Participating in a big sporting event like last weekend's Great North Run or playing in a major football tournament can strangely test your physical ability more so than when the pressure is off.

After all, there's not much physical difference between running 13 miles in preparation for the Great North Run, to actually running the thing on the day.

Yet nearly every one leaves the race feeling so much more tired than from practice. It can even have a physical effect on you if you're a spectator in the streets or an armchair expert trying to give Gary Neville a run for his money.

You see, the problem with being a spectator, never mind a participant in sport, is that it's very easy to over analyse what's happening in front of you - and all the time your body is experiencing a physical change.

Many people confuse this sort of thing with a mental strain, but these sort of events which require extra detailed focus and attention actually mean that each of your muscles have to be involved - and is often the reason that even a hard day at the office can leave your muscles feeling weak and tired.

Think back to watching Super Saturday of the Olympics, that famous night where Mo Farah, Jessica Ennis and Greg Rutherford each won a Gold medal. A number of people I spoke to after watching that night said that they felt as though they had run the races with those athletes, despite watching from the comfort of their own home.

Similarly, I've treated patients who have come to me thinking they have muscle problems and I have to explain to them that the only thing happening is they are thinking about too many things at one time.

And it's definitely the reason you can spend all day at your desk doing a job you think is not physically tasking, but by the time you get home you feel as though that run or that trip to the gym you were looking forward to is now out of the question.

What's happening to you here is that during the big sporting event, or even during the course of a more busy day than you expect, you will have been processing so much information that your brain could only do what you ask by pinching energy, oxygen, enzymes and pretty much anything it can get it's hands on from your muscles to get the task done.

These same muscles are the one's that you were hoping to use in the gym that night. As a result, you're feeling pretty goosed and lifeless. And it's possibly the reason for the fun and games you're seeing on the start line from athletes like Usain Bolt.

The sprinter is choosing not to analyse the race in his head in an attempt to preserve as much oxygen and energy in his muscles as possible to help him physically win the race - not the one in his head.

Think back to the days of the stony faced Linford Christie at the start line, the two couldn't be more far apart if they tried in how they approach the race. It's because athletes and coaches all over the world are beginning to understand the link between over-analysing and the physical effect it is having on your body.

In fact, some of the top athletes I know are encouraged to focus on nothing other than their left and right foot and precisely where their foot is going to land. Focusing on anything else would be a waste of vital oxygen and energy.

If you're a regular runner somewhere like the Cleveland Hills, why do you need to be thinking about those gut wrenching hills, your position in the race or even your fellow runners? To do so is a complete waste of energy and oxygen that you could have stored for the end of the race when it's more likely to be needed.

The same thing is happening in tennis, football and cricket and just about every top level sport. In play, players are seeing the benefits of not over-analysing, not thinking about every single strategy and what the opposition might or might not do.

If they do this, their brain is basically pinching nutrients, oxygen and energy from the muscles they need to perform the tasks and this can often be the vital difference at the end of the match.