appropriate neurotransmitters and hormones.

Heart and Breathing

Blood volume is drawn toward the heart by the suction effect of the right atrium and the vessels near the heart. Breathing expands the chest, thereby reducing pressure on the veins and increasing the pressure differential. As a result, more venous blood flows to the heart during inhalation than during exhalation.

Muscle Pump

The contraction of skeletal muscles causes the veins to compress, forcing blood toward the heart. When the muscles relax, the emptied venous volume increases again, resulting in a drop in pressure in the corresponding venous segment. The veins then refill with blood.

Arterial feedback

In the legs, there is also what is known as arterial recoil. Here, the veins and arteries lie immediately next to one another, so that the pulsating expansion of the arteries also exerts pressure on the veins. The effect is similar to that of the muscle pump during skeletal muscle contraction.

Other Processes

There are several other processes that influence blood pressure. However, for the sake of brevity, I will not elaborate on them further here.

Conclusion

Factors such as blood viscosity, vessel radius, and blood pressure determine the degree of blood flow. Blood viscosity changes due to factors such as exercise and fluid intake.

Blood pressure is a constantly changing variable. It depends on breathing, drops during sleep, during digestion, and when transitioning from a lying to a standing position. It tends to rise in response to psychological and physical stimuli, such as exercise. Vessel radius has the greatest influence on vascular resistance and blood flow.

PRACTICAL TIP:
Exercising on a full stomach is completely counterproductive, since the available  

blood volume must be divided between these two tasks and cannot be directed specifically toward supplying the muscles with nutrients and removing metabolic waste products.

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How Exercise Affects Peripheral Vascular Resistance (Vascular Radius)

Several systems and mechanisms influence resistance in our peripheral blood vessels. I would like to explain some of them in more detail here (the periphery refers to the blood vessels of the extremities).

[caption id="attachment_6952" align="alignleft" width="300" caption="Illustration: Artery"][/caption]

 Sympathetic Vasoconstrictor System

In response to psychological or physical stress, this system regulates the blood supply to certain areas to a greater or lesser extent. In principle, all blood vessels are innervated by sympathetic nerve fibers. The sympathetic nervous system is the part of the nervous system responsible for activating metabolism. This activation occurs through the release of catecholamines (adrenaline, norepinephrine, and dopamine). This activation causes a change in the firing rate of the nerves and thus influences the tension state of the vascular smooth muscle (tone), which then presses against the vessel wall. An increase in sympathetic impulses causes vasoconstriction, while a decrease leads to vasodilation.

During physical activity, we release norepinephrine and epinephrine. Some norepinephrine is already stored in presynaptic vesicles at the ends of nerve fibers. It is also produced in the adrenal medulla and released into the bloodstream. It travels to the adrenergic receptors of blood vessels in regions not involved in physical exertion (primarily α-receptors) and causes them to contract (narrow).

Adrenaline is also released into the blood via the adrenal medulla. It binds to the β-receptors of blood vessels in regions involved in physical exertion, causing vasodilation there.

Conclusion 

Exercise has a stimulating effect on the sympathetic nervous system. Catecholamines are released, causing vasoconstriction in blood vessels not involved in physical exertion. They cause vasodilation in blood vessels directly involved in physical exertion. The goal here is to redistribute blood and increase the supply of blood—along with all its constituents—to tissues and organs under physical stress (e.g., trained muscles during exercise).

Cholinergic Sympathetic System

This system is less important during physical exertion, as it primarily responds to emotions such as fear or anger. To respond to emotions, our blood vessels have receptors for the neurotransmitter ACh (acetylcholine). The binding of ACh to these receptors leads to dilation of the arterioles in the skeletal muscles as well as constriction of skin and blood vessels.

It is interesting to note that this mechanism also occurs shortly before exercise (the so-called “pre-exercise state”). However, as exercise progresses, its effect—and thus its significance—diminishes.

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Local-Chemical (Local-Metabolic) System

Muscle work causes an accumulation of potassium ions and a decrease in the partial pressure of oxygen both within the muscle cell and outside the cell (extracellular space). Potassium ions and oxygen diffuse toward the arterioles (small blood vessels) and increase the sensitivity of the receptors on the smooth vascular muscle. This results in vasodilation (widening) in the area of the working muscles. At the same time, the aforementioned parasympathetic-mediated vasoconstriction (narrowing of blood vessels) occurs in the non-working muscles. Peripheral vascular resistance decreases in the unloaded region and increases in the working muscles. In addition to the dilation of already perfused vessels, capillaries that are normally closed at rest also open.

Oxygen and Metabolite Transport in the Muscles

This allows the increased oxygen demand in the working muscles to be met; that is, aerobic energy production and the removal of metabolic byproducts (metabolites) such as lactate and CO₂ are ensured.

An increase in metabolite concentration within the muscles themselves also causes an increase in blood flow until a balance is finally reached between production and breakdown (lactate steady state).

A further increase in exertion pushes blood flow to its limit. A maximum of approximately 80–120 ml/min can be transported per 100 ml of muscle tissue. An imbalance develops from the lactate steady state. This leads to an accumulation of the aforementioned metabolites, resulting in a decline in performance and muscle fatigue.

Conclusion

Our training has a major influence on our vascular resistance and, consequently, on our blood flow. The training itself—and even the mental preparation for it—activates our sympathetic nervous system as well as acetylcholine (ACh) synthesis, thereby causing a redistribution of blood flow. A distinction is made between regions that are exposed to exertion and regions that are not involved in exertion. Depending on this classification, vasoconstriction or vasodilation of the blood vessels occurs. Vasodilation ultimately takes place via the synthesis of nitric oxide within the blood vessels.

Blood flow is therefore not equally good or poor throughout the entire body!!

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Summary

In Part 1, we discussed the fundamentals of blood circulation and all the factors involved. Many factors are involved in the initiation, maintenance, and regulation of our blood flow. We have seen that it is possible to significantly increase blood flow to our organs and muscles through exercise. More blood to the muscles provides more oxygen and nutrients and facilitates better removal of metabolic waste products. Combined with an adequate supply of nutrients, this ensures optimal conditions for muscle growth.

In Part 2, I will describe the role and function of nitric oxide in this system, how it is produced, how it works, and to what extent we can influence its production through diet and supplements.

Until then, I wish all readers the best of luck!

Best regards

Yours,

Holger Gugg

www.body-coaches.de

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