What Happens in the Nervous System When You Exercise? | Hardworkout Magazine

Key takeaways

- A workout is itself a form of stress, but a controlled and temporary one: when the session ends, parasympathetic activity rises and the body returns to its normal state.

- People who train regularly often show a less intense activation of the HPA axis during psychological stress, so the body releases less cortisol and returns to normal values faster.

- Higher vagus nerve activity is associated with higher heart rate variability (HRV), a sign that the nervous system can switch quickly between activity and recovery.

- Exercise increases the release of serotonin, dopamine and endorphins, as well as BDNF, a protein that promotes growth and communication between nerve cells.

- A very high training volume combined with too little rest can keep the nervous system in a persistently stressed state, leading to poorer sleep, more fatigue and reduced performance.

Stress affects not only the mind but also how the nervous system functions. Prolonged stress can leave the body in a state of high alert, which can impact both sleep, energy levels, and recovery.

Regular exercise can help normalize this response and better equip the body to handle stress. The effect is due to a number of physiological adaptations in both the brain and the autonomic nervous system.

What happens in the body during the first seconds of stress?

When the brain perceives a situation as demanding or threatening, the sympathetic nervous system is activated. This is the part of the autonomic nervous system that prepares the body for action.

The pulse increases, blood pressure rises, and breathing becomes faster. At the same time, the hormones adrenaline and noradrenaline are released, making the body more alert and ready to react quickly.

If the stress lasts over time, the hypothalamic-pituitary-adrenal axis (HPA axis) is also activated, leading to increased secretion of cortisol. This response is important when the body faces real challenges.

However, with prolonged stress, a persistently high level of activity in the nervous system can contribute to sleep problems, increased muscle tension, poorer concentration, and reduced ability to recover.

Why does training count as stress the body benefits from?

A workout is in itself a form of stress.

During activity, the heart rate, blood pressure, and activity in the sympathetic nervous system increase to meet the muscles' needs for oxygen and energy.

The difference is that this strain is controlled and temporary. When the workout is over, the activity in the parasympathetic nervous system increases, which is responsible for rest and recovery. The heart rate falls, breathing becomes calmer, and the body gradually returns to its normal state.

If this is repeated regularly, the nervous system becomes more efficient at switching between activity and rest.

Over time, this ability can also make the body better at dampening the stress response in situations other than during exercise.


What does the vagus nerve do when you exercise?

An important part of this process is the vagus nerve. It is the longest cranial nerve in the body and the most important connection in the parasympathetic nervous system.

When the vagus nerve is activated, signals are sent that slow the heart rate and promote a more relaxed state. In individuals who exercise regularly, higher activity in the vagus nerve is often observed when the body is at rest.

Higher activity in the vagus nerve is often associated with higher heart rate variability (HRV), which describes the variation in time between heartbeats.

A high HRV indicates that the nervous system can more easily adapt to both physical and mental stress, and switch more quickly between activity and recovery.

Does exercise lower cortisol during mental stress?

Regular exercise also seems to affect how the brain handles stress.

[Research](https://www.sciencedirect.com/science/article/pii/S0002934325003535) shows that physically active individuals often experience a less intense activation of the HPA axis when exposed to psychological stress. The body therefore does not need to release as much cortisol to handle the same situation.

At the same time, cortisol levels seem to return to normal values more quickly once the stress is over.

This does not mean that exercise removes stress, but that the body may become better at regulating the stress response and recovering after challenging situations.

Which neurotransmitters does exercise release?

Exercise also affects several of the brain's neurotransmitters.

During and after physical activity, the release of serotonin, dopamine, and endorphins increases. Serotonin contributes to the regulation of mood and sleep, dopamine is important for motivation and reward, while endorphins can reduce pain perception and provide a sense of well-being.

At the same time, the production of BDNF (brain-derived neurotrophic factor) increases, a protein that promotes growth and communication between nerve cells and helps them function normally.

BDNF appears to make the brain more resilient to prolonged stress and may contribute to better learning, memory, and emotional regulation.

Is calm or intense training best for stress?

How the nervous system reacts also depends on the type of training you perform.

Calm activities such as walking, moderate cycling, and yoga often lead to a quick increase in parasympathetic activity after the session. Many therefore find these forms of exercise particularly calming.

Intense interval training and heavy strength training result in a stronger activation of the sympathetic nervous system during the session itself. However, these forms of exercise can also contribute to a noticeable relaxing effect when the body enters the recovery phase.

Very high training volume combined with too little rest can, on the other hand, keep the nervous system in a persistent stressed state. The result can be poorer sleep, increased fatigue, and reduced performance.

This is why exercise works against stress

Regular physical activity improves the nervous system's ability to regulate when to ramp up the stress response and when to dampen it again.

At the same time, the brain becomes better equipped to handle challenging situations, and the body transitions more quickly from a state of high alert to one where it can rest and recover.

Over time, this can contribute to better stress management, increased resilience to prolonged stress, and a more stable balance between activity and rest.


Sources:

An Integrative Approach to HPA Axis Dysfunction: From Recognition to Recovery – [The American Journal of Medicine](https://www.sciencedirect.com/science/article/pii/S0002934325003535)

Physical activity moderates stressor-induced rumination on cortisol reactivity – [National Library of Medicine (NIH)](https://pmc.ncbi.nlm.nih.gov/articles/PMC3167008/)