Running While Sick: When to Train and When to Rest

We runners can be disciplined to a fault. We run through rain, snow, heat, and humidity because if you waited for perfect weather, you would rarely ever actually run. However, that “get-it-done-no-matter-what” logic can be stretched to other circumstances and drive runners to push through illness and run when sick. Is it okay to go running while sick?

Running builds a strong immune system, but that doesn’t make you completely immune to catching the cold, flu, or stomach bug. Especially if you are training hard or recently raced, you may have slight immunosuppression. Illness does not take your training plan into consideration. 

Runners are not by nature lazy people and the idea of skipping a run to spend extra time resting in bed is seriously unappealing. It’s hard enough to miss a run during the off-season, but it can be even harder to make the appropriate decision of whether or not to skip a run when you get sick during an important training cycle and are approaching a goal race. 

It can require more discipline to listen to your body and give it rest when needed than to go out for a run. In the era of Strava and Instagram, we are quick to praise those who run through illness or quickly after surgery. However, running when sick can be downright unhealthy. 

Rest is Best When Sick

A good rule of thumb is that if you feel sick and are asking the question of you should run, then you are best just resting. You will not lose fitness in the time it takes to recover from a cold or flu. However, you will quicken your recovery by resting. 

Can You Run with a Cold?

Running with a cold (in the acute days of illness) can be done, but it is generally still recommended to rest. Rest is recommended if you have a cough or sore throat. If it’s mild congestion, it may be okay to do short, easy runs. However, if you run and feel worse after the run, then rest is encouraged until you recover. (More on running with a cold in this article.)

Once the worst days are over, it is generally okay to run through lingering nasal congestion. You may feel best if you start back with a couple short, easy runs, depending on the length and severity of your cold.

Can You Run with Covid or the Flu?

For any illness that involves the pulmonary system (flu, Covid-19, bronchitis, etc), you will want to rest until your symptoms resolve – and perhaps a bit longer. The combination of respiratory system inflammation, fever, dehydration, and fatigue will make exercise feel bad – and make it risky to exercise.

Some viruses such as the flu may increase your risk of myocarditis, particularly in susceptible populations. Any cardiac-related symptoms (chest pain, shortness of breath, heart palpitations) should be evaluated by a doctor before you resume running. If you experienced these when you started running after illness, stop and see your doctor.

Both the flu and Covid-19 have an increased risk of post-viral fatigue. Many athletes experience weeks of feeling tired during exercise and unable to perform at their previous capacity. For this reason, it’s generally recommended that you take a week of shorter, easy runs after having the flu or Covid. If you need a longer, slower build back, take it – it’s better to build back slowly than deal with long-term fatigue. (For more on returning back to running after Covid, read here.)

Can You Run with a Stomach Virus?

If you have a gastrointestinal illness with vomiting and/or diarrhea, you should rest. Stomach viruses can be extremely dehydrating, whether you are losing fluids through vomiting or diarrhea. This dehydration can be dangerous while exercising – and at the very least, you will feel like hot garbage if you try to run.

You will want to ensure you are able to keep down food and fluids before you resume running. Once you can tolerate fluids, begin rehydrating with electrolytes. The goal is to rehydrate before resuming any exercise.

When you are able to start running again, begin with a short easy run to see how you feel.

Can You Run with a Fever?

Whether or not you abide by the “below the neck rule,” you should not run if you have a fever of 99 degrees Fahrenheit or above. Your core temperature increases during a run. If you run with a fever, you will cause your body temperature to increase even more. This can suppress your immune function and delay healing. Your heart pumps harder when your body temperature is increased, in an attempt to cool down. Because of this, you put your heart under greater strain when running with a fever. 

It is recommended to rest until your fever as been gone for approximately 24 hours. Once you are able to run, resume with a short, easy run first to test how you feel.

Training Modifications for Running When Sick

If you have a head cold and choose to run when sick, do not make this the week that you increase your mileage or do a hard interval workout – even if your training plan calls for it. Running for longer than 90 minutes or doing a hard speed workout stresses your immune system. If your body is already fighting illness, then you are only going to risk prolonging or exacerbating your illness. 

Opt for easy effort runs of 30-45 minutes in duration. Do not expect yourself to hit the same paces as you normally do when healthy. If it helps, run by time and leave the GPS watch at home, so you are not tempted to push too hard. 

If you miss a few training days, do not try to make them up by cramming more mileage or skipping a rest day. Simply resume your training plan as is, with the modification of having your first day back being an easy day. 

Running in the dry and cold conditions of winter can worsen irritation of the nasal passages and mouth. Running in extreme heat can raise your core temperature and expend extra energy. If you choose run while sick, take the impacts of these conditions into consideration. If you suffer from seasonal allergies, be cautious about running outside to avoid allergens worsening your head cold symptoms. 

Most of all, you are better off taking a couple of days off to let your body properly recover. This is far better than prolonging your recovery period or affecting your health and training down the road. Err on the side of caution and treat your body well. You will not lose fitness in just a few days off of running.

Can Running Make You Sick?

Generally speaking, exercise has a positive effect on the immune system. However, it’s not a direct dose-response relationship. Too much exercise does not translate to a stronger immune system. Instead, overtraining and low energy availability (LEA) can result in suppressed immune function.

Overtraining and low energy availability both alter stress hormone release. When combined with other variables such as poor sleep, the changes in stress hormones impair immune function. Athletes who experience overtraining and LEA are more likely to be sick more often

If you are sick all the time, it’s worth assessing your training for signs of overtraining and/or low energy availability:

• Do you have regular menstrual periods (if female) and a regular libido (for you)?
• Are you frequently sore or injured in training?
• Do you feel slower and weaker in workouts?
• Is your heart rate higher during exercise?
• Are you tired most of the time?

If you are concerned that overtraining and/or low energy availability are causing you to be sick all the time, it is encouraged to reach out to a running coach (for overtraining) or registered dietitian (for LEA). You will likely want to scale back to your training load while also increasing your energy intake.

How Can Runners Prevent Getting Sick?

Illness is inevitable – especially if you work in an office, travel often, or have a school-aged child. However, you can implement certain measures to reduce the duration and severity of illness. 

Eat Enough for Your Training Load

As discussed above, low energy availability can contribute to frequent illnesses and infections. Low energy availability is complex – it can be unintentional for many athletes. If you notice you are sick often, be deliberate in eating more total calories and carbohydrates, following guidelines such as these. If in doubt or if you have a history of disordered eating, it is advised to work with a sports dietitian. 

Supplement Deliberately

Many “immunity-boosting” supplements are expensive without any real benefits. However, research does demonstrate moderate effects for a few supplements. A 2019 review in Sports Medicine noted that vitamin C, vitamin D, and probiotics all may reduce the incidence, duration, and severity of illness.

 Importantly, you need the correct dose of supplements to benefit from increased immune tolerance. Vitamin C is recommended in doses of 250-1000 mg. Vitamin D is recommended in the range of 1000-4000 IU, depending on the athlete’s vitamin D levels. 

As with any supplement, choose from reputable, third-party tested brands and consult with your doctor or RD before starting. (Read more here on how to choose safe supplements.)

Sleep Enough

Without adequate sleep, your risk of illness increases – even if you are doing everything else right. Ideally, athletes should aim for 7-9 hours of sleep per night. If you struggle to meet this, simply focus on increasing your sleep needs – even an extra half hour helps.