Exercise when you have a cold: when it’s okay and when you should take a break

The quick check: traffic lights instead of gut feeling

Green: A cold with mild local symptoms

Mild cold symptoms, such as a runny or blocked nose, are particularly common during the colder months. Dry air from central heating and the constant shift between warm and cold temperatures irritate the mucous membranes and make them more susceptible to infection.

If you only have mild, localised symptoms such as a slight runny nose or a mild tickle in the throat, but otherwise feel fit, have no fever and do not feel particularly unwell, light exercise involving minimal physical exertion is usually fine. Suitable activities include, for example, walks, Nordic walking or a leisurely cycle.

It is important that you stay well below your normal level of exertion: reduce the intensity and duration of your exercise, listen to your body and avoid speed work, intervals or HIIT until you are fully fit again.

Yellow: Cold with systemic symptoms

If you experience several symptoms at once and feel sluggish, exhausted or ‘ill’, taking a break from training is the better option. Typical symptoms include a combination of a cough, a sore throat, a runny nose, a headache or aching limbs.
At the very latest when your resting heart rate is significantly higher than usual or your sleep quality noticeably deteriorates, you should allow your body to rest.

You should avoid exercising if you have a cough or a noticeable sore throat, especially if other symptoms develop. This applies even without a fever, as soon as several symptoms occur together.

Red: A cold with a fever and other warning signs

Exercise is strictly off-limits if you have a fever. This also applies if you feel very unwell or if symptoms appear that suggest a more serious condition. These include, in particular, chest pain, shortness of breath, dizziness, irregular heartbeat or palpitations. In these cases, your body needs complete rest.

Stop your training immediately if such symptoms occur during or after exercise, and seek medical advice to determine the cause. This is particularly important in the case of viral infections accompanied by a fever, or if you feel unusually weak. It is better to err on the side of caution than to resume exercise too soon.

What is the Neck Check?

The ‘neck rule’ (Neck-Check) is a rule of thumb and a practical guide: if symptoms occur only above the neckline (e.g. a runny nose, a slight tickle in the throat), these are considered mild cold symptoms. In such cases, light exercise may be possible under certain conditions. If symptoms occur below the neck (e.g. a cough with phlegm, aching limbs, gastrointestinal complaints, chest tightness), these are considered moderate to severe cold symptoms. In such cases, a break from training is clearly recommended.

Why can exercise be risky when you have an infection?

When you have an infection, your immune system is working flat out. During this phase, the body is more sensitive to additional stress because it needs energy and resources primarily for defence and recovery. Physical exertion can therefore exacerbate symptoms, prolong the recovery time and lead to you feeling significantly ‘sicker’ after your workout than you did before.

Intense exercise acts as an additional stressor. During an illness, stress hormones rise, your heart rate and body temperature increase, and your fluid requirements go up. At the same time, inflammatory and regenerative processes are already underway in the body.

If exercise is added to this, the immune system is challenged or even overwhelmed. In everyday life, this often manifests as symptoms persisting for longer or returning after a brief improvement – the cold is, as the saying goes, ‘dragged out’. Sometimes secondary bacterial infections (superinfections) occur – for example, if symptoms worsen significantly or are accompanied by new purulent sputum or a fever.

It is particularly important to note that, in rare cases, viral infections can also affect the heart and trigger myocarditis. Exercising whilst infected can increase the risk of myocarditis. Therefore, a fever, a severe feeling of being unwell, as well as chest pain, shortness of breath, dizziness or heart palpitations are clear warning signs that you should stop.

The rule is therefore: if you experience systemic symptoms, it is better to take a consistent break and only resume exercise once you feel stable and able to cope with the physical demands.

When you should resume exercise (return to sport)

When you can start training again after a cold depends mainly on how severe the infection was. For a mild cold without a fever, a practical guideline is: only start exercising again once you feel back to normal in your daily life and there has been a clear improvement for at least 24–48 hours, or you are symptom-free. This helps you avoid relapses and gives your immune system time to fully fight off the infection.

If you have a fever (from around 38 °C), feel very unwell, have a proper bout of flu or Covid-19, you should be much more cautious and plan for a longer break. A helpful indicator is your resting heart rate: only start exercising again once it’s back to around your normal level and you feel able to cope with the exertion.

When returning to exercise, the rule is: slowly and gradually. Start at a low intensity (e.g. 10–30 minutes at a very relaxed pace) and make a conscious effort to stay within the ‘aerobic comfort zone’ for the first few days. Increase the intensity of your training step by step. Train more frequently at first, then for longer, and only finally at a higher intensity.

During this phase, always keep an eye on the quality of your sleep, changes in your resting heart rate and how you feel in terms of your performance. You should always take any changes seriously. 

The ‘relapse’ rule: If symptoms become more severe again (e.g. a new cough, unusual tiredness) or you feel significantly worse the next day, you should take a break or go back one step in your plan. Impatience does not pay off. 

If you experience chest pain, shortness of breath, heart palpitations or dizziness, stop training immediately and seek medical advice. In cases of persistent or severe symptoms – particularly those involving heart or respiratory problems – the return to sport may take several weeks and, if in doubt, should be supervised by a doctor.

Will I lose my fitness whilst taking a break from sport?

With short breaks from exercise, the loss of fitness is minimal and can usually be made up for quickly. For most people, a cold typically leads to a break from training lasting a few days to a maximum of a couple of weeks. During this time, you may find that the first few sessions afterwards feel a bit harder or that your heart rate rises more quickly. This is normal and usually subsides quickly once you resume regular training.

The aspect most likely to change is endurance: studies on trained individuals show that performance levels drop measurably after just around 14 days of a complete break. The decline in maximum oxygen uptake (VO₂max) is approximately five per cent after about two weeks, depending on the initial level and the study in question.

When it comes to muscle mass, most people need to worry far less during a short break. Strength and the feeling of endurance may dip temporarily, but actual muscle loss is minimal for the vast majority of people during short breaks.

What aids recovery?

When you have a cold, your immune system is working flat out. To enable your body to fight off the infection as efficiently as possible, it needs, above all, rest, sleep and plenty of fluids. Many of the symptoms are part of the body’s defence response – and this takes energy. If you put yourself under additional strain during this phase, your recovery time may be prolonged. The aim is therefore to give your body a break, take your symptoms seriously and only increase your exercise load again once you feel stable.

Here’s what actually helps:

• Prioritise sleep: go to bed earlier and, if possible, take short rest periods during the day.
• Drink plenty of fluids: water, tea, broth – important for circulation and mucous membranes.
• Use warmth in moderation: keep warm, but avoid ‘sweating it out’ through strenuous exercise or a sauna if you’re feeling unwell.
• Inhalation: steam (e.g. with saline solution) can moisturise the mucous membranes and loosen thick mucus.
• Nasal rinsing / saline spray: helps with a blocked nose and can support mucous membrane care.
• Chicken soup / light meals: warm, easy to digest, often pleasant when you have little appetite.

Reduce everyday stress: postpone appointments, long evenings and high levels of mental strain where possible.

When you should seek medical advice for a cold

Seek medical advice promptly if warning signs appear – particularly chest pain, shortness of breath, irregular heartbeat or persistent palpitations, a fever lasting several days, or a significant deterioration in your condition despite taking it easy. Severe weakness, dizziness or circulatory problems are also reasons to stop exercising and seek medical advice. You should also consult a doctor if symptoms persist for longer than two weeks. 

This is particularly important because, in rare cases, viral infections can also affect the heart. If myocarditis is diagnosed, significantly stricter rules apply: in such cases, longer breaks from sport are necessary, and a return to exercise should only take place gradually and after medical clearance. Guidelines often recommend a break from sport lasting several months following a diagnosis of myocarditis.