Tiredness, it really is all in the mind

Scientists have been taking a fresh look at the hows and whys of feeling full of energy, or indeed tending more to the weary side.

One conclusion is that the feeling results from a subconscious body/brain estimate of how much energy is at hand in the body, the amount already accounted for, and an educated guess of whether we have enough left over for what we have to undertake next. This brain conversation is also influenced by ambient factors. When people were asked to exercise up to the point of exhaustion, they could keep going longer in the company of a supportive ally. This may be a sign that we can dig deeper into our energy stocks when we know there is help at hand.

The brain’s assessment of our metabolic state also has psychological repercussions in that we may sleep very well but still feel exhausted at the thought of an arduous day ahead. Likewise, hearing some good news can give us an energy boost.

A key player in all this is our mitochondria. These are cell factories that turn digested food into an energy form that cells can use. When they aren’t working efficiently we feel fatigued and lethargic. Growing evidence is also suggesting that high sugar intake affects mitochondrial effectiveness and can cause a “sugar crash”.

An excess of food also causes our mitochondria to switch jobs. They then change from releasing energy to storing it – hence the sudden onset of a not unexpected and not entirely unpleasant feeling of doziness after a surfeit of goodly nosh.

The word mitochondria has Greek roots from the word mitos ('thread') and khondrion, meaning 'tiny granule'.