Exercising When You Feel Under the Weather – Help or Hindrance?

Strength training for runners

Everybody feels unwell at some point in their life. The key question is, should you rest until you feel better, or would exercising help your body get back to full health quicker? This news piece, based on an article by Ryans Andrews at Precision Nutrition, aims to answer that question. If you want to skip the science bit and cut to the chase, scroll down to the conclusion section at the bottom of the piece.

The Immune System

Every day we’re confronted by bacteria, viruses, fungi and parasites. The most common are the upper respiratory tract invaders, or URTI’s, i.e. colds, coughs, flu, sinusitis, tonsillitis, throat infections and middle ear infections.

When faced with these invaders the immune system works hard to defend the body. Immune cells originating in the bone marrow and thymus, interact with invaders through the lymph nodes, spleen and the mucus membranes in the mouth, gut, lungs and urinary tract.

The Innate and Adaptive Immune Response

Our innate or natural immune system is our first line of defence. It includes:

• physical/structural barriers like the mucus lining in the nasal passages,
• chemical barriers e.g. stomach acids, and
• protective cells like the natural killer or NK cells, i.e. white blood cells that destroy harmful invaders.

Women tend to have a stronger overall innate immune response, which is probably why they often suffer less than men when it comes to colds.

The adaptive immune system is a more sophisticated system, composed of highly specialized cells and processes, which kick in when the innate immune system is overcome. The adaptive immune system helps us fight infections by destroying bacteria and viruses and preventing them from colonizing.

T and B cells are specialized white blood cells, which have a kind of memory. This enables them to “recognize” a specific disease, and mobilize effectively to fight against it. This is what we mean when we talk about “building immunity.” The reason children catch viruses more often than adults is because they haven’t had as much exposure to diseases so their adaptive immune system is less mature.


How Exercise Affects the Immune System

A structured workout routine – one where you’re breathing heavily, sweating, working hard and feeling some discomfort – awakens a stress response in the body. When we’re healthy, our bodies can easily adapt to this stress. Over time, this progressive adaptation is precisely what makes us fitter and stronger. However, when we’re ill, the stress of a vigorous workout can be more than our immune system can handle.

For those in good shape, non-strenuous exercise with minimal heart rate elevation, e.g. Pilates, walking, going for a leisurely bike ride, gardening and T’ai Chi, isn’t intense enough to create serious immune-compromising stress on the body. In fact it’s been shown to boost immunity.

Scientific research on exercise habits and influenza found:

• People who never exercised got ill quite often.
• People who exercised between once a month and three times a week did the best.
• People who exercised more than four times a week got sick most often.

In other words, being sedentary or exercising too much can lower immunity, whereas somewhere in the middle can actually improve immunity.

La Promessa by Matteo Pugliese

The Role of Stress

Exercise isn’t the only factor affecting the immune system. Stress plays a big role too. Here are the different stressors a person might face on any given day:

• Physical stress – playing sport, physical labour, infection, etc.
• Psychological stress – relationships, career, financial, etc.
• Environmental stress – hot, cold, dark, light, pollution, noise, altitude, etc.
• Lifestyle stress – diet, alcohol, smoking, hygiene, etc.

Stress affects hormone levels, which can result in chronic changes to the immune system. So, if you’re angry, worried, or scared every day for weeks, months or even years at a time, your immunity is being compromised and you’re more likely to become ill.

If you’re unwell and fighting an infection, your immune system is under stress. If you then include the additional stress of prolonged vigorous exercise, you might overload yourself, which is likely to make you even more unwell.

Sudden increases in exercise volume and/or intensity may also create additional stress, potentially allowing another virus or bacteria to take hold, resulting in further ill health. This seems to work the opposite way too, with chronic infections potentially being a sign of overtraining.

Other Factors Affecting Immunity

Besides stress, there are a number of other factors that can affect our immunity, and these combined with excessive exercise may increase the likelihood of us falling ill:

• Age: Our innate immune response works progressively less well as we get older. However, staying physically active and eating a nutritious diet can offset many of these changes.

• Gender: Menstrual phase and oral contraceptive use may influence how the immune system responds to exercise. Oestrogens generally enhance immunity while androgens can suppress it. This may explain why women tend to do better with colds than men.

• Sleep: Poor quality sleep and/or prolonged sleep deprivation jeopardize immune function.



Based on the above findings, potentially helpful activities to do when you’re under the weather are walking, Pilates, jogging, swimming, cycling, Qi gong, T’ai Chi and yoga. All of these activities are low intensity and involve minimal heart rate elevation. Ideally they should be done outdoors in mild temperatures and fresh air. Inside is fine though if you can’t get outside.

Activities to avoid when you’re feeling unwell are heavy strength training, endurance training, high intensity interval training, sprinting or power activities, team sports and exercise in extreme temperatures.

If you feel healthy and want to avoid becoming ill, try and stay moderately active most days of the week. If you take part in high intensity workouts, be sure to allow enough time to rest and recover. In addition, try to manage extreme variations in stress levels, get plenty of sleep, and wash your hands.

If you are already feeling unwell, let the symptoms be your guide as to how much to exercise. With a cold or sore throat (no fever or body aches and pains), low intensity exercise should help your recovery. Vigorous activity, no matter how long in duration is best avoided. If you have a systemic illness with a fever, elevated heart rate, fatigue, vomiting, diarrhoea, muscle and joint pain or weakness, and enlarged lymph nodes, you’re advised to just rest.

When you start to feel better, ease back into exercise in proportion to the length of time you were unwell, i.e. if you were sick for three days, take three days to ease back in.

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