by Michael Liberzon

Sick boy in bed with symptoms of fever

The benefits of aerobic training are many: from improved heart and lung health, to far lower rates of obesity and related disorders, to better bone and joint health. Even the immune system tends to perform better in active individuals – up to a point.

The plot below represents an approximate relationship between immune system impairment (represented here by the ‘risk of infection’) and exercise volume (that’s both duration AND intensity).

Photo: theconversation.com

Photo: theconversation.com

When we do nothing but Netflix, our immune system is about average. With a mild to moderate increase in exercise, the immune response improves (shown as a dip in the risk of infection). Yet at high training volume, the risk of infection increases rapidly. At that load, our immune systems are substantially compromised.

Sick already?

So with this in mind, we can tackle the subject of training when it’s too late – when we are already ill. It’s topical. As the overabundance of decongestant and cough suppressant ads on the TV are telling me: It’s cold and flu season.

ASIDE: The advice below applies to mild respiratory infections only. As always it is best to consult your health care professional.

The general prescription is actually fairly straightforward and depends on the severity of the illness and symptoms.

CASE 1: fever above 38 C OR chest congestion OR serious cough

Woman measuring her temperature

  • Avoid all exercise
  • Rest, appropriate medication, fluids, and good food are your best path to recovery

CASE 2: no CASE 1 symptoms, but nasal congestion AND / OR sore throat AND / OR mild headache

man is sick and sneezing with blue background, asian

  • Easy exercise only
    • Nothing exceeding Z2 (HR / power / pace) or nothing that feels hard
  • No long sessions
    • Nothing longer than 45 minutes

It’s important to note that everyone is unique, and our response to illness and training is greatly varied. These difference are both genetic and environmental. Sleep and nutrition, for example, are key environmental factors that must be considered. If you’re a parent of young children – as this coach is – and are not getting optimal sleep on good days, you may want to be more conservative with how much you train when ill. Adding the extra strain of training when battling an infection AND poor sleep is unwise.

Returning to activity

Depending on the duration of the illness, it may be necessary to ease back into activity. Protracted, severe illness can degrade fitness, so jumping back into the pre-illness training schedule as if nothing had happened is not a good idea. It makes good training sense to easy back to ‘normal’ training duration and intensity over the course of a week or two.

Happy (and healthy!) training.

Michael is an NCCP trained triathlon coach, certified personal trainer, and kettlebell instructor. His degree in mechanical engineering supports his evidence-based approach to coaching.

Michael is also the owner and head coach of the X3 Training Lab in Toronto. 


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