by Don Heatrick

Like many others, I used to believe that hard training left your immune system temporarily at a deficit, leaving an “open window” where you’re more likely to pick up an infection.

Lots of previous research assumed this, and that’s where I’d got it from….

But it’s a myth.

This video explains why this myth pervades, what the truth really is, and what you can do to make sure your immune system is fully operational when an infection comes knocking.

Recent research (published in 2020) shows that regular bouts of moderate to vigorous intensity exercise benefit the normal functioning of the immune system, and reduces the risk of respiratory infection and some cancers.

Let me lead you though a great summary image and then round up your action steps.

R. J. Simpson et al., “Can exercise affect immune function to increase susceptibility to infection?,” Exerc. Immunol. Rev., vol. 26, pp. 8–22, 2020.

ABC – Athletes competing at mass sporting events, and spectators,  are exposed to an increase risk of infection… it’s effectively the opposite of social distancing.

D – The assumed markers of immune competency in saliva used in previous research varies profoundly between different individuals, and even within the same person – due to oral health, psychological stress levels, sleep, time of the day, and even seasonal changes.

E – Non-exercise factors influence infection risk, including poor sleep quality and quantity, psychological stress, inadequate nutrition, extreme environmental conditions, air travel (particularly across multiple time zones) and genetic “snip” variations in critical immune defence genes.

F – While there is an observed drop in the normal number of lymphocytes (white blood cells) in the blood after high intensity or prolonged exercise, this biomarker doesn’t support the 1990’s concept of an “open window” where the immune system is compromised and vulnerable to infection.

Current understanding is this biomarker reflects a redistribution of lymphocytes after exercise from the blood to other tissues in the body (such as lungs, parts of the small intestine, bone marrow, and skin) for immune-surveillance (detecting and destroying virally infected and abnormal cells in the body).

So research shows that even vigorous exercise benefits your immune system and reduces your risk of infection.

The resulting increased exchange of immune cells between the blood and tissues with each bout of exercise likely contributes to enhanced immune “surveillance”, improved health and lower risk of illness.

It’s a myth that training temporarily lays the immune system low (known as “open window” theory), putting us at increased risk of infection after a workout.

Factors such as stress, sleep, nutrition, inappropriately timed sleep and wake, misaligned sleep/wake and feeding rhythms, infection/vaccination history, and underlying medical conditions could directly impact or contribute to impaired immunity and infection risk, particularly in situations when infection exposure is more likely.

The primary risk factor for infections is exposure.

Your immune system performs best when its not exposed to environmental sabotage, and when bolstered by healthy-living strategies such as:

  • Don’t smoke
  • Eat a diet high in fruits and vegetables
  • Exercise regularly
  • Maintain a healthy weight
  • If you drink alcohol, drink only in moderation
  • Get adequate sleep
  • Take steps to avoid infection, such as washing your hands frequently – and right now, social distancing
  • Try to minimise stress – develop emotional intelligence and learn to meditate etc.

And I’d add to this that exercise should still be progressive and provide enough overload to result in fitness adaptations.

This means overloading the combination of intensity (such as weight lifted, or heart rate achieved) along with the volume (such as exercises sets and reps, or minutes duration), should be “developmental”, and not “maximal”.

You just need to tip over the threshold that makes you fitter, stronger, more powerful, or faster. As always, minimal dose is the objective. There’s no need to completely wipe yourself out to improve. Train smart.

All this is relevant before you pick up the COVID-19 virus. If you become infected, even with mild symptoms, rest, don’t train. Prioritise recovery.

Once you’ve fully recovered, follow the points I made in the previous video

  • Progressively target aerobic capacity and aerobic power to restore your damaged lung capacity…
  • Resume strength and power training with minimal interruption!

But right now, observe those healthy living strategies, and keep training with a clear conscience.

Don Heatrick

Founder of Heatrick Strength and Conditioning

Don Heatrick is a family man from the UK, former mechanical design engineer, European Muay Thai silver medallist, former pro Thai boxer (ranked 4th in UK while aged 40-years), a Muay Thai coach, podcast host, and the go-to expert on Muay Thai performance training with over 25 years of coaching experience.

Don helps ambitious fighters and coaches take their game to the next level by bridging the gap between Strength & Conditioning, Performance Science, and Muay Thai.

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