Mononucleosis — “mono,” or glandular fever — is a viral infection that causes symptoms for weeks or months. Known as the “kissing disease” because it spreads through saliva, it often affects teenagers and young adults who play sports. So what do you need to know about mononucleosis and exercise, and when can you safely return to training after mono?
What is mononucleosis?
Mono is a common illness caused by the Epstein-Barr virus. Most people are infected at some point in life, though it’s most common in teenagers and college students. Symptoms usually appear about a month after exposure.
How does mononucleosis present?
Infection can feel like the worst cold you’ve ever had. It usually starts with general tiredness, aches, and loss of appetite, then progresses to high fever, tonsillitis, and swollen lymph glands. A body rash occurs in 10–40% of cases. Liver infection sometimes causes yellowing of the skin (jaundice). Importantly, the spleen — sitting under the left rib cage — can swell, raising the risk of rupture after trauma or contact sport.
Most symptoms settle within 2–4 weeks, though tiredness can last for months. Occasionally, fatigue persists much longer, leading to chronic fatigue.
How do we diagnose mono?
Diagnosis involves an examination, blood tests, and sometimes a monospot test. Blood tests often show raised, abnormal white cells called atypical lymphocytes, and liver tests may be abnormal. Because other infections cause similar symptoms, your doctor should also check for CMV, HIV, herpes, and bacterial tonsillitis.
Recovering from mono: getting better safely.
There’s no specific antiviral treatment for mono, so the focus is on managing symptoms:
- Rest — essential, as overexertion prolongs symptoms.
- Hydration — aim for plenty of fluids (water, soup, herbal tea), more if you have a fever.
- Pain relief — ibuprofen or paracetamol helps with pain and fever. Avoid aspirin in children and teenagers, because of the risk of Reye’s syndrome, a rare but dangerous condition that can damage the liver and brain.
- Saltwater gargles — soothe a sore throat.
Mononucleosis and exercise
Two issues drive the advice on mono and exercise. First, returning too early can prolong symptoms or raise the risk of complications such as pneumonia or liver inflammation. Second, mono enlarges the spleen, making it more prone to rupture — especially after contact-sport trauma.
When can you return to exercise safely?
Doctors usually apply the “neck rule.”
If you have symptoms below the neck — fever, sweats, muscle aches, or tummy pain — rest from all training, though you needn’t be bed-bound; gentle stretching or a light 5–10 minute walk is fine.
If symptoms are above the neck — a sore throat or runny nose, with no fever or aches — you’re ready to restart gradually. Begin with light exercise, such as walking or gentle yoga, for 10–15 minutes. Listen to your body, and stop if you feel fatigued or hurt. Build duration and intensity slowly, progress to moderate activity such as swimming and cycling, then reintroduce strength training with lighter weights and fewer sets before returning to your pre-illness routine.
Mononucleosis and sport: contact-sport restrictions
Return to sport depends on whether it’s contact or non-contact.
Athletes in non-contact sports (marathon running, triathlon, cycling) can begin sport-specific training once they tolerate light training and weightlifting without fatigue or recurrence of symptoms.
Contact sport is the bigger concern. Mono enlarges the spleen, and as it grows, it’s no longer protected by the rib cage, leaving it exposed to trauma. Returning to contact sport (rugby, football, netball, basketball) with an enlarged spleen risks splenic rupture, which — though rare — is severe and potentially life-threatening.
The spleen enlarges in everyone with acute mono. Studies suggest it remains enlarged for about three and a half weeks, and rupture usually occurs within the first three weeks, becoming rare after four weeks. So avoid contact sports for at least four weeks from the start of the infection. If you need to return sooner, speak to your doctor about an ultrasound scan to measure the spleen — sometimes repeated scans guide the decision.
Frequently asked questions about mononucleosis and exercise
How long after mononucleosis can you play sports?
It depends on the sport. For non-contact sport, resume once fever, aches, and sweats have settled and you tolerate lighter activity such as walking, swimming, and light weights. For contact sports, avoid contact training for at least 4 weeks because of the risk of spleen rupture. Where there’s pressure to return early, an ultrasound can measure spleen size, since a larger spleen means a greater risk.
Should I isolate to avoid spreading mono?
Strict isolation isn’t necessary — mono spreads through close contact with saliva, not easily through the air. Basic hygiene helps: wash your hands, and don’t share utensils or water bottles.
Are steroid (cortisone) tablets recommended for mono?
No, not for most cases. We reserve cortisone tablets for complications such as severe tonsillitis (where the airway is threatened) or heart inflammation. Routine use isn’t advised and can cause side effects.
How long does the tiredness from mono last?
It varies — some people feel tired for a week, others for months. The key is not to push back into exercise too early, which tends to prolong the fatigue rather than shorten it.
Can I exercise with a mild cold instead of mono?
That’s a different question — mild upper-respiratory symptoms follow the same “neck rule.” See our guide on working out while sick for exercising with a cold, and how to tell when an illness is more than a simple cold.
Final word from Sport Doctor London about mononucleosis and exercise
Recovering from mono and returning to exercise takes patience and careful monitoring. Follow a structured, gradual plan and use the “neck rule” to decide when to resume. Above all, be cautious about returning to contact sport too early, because of the risk of splenic rupture — when in doubt, an ultrasound and a doctor’s advice are worthwhile.
If you’re an athlete recovering from mono and unsure when to return to sport, Dr Masci can assess you in London, including an ultrasound of the spleen where needed. Contact the team here or call +44 (0) 203 488 0350.
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