Now that doctors have decided that being fat is even worse for us than smoking, you might think your boss will be impressed when he sees you in your exercise kit. Think again.

By all means cycle to work, go for a run at lunchtime or use the company gym. All these give you valuable thinking time to plot the downfall of rivals and your own rise. But never, never let anyone in the office see you wearing anything other than your business clothes. You just can’t win with sports gear: if you are fit you look vain, if you’re not you look sad.

One day, I found myself riding in the lift with my chairman. He was going out for lunch. I was off for a run.

The tension was unbearable, for I knew as soon as I stepped through those sliding doors that the image of an elegant, well-dressed business leader I had worked so hard to create would lie in pieces somewhere between the tenth and eighth floors.

If the boss is unfit your vigour looks like a reproach. If you are young it makes the boss feel old. You look pathetic if you are chubby and like a threat if you are lean. Worse, next time you are making an important presentation, your colleagues will think of you only as that funny figure who arrives in the office wearing nylon shorts.

I have known bright men and women on their way up lose all respect when colleagues saw them in the cycle shorts they wore for their journey home. One never recovered from the day he came in early on his bike, thought he would return a couple of calls before heading for the showers and got so caught up that he was still in figure-hugging Lycra at half past nine, when his boss called by to see him.

So do exercise ferociously. It’s good to get endorphins racing round the body before the daily fight that is office life. Just make sure you find somewhere private to change.

Times Recommends

• Inspirational leadership
• How to get a new job
• The reluctant CEO