You might not expect me to say this, but I think exercise is bad for you writes our fitness blogger Jamie Johnston.

In the last three weeks I’ve only trained twice and spent a lot of time lying on the sofa. Here’s the reason why:

I had been carrying a couple of injuries so I took a week off training to give them time to recover. This did the trick, but I felt I had some catching up to so I started training extra hard.

Then I got the flu.

I’ve spent most of this week lying on the sofa, coughing violently, aching and feeling very sorry for myself. What did I do wrong?

Well, you should always rest injuries to let them fully recover, but if possible try to keep training the uninjured bits of your body.

The week off that allowed my niggles to recover was the right thing to do, but I should have eased my way back in gently. Trying to cram a weeks’ missed training into two sessions was a schoolboy error.

And let me make it clear – you should not exercise with flu. In fact any time you have a virus that affects the chest you must rest completely because training with flu can literally kill you.  The excessive training I did before getting ill weakened my immune system and left me vulnerable to viruses.

Now only a fool makes the same mistake twice. Next week I will feel better and I mustn’t try to make up for this week’s missed training by training doubly hard. The proof of whether I’ve learned my lesson will be whether I manage to train at a sensible level over the next fortnight.

So maybe my example is a little extreme, but there are other times when you shouldn’t exercise too.

If you get severe pain when exercising it is always advisable to get your GP to check you over. Also if you haven’t trained for quite a while, are over 60 years, very overweight or if you have any known medical condition you should see your doctor before starting exercise. Finally, if you’re pregnant or recently given birth get some advice on what exercises it is safe to do.

However, for everyone else, exercise is a good idea and may even prove a lifesaver. Everyone should get their blood pressure checked when they start because undiagnosed high blood pressure is quite common. Ask your local pharmacy, practice nurse or a Personal Trainer at your gym to do it.

Then just go for it, but start slowly. If you feel overly tired or sore after training that means you overdid it so you’ll need to reign it in a little next time.

If you’ve had the day from hell and feel tired, have a shorter workout, but still do something – just to keep active.

Most importantly find a sport, activity or training regime you enjoy most of the time. We all have the odd off day, but if you enjoy it most of the time you’ll stay with it and stay fit.

Jamie Johnston runs At Home Fitness, providing personal training across the West Midlands and Staffordshire. See www.athomefitness.co.uk for more details.