Should you train when you are ill?

Why a fever is a hard stop

A fever means your body is actively fighting an infection. Exercise raises your core temperature further, increases fluid loss and adds demand on your heart at a time when it is already working harder.

There is a more serious reason too. Some viral infections can cause inflammation of the heart muscle, called myocarditis. It is rare, but strenuous exercise during a viral illness with fever may increase the risk of complications. This is one of the few areas of exercise advice where doctors are firmly on the side of caution.

So if your temperature is 38°C or above, or you have shivers, sweats and aching all over, stay home. Rest, drink plenty and wait until you have been fever-free for at least a day or two, without paracetamol or ibuprofen masking it, before thinking about training.

The same goes for aching all over. Widespread muscle aches during a virus are a sign your whole body is under strain, and they are not the same as training soreness. Rest through them rather than trying to loosen them off with exercise.

Training with a head cold

If your symptoms are mild and above the neck, some movement can make you feel better. The key is to keep it genuinely easy.

• Cut volume and intensity to around half of normal.
• Swap hard intervals for easy aerobic work: a brisk walk, a steady bike or a relaxed row.
• Lift lighter, with plenty of reps left in the tank. Skip maximal lifts.
• Give it ten to fifteen minutes. If you feel worse, stop and go home.
• Drink more than usual, as a blocked nose and mouth breathing dry you out.

Think about the people around you. A class or gym floor involves shared equipment and heavy breathing in close quarters. If you are coughing and sneezing a lot, your training partners will thank you for staying home, however well you feel. If you do go in, wipe down everything you use.

Stomach bugs

Vomiting and diarrhoea drain fluid and salts quickly and leave you with little energy. Training on top of that is a recipe for dizziness and a slow recovery. Stomach bugs also spread easily, and NHS advice is to stay off work or school until 48 hours after the last episode of vomiting or diarrhoea. The same logic applies to the gym.

Focus on small, frequent drinks, and consider oral rehydration sachets from a pharmacy if you have lost a lot of fluid. Our guides to hydration and electrolytes explain why salts matter. When you return, start with an easy session. It is common to feel weak for a few days after even a short bug.

Coming back after illness

The most common mistake is jumping straight back to your old sessions because you feel fine at rest. Exercise asks a lot more of your body than sitting at a desk, and fitness dips slightly after a week off.

1. Wait until you are symptom-free at rest, with no fever, for at least 24 to 48 hours.
2. Start at around half your usual volume and intensity for the first few sessions.
3. If that feels fine, build up over the next week or two. A longer or more severe illness needs a slower return.
4. Expect a lingering cough or slightly higher breathing for a while. Keep conditioning easier until it settles.
5. If you feel unusually wiped out after light sessions for more than a couple of weeks, stop pushing and speak to your GP.

Some coaches use a rough rule of thumb of allowing at least a couple of days of gradual return for every day you were properly ill. It is not precise, but it stops the classic mistake of missing a week with flu and trying to make up for it with a double session on your first day back.

Returning to a class after a week or two off is easier than people expect. At Lycan Strength every class is scalable, so coaches can adjust movements and loads while you get back up to speed. Our guide to getting back into fitness covers longer breaks.

Staying well in the first place

Regular moderate exercise is associated with fewer colds, not more. What seems to increase the risk is the combination of very hard training, poor sleep, stress and under-eating. Prioritising sleep, eating enough, and managing training load is the best protection you have. The UK government also advises that everyone considers a daily vitamin D supplement of 10 micrograms in autumn and winter, which our guide to vitamin D covers in more detail.

Simple hygiene helps as well. Wash your hands after training, do not share water bottles, and wipe down equipment before and after you use it, particularly during winter when colds and stomach bugs are doing the rounds.

When to get medical help

• Chest pain, a racing or irregular heartbeat, or fainting during or after exercise: stop and call 999 if severe or ongoing
• Breathlessness far beyond what the effort explains, especially after a recent viral illness
• A high temperature that is not coming down, or you feel very unwell: contact NHS 111
• A cough lasting more than three weeks: see your GP
• Signs of dehydration that are not improving, such as very dark urine, dizziness and passing little urine