Is it advisable to exercise when sick?

Exercise During Illness: A Risk-Stratified Approach

You should avoid exercise during active systemic infection and only resume after being symptom-free (including fever) for 2 days, then gradually return to activity at reduced intensity. 1, 2

When Exercise is Contraindicated

Active systemic infections can be adversely affected by physical activity, and rest is superior to exercise during the acute symptomatic phase. 3 The following represent absolute contraindications:

• Active myocarditis - poses risk of malignant arrhythmias and sudden death 1
• Fever or systemic symptoms - never exercise during the first 3 days of acute illness 1
• Active viral infection with cardiopulmonary symptoms - requires cardiac screening (ECG, troponin, echocardiogram) before any return to exercise 1
• Infective endocarditis - avoid exercise until disease is stable and antibiotic course completed 3

The "Above the Neck" Rule Has Important Limitations

While solo exercise at reduced intensity may be safe for symptoms confined above the neck 4, the American Heart Association recommends waiting until all symptoms and fever have been absent for 2 days before resuming any activity 2. This 2-day symptom-free period is critical for preventing complications including myocarditis 2.

Safe Return to Exercise Protocol

After meeting the 2-day symptom-free criterion 2:

1. Start with reduced intensity and duration compared to pre-illness levels 2
2. Begin with 5-10 minutes of recumbent or semi-recumbent exercise at an intensity allowing full sentences 1
3. Increase duration by approximately 2 minutes per day each week as tolerated 1
4. Monitor for symptom recurrence during the first several sessions 2
5. Maintain adequate fluid intake before, during, and after exercise, as dehydration from illness may persist 2

Special Populations Requiring Extended Restrictions

Athletes with confirmed myocarditis must abstain from all exercise for 3-6 months, with return only after normalization of cardiac function, biomarkers, and absence of arrhythmias 1. This extended restriction reflects the risk of sudden death in an electrically unstable myocardium 1.

Common Pitfalls to Avoid

• Do not measure cardiac troponin within 24-48 hours of strenuous exercise, as physiologic elevation occurs and confounds interpretation 1
• Intense physical activity during the incubation period of serious infectious diseases is especially disadvantageous for disease course 5
• Extreme physical exertion may suppress the immune system and enhance susceptibility to infections 5
• Pericarditis requires exercise restriction during the acute phase, as activity exacerbates inflammation and precipitates recurrences 1

The Evidence on Exercise and Infection Prevention

While moderate-intensity exercise may reduce the severity of respiratory infection symptoms and total symptom days during follow-up 6, exercise does not reduce the number of infection episodes or the proportion of people who get sick 6. The preventive benefit is modest at best, and attempting to exercise through active illness carries significant risks that outweigh any theoretical immune benefits 1, 5.