Monday, 31 March 2014

You Decide: Fight & Flight or Rest & Digest


Amongst the myriad of information of fitness you rarely hear anything of the autonomic nervous system. There’s probably a reason for this. It’s heavy stuff. 

It’s much easier for a hapless fit pro to bitch about the pro’s and cons of the calorie. Or even to write about the effects of cortisol on belly fat, thyroid on metabolism or the role of insulin on fat burning...

BUT truth be known understanding about the sympathetic and parasympathetic nervous system and more so being able to stimulate them at the right time is important and is why some people get results and others don’t.

Something we have limited control over, the autonomic nervous system (ANS) regulates functions of our internal organs like the heart and stomach. Functioning involuntarily, we are often unaware of what it does. 

I guess this is useful because it would be a pain in the butt to think about dilating our blood vessels when our heart beats faster or slowing it down when it doesn’t.

But, with some level of training, or with a little stimulation, we can take some control and this can be useful for fat loss and fitness.

Of particular notes are the conditions of the ANS in ‘rest and digest’ and ‘fight or flight’.

Imagine the scene, you’re taking a nice walk on a sunny day. Walking through the woods you are pounced upon by a bear. In an instant your heart rate elevates and you either run away or strike. This is your bodies fight and flight response. 

A symptom of the sympathetic nervous system, your body finds the energy in an instant and reacts. You find hidden strengths when your body releases adrenalin and shunts blood to the muscles.

On the flip side, you take a nice walk on a sunny day. You find a comfortable chair and sit and relax. In this example your heart rate lowers, your body becomes calm and rested. This state is known as ‘rest and digest’.

A symptom of the parasympathetic nervous system, your blood pressure reduces, pulse rate reduces and blood shifts to vital organs like the stomach for digestive processes and the like.

At this stage you can be excused for wondering how this is going to help you look better in your bikini. Let me elaborate...

Think about it, under what conditions would you do better in exercise? Rest and digest? I think not. What conditions would you better recover? I think you know the answer.

I need to qualify this and say the ANS is always in operation. You’re rarely one or the other. Most of the day you are somewhere between the two.

However, being able to ramp up the fight and flight response before exercise will obviously improve your performance, whilst stimulating rest and digest can clearly speed up recovery. 

Therefore, it can be down to what you do before and after exercise to manipulate this state of flux which make the difference.

One way I’ve found to bring about a fight and flight response is to eat a reduced carb diet. If you think about how you feel after a carbohydrate-dense meal, I’m certain it’s pretty sleepy and relaxed. That’s not great conditions for a barnstorming gym session, right?!

On top of this I like to use caffeine. A black coffee and small bar of dark chocolate seem to work for me. This gives me the focus I need to hit the gym.

Somewhat unsociably a gut wrenching scream before you lift can help. Use this cautiously because your gym manager might not be so supportive. Especially if you’re taking part in a zumba class...

On the other hand, to bring about a speedy recovery assuming a rest and digest state can be useful. If you’re session is suitably intense (not spinning or body pump...) then a protein shake might help.

With a liquid protein being fast absorbed it can immediately replenish glycogen stores and preserve metabolically demanding muscle tissue. This is an important aspect in fat loss, fitness and muscle building programs. 

Followed by a meal containing carbohydrates (think sweet potato or white basmati rice) you’ll further support this process. Even more so if you take some time to rest and relax too.

Bearing mind carbohydrate-dense meals can bring about a state of rest and digest, this further supports my position of eating your carbohydrates with your evening meal rather than your breakfast. It fits your bodies natural rhythms regardless of whether you exercise or not.

For the opposite of the reasons above (you don’t want to induce fight or flight), avoiding caffeine after exercise can be smart too. Stick to drinks like herbal tea.

Further to this it should be noted how excessive stress and lack of sleep can mistime these responses and effect results.


There you have it. Think about your bodies ‘fight and flight’ and ‘rest and digest’ responses and time them with your exercise for maximum results. 

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