As the dog days of summer arrive, its time to discuss heat and how it impacts performance. Knowing the difference between ideal and adverse conditions is what separates focused athletes from those struggling to make improvements. As temperatures rise, its important to shift focus and attention. Here are a few tips to help you perform as the heat builds.

Running Pace in the Heat

Through multiple studies (1,2), it has been shown that running speeds will decrease as temperatures rise. When looking at elite runners (in the marathon distance), ideal temperatures range from between 3.8°-9.9°C (38.8°-49.8°F). For elite runners, as you get above these ranges, you can expect to lose roughly 1 sec/mile for every 1°C. For amateur runners who finish between 3:30-5:00 hours for a marathon, they can expect to lose 4 seconds/mile for every 1°C. Elite runners tend to have less of an impact due to their lower body mass and shorter duration exposed to these conditions. For amateurs however, larger body masses and more exposure (longer time in conditions) compounds the heat and slows individuals even further. These are important findings that all runners should be aware of as they plan their training and racing during the summer months.

Pro tip: If you’re going out for a focused run, scale your pace expectations with the temperature. If you normally run 7:00/mile pace in cooler temps, perhaps you’ll run 7:30/mile pace as the temperature goes above 70° F. Being aware of this will help with your pacing and confidence going forward.

Wet Bulb Global Temperature

This is a metric that many athletes should be aware of. While heat plays an important part in performance, Wet Bulb Global Temperature (WBGT) factors in heat, humidity, cloud coverage, wind, and sun angle. Therefore, even if temperatures are hovering in the 60’s (°F), if humidity is high and cloud coverage is low, it may impact performance far greater than the pace guidelines above. Based on studies, the best marathon performances happen between 10°-15°C (50°-59°F). As you get out for your next training run or race, be sure to look at the temperature, but also the WBGT. This will provide you with the insights needed for better pacing.

Pro tip: Regardless of temperature, WGBT will change throughout the day based on the other factors. If you have a key training session that day, identify the lowest WBGT throughout the day and plan your workout for that time!

Training For The Heat

There is a difference between going out for a mid-summer day run, and training for a mid-summer race. If you’re just going out for a run, you need to be aware of the notes above. If you’re training for a mid-summer race, you need to build your heat tolerance (acclimatization). When athletes travel to a warmer/more humid climates to race, they often suffer from not being acclimated to the heat. As you train in the heat, your body will adapt and increase its cardiac output and plasma volume. By doing so, you will build your performance in both the heat and cooler temperatures. For all of those expecting to race in hotter conditions, it would be wise to mix heat training into your training plan.

Health Concerns

When discussing training in the heat, there are health concerns that begin to take place. As temperatures rise, your body produces sweat to cool itself. As you produce sweat, your body is utilizing fluids that must be replaced. Without proper hydration, you run the risk of becoming dehydrated, and potentially exposing yourself to heat exhaustion or worse. While dehydration can be dangerous, over-hydrating can also take place if not careful. When athletes only hydrate with water when sweating excessively, they run the risk of not replenishing the electrolytes needed. This is called hyponatremia. This also can create serious consequences. As you begin to exercise in the heat, you need to identify the right amount of hydration/electrolytes and find best practices for keeping your body as cool as possible. To dial in your own approach, you should seek the help of a registered dietician or sports medicine practitioner.

Curious to know more? Read our article on Heat Illness

Coaching Tips

If you’re heading out to train in the heat, it’s important to note the performance metrics and safety concerns above. If however, you are training for a race that will take place in the heat, it’s important to have a performance plan in place. To help you adapt to the heat, you should perform your aerobic endurance runs in the heat of the day. The purpose of these runs is to build your endurance, but not necessarily build speed. By doing these runs outdoors, you can better acclimate to the heat without sacrificing performance. For your speed and threshold workouts, you need to identify the coolest times of the day with the lowest WBGT. When performing intervals, we are looking to get the most out of your workouts. It’s critical to run these in cooler temps so you can maximize your results. With this focus of heat adaptation on base runs and speed workouts done in cooler temps, you’ll be sure to maximize your performance at your next hot event.

Sources:

Knechtle, et.al: “The role of weather conditions on running performance in the Boston Marathon from 1972 to 2018”, (2019)

Helou, et.al: “Impact of Environmental Parameters on Marathon Running Performance”, (2012)