This week, I’ve been under the weather with some sort of flu-like respiratory crud. I doubt it’s the dreaded H1N1 virus – but if so, I sure got off lightly.

This raises some questions for my exercise addiction. Should I exercise when I’m sick? And how does exercise play into immune response? I did some research and found great answers.

Exercising when Ill. It’s important to be attentive to your body’s needs when evaluating whether or not to continue an exercise routine when feeling ill. Many experts recommend that if your symptoms are above the neck and you have no fever, light to moderate exercise is probably safe.

If you are already ill, you should be careful about exercising too intensely. Your immune system is already taxed by fighting your infection. Additional stress could undermine your recovery; it will only make things worse and likely extend your illness.

However, if there are symptoms or signs of the flu or more serious illness, such as fever, extreme tiredness, muscle aches, swollen lymph glands, or bronchial symptoms, then many sources indicate more time should be allowed before you resume intensive training. In such cases, online resources are no substitute for consulting your doctor.

In my case, I did have a low-grade fever, a cough, and enough exhaustion that I didn’t try to exercise through it. Now that I’m back to nearly 100%, I’m going to ease back in, to make sure I don’t overtire myself. I wanted to start back today but work demands were prohibitive; that’s probably a good thing as I’m still coughing a little. Tomorrow, though, I’ll be at the pool mid-morning,

Regular Moderate Exercise Boosts Immunity. Moderate, consistent exercise has been proven to build a strong immune system. It’s been linked to a positive immune system response and a temporary boost in the production of macrophages, the cells that attack bacteria. In addition, when moderate exercise is repeated on a near-daily basis, the cumulative effect can build a long-term immune response.

Too Much Exercise May Decrease Immunity Conversely, there is also evidence that too much intense exercise can reduce immunity. This research is showing that more than 90 minutes of high-intensity endurance exercise can make athletes susceptible to illness for up to 72 hours after the exercise session.

Intense exercise seems to cause a temporary decrease in immune system function.
Cortisol and adrenaline, known as the stress hormones, are produced during intense exercise, raise blood pressure and cholesterol levels and suppress the immune system.

Ultra-distance training should include enough rest and recovery days to allow the body and immune system to recover. Feeling run-down or displaying other symptoms of overtraining–heart rate changes, irritability, general heaviness or fatigue–may indicate the need to reduce duration or frequency of workouts.

I am really bad about taking my regularly scheduled rest day because I find the mental health benefits of the workout outweigh the rest and recuperation value of a own day. I may have undermined my own immune system. I’ll have to watch that in the future.