To Train, or Not To Train (when sick)

To Train, or Not To Train (when sick)

I’m sick for what feels like the fourteenth time this season. I blame my three year-old – the cutest disease vector I know. I blame this not-yet-spring climatic purgatory that seems to have no end. I blame my own impatience in getting back to hard training in response to the dread of my near race-ready fitness that I felt slipping away as I ‘rested’.

With all that, I feel it relevant to rehash a post I originally wrote for Triathlon Magazine Canada on the subject of illness and training.

Opinions espoused by click-bait ‘marathons kill’ articles notwithstanding, exercise is good for you.  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).

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.

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

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

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

CASE 2: no CASE1 symptoms, but nasal congestion AND / OR sore throat AND / OR mild headache

  • 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.

To be clear: The advice above applies to mild respiratory infections only. As always it is best to consult your health care professional.


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