The saying, “Some like it hot, some like it cold” certainly applies to runners’ opinions about the best temperature for running.
Although you’ll find runners who contest that running in the hot summer heat is easier than going for a frigid winter run, every runner will most likely agree that the middle is best.
But what is the Goldilocks temperature for running? In other words, what’s the best temperature for running well?
In this article, we will see what research suggests is the best temperature for running or the best running weather.
We will also share why running in the heat is difficult on days when Mother Nature grants you running weather that’s akin to Mama Bear or Papa Bear, rather than that optimal running temperature at a happy medium.
We will cover:
- Why Running In the Heat and Humidity Is Hard
- What Is the Best Temperature for Running?
- How Much Slower Do You Run In the Heat?
Let’s get started!
Why Running In the Heat and Humidity Is Hard
Every runner who has ventured out for a run on a hot and humid day knows that running in an environment that feels reminiscent of a tropical rain forest is not easy.
Running increases your core body temperature, but the body wants to maintain your temperature within a very narrow range to protect your brain and other tissues from overheating.
This is where the sweating response comes into a play. The evaporative cooling process can help lower your core temperature by releasing heat energy through evaporating the sweat droplets on the surface of your skin.
On a hot, dry day, sweating can be a fairly effective means of reducing your body temperature, yet when it’s humid, the moisture content in the air prevents sweat from evaporating readily.
Consequently, most of the heat energy stays trapped in your body without the ability to get released.
This causes heat to build up in your body, increasing the risk of heat illnesses like heat exhaustion and heat stroke.
From a practical standpoint, the real reason that running in the heat or humidity feels harder is because your heart rate increases compared to running at optimal temperatures.
Thermal strain—being too hot or having an elevated body temperature—is stressful for the body, which in and of itself can raise your heart rate, but the primary reasons that your heart rate is higher running in the heat are because skin blood flow increases and plasma volume drops.
In addition to sweating, one of the natural thermoregulatory mechanisms your body has to maintain temperature homeostasis is increasing blood flow to the skin.
Pulling blood away from the core towards the surface of the skin helps cool the blood, effectively helping release excess heat.
When you are running in the heat, your muscles are already demanding a ton of oxygen and nutrients, so cardiac output is high.
Note that cardiac output refers to the total amount of blood your heart is circulating per minute, and is the product of your heart rate in beats per minute multiplied by the stroke volume (the amount of blood ejected from the heart into circulation per beat).
When any tissue, such as your muscles, need more oxygen and nutrients, the heart responds by beating faster and/or contracting more forcefully so that a greater volume of blood is circulated to the tissues.
This is why your heart rate is much faster when you run than when you sit at your desk; your muscles are demanding more blood.
In terms of running in the heat and humidity, when the thermoregulatory mechanisms kick in and the body starts shuttling a lot of blood towards the skin for cooling, the cardiac output has to increase even further than it had to beyond satisfying the oxygen and nutritional demands from the muscles.
As a result, your heart beats even faster.
Furthermore, unless you are so on top of your hydration needs while running in the heat that you’re not becoming dehydrated at all, your blood plasma volume will decrease due to water lost through sweat.
The more dehydrated you become, the smaller the amount of blood you’ll have in circulation.
This means that your stroke volume will decrease.
Because stroke volume is the other component of cardiac output, any decreases in stroke volume must be compensated for by further increasing heart rate.
Most runners will experience a heart rate increase of about 10-20 beats per minute when running in 90° F (32° C) compared to running when it is 75° F (23° C).
Similarly, your breathing rate will increase because the lungs need to take in more oxygen to fuel the overworking heart and muscles.
As can be seen, running in the heat can substantially elevate your heart rate and respiration rate, which is why it can feel so much harder to run on a hot day than at the ideal running temperature.
What Is the Best Temperature for Running?
The best temperature for running is really only a piece of the puzzle.
Other environmental factors, such as humidity and dew point can significantly impact the “real feel” or heat index.
The heat index is a composite score that considers not only the air temperature, but also the relative humidity, giving you a sense of how hot it actually feels.
Running when it is hot and humid is even more taxing for the body than just running in the heat because when the moisture content of the air is higher, it feels hotter.
In fact, the thermal strain of running in the heat increases exponentially—not linearly—with an increase in humidity.
For example, when the temperature is 88° F (31° C) and there is 40% humidity, it will feel like 88° F.
However, when it’s 88° F with 70% humidity, it will feel like 100° F (38° C), and when you bump up to 85% humidity at the same temperature, the heat index jumps all the way to 110° F (43° C).
When the humidity is 40% or less, it has little effect on the heat index or how hot it actually feels running in the heat.
However, once the humidity is above 40%, there’s an exponential impact on the heat index.
This mathematical relationship makes it difficult to calculate the heat index by hand, but there are plenty of online calculators such as the one here.
One study that compared the results of six marathons based on four environmental factors: temperature, humidity, dew point, and the atmospheric pressure at sea level.
The results suggested that of the four environmental factors considered, air temperature had the most significant effect on running performance and dropout rates.
Air temperature was correlated with running for both genders and all performance levels, while humidity affected faster women and men of all levels.
The more the air temperature increased above the “optimal running temperature,” the slower the running speeds and the higher the withdrawal rates became.
These optimal running temperatures are likely colder than many runners would anticipate, ranging between 3.8°C and 9.9°C (38.9°F and 49.8°F), depending on the performance level.
Interestingly, these two extremes were seen between the men and women elite runners, with male elites running fastest in the coldest end of this “ideal running temperature” range (3.8°C or 38.9°F), while the elite women runners were at the other extreme, 9.9°C or 49.8°F.
The optimal temperature for running for average runners fell in the middle.
The best temperature for running—which was the temperature where runners ran the fastest—for each performance level were as follows:
|Performance Level||Ideal Running Temperature for Men (°F)||Ideal Running Temperature for Men (°C)||Ideal Running Temperature for Women (°F)||Ideal Running Temperature for Women (°C)|
|Elite Runners (top 1% of runners)||38.9||3.81||49.8||9.91|
|Top Quartile (top 25% of finishers)|
These results suggest that the best temperature for running or best running weather for most runners is around 5.9°C or 42.6°F for men and 7.7°C or 45.9°F for women.
These ideal running temperatures were determined by taking the average ideal temperature for the the top quartile, median, and third quartile of runners for each sex.
A separate study that just examined the relationship between Boston Marathon race results and the weather on race day found that the optimal temperature for running performance is between 44° F and 59° F (7–15° C), though the best results occur at wet bulb temperatures below 7.8 °C (46 °F).
The researchers noted a fairly linear relationship of slower average finish times for each additional 1 °C increase in temperature.
How Much Slower Do You Run In the Heat?
The extent to which the temperature affects your running performance seems to be influenced by your pace.
The research indicates that runners who average 5:45 min/mile pace or faster slow down about 1 second per mile for each 1° C (1.8° F) increase in temperature above 15° C (59° F), whereas runners who average 7:25-10:00 min/mile pace slow down 4-4.5 seconds per mile with this same temperature increase.
Even though we’d expect to see less of a time consequence for faster runners having a quicker pace, the relative effect of temperature seems to be less impactful for elite runners, perhaps due to the thermoregulatory benefits of having lower body fat.
So, what should you do when it’s hotter than that sweet spot of 44° F and 59° F (7–15° C)? Make sure you’re staying as hydrated as possible, run in the shade, and give yourself grace–it’s normal to slow down.
To ensure you stay as well-hydrated as possible, check out our hydration guides for runners!