Ian Cleary

Is Fatigue a lack of Energy?

There’s nothing like a good night’s sleep to recharge the body’s batteries – except that’s not how it works.

Some people think that going to sleep is like plugging in your phone to the charger at night.

Give it 8 hours and you wake with full batteries and you’re good to go all day. If you don’t get your 8 hours, it’s like you haven’t ‘fully recharged’ or your body’s batteries are not at 100%.  This common human experience easily leads to assumptions about fatigue and we use the metaphor a ‘lack of energy’. We make ‘energy’ a thing. And ‘fatigue’ is also a thing …. or a depletion of a ‘thing’.

We equate the sensation of ‘tired’ with a biological lack of energy.

This is sometimes known as the Energy Depletion Model of fatigue and while it makes intuitive sense – like other insights from science, sometimes things aren’t as they seem. The link between tiredness and biological energy is not as direct as we usually think.

It might surprise you that TOO MUCH sleep is also associated with fatigue. I’ll just repeat that. Sleeping too much is associated with fatigue. Did I plug my phone in for so long that I am somehow back to a flat battery? So there goes my phone recharge metaphor! 🙁

Now think of what you know about a symptom of low iron levels – FATIGUE. Fits nicely into the ‘Energy Depletion’ Model. Low Iron = Low batteries = Fatigue.  Bingo! Depletion Model of fatigue is back on the table – dust off the phone recharger metaphor.

However unusually HIGH iron levels are ALSO associated with fatigue. Sorry phone recharger metaphor. Back to the middle drawer of useless cables for you.

Too little protein AND too much protein is associated with fatigue. Too little fat in a diet is associated with fatigue ….. and you can probably guess now what is ALSO associated with a diet too high in fat. Our old friend – Fatigue.

A lifestyle excessively high in exercise …. fatigue. But a life style too low in exercise ….. fatigue.

Not quite ready to ditch the ‘energy depletion model’? Well did you know that sleeping USES biological energy.   How much? Approximately the same energy as a 30 minute session in the pool swimming BUTTERFLY – about 360 calories! So by rights plugging in that phone recharger overnight should show up as fewer ‘bars’ on the phone in the morning due to all that energy-draining sleep!

So sleep uses biological energy yet we wake up ‘energized’. Well some of us do. Other don’t – regardless of how much sleep they have.

And if you are one of those people – a different understanding fatigue could be invaluable.

Understanding that fatigue is not a depletion of biological energy, as counter-intuitive as that may seem, is a game changer – particularly if you are chronically fatigued.

Those people already know that NO amount of sleep gets them to “fully charged” (even if you add day naps or pre-emptive sleep before an activity). Neither do they hit fully charged if they sleep lots AND do very little. Other have the most intense healthy diet to build up those batteries and still – fatigue.

YET people still hang onto that historic model of fatigue.

Believing that tiredness is a lack of biological energy may put in place behaviours, management techniques and strategies that are counter productive and keeps people from finding actual solutions to the problem.

Trying to rest one’s way out of a chronic fatigue is NOT associated with positive outcomes. It might be managed by rest but unlikely to be solved.

So what is fatigue if it is not a lack of energy?

The clue is to look where it is present. Sleep problems, food intake issues (quantity or quality), stress issues, a virus, bacteria or active illness, recovering injury, undergoing cancer treatment, anxiety, depression, past trauma and grief.

A different model of fatigue now sees it not caused by a depletion of energy but rather a neurological protection response associated with a THREAT. When the brain detects a threat it can turn on fatigue to help us.

So why do I feel tired after a poor night’s sleep? Sleep is primarily for the brain so if the brain hasn’t had enough time to do its important nightly function that’s a problem (threat) so the brain turns on fatigue. Interestingly, and inline with this model, studies also show that fatigue can be triggered by someone believing they haven’t had enough sleep when they actually have. So a perceived threat or actual threat can trigger the fatigue.

So a more useful metaphor might be that it’s not a ‘running out of petrol’. It’s the brain slamming on the emergency breaks. And before people start to email me that I am claiming it’s ‘All in the Head’ remember neurological not psychological.

When the brain detects a virus (threat), it’s not in our interest to run around so the brain turns on fatigue. Neurological not psychological. The fatigue is real AND your body also has sufficient biological to go about its daily functions. It’s just not in our interest to go about our daily functions. So you can have biological energy AND real fatigue at the same time. (Petrol in the tank AND the brakes jammed on).

For some people, the viral threat passes yet it is as if the brakes are jammed on and they are left with ‘Post Viral Fatigue’. The threat has passed but the brain is still triggering fatigue. The energy was there all along and it still is –  the only issue is that the fatigue is also still there. Real fatigue just no longer appropriate fatigue. It’s not ‘all in the head’. It’s the exact same crushing fatigue as when the virus was present. It’s now just no longer appropriate.

And that is the dark side of Neural Plasticity (the brain’s ability to change with experience). Anything that goes on for long enough can create changes or adaptations in the brain. Neurological not psychological.

The THREAT has past but the fatigue remains.  Real fatigue just no longer appropriate.

We can see a similar patterns play out neurologically with Post Traumatic Stress Disorder. The original threat has passed but the brain is still turning on its protections mechanisms. We see it with some Chronic Pain conditions where an original injury (threat) has passed but the brain is still tuning on another neurological protective mechanism – pain. We see it with childhood trauma. The childhood threat has passed, yet the body is still turning on protective responses. (Fear, pain, fatigue, behaviours, anxiety).

These are the neuroplastic adaptations that have occurred in the brain and nervous system.

Within this model, you can probably see why rest is NOT associated with recovery. You already know what is associated with excessive inactivity – fatigue. Suffers of chronic fatigue also know that just pushing through and exercising isn’t going to work. Because the brain has put a threat value on exercise. Just like when people have a virus. Activity can trigger the protective response of fatigue. You’re stuck ….  fatigue if you rest or if you exercise. Being told there ‘Is no cure’ also doesn’t help the brain’s assessment of threat but that’s another story.

So if resting isn’t the answer and pushing through and exercising isn’t the answer then what?

Well there are actually many options available. A great starting point though is to have a better understanding fatigue.

Now that’s something to sleep on. 


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