Fight or Flight v Rest and Digest

What comes to mind when you hear the word stress? For most people they have negative connotations with the word.

When someone is stressed this may mean they are anxious. Or maybe in an uncomfortable situation. This could mean having too much on their plate. Sometimes this can be associated with tight traps, headaches and overall body tension.

Stress might be related to someone pushed to their limit. And feeling as though there is no end in sight to the work or tough times.

But the truth is that stress is not all bad. When stress is beneficial for the individual we would refer to this as eustress as opposed to a distress that has a negative effect.

And this is similar to our autonomic nervous system (ANS) which can be divided into the sympathetic and parasympathetic nervous systems. Just as when we talk about stress in general most people associate this with distress so too when we think about the branches of the autonomic nervous system we are probably more familiar with the sympathetic nervous system.

Think about it this way. What sounds more familiar, 'fight or flight' or 'rest and digest'?

For most people they are more familiar with the term fight or flight. Although the words 'rest and digest' are uncommon we don't use this expression as commonly. And this is telling as to where the needle tends to sit for most people.

So what do we mean by the sympathetic and parasympathetic nervous systems?

The graphic below does a great job of illustrating how the physiology of the body changes depending on whether we are in a parasympathetic or sympathetic state.

[caption id="attachment_5648" align="aligncenter" width="300"] An illustration of how the physiology of the body changes depending on whether it is in a sympathetic or parasympathetic state.


On the left are the physiological functions associated with being in a parasympathetic state. These are represented in purple and this branch of the ANS is also known as rest and digest.

When we in a parasympathetic state the pupils dilate and we produce saliva. Breathing is diaphragmatic and nasal. Heartbeats are slower, we are able to digest food and we have control of our bladder.

If you can picture a baby in its diaper this is exactly what we're talking about here. The limbs are relaxed. Respiration involves lowering and raising of the diaphragm. Breathing is primarily through the nose, is calm and regular. And I know babies drool due to new teeth coming in but saliva is commonly produced when in a parasympathetic state.

Imagine a smiley baby picture and you can picture the big eyes with constricted pupils. And for ourselves we know the feeling of comfort after a big holiday meal with friends and family.

Contrast this with times when we're in a sympathetic or flight or fight state.

Now the pupils are constricted as the nervous system wants us to key in and focus on the threat, real or perceived, we are facing. We stop producing saliva and we can all relate to the times we've been nervous and our mouth went dry.

Heart rate increases with a sympathetic stress to move blood and nutrients more quickly in case we need to move quickly or defend ourselves. Breathing is also more rapid and oral rather than nasal. We also tend to inhale more than we exhale when in a sympathetic state.

I tend to think of a threatened animal. It growls and shows its fangs. You may see the traps puff up in order to appear more intimidating to an adversary.

[caption id="attachment_5651" align="aligncenter" width="300"] Respiration is thoracic and increased in rate. Breathing is oral with fangs bared. Pupils are constricted. All indications this wolf is in a sympathetic state.


There is inhibited activity of the stomach and intestines which makes sense when you consider how nervous people may be nauseous or have indigestion when they are stressed.

There are more physiological responses associated with being in either a sympathetic or parasympathetic state but these are the major ones. And the goal is not to be purely in a parasympathetic state. In a similar way that a small bit of a poison can serve as an antibiotic certain doses of sympathetic stress can help strengthen us as well.

Most people however live in a more sympathetic than parasympathetic state. So for the masses, the goal should be find more time to rest and relax.