Mercury Rising: How the Wind, Heat and Cold Affect Running Performance

Have you ever tried running against a strong headwind? How about running on a cold and windy day, or a hot and humid day with nary a breeze to lift your spirits up? Save for the occasional indoor treadmill session, runners constantly have to deal with different environmental conditions.

Nature can be unforgiving, and extreme weather conditions can impact running performance. Here are a few things you need to know about running in the elements and what to do to come out on top.


snow run

Cold Runnings

It’s only natural that people be a little apprehensive when running in the cold. A 1991 study found a drop in temperature resulted in the following effects on the body:

Less Muscle Contractions
Muscle contractions are reduced and less powerful, this increases the usage demands of fast-twitch muscle fibres (type II), which are normally reserved for generating short bursts of speed or strength. Type II muscles fatigue more quickly than type I muscles (slow twitch), which is why you run slower in the cold.

Changes in Energy Source
As the temperature drops, the body will switch fuels and increase its carbohydrate consumption while reducing consumption of fat. Carbohydrate reserves will be drained faster in cold weather because they are easier to get to and the body processes it faster than fat. The body’s ability to use oxygen as fuel also decreases as it gets colder.

Increased Lactate Production
During running, the body can enter two states: the aerobic state which efficiently uses oxygen as fuel, or the anaerobic state which uses lactic acid from broken down carbohydrates as fuel. Being in the aerobic state is ideal because when the body produces a lot of lactic acid as fuel, the hydrogen byproducts will be too much for the muscles to handle. This type of fuel isn’t used as efficiently as oxygen, causing lactic acid build-up and slower run times.

Overall running performance also drops when the air temperature does because the body has a higher metabolic rate when it’s cold and maintaining core temperature requires energy, which then taxes your reserves even further.

Hydration is Different when it’s Cold

Ever notice that you pee a lot when it’s cold? This is because your blood pressure rises when the temperature drops, and to counter this, your body needs to remove excess water. Since you’re not likely to sweat as much, the excess water is expelled through urine. Water losses from breathing and sweat can also add up, making dehydration an issue.

The signals for thirst won’t be very strong when it’s cold, so it’s easy to miss out on drinking and become dehydrated. If you’re going to be running in cold weather, try using this basic hydration chart from Runner Academy:

For 5 – 7 mile (8-11 km) runs or 90 minute runs, whichever comes first:

• Slower than 8 mins per mile (5 mins per km) pace – 4-6 oz (120-175 ml) of water every 20 minutes
• Faster than 8 mins per mile (5 mins per km) pace – 6-8 oz (175-240 ml) of water every 20 minutes

Longer runs than this require sports drinks with sodium and electrolyte replacement.

Remember that the threat of hypothermia and frostbite are real, especially when you sweat excessively. Don’t worry about damaging your airways or freezing your lungs. Your body will heat the cold air to the appropriate temperature before it ever reaches your lungs. If your throat becomes dry, try breathing through your nose, or wear a training mask.

sun run

Feel The Heat

Running in sweltering conditions is another beast altogether. Everyone knows that it’s harder to run when it’s hot: you have to exert more effort, race times suffer and there are inherent dangers as the temperature rises. But why? Isn’t running in hot weather supposed to help the muscles be more loose and powerful? Let’s take a look at what happens when it’s hot:

You Run Slower
It’s generally recognized that for every 10° increase in air temperature above 55°F (12°C), there’s a 1.5% – 3% increase in the average finishing time for a marathon. (i.e. every 10° increase in air temp. is an extra 3 – 6 mins for a 3:30 marathon).

The Body Takes a Hit
Heat impacts all runners at the physiological level – increased heart rate, dehydration and reduced blood flow (and oxygen) to the leg muscles.

Excess Fluid Loss
You’re pretty much guaranteed to sweat buckets during a run in hot weather. Dehydration from fluid loss plays a major role in performance, especially when sodium and other minerals aren’t replaced fast enough.

If you’re not used to running in hot weather, it can be a disorienting, painful and demoralising affair. Your body needs up to two weeks to fully acclimate to the heat. The first five days are the most crucial time for adjustment as accumulative fatigue sets in faster, so slow down your pace to avoid overheating.

Humidity: Guilty as Charged

I live in a hot and humid country, and it’s not the heat that gets to you – it’s the humidity. When you run, your body generates heat and the fastest way to avoid overheating is through sweat. It’s called thermoregulation, or the way our body cools itself. The problem is, high humidity prevents sweat from evaporating.

When your body can’t get rid of heat fast enough, it will automatically go into self defence mode to avoid succumbing to heat exhaustion: your brain will send signals to every part of your body and you’ll feel tired, heavy and fatigued even though your muscles are far from the point of failure.

Because of this sensation, you’ll either cut your run short and head home or be forced to slow things down considerably. Some people handle humidity better than others, because the more body mass you have, the more body heat you generate. Check the humidity levels before heading out, or try to run either early in the morning or at night.

Follow the same hydration guidelines mentioned earlier when running in hot and muggy weather to avoid dehydration.


This wind vane warns you how windy it can get in parts of the Isle of Wight.

Image credit

Wind Resistance

When running, the wind is your best frenemy. Common sense and physics dictate that running against a headwind will make you slower.

Research from a 1971 study by L.G. Pugh found that “oxygen intake increased as the square of wind velocity”. What this basically means is due to wind resistance, you’ll be pushing harder, and the harder you push, the more oxygen you consume. Don’t expect your pace to be the same. It’s natural that you’ll be a little slower running into the wind.

You can counter this by drafting about a metre or so behind another runner. You can cut as much as 80% of the resistance this way, saving much needed energy for a later push. Get a few running buddies and practice drafting. Study what happens to air pockets when the wind changes direction and look for spots where air resistance is lowest.

Running in a cold wind
Head into the wind at the start of your run and have the wind on your back when coming home so you won’t get the chills right from the start.

Running in a hot wind
Reverse directions and run with the wind on your back at the beginning and end it running against the wind so you can use it to cool yourself, lowering core temperature significantly to avoid overheating.

Can the wind be helpful?
Runner’s Connect state a “substantial” wind (i.e. one approximately equal to the pace you are running at) will set you back 12 seconds per mile with a headwind, and aid you by 6 seconds per mile with a tailwind. So don’t expect to make up for lost time when there’s a tailwind, because you’ll only be getting half of what you lost.

Perfect Conditions

The ideal running conditions are 50°F/10°C, with low humidity, slightly overcast sky and a light breeze. That’s the day you should look for! But we all know that the weather is fickle and unpredictable, and the best thing you can do is be prepared for any type of day. So, keep yourself hydrated, look for the breeze and stay safe.