Why Stress Causes Headaches and Stiff Shoulders: Explaining the Mechanisms of the Autonomic Nervous System and Inflammation - Nutritional Strategies for 'Stress'

You work in a high-stress environment and your stiff shoulders just won't go away.
Before you know it, you have a persistent headache.

Does this sound familiar?

Many people experience a state of 'feeling generally unwell' while dealing with ongoing busyness and pressure. However, these symptoms are often not just simple fatigue, but the result of reactions occurring within the body.

In fact, behind this lies physiological reactions to stress and the accompanying changes in the body.

In this article, we will structurally organize why physical symptoms like headaches and stiff shoulders occur when you are under stress. We will delve deeper from the perspective of 'what is happening inside the body' rather than just talking about sensations.

First, as a premise, headaches and stiff shoulders often begin with the accumulation of physical load. For example, this is a state where the muscles of the neck and shoulders are continuously burdened by long hours of desk work or maintaining the same posture.

At this stage, it is, so to speak, a state where stimulation to the muscles is accumulating.

However, the problem comes after that.

When you are under stress, your body reacts in various ways to try to adapt. In that process, stimuli or discomfort that would normally be mild start to be perceived as stronger 'pain'.

The following two elements become important here.

• Disturbance of the autonomic nervous system

• Promotion of chronic inflammation in the body

When these are combined, muscle tension becomes harder to release, nerves become sensitive to stimulation, and as a result, it leads to states like 'persistent stiff shoulders' and 'chronic headaches'.

In other words, the influence of stress is deeply involved in areas that cannot be fully explained by posture problems alone.

We have summarized what happens inside the body when it is under stress in this article. Please be sure to check it out.

In the following chapters,
we will first organize 'why physical load accumulates due to posture,' and then look at the mechanism by which symptoms intensify from the two axes of the autonomic nervous system and inflammation.

It doesn't end with 'posture': The mechanism behind the onset of stiff shoulders and headaches

When long hours of desk work or tasks in the same posture continue, your shoulders and neck feel heavy.
In severe cases, it leads directly to headaches.

This is not just 'all in your head,' but a phenomenon that can be explained as a problem of muscles and blood flow.

First, as a premise, muscles are structured so that blood flow is maintained through movement.
By repeating contraction and relaxation, blood circulates, oxygen and nutrients are supplied, and waste products are removed.

However, what happens when your posture remains fixed?

The same muscles remain in a state of slight tension for a long time. This is what is known as 'a state where you don't feel like you are exerting force, but you are using them the whole time.'

If this state continues, blood flow within the muscles gradually decreases.
When blood flow worsens, oxygen supply becomes insufficient, and metabolic products (such as lactic acid and bradykinin) accumulate locally.

As a result, receptors within the muscles are stimulated and perceived as 'dullness' or 'pain.'

Even more important is the structure around the neck and shoulders.

This area is constantly under load to support the head. Especially with desk work, it is easy to fall into a posture where the head juts forward (a tendency toward so-called straight neck), resulting in a state where greater-than-normal load is placed on the neck and shoulder muscles.

As a result,

• the trapezius and levator scapulae muscles become chronically tense

• stress is placed on the fascia and connective tissues

• trigger points (sources of pain) are formed

and other such changes become likely to occur.

This is the mechanism of 'stiff shoulders.'

So, why does this lead to headaches? The key is the relationship between muscle tension and nerves.

When the neck and shoulder muscles become over-tense, the nerves running through the surrounding area are easily stimulated mechanically. In particular, the nerves that spread to the back of the head (such as the greater occipital nerve) are structured to be easily affected by this.

Furthermore, pain signals originating from muscles are processed via the brainstem, and this pathway is closely related to sensations in the head. Therefore, problems in the neck and shoulders are perceived as 'head pain'.

Looking at this so far, you might feel that 'this could be explained by posture problems alone.'

In reality, physical load is certainly a starting point. However, that alone cannot explain why some people develop symptoms with the same posture while others do not.

This is where another trigger that "amplifies pain"—such as autonomic nervous system imbalance or chronic inflammation—becomes important. We will delve deeper into these triggers in the following chapters.

Why does stiffness not go away? The "tense state" created by the autonomic nervous system

So far, we have seen that posture puts a load on muscles, creating the "seeds" of pain.
Now, why does that pain "last a long time" and "feel so intense"?

This is where the state of the autonomic nervous system becomes important.

The autonomic nervous system is a system that controls the body unconsciously, and it is broadly composed of two parts: the "sympathetic nervous system" and the "parasympathetic nervous system."

• Sympathetic nervous system: Activity, tension, and stress response

• Parasympathetic nervous system: Recovery, rest, and relaxation

Normally, these two work while maintaining a balance, but when stress is applied, the sympathetic nervous system tends to remain dominant.

So, how does this state affect muscles and pain?

First, it becomes difficult for muscle tension to dissipate.

When the sympathetic nervous system becomes dominant, muscles try to maintain a state of slight contraction so they can "move at any time." Normally, this tension would loosen within the rhythm of activity and rest, but if stress continues, that switch becomes difficult to flip. As a result, a vicious cycle occurs where:

• The muscles in the neck and shoulders are constantly in a strained state

• Blood flow does not recover

• Fatigue substances are not removed

occurs.

Furthermore, the impact on blood vessels and nerves is important.

In a state where the sympathetic nervous system is dominant, blood vessels tend to constrict. Peripheral blood flow, in particular, is likely to decrease, which further worsens the oxygen supply to the muscles.

Also, hormones such as cortisol and noradrenaline, which are secreted during the stress response, affect nerve excitability. Because of this, it is believed that what would normally be only a minor stimulus is more easily perceived intensely as "pain."

This state is also related to a phenomenon called "central sensitization." This is a condition where the nervous system that processes pain becomes hypersensitive, causing you to feel pain more intensely and for longer than usual.

In fact, the relationship between stress and pain has been demonstrated in research.
For example, McEwen et al. (McEwen, 2007) point out that chronic stress can affect the plasticity of the nervous system and alter pain sensitivity.

This study suggests that the long-term secretion of stress hormones leads to the restructuring of neural circuits in the brain, intensifying the response to pain and discomfort.
In other words, stress is not just a temporary reaction, but has the potential to change the very way your nerves "perceive" things.

To summarize what we have covered so far, when the muscle load caused by posture is compounded by autonomic nervous system imbalance,

• muscles do not relax

• blood flow does not recover

• pain is amplified

a state is established where these things occur.

In short, the state of "persistent stiffness" or "ongoing headaches" is not just a muscle problem, but also a nervous system problem.

And as this state progresses further, the next factor involved is "inflammation."
In the next chapter, we will look at how stress changes inflammatory responses in the body and how that affects pain.

Why pain lingers: The "silent inflammation" caused by stress

So far, we have looked at the process by which muscle load from posture and autonomic nervous system imbalance amplify pain.

Now, what happens inside the body when that state continues for even longer?

This is where chronic inflammation comes into play.

When you hear the word inflammation, you might imagine obvious reactions like "swelling" or "feeling hot."
However, stress-related inflammation is often a "low-grade inflammation" that persists at a level that is difficult to notice, rather than such a strong reaction.

When you are under stress, cortisol and catecholamines (such as adrenaline) are secreted in the body. Originally, these work to suppress inflammation in the short term, but if stress continues chronically, that regulatory function breaks down.

As a result, the balance of the immune system changes, and substances called **inflammatory cytokines (such as IL-6 and TNF-α)** become more likely to increase.

These substances are originally necessary to deal with infection and injury, but when present in excess, they become a persistent stimulus to nerves and tissues.

So, how does that lead to stiff shoulders and headaches?

The key is changes in nerve sensitivity.

Inflammatory cytokines have the effect of increasing the sensitivity of nerves that transmit pain (nociceptors). In other words, you enter a state where even the same stimulus is perceived as 'stronger pain'.

Furthermore, when micro-inflammation occurs in muscles and surrounding tissues, changes such as

• impaired gliding of the fascia

• further reduction in local blood flow

• an increase in pain-inducing substances (such as prostaglandins)

occur.

As a result, muscle stiffness and pain become more likely to become 'fixed'.

Regarding this point, there is research showing the relationship between stress and inflammation.
For example, Slavich et al. (Slavich & Irwin, 2014) reported that psychological stress can activate the immune system and influence physical symptoms, depression, and pain through an increase in inflammatory cytokines.

This study showed that people in a state of chronic stress tend to have higher inflammatory markers and are more likely to feel physical discomfort.
In other words, stress does not just change how you 'feel,' it actually changes the internal environment of the body itself.

Conclusion: Headaches and stiff shoulders are caused by 'external' and 'internal' problems

As we have seen so far, headaches and stiff shoulders are not just 'posture problems'.

Certainly, physical load accumulating in muscles due to long hours of desk work or maintaining the same posture is a starting point. However, that alone cannot fully explain 'why it becomes chronic' or 'why there are individual differences'.

What overlaps with that is changes in the body's internal balance, namely autonomic nervous system disruption and chronic inflammation.

These are not independent of each other, but rather form a structure where they influence each other and intensify symptoms.

Conversely, looking at only one side will not lead to an essential understanding.
Grasping this structure is important when considering the next step.

In this note, I place importance on breaking down these 'vague discomforts' as structurally as possible.

If you are currently experiencing any symptoms related to stress, please let me know in the comments. I would like to organize more practical information based on themes that resonate with readers' actual experiences.

In the next article, based on the structure we have organized here, we will take a concrete look at what kind of nutritional strategies can be considered for symptoms such as headaches and stiff shoulders.

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Wishing you all good health ✋