Ever completed a chunk of mental exercise, such as a day at the office or a long drive, and then experienced post-work lassitude (PWL)? PWL tends to find one drained and tired. During PWL it is common to feel as inclined towards further exertion as one feels drawn to naturism with fire ants. PWL associated inertia is one of the commonest obstacles we face when it comes to us getting a healthy amount of whole person exercise and recreation. It is also, paradoxically, one of the surest indicators that vigorous physical activity is exactly what we’re in need of.
PWL can last for hours, days, weeks, possibly whole career spans. It is easily mistaken for tiredness and it conspires to deprive us of health and resourcefulness. It creates a positive feedback cycle – the worse it is, the worse it gets: PWL leaves us feeling listless and inclined towards inactivity so our fitness declines and so we feel less energetic and so on.
There are lots of reasons why comprehensive muscular function increases our energy levels rather than depletes them further. During exercise:
- Our bodies secrete brain stimulating hormones
- Heat is generated
- Stored energy is released and becomes available to our brains as much as for the rest of our body
- Our whole bodies are employed in thought and emotion processing.
These are some of the immediate effects of exercise – ignoring all the long term adaptive benefits such as reduction in blood lipid levels, blood pressure and so on.
One other, now documented, immediate benefit of exercise on mental energy is oxygenation of the brain. Our brain uses about 20% of our total oxygen intake. During exercise the amount of oxygen present in the blood is raised and so more oxygen is available to the brain. More exercise = more oxygen = a more resourceful brain.
So it seems that our PWL may in part be caused by a shortage of oxygen in the brain and the best remedy for this, far from being a lie down or another coffee, may be to slip into that wetsuit and take the llama for a swim (or whatever you like to do for exercise).
Interestingly we experience a 1% decrease in ability to take up oxygen per year of life after 20. This may explain why teenagers are better @ computer games – their brains are able to function just fine from the depths of the settee / duvet.
One control experiment that indicates it’s the oxygen our brain gets through vigorous exercise that is recreational - more than all those stimulating benefits of exercise: One summer I was at altitude ascending an alpine peak. I wasn’t very well acclimatised. There were lots of other folk ascending the same route. And descending it. I thought it was my turn to ascend a particular bottle-neck. I must have been wrong because it turns out it was the turn of a large French gentleman to descend it. He landed on me, 24 sharp points of steel first. Under standard conditions of temperature and pressure I’m sure I would have reacted with some emotion. On this occasion I shrugged and waited until he had stepped off me. I carried on, not with stoicism or courage, just with the thickness that comes from oxygen deprivation. The other physiological benefits of exercise were clearly not enough to maintain my mental sharpness.
So for sharp thinking and a resourceful brain, sack off the desk, ditch the caffeine, resist the urge to vegetate and get out there and get panting…
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