How Cold Is Too Cold to Run?

Another polar vortex has drifted down over the country this week. Here on just the other side of Lake Michigan from Chicago, our wind chills will drop into the negative 40 Fahrenheit range. For even the heartiest of runners, the dangerously cold wind chills raise the question “how cold is too cold to run outside?”

If you ask runners this question, the answers will widely vary. I asked the question in my Instagram stories and received answers ranging from 40 degrees to “frostbitey cold.” I love running in 10 to 20-degree temperatures. Some runners refuse to run in anything below freezing. Other runners will claim that there’s no such thing as bad weather, just bad gear. But what about beyond preference? Is there actually a threshold at which it is physically unsafe to run? (As a note: all references to temperature in this post are in Fahrenheit unless otherwise noted.)

How Cold is Too Cold to Run?

The windchill matters as much as the actual temperature. There is a significant difference between 10 degrees and sunny with little wind and 10 degrees but overcast with 20mph winds. When looking at the conditions, always consider the wind chills.

In terms of performance, you cannot expect to run the same pace when the wind chills drop to zero Fahrenheit or below – even if you are properly dressed. In frigid conditions, your body prioritizes blood flow to your core in order to protect your vital organs. As a result, your extremities – including your working muscles – receive less blood flow and the blood vessels constrict. Without normal blood flow to your working muscles, you cannot expect to run like you would in milder temperatures.

Beyond performance, health concerns arise in frigid conditions. Sub-zero temperatures pose risks such as hypothermia and frostbite.

Hypothermia becomes a concern in negative temperatures. Hypothermia occurs when your core temperature dips below 95 degrees. In frigid sub-zero temperatures, the risk of hypothermia occurs within just 30 to 60 minutes – the average amount of time you would spend on a run. Wind chills reaching well below zero can increase the risk of hypothermia. The symptoms of hypothermia can range from extreme shivering and blue fingernails (in mild cases) to shallow breathing, exhaustion, confusion, loss of coordination, slurred speech, and a weak pulse. 

Frostbite poses another risk. The colder it is, the higher the risk; the risk of frostbite increases when the temperatures drop below minus 5 degrees Fahrenheit/-20 Celsius. Once the wind chill reaches below minus 16 degrees, frostbite on exposed skin can occur within 30 minutes. The colder it gets, the shorter amount of time it takes for frostbite to happen.

What I always consider in any aspect of running are the risks versus the rewards. What are the risks of running outside in the extreme cold? Do they outweigh the benefits of a single run (or, in very bad conditions, a week of training)?

Ultimately, you have to respect your personal comfort zone. Just because someone on Instagram ran in 10 below F temperatures doesn’t mean you have to. If you do not feel comfortable running outdoors in the cold, stick to the treadmill or indoor track, or cross-train instead. There is no shame in using the treadmill! And if the temperatures are so far below zero that you do not even want to leave the house, take a rest day or do an indoor workout from the warmth of home.

Personally? After examining the evidence, I would not run in anything colder than a negative 5-degree F wind chill. Any colder than that and run is not worth the risk of frostbite and hypothermia. Others will have different conclusions than I do – some will head indoors much sooner and some will run in even colder conditions.

If you are going to run outdoors in very cold temperatures – whatever those are to you – optimize your safety and performance with the following tips:

Warm Up Indoors

You do not want to break a sweat in this warm-up since anything damp against your skin can increase the risk of hypothermia. The purpose of an indoor warm-up is to start sending oxygen-rich blood to your working muscles and improve your range of motion before you head into the cold.

Try a simple warm-up such as this pre-run warm-up or one of these dynamic warm-ups for runners. Do your warm-up right before you head out the door.

Dress Appropriately

If you are going to run when the wind chill dips below zero, you need to take precautions in how you dress. Wear wicking layers that will keep you warm and help you stay dry. If it is very windy, top off with a wind-resistant jacket. Cover up as much exposed skin as possible to prevent frostbite. Mittens, neck gaiters, hats, tall socks, and balaclavas can protect sensitive areas. Even if it’s not very sunny out, sunglasses or even ski goggles can protect your eyes from the sting of the cold and wind. Duct tape your shoes to prevent heat loss.

Eat Well and Hydrate Before Your Run

When you run in very cold temperatures, you are asking a lot of your body – so provide it with the resources it needs. While running in the cold does not necessarily burn more calories, an empty stomach is not to your advantage. Running in the cold relies more on aerobic metabolism using carbohydrates (vs aerobic metabolism using fats). Your body needs available energy to run in the cold. 

Hydration is essential also. The cold can mask thirst, but the dry air can be dehydrating. As you run in dry air, your body loses fluids as it works to humidify the dry air.

Run by Time Instead of Distance

The combination of the cold, wind, ice, and snow will slow you down. If you run 5 miles in 45 minutes in normal conditions, then run for 45 minutes – without worrying about pace – in the cold conditions. Training by time ensures you get the same benefits of the run (45 min at an easy pace is the same no matter how far you go!) while also accounting for conditions affecting your pace. 

Easy runs are a better option in the bitter cold. Snow and ice often accompany sub-zero temperatures. Even if you find a clear stretch, the cold can increase the risk for pulling a muscle or tendon.

Be Flexible in Your Training

Your training plan should not dictate your life. During bad winter weather, adjust your training plan as needed. If the weather is ideal one day, try doing your long run or hard workout that day. If it’s too cold to run outside, either take a rest day, cross-train, or adapt your run for the treadmill.

Try one of these treadmill workouts for runners or, if you are training for a race, these race-specific treadmill workouts. If you have to do a long run, try these tips for surviving a long run on the treadmill. 

Running in the Cold with Dogs and Kids

If the wind chill reaches below zero, leave your dog at home. They are more sensitive to the cold than humans, even with booties and a jacket. Sub-zero temperatures are certainly not the weather to take an infant or toddler out in a jogging stroller. Just because you can bundle up and tolerate bitter windchills as an adult doesn’t mean your pets or child can.