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1:54 My story of illness and exercise

4:31 Low back pain

8:16 Colds

11:36 Sauna use and colds

14:16 COVID

When you’re feeling under the weather, whether due to a cold, flu, or other minor illness, one question often arises: should you push through and stay active, or should you rest and let your body recover? The answer isn’t as straightforward as you might think. Let’s take a look at the evidence, break down some common misconceptions, and explore how you can make the best decision based on your own body and circumstances.

The Old Paradigm: Rest Is Best

For decades, conventional wisdom dictated that rest was essential for healing. Bed rest was often prescribed for conditions like acute back pain, and it was commonly believed that exercising when sick could worsen your symptoms or prolong the illness. In more serious chronic conditions, such as multiple sclerosis (MS), there was also concern that physical activity could exacerbate symptoms. Rest, it seemed, was a safe bet.

This approach wasn’t without logic. If you’ve torn a muscle, strained your back, or have a fever, wouldn’t it make sense to rest? But over the last 30 years, studies have challenged this blanket prescription for inactivity.

What the Evidence Says About Rest and Exercise

Let’s start with acute low back pain. As recently as the 1980s, the standard recommendation was to rest for a week after an episode of acute back pain. The idea was that inflammation would resolve with rest, allowing muscles and tissues to heal. However, a pivotal randomized clinical trial in 1986 turned this recommendation on its head. It compared a group that rested for a week with another that stayed active after just two days of rest. The results showed no significant difference between the groups in terms of pain or recovery. In fact, staying active had potential benefits, as prolonged rest could lead to muscle weakening and stiffness, which might worsen the condition over time. Today, the standard advice for back pain is to remain as active as possible, within the limits of pain.

When it comes to minor illnesses like the common cold, the science is equally enlightening. A fascinating study inoculated participants with the rhinovirus—the virus responsible for most colds—and then randomly assigned them to either an exercise group or a rest group. The exercise group engaged in moderate activity (70% of their maximum heart rate) every other day, while the rest group remained inactive. Over a 10-day period, the researchers found no significant difference in the severity or duration of cold symptoms between the two groups. This suggests that moderate exercise neither speeds up nor slows down recovery from a cold. However, it’s important to listen to your body; if you feel fatigued, pushing through might not be wise.

There is, however, a silver lining for exercise enthusiasts. Several clinical trials suggest that regular moderate exercise can reduce the risk of catching a cold in the first place. In one study, individuals who engaged in moderate physical activity experienced three and a half fewer days of cold symptoms compared to those who were sedentary. The takeaway? While exercise won’t necessarily help you recover faster, it might help you get sick less often.

Neck Check: A Useful Rule of Thumb?

One popular guideline for determining whether it’s safe to exercise while sick is the “neck check.” This suggests that if your symptoms are confined above the neck—such as a runny nose or sore throat—you’re generally safe to exercise. But if your symptoms are below the neck—such as chest congestion or body aches—it’s best to rest. Although this approach is widely endorsed, there’s little scientific evidence supporting it. The decision to exercise when sick should be more about how you feel overall rather than where your symptoms are located. If your body feels tired, it may be better to rest.

What About Fevers?

Exercise and fever don’t mix. A fever signifies that your body is fighting an infection, and pushing through with exercise can potentially worsen your condition. Some experts believe that exertion during a fever can increase the risk of complications, such as myocarditis (inflammation of the heart muscle). While evidence for this is mostly anecdotal, it’s better to err on the side of caution. When you have a fever, your body is already under stress, so give it the rest it needs to recover.COVID-19 and Exercise

Given the global experience with COVID-19, the question of whether to exercise during or after infection is particularly relevant. A study of over 800 individuals looked at the effects of physical activity during and after COVID-19 infection. It found that those who exercised regularly during their recovery experienced fewer long-term mental and neurological symptoms, such as fatigue and anxiety. While the evidence isn’t definitive, it suggests that moderate physical activity could be beneficial for recovery and may even reduce the risk of long COVID.

Impact of Short-Term Rest on Fitness

A common concern among athletes and fitness enthusiasts is that a short break due to illness will derail their hard-earned progress. Fortunately, studies show that a few days off won’t significantly affect fitness levels. Research has found that strength levels remain stable for up to three weeks without training, and aerobic fitness doesn’t begin to decline until around 12 days of inactivity. So, if you need to take a break for a week or so due to illness, rest assured that you won’t lose all your gains.

Chronic Illness and Exercise

The role of exercise in chronic illness has evolved significantly. For example, it was once feared that exercise could worsen conditions like multiple sclerosis (MS) by triggering symptom flare-ups. However, modern evidence suggests that regular physical activity is beneficial for individuals with MS, and the disease’s leading organizations now recommends 150 minutes of moderate exercise per week—the same as for the general population.

Final Thoughts: Listen to Your Body

In summary, the evidence suggests that moderate exercise is generally safe for minor illnesses like the common cold and might even reduce the risk of getting sick in the first place. However, if you’re feeling fatigued, have a fever, or are dealing with something more serious, rest may be the better option. Ultimately, the best advice is to listen to your body. If you feel well enough to move, go ahead and do so. If you feel exhausted, take it easy—you won’t lose your fitness by resting for a few days.