Can exercise be detrimental to your health? Joanne Christie discovers working out isn't always the best idea

I should have seen it coming. The 'buy one, get one free' antihistamine offers in the pharmacies had been replaced by similar deals on cold and flu remedies, and every time I went out in public it felt like people were coughing and spluttering in my direction. Still, it was a nasty surprise to wake up one day with a fuzzy head and a sore throat. Like many people, I tried to fight it, but after a few days it became clear I was losing the battle, miserably.

One emergency appointment at the doctor later, and I was under strict instructions to rest. It wasn't just a cold, but a tonsil infection and the only cure was painkillers, gargling salty water, and staying at home, said my doctor. My timid 'so I guess the gym is out of the question?' was greeted with a look of bewilderment, and a firm 'yes'.

Okay, admittedly I didn't actually feel like working out, but I still felt guilty about not doing it. While some people might relish the chance to give up exercise for a couple of weeks, others, like me, can't stand the thought of all their previous hard work going to waste. I mean, what's the worst that could happen if we work out when we're a bit under the weather?

For a start, exercise can have the effect of prolonging an illness, says John Buckley, an exercise physiologist.

'If you have the flu or a cold, your immune system is struggling, so by exercising you're potentially adding insult to injury,' he warns.

Studies have consistently found that exercising is a good way to boost your immune system and keep infections away, but it's unlikely to have the same effect if your health is already compromised.

A good rule of thumb, says Craig Williams, an associate professor in the school of sport and health sciences at the University of Exeter, is employing what's sometimes referred to as the 'neck check'.

'If the source of cold and flu is from the throat upwards, it is probably okay to continue training, though you might want to reduce the intensity,' he explains. 'But if the symptoms appear to be going from the throat into the chest, or if there is achiness or fever, it is definitely advisable to stop training.'

So, if it's just a case of a runny nose and a stuffy head, it might be alright to do gentle exercise. But, even if you do get the all-clear on the neck check, Williams says taking a break might be better in the long run.

'I would suggest that if you have got a cold or the flu, it is probably best to rest, keep warm and hydrated, take Vitamin C and just try to get rid of it as soon as possible. Then you can get back to training,' he says.

If you ignore more serious symptoms, such as swollen glands, vomiting, chills, a fever or an aching or very tired body, you could do your health serious damage, says GP and medical columnist Naomi Craft.

'It's not safe to exercise with a fever because of the risk of sudden death from abnormal cardiac rhythm. This is very rare, but can happen if a virus that causes symptoms affects the heart muscle,' explains Craft. 'I recommend no exercise with a fever, and waiting 24 hours after a fever has settled before starting again.'

Reluctantly, me and my fever stayed well away from the gym for three entire weeks. By the time I went back, I felt like a novice. I was exhausted after only 10 minutes on the cross trainer, a machine I've been known to spend an entire hour on.

Fitness expert Joanna Hall says getting back to exercise after an illness can be tough, but it's worth persevering.

'It gnaws away at your confidence and you can feel frustrated and irritated, but if it has only been a few weeks, you don't actually lose as much of your fitness as you think,' she says.

While it can be tempting to go extra hard to make up for lost time, Hall advises a gentler approach.

'If you've had time off, it's a good idea to ease into things. Start out at a lower intensity and work out for a shorter length of time. Try things that focus on your posture, like Pilates, which can boost your confidence if you've been lying in bed a lot.'

Though you might feel like you're right back where you started when it comes to working out, you'll regain your strength and fitness much faster than someone starting to exercise for the first time as your muscle memory will be better developed.

If your gym offers personal sessions to reassess your workout, sign up for one when you go back. Learning some new moves will give you something to focus on and draw your attention away from your break.