The relationship between exercise and the immune systems is intensely complex with many moving variables. Exercise generally improves the immune system. The more exercise done, and the more regularly, the more the immune system is boosted. However, there is always a tipping point. Athletes are often pushed into longer bouts of exercise, and/or more intense training. This goes as well for some “general exercisers” who don’t consider themselves “athletes,” but will grind out intense workouts that are on par for athletes. I have seen this with recreational marathon runners, obstacle course racers, and people going “all in” for 30-, 60-, or 90-day challenges with their gyms or trainers. They may not think of themselves as “athletes,” yet they are putting in long hours and hard sessions, sometimes multiple workouts per day. Anyone working out intensely for over 45 minutes, more than 4 times a week, I would argue should call themselves at least “recreational athletes.”
In addition to increases in bodily pains and risk of injury, it’s not uncommon to see upper respiratory illnesses (URIs, ie: coughing, congestion, sinus drainage) and upper respiratory tract infections (URTIs, ie: common cold and influenza) in recreational and elite athletes. In fact, URTIs are suggested to be the most common type of infection in the athletic population. But if exercise boosts the immune system, why is this happening?
Some exercise is good.
Indeed, some movement is good. Quality and consistent movement is great. Studies show that “moderately active” living poses greater resistance to pathogens by boosting the immune system surveillance of the body. “Moderate exercise” is somewhat subjective, but tends to range around 30 minutes of movement at 60-75% intensity, 4-6 days a week.
Animal studies showed that exercising for 20-30 minutes right before being exposed to a virus decreased morbidity and mortality from it, even if it was just a single session of exercise and the mouse had been sedentary outside of that bout. That lead to suggestions that exercising before traveling on an airplane, or going into other high-crowd areas, could help prevent illness.
Now, extend that exercise from a single session to a routine: research that looked at 12-15 weeks of moderate exercise saw that incidence and duration of URTIs was significantly lowered compared to sedentary individuals. Longer duration of the routine meant better adaptations in the immune system.
Acute Exercise, or just getting started
Some of you have heard me say over and over that “stress causes inflammation and health problems” and expand that ‘stress’ can mean emotional, mental, chemical, or physical. In this case, we’re looking at the physical stress of exercise, which also elevates cortisol (chemical stress.) You are tearing muscles, straining lungs, and working your heart. As many people who have “fallen off the wagon” of exercise can attest, getting back into the workout routine is the most physically painful part, compared to a few weeks in after your body has adapted. This is called the “General Adaptation Syndrome” (GAS) where the body isn’t used to the physical stress. Every exercise stress applied results in specific biochemical, neurological, and mechanical adaptions in the body. The first 2-3 weeks of this are called the “Alarm Phase” or “Shock Phase”, and typically muscle and joint pain, fatigue, and discomfort are all more extreme at this time.
Training load or volume alone does not give full information on the level of stress that an athlete (and their immune system) is under. Indeed, the way training in distributed or periodized is of key important also. Periodization is breaking down a training plan into smaller, progressive stages to build safely over several weeks or months. Rapid changes in training load (i.e., increasing too quickly) was a better predictor of URI risk than total load alone. This shows that it’s not just the amount of training, but jumping in too quickly can be detrimental to the immune system.
This is different than someone who has adapted to longer or more intense levels of exercise over time. Much like their bodies are adapted to recover faster between training sessions, the immune system also learned to rebound more rapidly.
Can it be too much?
That tipping point of “too much” strenuous and/or prolonged bouts of exercise can temporarily reduce the immune system (“exercise-induced immunodepression”) for a few hours to a few days, depending on the nature of the exercise and the health status of the person, as well as the rest time before the next round of exercise. This immunodepressed state is the time the individual is at higher risk of contracting a URI or URTI.
The less adapted to high frequency/intensity/duration of training, the higher the stress levels spike, and the lower the immune system plummets after. What goes up, must come down. But in time, you can taper the peak and the drop.
After Intense, Acute Exercise
How many people have had the experience of going through a prolonged period of intense stress (semester at school, large work projects, extended home situation) and when this intense period finally eases up, they get sick? It’s like the immune system fires on all cylinders to help get you through the stressful time, and then it rests when you do. Likewise, this can be seen in athletes.
A research review by Walsh et al. suggested that athletes most often would report URTIs either during the high-intensity and tapering period prior to competition (e.g., swimming, team sports) or in the period following competition (e.g., long distance running). Essentially, the times of illness were more common during the high intensity period (high stress and inflammation in the body), or about 1-2 weeks after as the body gets to rest (incubation period.)
Nieman et al reviewed marathon runners and respiratory illness. “Taking into account other factors influencing risk of URI (age, stress levels, and illness at home), the likelihood of URI was doubled in those who ran >96 km compared to those who ran 32 km as part of their weekly training programmes leading up to the event.”
It is interesting to note, as well, that some studies then went on to break down infectious versus non-infectious URIs. Meaning, sometimes the URI or URTI is based on a pathogenic infection (ie: bacteria, virus), and other times there is some other reason for feeling sick that didn’t have to do with a microbe. Reports show it can be due to inhaled pollutants or allergies, chlorine vapors for swimmers, cold and dry air; age; sleep quality; and more. These factors are less related to the immune system directly than they are related to inflammation. Once again, lifestyle factors pop up as important keys for staying healthy and keeping optimal respiratory functions. Keeping inflammation low before exercising may help reduce the over-inflammatory state brought on by intense exercise, and protect respiratory health.
So… What is the “Goldilocks” level? Not too little, but not too much too fast.
The J-Curve versus the S-Curve
The J-curve model suggests that an individual involved in regular moderate exercise is less likely to contract a URTI compared to a sedentary individual, but prolonged high-intensity exercise or periods of strenuous exercise training are associated with an above-average risk of a URTI. Like so:
The J-curves are the bold purple and red lines, showing that infection risk is average with a sedentary life. Then the immune system gets a boost, thus reducing infection risk, as a person moves into active or moderate exercise. But following that curve then leads to a split in research. At first, heavy or prolonged training seems to have a rebound effect, causing infection risk to go above average – but not always!
It seems that some athletes can reach “elite” status, and as their body adapts to these bouts of exercise, the curve instead moves into an S-curve and infection risk normalizes again, and the immune system can recover, coming back to average as the athlete-in-training adapts.
Lifestyle and the Elite Athlete
There have been some that suggest a prerequisite to achieving “elite” athlete status is an immune system which can withstand the strenuous nature of training and competition. Essentially, one cannot push to elite levels of training if the immune system cannot keep up.
And as past articles and posts have shown, there are ways you can help enhance your immune system through lifestyle, diet, and supplements.
Again, let’s think about that Alarm Phase. If the body is not used to the intense exercise, there is more inflammation and damage to the muscle fibers and tissues. Elite athletes, however, are trained better for this stress on the body. Likewise, elite athletes are usually tackling many aspects of their lifestyle to optimize their performance: sleeping well; properly fueling before, during, and after workouts; keeping a focused mindset; drinking plenty of water; stretching and recovering. They often tap into additional resources for support: keeping up on the latest in sport science, seeking out medical professionals, getting advice from nutrition professionals, working with trainers, and more. Genes may play a role, but this support team shows that managing other aspects is important and can help in prevention.
In the complexity of the immune system, the research does note that humans have demonstrated lower resistance to URTI when there is weakness or problems with other life stressors such as dietary deficiencies, psychological stress, sleep disturbance. In fact, the presence of nearly any of these other risk factors will cause a weaker immune response, and increase the risk of illness following prolonged exercise.
Could these lifestyle behaviors be another layer of protection for athletes and people looking to begin exercising, or boost their current training? Absolutely.
Athletes and individuals involved in heavy training programs and/or prolonged bouts of exercise appear to have an increased risk of contracting URIs. This is likely related to regular acute (and possibly chronic) periods of exercise-induced immunodepression. Regular moderate exercise, on the other hand, appears to have the opposite effect and reduces infection risk. So if you are looking to boost your training, pair gradual increases in exercise with healthy lifestyle habits to keep your infection risk as low as possible.
WHAT SHOULD I DO, ESPECIALLY DURING THIS CORONAVIRUS CRISIS?
- Move at least 30 minutes, 4-6 times per week. If you want to go above that, do so mindfully. There are benefits, but you want to give your body time to rest and adapt to an increased load. It is tempting for some who are finally getting their new quarantine routines down to want to double up workouts, or go for longer runs than they normally have time for. Be mindful, and gradually work your way up. This will reduce your risk of injury and illness.
- Be sure to warm up and cool down appropriately.
- Recover well. Stretch and foam roll. Rest and sleep to give your body enough time to recover between bouts of exercise.
- Learn about proper form, get proper shoes, and ensure all other ergonomic aspects of exercise are optimized to reduce physical stress and injury.
- Work with a trainer who knows how to periodize properly and can create workout plans that challenge you without shocking your system
- Get a quality 7-8 hours of sleep each night
- Fuel properly before, during, and after workouts to enhance the workout efforts as well as maximize post-workout recovery.
- Nourish your body throughout the rest of the day as well to feed your cells with antioxidants, anti-inflammatories, vitamins, minerals, and more. Again, part of the risk of URI is the inflammation that the physical stress causes on the body, within the tissues and lungs as well as the muscles. Consider joining the Wolf program.
- Work with a dietitian/nutritionist to personalize your food and supplement needs.
Ready to take your exercise up safely, and protect your health? I invite you to schedule a complimentary New Client call with me, so we can discuss possible best options for you and your fitness!
Cohen, S., Tyrrell, D.A., Smith, A.P., 1991. Psychological stress and susceptibility to the common cold. N. Engl. J. Med. 325, 606-612.
Cohen, S., Doyle, W.J., et all, 2009. Sleep habits and susceptibility to the common cold. Arch. Intern. Med. 169, 62-67.
Jones, A.W., and Dvison, Glen. Exercise, Immunity, and Illness. Muscle Metabolism and Exercise Physiolog. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7149380/pdf/main.pdf Accessed 20th April, 2020.
McGill, E.A. & Montel, I.N. (Eds). 2017. NASM Essentials of Personal Fitness Training. 5th ed.
Nieman, D.C, et al. 1990. Infectious episodes in runners before and after the Los Angeles Marathon. J. Sports Med. Phys. Fitness 30, 316-328.
Walsh, N.P., et al. 2011. Position statement. Part one: immune function and exercise. Exerc. Immunol. Rev. 17, 6-63.