With everyone sharing equipment, breathing heavily, and dripping sweat, it's easy for a novel respiratory virus like COVID-19 to spread quickly in places like gyms and fitness centers. So once social distancing guidelines were put into place, they were some of the first businesses to close their doors—and rightfully so. But while it might feel like fitness gains are being forced to take a backseat, it's imperative to get the right amount of exercise when your immune system is in the hot seat. In fact, adequate exercise (paired with recovery) is one of the best things you can be doing to stay ahead of COVID-19.
Exercise can be key for supporting immunity against infectionExercise doesn't just keep your body physically fit—it keeps your immune system fit as well. When we exercise and lift weights, we cause small amounts of muscular and cellular stress, which initiates an inflammatory response to repair the damage. It's this process that allows us to build muscle over time. But this inflammatory response isn’t drastically different from that caused by an infection; it can also help fight off any infectious invaders that might be hitching a ride in the body.
Exercise has, therefore, shown to have an affect on our immune system fighter cells, our white blood cells (WBC). Both certain types of interval training and moderate-to-intense aerobic exercise can help optimize T lymphocytes (aka "T cells"), a type of WBC that fights viral and bacterial infections. In fact, several studies have shown that regular exercise, including moderate and high intensity interval training (HIIT), have been shown to decrease the frequency, severity and duration of respiratory infections. [2,3,4]
But, now more than ever, it's important to not overdo itSure, "overdoing it" might feel impossible without access to your typical equipment. But overcompensation for this change is a real risk, as too much training without adequate recovery can push your immune system over the edge, preventing it from fighting any oncoming infections. For all the evidence supporting regular exercise's beneficial effects on the immune system, there’s just as much showing that overdoing it has the opposite effect.
Those who participate in long aerobic bouts (such as marathons) or frequent HIIT without allowing for proper physical recovery are at greater risk for impaired immunity and increased frequency of upper respiratory tract infections (URTI).[5,6,7] But don’t worry—by recognizing the signs of overtraining and following some simple nutrition and lifestyle tips, you can help keep your immune system strong at a time when your body needs it most. If you want to know which symptoms mean you should absolutely skip a workout, read our blog on the topic.
What to look for to avoid training-related impaired immunityFor a lot of people right now, merely maintaining a normal training volume has become very difficult—and that’s perfectly OK! If you're unable to stick to your usual routine, use this time to focus on recovery, healing nagging injuries, and other areas of your life that may typically take the back seat to daily training. For others, extra free time may mean extra training time, resulting in even higher physical load than before. Either way, there are several blood and physiological biomarkers you can watch to monitor your balance of exercise and recovery and its impact on your immunity. Here are some that you should keep an eye on to make sure you don’t go overboard.
Commonly referred to as "the stress hormone," cortisol becomes elevated in times of heightened emotional and physical stress. We're in an emotionally stressful time, so we need to be careful not to pile excessive physical stress on top of it, which could cause cortisol levels to spike. And studies have shown that people who experience high levels of stress (accompanied with elevated levels of cortisol) are more likely to succumb to infections. You can read more about cortisol's relationship with respiratory infections in this blog.
Generally, with high levels of cortisol comes low levels of testosterone, particularly from intense training sessions. In fact, InsideTracker uses the testosterone:cortisol ratio as an indicator of overtraining in both men and women. But conversely, excessively high levels of testosterone can also impair immunity. Make sure your levels are optimized for proper immune function.
Long and intense training sessions can result in excessive muscle breakdown. And when muscle cells are destroyed, an enzyme called creatine kinase (CK) can leach into the bloodstream, making it detectable in a blood test. Therefore, your blood CK levels are an important indicator of muscle damage. If they're high, it means you're not taking enough time to recover after training sessions.
Two enzymes commonly found and produced in the liver can be used to indicate muscle damage. Similar to creatine kinase, ALT and AST are also found in muscle cells and can be a sign that you overdid it during a recent training session.
Resting heart rate
Your resting heart rate can be a great indicator of health status and overtraining. Just as it can increase immunity, regular exercise—and HIIT in particular—can significantly improve RHR.[13,14] Again, though, excessive training can have the opposite effect; overtraining can lead to an elevation in resting heart rate. And why does this matter? Those with chronically-high resting heart rates have presented elevated WBC and increased inflammation. Most smart watches continuously track your heart rate, making comparing changes over time quite easy. Alternatively, here's a reputable resource to help you check and monitor your resting heart rate.
Your immune system (and recovery) is most active during sleepArguably the best way to increase your body’s recovery and solidify your immune system is to get 7-8 quality hours of sleep every night! Lack of sleep inhibits your body’s ability to recover physically and can increase your susceptibility to viral infections, making quality sleep as important as ever. Quality sleep can reduce your risk of getting sick—it actually promotes a favorable environment for immune cell function and cytokine (inflammatory molecules) production, both of which peak during the night. And lastly, the activation of specific virus-fighting T cells is higher during sleep than when you’re awake. So while you're resting, your immune system is hard at work. Here's a good resource for improving your sleep quality.
Besides sleep, making sure that you are staying hydrated and eating nutritious, whole foods is key for supporting your immune system. Avoid processed foods that are high in fat and added sugar, and focus on adding foods like fruits that are high in antioxidants, carbs with high fiber content, and protein sources that also have omega-3 fatty acids. When it comes to supplementation, vitamins D and C and minerals like zinc have been shown to decrease susceptibility and severity of viral infections.[20,21,22] For a complete list of immunity-supporting supplements, check this blog out.
How to ensure your exercise is supporting immunity, not hindering it
- Exercise and physical activity are great ways to support a healthy immune system, but make sure you don’t over do it. When in doubt, stick to moderate-intensity work.
- Know which symptoms mandate a day off from exercise.
- Making sure you’re keeping your cortisol levels low and testosterone optimized to best prepare your immune system against infection.
- Check biomarkers like CK, ALT and AST to make sure you’re allowing for full recovery after your at-home training sessions.
- Monitoring your RHR is an easy way to assess your recovery and health on a daily basis.
- Prioritize 7-8 hours of quality sleep to keep your immune system in fighting shape.
- Focus on nutritious, whole foods and supplement with key vitamins and minerals that are scientifically proven to support immunity.
- Lastly, if you are sick, know when it’s time to completely avoid working out and let your body recover. Here’s a guide to know when it’s ok and more importantly, when it’s not ok to train if you’re feeling under the weather.