GirlinSummerFor many runners a bulk of their running and race preparation happens over the summer preparing for fall goal races. Staying motivated in hot weather along with interruptions in your regular running schedule for vacation all present challenges for us.

With summer comes heat and humidity. Many runners know the basics of the importance of staying hydrated and precautions to take in hot weather but the performance impacts are lesser known.

Summer heat and humidity has a performance impact to runners just as running in cold temperatures does.

Impact of Hot Weather on Running Performance

The most ideal conditions for running are about 50°F/10°C, with low humidity, a light wind and overcast/cloudy. These conditions will allow you to run your best and in a race situation having the best chance of establishing a new PR.

As you begin to have variation in any of these factors performance can be affected modestly at first but become more pronounced as conditions become inclimate.

As you run your body generates heat. The ability of heat to escape from your body is reduced in higher temperatures and severely curtailed in humid conditions that prevent sweat evaporation from the skin which is the main principle sweat uses to cool the body.

Dr. Tim Noakes has done extensive research on the Central Governor Model which suggests that your brain will make changes to your running as a defense mechanism long before you actually reach a point of dangerous fatigue or succumb to heat exhaustion.

In hot weather, this translates to feeling fatigued early as your body is actively adjusting your pace when it starts to overheat or the threat of overheating presents itself. Your muscles are actually nowhere near their true point of fatigue, but you are given the sensation as if they are to slow your pace.

Hot weather has a greater impact on performance than cold weather does for this reason.

The table below is a guide to the performance impact on your running pace as the temperature increases:


Your actual performance degradation will vary as temperature is only part of the story. If it is a sunny vs. cloudy day, low humidity vs. high humidity and how acclimated you are to hot weather all factor in to how much your individual performance will suffer in warm conditions.

The length of time you are running also can impact your overall performance. For shorter distance events such as a 5K the performance impact may be felt less than that of a 10K, half or full marathon.

Training Considerations

Training in hot weather can be a demoralizing experience if you are not accustomed to hot weather. Think of that first hot day in the spring or early summer when you go running, especially following a cold Spring. It can feel as if you are completely out of shape! The good news is, you are not.

Your body needs up to two weeks to fully acclimate to the heat. However, the acclimation process is not linear over those 14 days. In fact, you will make most of your acclimation during the first five days of exposure to exercise in hot weather.

When hot weather first arrives preemptively slow your pace using the table above as a guide. You may find you need to slow your pace even further at first. The goal of your running when you are first exposed to heat should not be to run your regular pace or planned workout, but to just spend time on your feet in the conditions.

Even though you may feel that you are slow and question the workout being worthwhile, valuable adaptations are being made by your body during this process. Just be sure to run safe in the heat.

Hot weather can also result in an increase in accumulative fatigue – that is how fatigued you feel as the result of the entirety of all of your training over a period of time. Even when adaptations are made by the body for heat, day after day, week after week can take it’s toll. The effects of this are diminished once cooler weather returns.

Racing Considerations

Racing in hot weather is a different experience as you have been putting in considerable effort and the event is more than just a training run.

There is little you can do about the weather however the key to racing successfully in the heat is to be as acclimated as possible and to adjust your goals for the conditions. Every runner is faced with the same conditions as you are.

If you are running an event in a warm weather location and have been training in the cold for the event, don’t plan to just show up and race as usual. Try to arrive a few days early to allow your body time to adjust to the conditions as much as possible. If you have been running in the heat all summer and your race day presents similar conditions, you’ll have a better idea of your abilities but you’ll be running faster in a race than you do in your training.

As such, it is wise to re-evaluate your goals.  Depending on the length of your event, slowing your planned pace will allow you to race with confidence rather than overheating in the early miles and having a terrible experience later on.  If you run a slower pace early on you will likely finish faster than if you go out fast, succumb to the effects of the conditions and slow dramatically in the later miles.

The Silver Lining

Running in the heat can be punishing at times, but there is a reward. You will likely find that even though hot weather may make you feel less fit than you really are when cooler weather returns you will be surprised at how you are in better condition and can run faster than you expect – often coinciding just in time for your goal fall race. This can be a great mental boost at a time you need it most!

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