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It's getting hot in here..... Adapting training in summer HEAT

Does endurance exercise 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. Read on for tips, or skip to the bottom for key takeaways.

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.

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.

Simply living in a hot climate will help with heat adaptation. Daily activities that take you outside help with passive heat acclimatization.

After you’re adapted, you’ll have more success with longer runs and higher intensity workouts, but paces will still need to be adjusted (see next section).

Heat adaptations come quickly but also disappear relatively quickly too (within days). If you’ve spent time away from the heat, ease back into hot outdoor training upon your return.

All this said - if you enjoy training inside and aren’t competing outside in the near future, there is nothing wrong with keeping your workouts inside!

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!

Here is a handy calculator to calculate adjusted training paces based on temperature and humidity: . *Note - you must input dew point, not humidity.

Here’s another option with a slightly different interface: (click “advanced options”)

As you can see, heat impacts pace A LOT!

How to Adjust Workouts

In addition to adjusting pace expectations, it may be necessary 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. It’s also worth considering reducing volume in long workouts (ie cut them short!).

Your workout may not look as was originally planned, but it’s more important to complete something doable and realistic.

General Training Tips

  • Gauge intensity using RPE (rating of perceived exertion) - pace and heart rate will be altered compared to cool dry conditions

  • If you can, train outside in the morning or evening

  • Shorten your warm up and cool down to ~ 5-10 mins

  • 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.

  • Train in the shade when possible

  • 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!


Dehydration causes a decrease in performance and can lead to heat exhaustion and heat stroke. Research has shown that heart rate increases by 3-5 beats/min for every 1% of bodyweight loss due to dehydration, and dehydration of more than 2% of body weight substantially impairs performance and can have dangerous health consequences.

Sweating, as we know, is one of the body’s primary cooling mechanisms and heat adaptation makes us better sweaters. It’s important to begin activity hydrated to improve your capacity to sweat - if you begin dehydrated, you have less fluid to lose through sweat. It’s also important to replenish lost fluids and electrolytes during and after exercise.

To stay hydrated, drink water with electrolytes (Nuun is great!) throughout the day. Urine should be light yellow, and you shouldn’t feel thirsty at rest. Consider adding a bit of salt to your food for extra electrolytes. Drink 16-20 oz of water when you wake up, after meals, and before exercise.

It’s generally recommended to consume 16 – 24 ounces of fluid an hour during endurance activity, but it’s not uncommon to need 2-3 times that much in hot environments. It can be helpful to weigh yourself before and after hot exercise - each kilogram of body weight lost is one liter of fluid that needs to be replaced (ON TOP of regular hydration!).

Heat Exhaustion and Heat Stroke

Heat cramps, heat exhaustion, and heat stroke are considered “heat-related illness” and are extremely dangerous. If you experience symptoms, 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.

It’s important to know signs and symptoms in yourself and others.

Heat cramps are painful, sudden muscle cramps that usually occur during heavy exercise in hot environments. Rest, cool down, drink fluids with electrolytes, and massage the area.

Heat exhaustion symptoms include:

  • Cool, moist skin with goose bumps when in the heat.

  • Heavy sweating.

  • Faintness.

  • Dizziness.

  • Fatigue.

  • Weak, rapid pulse.

  • Low blood pressure upon standing.

  • Muscle cramps.

  • Nausea.

  • Headache.

Similar to heat cramps, stop activity, cool down (with ice, water etc), and rehydrate. Seek medical attention if core temperature is 104 F or higher, or if symptoms get worse or don’t improve within an hour.(Source: Mayo Clinic).

Don’t return to exercise for 24 hours.

Heat Stroke is a medical emergency and requires emergency attention.Symptoms include:

  • High body temperature (104 F or higher)

  • Altered mental state or behavior ie Confusion, agitation, slurred speech, irritability, delirium, seizures and coma

  • Alteration in sweating. In heatstroke brought on by hot weather, your skin will feel hot and dry to the touch. However, in heatstroke brought on by strenuous exercise, your skin may feel dry or slightly moist.

  • Nausea and vomiting.

  • Flushed skin

  • Rapid breathing.

  • Racing heart rat

  • Headache

(Source: Mayo Clinic)

Expect to return to exercise within 7-21 days (guided by a medical professional).

Heat stroke victims often can’t take care of themselves - be aware of symptoms in others. If someone you’re with has heat stroke, seek emergency help and work to cool the victim.

Is it ever “too hot” to exercise?

It can be. You can find public health recommendations HERE.

NOTE: Heat index values are taken in shady locations - sunny areas are much hotter than may be reported.

Benefits of Heat Training

Training through the summer is challenging, but doesn’t come without reward! Adaptations to heat improve performance in cooler conditions, and training adaptations absolutely still occur, even if paces aren’t what they were previously.

Key Take-Home Messages (because there is a lot of wordy information above!!)

When exercising in the heat and humidity:

  • Heart rate zones don’t apply in the same way - heart rate will be higher at a given pace, and will rise rapidly during the session

  • Training paces will be slower because it takes more energy to run at a given pace. Use a calculator to give guidelines and guide yourself by RPE

  • Perform key workouts inside or at the coolest part of the day

  • It may be wise to add more rest or reduce the volume of workouts

  • Acclimatization helps and takes 10-14 days. Start with shorter-duration, easy intensity exercise outside. Another option is to choose to train inside, if possible.

  • Ensure proper hydration

  • Prepare for the heat as best you can by wearing light clothes, sunscreen, trying to find shade etc

  • Know the signs of symptoms of heat illness and stop exercise + cool your body immediately if you experience any

  • Trust that work is work, adapt when necessary, and be safe and smart!


More info:,is%20necessary%20during%20this%20time.

Cool stories about athletes and heat:

By Jessica O’Connell, CSEP-CEP, MSc, OLY

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