For years, research has shown that regular physical activity and exercise reduces the risk for developing many chronic diseases in older age, including communicable diseases such as viral/bacterial infections, as well as non-communicable diseases such as cancer, diabetes and chronic inflammation.

But how is it that we actually develop our immune system through performing exercise and how exactly can movement be medicine for those at risk of immune compromise?

One of the largest influences exercise can have on our immune system is through regulating inflammation and inflammatory processes. The mechanism behind this improvement is not entirely understood, but some of the factors considered are the increased production of free radicals, Natural Killer Cells and T- Cells with decreases in pro-inflammatory cytokines and adipose/fat tissue (which is a mediator of inflammation itself).

As the human body ages, many of bodies organ systems will begin ot deteriorate in some way, including the immune system. This process is thought to involve a chronic low-grade inflammation that may contribute to a range of diseases and ailments – sometime referred to as ‘inflammaging’.

Despite normal age associated declines in fitness and immune competency, aging does not appear to negatively affect the immunological benefits of exercise. Furthermore, regular exercise participation across the lifespan is quite effective at inducing immune benefits, even in older age.

More physically conditioned elderly humans seem to have a better-preserved immune system, although it isn’t 100% clear whether this is entirely the result of training or other lifestyle-related factors linked with physically active behaviour.

So, what happens when the body undertakes intense exercise?

The normal response to physical exertion is an elevation in stress hormones, such as adrenaline and cortisol, that are important for allowing

- Conversion of stored glycogen in our muscles and liver into glucose for energy,

- Increased blood flow away from our digestive organs towards our working muscles

- Enhanced nervous system reactivity and alertness

- A range of other physiological changes associated with the ‘fight or flight’ adrenal response due to enhanced drive to the sympathetic nervous system

These sorts of natural reactions are the type of thing you can imagine being incredibly useful in a true fight or flight situation (e.g. running away from true dangerous) and could ultimately lead to your survival.

Along with these responses to physical exertion and stress hormone elevation, are changes to multiple cell pathways that are also involved with inflammation and immune function.

Optimal Dosage?

Although this maximum intensity exertion isn’t what all exercise looks like, similar physiological responses occur at a lower level with more moderate intensity physical activity. In general, acute exercise bouts of moderate duration (< 60 min) and intensity (< 60% VO2max) are less stressful to the immune system than prolonged, higher intensity sessions.

A study in university students showed that after 6 weeks of moderate intensity exercise significant improvements in markers of inflammation (IL6 and TNF-α) along with other depressive symptoms and mental health measures. Although HIIT improved mental health, even after 6 weeks IL6 and TNF-α were elevated more than those who did no exercise at all.

Other research has shown that after 4 weeks of HIIT, the inflammatory response to an acute bout of intense exercise can be reduced, which may explain why people doing high intensity exercise aren’t consistently getting sick – and in fact can often be less prone to illness.

This goes to show how adaptable the body can be but is also a reminder that the acute effects of strenuous exercise do raise inflammatory markers and it does take time to develop tolerance to this level of stress/intensity.

This adaptability to stress is really the cornerstone of many of the chronic health benefits of being physically active. Specifically, long-term adaptations to inflammatory stimulus and stress hormone fluctuation as well as reductions in fat mass all contribute to enhanced immune function over time. These factors also delay the aging of the immune system and allow for heightened immunity

Recently, there has been debate over whether the ‘window of threat’ poses any real threat to immunity. Based on everything I’ve said above about T Cells Natural Killer Cells and inflammation, it seems clear there are some important changes that exercise elicits in the body.

While there is strong evidence showing enhancement of the cellular functions responsible for immune system function during exercise. The so called ‘threat’ appears to be present in the short period after exercise (1-6 hours, and to a lesser extent ~ 24 hours) - where there is an acute spike in inflammatory markers and drastic drop in certain immune cells in response to prolonged elevation of stress hormones.

A more critical look at the evidence is now leaning further toward this simply being the human body heightening its surveillance systems and displaying a hyper-vigilance to scavenge viral and bacterial infection.

What does the research actually say?

It’s hard to say – but like with all research, it’s worthwhile taking information with a pinch of salt and have someone in the field read the fine print to get an accurate interpretation of what the research is saying.

Study findings, around cellular reactions to exercise (much like the information I’ve shared above) could lead us to think that regular levels of exercise may be continuously blunting our immune system and opening us up to a range of infections – when this really isn’t the case.

While it is true that there are large, temporary, fluctuations in immune cells with intense exercise - this is very unlikely to significantly affect the average person with generally good health.

A lot of the studies in this area that measure the amount of people actually getting sick and developing infections tend to look at ultra-endurance performances and elite level athletes – although there is research to show most Olympic athletes are equally as prone to getting sick as the average person.

Nonetheless, in those pursuing high level competition/training demands, there are greater stresses on the body as a whole that may increase risk for illness. Risk factors that are known to further elevate this risk include:

- Engaging in unusually intensive training periods with large fluctuations,

- International travel across several time zones,

- Participation in competitive events especially during the winter,

- Lack of sleep,

- High levels of depression or anxiety

- Low dietary energy intake

In chronically diseased individuals, this is obviously a different story. Having a baseline of compromised immunity on top of changing physiology (due to illness and/or medications) changes a few things – but with the right guidance and appropriately prescribed exercise, most of the benefits are still achievable.

In fact, benefits to the immune system are one of the most potent effects of movement as medicine in preventing and managing chronic disease.

In healthy individuals, it seems that regular exercise at the appropriate dosage has profound benefits to the human immune system, while the evidence behind an important acute immunosuppressive effect after exercise is not quite as convincing.

What does this mean for the physically active individual in this day and age, where infection control and risk mitigation are at the forefront of our minds?

Exercise and movement is still medicine, one that is well established to promote good health and immunity. And to maintain the benefits of this medicine, we should still be taking it regularly.

“We all understand that exercise supports our physical health, however, during times of crisis such as this, it is the first activity we tend to ignore. Being active can not only keep us healthy, it can also help us fight off infection.
Exercise is also unique in that it can boost our mental health, and during this anxious time it’s more important than ever to keep our minds clear and focused” - ESSA CEO

The difficulties and differences now faced with social distancing restrictions shouldn’t negatively affect our health further than it already does. But to do this with the best safety of ourselves and others in mind it is crucial that we stay vigilant with social distancing and hygiene control (where possible) both indoors and outdoors, particularly when exercising.

The reason this is important is due to the nature of physical exercise being an ‘Aerosol Generating Procedure’ (AGP) or something that makes you breath air (and the particles within it), more heavily into the atmosphere. While there is some conflicting information around specifics of COVID19 transmission and how social distancing best influences infection risk – we do know that exercising increases the capacity of any droplet or airborne particle to project in the air through heavy breathing.

While health agencies have done a great job at informing he public that droplet transmission is the primary method of infection - from the perspective of a clinician who has worked in Respiratory care within Intensive Care/Critical Care Units unspoken truth about these types of activities (AGPs) is that following any AGP (heavy breathing or inducing cough) in any suspected COVID19 case - it’s usually necessary to follow Airborne particle precautions in that room/space for at least 30 minutes after (ie the mask/face shield and all !).

Yes - this information specifically applies to managing COVID19 cases but the science behind transmission and potential risk is no different.

What should we do about it?

The likely answer is nothing special, apart from be mindful of the fact that usual social distancing guidelines are generally based on the assumption of being at rest, where heavy breathing and sweating are not as common.

Do we need to be wearing a face shield when entering a public gym - unlikely. Do we need to wear face masks when going for a walk on our personal treadmill - also unlikely.

In reality our approach should be minimally different to what we should normally be doing if at all unwell or when we start noticing the early sign of seasonal sickness/allergies. By isolating ourself from exposure to other individuals when we have any symptoms of illness - if not for the sake of preventing further pandemic outbreaks but at least in courtesy for others’ health.

But while infection control is a hot topic, its worthwhile having some clarity around the risk (or inherent lack of) of immune system compromise with regular, sensible, appropriately prescribed exercise.

Exercise & Sports Science Australia’s (ESSA) Top Tips:

• Be aware of your own health. If you do have symptoms of COVID-19, please follow the Department of Health’sdirections and refrain from exercise.
• If you are nervous about attending a physical gym or exercise facility, contact the provider to understand what measures are in place for hygiene.
• If you are in self-isolation, this doesn’t not mean you have to stop exercising. In fact, this is a great time to move more and keep your body and mind healthy.
• Trust an accredited exercise professional who has the expertise and education to help you stay fit and healthy, and can work with you based on your current health and existing conditions.

If you’d like more information on any of the information above or would like to get a better understanding of how movement can be used as medicine for you, keep an eye out for more content like this or get in touch for a personalised plan of action today.

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