Training in Hot Weather

Does running suddenly feel…slow, uncomfortable, and real sweaty? Welcome to summer training! 

Summer weather throws a wrench into meticulously calculated training paces and heart rate zones, and it’s essential to approach training prepared and with realistic expectations.

Why is exercising in the heat and humidity SO brutal?

One of our body’s most important jobs is to control its core temperature. Core temperature only varies by about 5-6 degrees Fahrenheit - anything outside this range is extremely dangerous. 

When we exercise, about 80% of the energy produced in a muscle contraction is lost through heat - this is why we literally feel warmer during a “warm up”.  Our bodies dissipate heat in various ways, and the bigger the temperature difference between your body and the environment, the easier you’ll stay cool.

Humidity adds another serious challenge - when the air is very moist, sweat doesn’t really evaporate - instead it just drips off your body, dehydrating you without cooling. Thanks to Calgary’s extremely dry climate, humidity isn’t often a significant factor, though you may notice that you feel different after a rainstorm when there is more moisture in the air. 

Heat Acclimatization

It’s impossible to run as fast in hot, humid conditions as it is in dry, cool conditions, but acclimatization will improve performance and make training substantially more doable. Humans are incredibly adaptable to heat and it takes 10-14 days to acclimate.

With consistent heat exposure, your body will:

  • Increase sweat rate
  • Increase blood plasma volume (to assist with cooling and blood supply to the skin and muscles)
  • Start sweating earlier (i.e. after a smaller increase in core temperature)
  • Lower baseline core temperature
  • A number of other physical and metabolic adaptations


To acclimate, perform easy aerobic activity outside (safely, with proper hydration of course!). If possible, try to do long runs and intensity like intervals or tempo runs at a cooler time of day or inside, especially when you’re not yet acclimated.

Fun fact: daily activities that take you outside help with passive heat acclimatization. Yes, that means that you *may* be able to justify hanging out on your patio as “training”! 

After you’re adapted, you’ll have more success with longer runs and higher intensity workouts, but paces will still need to be adjusted. Heat adaptations come quickly but also disappear relatively quickly too (within days). This can be especially challenging with Calgary’s wildly variable weather. If you’ve spent time away from the heat, ease back into hot outdoor training upon your return. 

How to adapt paces

After acclimating to heat, your training paces will still be impacted by the environment because it takes energy for your body to cool itself - energy that is no longer going towards exercise! This is no different than expecting to be slower when running into the wind, at altitude, or uphill - training at a given pace is simply harder.

There is sometimes resistance amongst athletes to accept that they will be slower in the summer in spite of their consistent hard work. Though that determination is great, slowing down in training due to heat and humidity DOES NOT mean that you’re out of shape or losing fitness - it just means you’re exercising in the heat and humidity. If you’ve been training in a very warm location and go to race somewhere cooler and drier, you’ll most likely be pleasantly surprised by how fast you can go! 

There are many running calculators available online that “convert” paces or race times at various temperatures and humidity levels. Though their individual accuracy will vary, these calculators make it very clear that heat impacts pace A LOT! Since pace and heart rate are altered in the heat, gauging intensity using RPE (Rating of Perceived Exertion) is useful.

How to Adjust Workouts

In addition to adjusting pace expectations, it may be helpful to adjust the workout itself.

Shorter periods of work and more rest can be helpful to allow your heart rate to settle down. Break long intervals or tempos into pieces, and add 30-60 sec to your assigned rests as needed. Your workout may not look as was originally planned, but it’s more important to complete something doable and realistic. Depending on your schedule and training goals, it may be worth moving a high volume or key session to a cooler day.

Other Training Hacks 

  • If you can, train outside in the morning or evening, ideally in the shade
  • Shorten your warm up and cool down to ~ 5-10 mins - the temperature will warm you up! 
  • Prioritize good conditions for your most important workouts. Move key workouts inside or do them at the coolest time of day.
  • Wear light clothing, a hat, and sun screen. 
  • Take a cool shower before or wear a ice vest to lower your core temperature
  • Carry a water bottle with you during the day to remind you to drink fluids
  • Pour water over your head and body
  • Hydrate with electrolytes! Plan a route with water access and/or bring some along. Begin your training session hydrated and replenish lost fluids after.
  • Review your training log from this time last year as a reminder that seasonal fluctuations in pace happen due to environmental conditions and YOU ARE NOT UNFIT! 

Heat Exhaustion and Heat Stroke

Heat cramps, heat exhaustion, and heat stroke are considered “heat-related illnesses” and are extremely dangerous. If you feel unwell and experience symptoms of heat illness, you DO NOT want to push through to complete your workout or race. It’s important that you stop, cool yourself, and seek help if necessary. 

Benefits of Heat Training

Here’s the good news: training through the summer is challenging, but doesn’t come without reward! Even if running feels like more of a slog than a sprint and your paces aren’t what they were in milder conditions, remember that work is work, and so long as you’re working hard, your fitness is improving. Beyond that, the adaptations you get while acclimating to the heat will give you an extra boost when performing in cooler conditions! Hot summer miles bring speedy fall smiles. 

Written by Jessica O'Connell, 5000m Olympian and MSc Exercise Physiologist. Jess is the coach of the University of Calgary Dinos distance track/XC teams and provides personalized online coaching for runners of all levels through her businessGrit Coaching. “