Spontaneous combustion anyone?

  As I’m fond of mentioning.....

  .....we forget sometimes that we’re animals and have gone through pretty much the same evolutionary mill as other critters with backbones to get where we are.

  Our athletic ability is a legacy of our more active ancestors, both human and non-human.  If you think about it, we have a massive spectrum of metabolic rates in our daily lives – at the bottom end is sleeping where we are basically just ticking over and the other end is running flat out for a bus or doing something stupid like participating in a bicycle race.  The difference in oxygen consumption between resting and going flat out can be about 15 fold in mammals and birds.

  But it’s not just more oxygen we need:

• More fuel
• Waste products to get rid of (they are invariably toxic)
• More blood flow
• All that waste heat to get rid of so we don’t cook – a fit person flat out can generate nearly 2 kw of waste heat!

  Mammalian bodies have incredibly tight parameters regarding temperature, oxygen levels, fuel levels, electrolytes, blood pressure, pH etc etc and if anyone of these goes slightly off limits it could kill us.  It’s a mechanism called ‘homeostasis’, controlled by the hypothalamus in our brain.  Without it, soon after sprinting for the bus we’d be drowning in our metabolic waste products, probably have lost consciousness due to low glucose and low oxygen levels whilst dissolving in the low pH of our blood and slowly cooking from the inside.  You may even have died instantly when the blood pressure from your pounding heart burst every artery in your brain.  Like I said – amazing!

  Body pH and temperature are particularly tightly controlled because the enzymes which power all the chemical reactions in our bodies require very specific conditions in which to work optimally. They are made of protein so, as well as stopping functioning if things go off limits, they can also irreversibly ‘denature’ and permanently change shape – exactly what happens to an egg white in a frying pan.

  Our usual body temperature is around 37 degrees C but anything above 42 Celsius is rapidly fatal.

  Our usual body pH is almost exactly always 7.365 – anything more than 8 or less than 6.8 would also be rapidly lethal. This is also why all those quack health products promising to ‘alkalise’ your blood are complete horses**t.  Anaerobic glycolysis yields loads of lactic acid which could quite easily kill you if allowed to become too concentrated - As if you didn’t have enough to worry about whilst tearing down the A11 on a Saturday afternoon!

  But don’t worry, the hypothalamus takes care of all this for us.

 Below is a picture of my actual brain (yes, really!). The arrow is pointing to my hypothalamus….

 

  All these systems and machinery to keep us alive are fantastically complex – the metabolic cost of maintaining it all is huge. If we were animals of just one speed, like a slug or an amoeba, life would be so much easier for our bodies, but we’re not.  As with most complex biological stuff, our homeostatic system seems like a mind-boggling feat of evolution but having a metabolic rate you can throttle up and down at will is a massive competitive advantage for animals.  You can chill out and conserve energy for most of the time but run like the clappers when you need to.  Even more remarkably, long term stressing of this system causes the body to supercompensate so that we can rev our metabolic engines even higher  - the training effect.

  The downside is that maintaining fitness requires a lot of extra metabolic cost, that’s why we rapidly ‘detrain’ if we stop exercising – the body defaults to ‘energy saving mode’. Why waste all those food resources and calories in maintaining a super fit body if there nothing around to chase you?

  Interestingly, mammals such as rabbits can apparently go from couch potato to Olympic athlete in just a couple of weeks in response to predators chasing them more frequently.  The trade off comes down to greater energy expenditure from an increased metabolic rate vs being eaten – a no brainer really!

  I wonder how much faster we’d go if we had a saber-tooth tiger chasing us along the dual carriageway on race days….